ALBERT

Description: The pine-wood nematode, Bursaphelenchusxylophilus (Steiner and Buhrer), was most commonly extracted from Cerambycidae emerging from nematode-infested pines in Minnesota and Wisconsin during 1981 and 1982. The greatest number of nematodes were extracted from Monochamusscutellatus (Say) and Monochamuscarolinensis (Olivier). Low numbers of B. xylophilus were found in some buprestids but no nematodes were found in the curulionid and scolytid beetles examined. Two species of Cerambycidae, Monochamusmannorator (Kiby.) and M. scutellatus were associated with B. xylophilus from balsam fir in Minnesota. Bursaphelenchusxylophilus from insects associated with balsam fir were morphologically different from insects associated with pine. Dauer larvae of B. xylophilus were concentrated in the thoracic segments of M. scutellatus and Monochamusmutator (Lec.) examined. Bursaphelenchusxylophilus was transmitted to twigs during maturation feeding and to logs during oviposition by M. carolinensis, M. mutator, and M. scutellatus.

Description: Alnusrubra Bong, dominates the first 65 – 80 years of a sere that is initiated naturally on the terraces of the Hoh River. Stands of 14, 24, and 65 years were studied to determine to what extent the Alnus stage enriched the nitrogen inventory of the site. Bare sandbars deposited by the river had a mean of 783 kg/ha nitrogen. Alnus communities caused an increase in the nitrogen inventory so that, by 65 years, total community nitrogen was 4659 kg/ha, soils held 3594 kg/ha N in the upper 45 cm, and Alnus trees held 942 kg/ha N. The nitrogen contents of the soil, Alnus wood, bark, and branches, grasses, total aboveground biomass, total belowground biomass, and sticks less than 1 cm diameter all showed significant increases from 14 to 65 years. The A. rubra stage is an important link in the nutrient inventory between unvegetated, recently deposited sandbars and the climax coniferous forests dominated by Tsugaheterophylla (Raf.) Sarg. and Piceasitchensis (Bong.) Carr.

Description: Morphological plasticity in terms of asymmetric display of crowns was compared between Piceaabies (L.) Karst. and Betulamaximowicziana Regel. To evaluate crown asymmetry in relation to local environment, a model that predicts crown asymmetry from topography and configuration of neighbors was applied to data derived from a mixed forest in Hokkaido, northern Japan. Betulamaximowicziana had greater crown asymmetry than P. abies in absolute value. However, observed crown asymmetry of both species was determined by local environment to similar degrees. Some other differences were found between the two species. Crowns of P. abies were more influenced by neighbors than topography, while crowns of B. maximowicziana were more influenced by topography than neighbors. Crowns of P. abies were influenced mainly by larger neighbors, while crowns of B. maximowicziana were influenced by large and by relatively small neighbors.

Description: Flooding for 30 days induced several changes in Quercusmacrocarpa Michx. seedlings, with stomatal closure among the earliest responses. Stomata remained more closed in flooded than in unflooded plants during the entire experimental period. Leaf water potential was consistently higher in flooded than in unflooded plants. Other responses to flooding included acceleration of ethylene production by stems; formation of hypertrophied lenticels on submerged portions of stems; growth inhibition, with greatest reduction in roots; and formation of a few adventitious roots on submerged portions of the stem above the soil line. Some of the morphological responses to flooding, especially formation of hypertrophied lenticels, appeared to be associated with increased ethylene production. Quercusmacrocarpa seedlings adapted poorly to flooding as shown by failure of stomata to reopen after an early period of flooding and low capacity for production of adventitious roots. The much greater inhibition of root growth than shoot growth by flooding will reduce drought tolerance after floodwaters recede.

Description: Root elongation of greenhouse-grown Alaskan taiga tree seedlings increased with increasing root temperature in all six species examined and was most temperature sensitive in warm-adapted aspen (Populustremuloides Michx.). Root elongation was slower in fine than large roots and in black spruce (Piceamariana (Mill.) B.S.P.) was less temperature sensitive in fine than in large roots. Root elongation in the laboratory was slowest in black spruce, which has an inherently slow growth rate, and most rapid in poplar (Populusbalsamifera L.) and aspen, which grow more rapidly. In contrast, field root elongation rates tended to be highest in black spruce from cold wet sites, suggesting that site factors other than soil temperature (e.g., moisture) predominated over genetic differences among species in determining field root elongation rates. The seasonal pattern of root elongation was closely correlated with soil temperature and reached maximum rates in July for all tree species (except aspen medium-sized roots). Most roots of each species were in the top 20 cm of soil. However, root growth penetrated to greater depth in warm compared with cold sites. Root biomass in a 130-year black spruce forest (1230 g/m2) comprised only 15% of total tree biomass. Root biomass of 25-year aspen and 60-year poplar sites (517 and 5385 g/m2, respectively) comprised a greater proportion (57% in poplar) of total tree biomass than in spruce.

Description: The patterns of translocation of carbon in different-age tissues of four common moss species in a black spruce (Piceamariana (Mill.) B.S.P.) dominated forest near Fairbanks, Alaska, were studied by 14C labelling and carbohydrate analysis. A simple, in-vial combustion technique was developed for combustion of small (

Description: Water stress of subalpine conifer species may be measured with the pressure chamber after several hours of tissue storage. Tissue samples stored in cool, humid vials exhibited very little change in xylem pressure potential over a 4-h period. However, xylem pressure potential declined steadily when a source of water vapor was not available. Xylem pressure potentials of current-year and 1-year-old needles of lodgepole pine (Pinuscontorta var. latifolia Engelm.) were slightly lower than those of older needles.

Description: The rates of nutrient release were investigated during the Castanopsiskawakamii (Hayata) leaf, branch, and bark litter decomposition processes over a 360-day period within five different size classes of forest gaps that comprise a gap size gradient. Five different size classes of gaps were gap 1, under the closed canopy of pure C. kawakamii vegetation; gap 2, small gaps with a diameter of less than 5 m; gap 3, small to intermediate gaps with a diameter of 5–15 m; gap 4, intermediate to large gaps with a diameter of 15–30 m; gap 5, large gaps with a diameter of bigger than 30 m. After 360 days, decomposing plant litter under canopy condition or small gaps lost weight more rapidly than those in large gaps. Loss of K was highest among all nutrients measured for all three types of litter in all five size classes of gaps. Net immobilization of N and P occurred for all three types of litter in the first 2 or 4 months. Litter residue concentrations of N and P then declined until the end of this study, decreasing to 47% and 70%, respectively, of initial amounts. Loss of Ca and Mg averaged 60 and 40%, respectively, during the period of this study; loss of S averaged 50% and was continuous. Loss of nutrients measured were highest in leaves, intermediate in bark, and lowest in branches under the same size class of gaps, and were highest in gaps 1 and 2, intermediate in gap 3, and lowest in gaps 4 and 5 for the same type of litter. Cellulose and lignin components showed the similar patterns of mass loss as nutrients with highest in gaps 1 and 2, intermediate in gap 3, lowest in gaps 4 and 5 (P ≤ 0.001). Annual decomposition rate was correlated to the microclimatic factors for all types of litter within five different gap size conditions. Soil moisture content was the best predictor of annual decay rate (R2 = 0.922, P ≤ 0.001) among the microclimatic factors. The results indicated that small scale of natural disturbance do not influence the nutrient dynamics during plant litter decomposition; however, rates of nutrient release are strongly inhibited with the increase of scales of disturbance. In this study, gap size of 15 m in diameter is critical in determining the rates of nutrient release from plant litter decomposition processes.

Description: Six old-growth, late postfire Scots pine (Pinussylvestris L.) dominated forest stands of the Vaccinium–Cladina type were selected along a latitudinal gradient in northern Sweden. In two of the stands, Scots pine seedlings that had naturally regenerated during the last 40 years were surveyed in relation to field- and bottom-layer vegetation. The most abundant forest floor species, viz. Cladina spp., occupied 41% of the ground cover and dominated the microhabitat of Scots pine seedlings

Description: In northern Patagonia, Argentina, we examined the influences of climatic variation and inter-site variation in substrate stability on the dendroecological effects of earthquakes. In association with the great earthquake in 1960 centered off the coast of nearby Valdivia, Chile, extensive tree mortality occurred in northern Patagonia in Nothofagusdombeyi–Austrocedruschilensis stands on unstable debris fans. To examine the effects of the 1960 and earlier earthquakes on tree growth, we developed tree-ring chronologies from samples of the surviving A. chilensis on unstable debris fan sites and at adjacent nonfan sites of more stable substrates. For controlling the effects of regional climatic variation, we also produced a tree-ring chronology from this species in a more distant and undisturbed stand. Strong variations in tree-growth patterns on fan sites were associated with the historically documented major seismic events of south central Chile that occurred in 1737, 1751, 1837, and 1960. Tree-ring chronologies from nonfan sites (i.e., sites of greater substrate stability) showed much less response to these earthquakes. On the fan sites, strong growth suppressions were associated with the former three earthquakes, whereas strong releases followed the 1960 earthquake. The difference in response is explained by the occurrence of the 1960 earthquake during a period of drought, which in combination with the violent shaking of the ground, resulted in extensive tree mortality followed by growth releases of the survivors. However, severe droughts in the absence of earthquakes also can produce tree mortality and subsequent release of the survivors. Consequently, the synergistic effects of climatic variation and earthquake events must be carefully considered in developing records of both climatic variation and earthquakes.

Description: The relationships between site index and measures of soil, understory vegetation, and foliar nutrients were examined using data from 102 white spruce (Piceaglauca (Moench) Voss) stands in the Sub-boreal Spruce zone of British Columbia. Compared with soil physical properties (adjusted.R2 = 0.54), soil nutrient properties (adjusted.R2 = 0.29) were poor predictors of white spruce site index. The best soil model, using depth of major rooting zone, total nitrogen, and slope as predictors, explained 60% of the total variance in site index. The best understory vegetation model, using frequencies of soil-moisture and nitrogen indicator species groups as predictors, explained 53% of the total variance in site index. The best foliar nutrient model, using foliar phosphorus and sulphur as predictors, explained 64% of the total variance in site index. Adding variables from understory vegetation, foliar nutrients, or both into the best soil model significantly improved site index prediction. The resultant models explained up to 83% of the total variance in site index. When stands were stratified according to groundwater influence, regression models developed for three delineated strata were significantly improved compared with unstratified models. Based on practical consideration, four regression models were considered for predicting white spruce site index. Independent testing indicated that the stratified model, which used only soil variables as predictors, predicted white spruce site index with 79% of the estimate errors within 2 m in the study area.

Description: The aboveground biomass of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and annual production over 7 years was studied in relation to thinning and nitrogen fertilization. Biomass yield of both treatments increased during the first 3–4 years then decreased for fertilization but not with thinning. Treatments doubled biomass production of individual trees over the study period when applied separately and quadrupled it when combined. Annual biomass production per unit of foliage (E) increased during the first 3–4 years, but was at or below control level after 7 years. The increased E accounted for 20, 37, and 27% of the stemwood dry matter response to thinning, fertilization and the combined treatments, respectively; the remainder was attributed to an increase in foliage biomass. Thinning, but not fertilization, influenced distribution of radial growth along the stem, increasing growth only below the top one-third of the stem. This pattern was related to crown development.

Description: Carbohydrate reserves and root growth potential (RGP) of 2 + 0 Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings were monitored through a lifting season and during dark, cold storage. Concentrations of total nonstructural carbohydrate and extractable sugars in root and stem tissues remained relatively constant through winter, while foliar sugars showed a sharp midwinter peak at about 195 mg•g−1 dry weight. RGP was lowest in November and March and peaked in January. During storage at +2 and −1 °C, carbohydrates were depleted in all tissues through respiratory consumption. In contrast, RGP increased during the first 6 months in storage and then fell rapidly. The results do not support the view that changes in RGP are driven by changes in carbohydrate concentrations. Storage may affect frost hardiness and drought resistance through its effect on sugar concentrations.

Description: Experiments were conducted using black spruce (Piceamariana (Mill.) B.S.P.) seedlings to evaluate diurnal variability in heat tolerance of roots and shoots and in levels of root heat shock proteins (HSPs). Shoot heat tolerance was significantly lower in the morning than in the afternoon. Similarly, root systems exposed to high temperatures in the morning suffered significantly more damage than those exposed in the afternoon. Root HSPs were identified using an antibody specific for the constitutive HSP73 and inducible HSP72. Both the constitutive levels of root HSPs and the levels of root HSPs following heat shock varied diurnally, and in different patterns for different protein fractions. The levels of soluble and nuclear root HSP72/73 were enhanced by heat shock, both in the morning and afternoon. In comparison, HSP levels in the root mitochondrial protein fractions increased after heat shock in the morning, but decreased after heat shock in the afternoon. HSPs in the root microsomal protein fraction declined following both morning and afternoon heat shock. The higher afternoon levels of root heat tolerance were associated with the greater constitutive levels of HSP73 in the mitochondrial and microsomal root protein fractions in the afternoon. To examine the effects of the shoot on diurnal variation in root system heat tolerance, root heat damage was compared between seedlings with intact shoots versus seedlings with shoots excised either 4–6 h prior to, or immediately before, heat treatment. Regardless of time of day, root systems died when shoots were excised and root systems were treated with high temperatures. In contrast, shoot excision or root heating alone resulted in no root mortality.

Description: The pipe model theory presents the idea that a unit weight of tree foliage is serviced by a specific cross-sectional area of conducting sapwood in the crown. Below the crown, a large fraction of the tree bole may be nonconducting tissue, so the sapwood area would have to be known to estimate foliage. We applied the pipe model theory to the analysis of several western coniferous species to learn whether the distribution of canopy leaf area could be accurately estimated from knowledge of the sapwood cross-sectional area at various heights, including breast height (1.37 m). Results are excellent, but taper in the conducting area must be considered when sapwood area is measured below the crown.

Description: The self-thinning rule describes in overcrowded even-aged plant monocultures a consistent relationship of mean mass to the approximately −3/2 power of plant density. Recent analyses revealed cases of statistically significant departures of the exponent from −3/2, confirming earlier suggestions. Shade tolerance, crown structure, and stand conditions have been suggested to influence variation in the self-thinning exponent; however, quantitative relationships of the species' traits to thinning exponent have been unclear. I examined patterns of crown fractal dimension, a quantitative measure of crown structure, and their relationship to the self-thinning exponent in four tree species, Nothofagussolandri var. cliffortioides (Hook. f.) Poole, Pinusbanksiana Lamb., Pinusdensiflora Sieb. et Zucc., and Cryptomeriajaponica (Linn. fil.) D. Don. Only stands at maximum crowding were used for analysis. Crown fractal dimension of monocultures is hypothesized to be a factor determining the species-specific variation in the self-thinning exponent of tree populations and is inversely proportional to the thinning exponent. Species-specific change in foliage packing through development of overcrowded populations is suggested to be closely related to variation in crown fractal dimension and the self-thinning exponent. Implications to possible effects of leaf shape and structural characteristics of crowns to crown fractal dimensions are discussed.

Description: The history of spruce budworm (Choristoneurafumiferana (Clem.)) outbreaks for the past 200 to 300 years, for nine regions in eastern Canada, indicates that outbreaks have occurred more frequently in the 20th century than previously. Regionally, 21 outbreaks took place in the past 80 years compared with 9 in the preceding 100 years. Earlier infestations were restricted to specific regions, but in the 20th century they have coalesced and increased in size, the outbreaks of 1910, 1940, and 1970 having covered 10, 25, and 55 million ha respectively. Reasons for the increase in frequency, extent, and severity of outbreaks appear mostly attributable to changes caused by man, in the forest ecosystem. Clear-cutting of pulpwood stands, fire protection, and use of pesticides against budworm favor fir–spruce stands, rendering the forest more prone to budworm attack. The manner and degree to which each of these practices has altered forest composition is discussed. In the future, most of these practices are expected to continue and their effects could intensify, especially in regions of recent application. Other practices, including large-scale planting of white spruce, could further increase the susceptibility of forest stands. Forest management, aimed at reducing the occurrence of extensive fir–spruce stands, has been advocated as a long-term solution to the budworm problem. The implementation of this measure at a time when man's actions result in the proliferation of fir presents a most serious challenge to forest managers.

Description: At 10 locations in Oregon and Washington, tree mortality resulted in dry-matter transfer of 1.5–4.5 Mg•ha−1•year−1 of boles and branches to the forest floor and 0.3–1.3 Mg•ha−1•year−1 of large-diameter roots directly to the mineral soil. The first value is about the same as that reported for leaf fall in similar stands; the second value generally is smaller than that reported for fine root turnover. Results are based on measurements by the U.S. Forest Service spanning 16–46 years and areas as large as 42 ha. Values based on intervals

Description: Flooding of soil for 45 days severely inhibited growth of 115-day-old Pinusbanksiana Lamb, and P. resinosa Ait. seedlings, with significant effects apparent within 15 days after initiation of flooding. Both species adapted poorly to flooding of soil but P. banksiana was more adversely affected than P. resinosa as shown by earlier and more drastic reduction of growth in the former species. In both species flooding decreased the rate of height growth, production of secondary needles, dry weight increment, and relative growth rates of various plant parts. Root growth of both species was reduced more than shoot growth. The reduction in dry weight increment of root systems of both species reflected arrested branching and elongation of roots as well as decay of roots, mainly the very small nonwoody roots. Flooding slightly stimulated ethylene production by submerged stems.

Description: The presence of ectomycorrhizal and vesicular–arbuscular (VA) mycorrhizal fungi in soils from five sites in a mixed conifer zone in southwest Oregon, each consisting of a 1- to 1.5-year-old clear-cut adjacent to an undisturbed forest stand, was determined by bioassay with Pseudotsugamenziesii (Mirb.) Franco, Pinusponderosa Dougl. ex P. Laws & C. Laws, and Trifoliumsubterraneum L. 'Mt. Barker' as hosts grown at root zone temperatures ranging from 7.5 to 35 °C. Maximum formation of both ectomycorrhizae and VA mycorrhizae occurred at 18.5–24 °C in soils from all sites, and there were no significant qualitative or quantitative differences between disturbed (clear-cut) or undisturbed (forest) soils. Mycorrhiza formation was moderate even at the lowest temperature tested (7.5 °C) but was greatly reduced or prevented at or above 29.5 °C. Treatment of soil at 35 °C for 1 week did not appear to adversely affect viability of ectomycorrhizal fungus propagules, but young mycorrhizae subjected to the same treatment appeared to be severely injured. Thus the ability of native mycorrhizal fungi to grow at low soil temperatures is especially important as they may contribute to the survival of seedlings outplanted into climatic zones characterized by warm, dry summers following cool, wet winters and springs.

Description: Previous research on chronosequences of even-aged northern hardwood stands has suggested that forest clearing is accompanied by large losses of nitrogen from the forest floor. The timing of the losses and the fate of a large fraction of the lost nitrogen are unclear. The purpose of this investigation was to study these questions through direct measurement of soil nitrogen concentrations and pools through time on an experimental catchment cleared in a whole-tree harvest in 1983–1984. Nitrogen losses from the forest floor at the site, the Hubbard Brook Experimental Forest, New Hampshire, were lower than predictions based on previous research. The mean forest floor nitrogen pool was 17% lower 8 years after clear-cutting of the site (P = 0.18). Predictions based on chronosequence studies suggest that 25–40% of the forest floor nitrogen would be lost after 8 years. Mechanical disturbance during logging may play a role in limiting short-term nitrogen losses. The steep midsection of the catchment experienced the greatest losses of nitrogen and carbon, while pools in the relatively flat spruce-fir zone at the upper elevations were unchanged. Carbon was preferentially lost from soil organic matter, relative to nitrogen, resulting in significant decreases in the C/N and C/organic matter ratios in the soil. The N/organic matter ratio was generally unchanged. Nitrogen losses can be limited after clear-cutting by minimizing organic matter losses and promoting rapid regrowth.

Description: Effect of aluminum (Al) on the growth, anatomy, and nutrient content of eastern white pine (Pinusstrobus L.) was determined by growing newly germinated seedlings for 12 weeks in sand irrigated with nutrient solution (pH 3.8) containing 0, 12.5, 25, 50, 75, or 100 mg/L of Al. To determine the influence of mycorrhizal infection on Al toxicity, half of the seedlings were inoculated with the ectomycorrhizal fungus Pisolithustinctorius (Pers.) Coker & Couch. Across Al concentrations, shoot growth (height, needle length, biomass) but not root growth (lateral root length, biomass) was significantly greater in ectomycorrhizal (ECT) than nonmycorrhizal (NM) seedlings. Aluminum significantly decreased shoot and root growth in ECT and NM seedlings but had less effect on growth in ECT seedlings. Foliar symptoms of Al toxicity (chlorosis, tip necrosis) were more pronounced in NM than in ECT seedlings. Cellular and ultrastructural injury to needles and root meristematic tissues was observed at lower concentrations of Al in NM seedlings than in ECT seedlings. Amelioration of Al toxicity by mycorrhizal colonization appeared to result from enhanced uptake of nutrients, especially P, rather than to reduced uptake of Al.

Description: Techniques are described for field and laboratory extraction of small quantities of sugar maple (Acersaccharum Marsh.) xylem sap when pressure in the xylem is less than atmospheric. Accurate estimates of sap sugar concentration can be made with a hand refractometer most of the year. There is, however, appreciable within-tree variation in sap sugar concentration at any given time and within short periods of time.

Description: Ecotone vegetation may be especially sensitive to climate change. In particular, the invasion of subalpine meadows by tree seedlings has been well documented. However, there has been no systematic analysis of tree regeneration across the environmental heterogeneity of the alpine forest–tundra ecotone (FTE). Also, the position of the FTE may be relictual from more favorable climates of the past and therefore unresponsive to changing climate. To assess the environmental controls on FTE tree regeneration, to determine whether the ecotone might be relictual, and to determine whether tree invasion of nonforested FTE areas is occurring, we measured tree regeneration in various environments within the FTE of Rocky Mountain National Park, Colorado. Generally, seedling establishment appears to be controlled by patterns of soil moisture. Little seedling establishment was observed in krummholz openings, except for high seedling densities in willow wetlands. Tree seedling invasion of tundra is rare. Therefore, the upper limits of the FTE in Rocky Mountain National Park may be relictual from more favorable climates of the past. Abundant seedling establishment in patch forest openings suggests that patch forest may be poised to change to closed forest.

Description: Water chemistry profiles of an 18-year-old forest ecosystem are compared with those of a 70- to 90-year-old forest ecosystem for a 9-month period. The younger ecosystem was dominated by Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnusrubra Bong.) whereas western hemlock (Tsugaheterophylla (Raf.) Sarg.), Douglas-fir, and western red cedar (Thujaplicata Donn.) dominated the older ecosystem. Concentrations of nutrients and other chemicals were measured in throughfall, forest floor and mineral soil lecachates, saturated-zone water, and stream water. Concentrations of dissolved chemicals were much greater in the younger ecosystem than in the older ecosystem at intermediate stages in the profiles. However, stream water concentrations differed less between the two ecosystems for most of the chemicals investigated. Nitrate and silica were exceptional; stream water nitrate concentrations in the younger ecosystem averaged 16 times greater than those in the older ecosystem. This was probably a result of biological nitrogen fixation by red alder in the younger ecosystem, a process which would more than compensate for the higher nitrate losses. Silica concentrations in the younger ecosystem consistently exceeded levels in the older ecosystem by 40 to 100%. suggesting a possibility of a greater rate of mineral weathering in the younger ecosystem.Although nutrient concentrations were higher in the soil leachates of the younger ecosystem, these higher levels failed to persist through the saturated-zone water and stream water stages of the water chemistry profile. Consequently, the younger ecosystem appeared relatively more efficient at retaining dissolved nutrients than the older ecosystem. Stream water chemistry was relatively insensitive to the magnitudes of the differences in biogeochemical process rates of the two ecosystems.

Description: A data screening algorithm (SCREEN) identified stand age, average stand diameter, timber type, soil type, aspect, habitat type, and elevation as forest stand or site characteristics strongly associated with root-disease occurrence in northern Idaho forests. The logistic regression model was used to predict root disease center occurrence. A second algorithm (RISK) was used to compute the estimates for the coefficients and to test different prediction equations. On wet aspects, highest probability of root disease centers was found on soils with lowest year-round moisture availability. The reverse was true on dry aspects. Increased slope was associated with increased root disease. Root disease center frequency was inversely related to elevation and directly related to occurrence of Pseudotsugamenziesii (Mirb.) Franco and Abiesgrandis (Dougl.) Lindl. Expression of disease centers was maximum at 60–100 years of stand age on all habitat types. A habitat-type–age interaction was observed in oldest aged stands.

Description: Current research suggests that projected climate change may influence the growth of individual trees. Therefore, growth and yield models that can respond to potential changes in climate must be developed, TREE-BGC, a variant of the ecosystem process model FOREST-BGC, calculates the cycling of carbon, water, and nitrogen in and through forested ecosystems. TREE-BGC allocates stand-level estimates of photosynthesis to "each tree using a competition algorithm that incorporates tree height, relative radiation-use efficiency, and absorbed photosynthetically active radiation, TREE-BGC simulated the growth of trees grown in a dense and an open stand of interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) near Kamloops, B.C. The competition algorithm dynamically allocated stand estimates of photosynthesis to individual trees, and the trees were grown using an allometric relationship between biomass increment and height and diameter increment. Asymptotic height growth and the changes in the height–diameter relationship with competition were also incorporated in the model algorithms. Sapwood and phloem volume were used to calculate maintenance respiration. Predicted reductions in diameter growth with stand density were similar to those observed in the study stands. Although the carbon balance of individual trees was not tested, simulated tree diameter increments and height increments were correlated with the actual measurements of tree diameter increment (r2 = 0.89) and tree height increment (r2 = 0.78) for the 5-year period (n = 352). Although the model did not work well with trees that had diameters

Description: This study related age structure and composition of forests in southeastern Pennsylvania to edaphic properties caused by the activities of a local charcoal iron furnace from the late 18th to the late 19th century. Forests surrounding charcoal hearths were harvested on 20- to 30-year rotations to supply wood for charcoal production in earthmound kilns. Charcoal hearths were created by a recurring cycle of disturbance, including the removal of established vegetation, intense heat, and the deposition of charcoal. Thirty-eight hearths of Hopewell Furnace National Historic Site were examined to describe differences in vegetation relative to surrounding forests that have developed since the cessation of charcoal production in 1883. Hearth forests were significantly younger than surrounding forests, with lower tree density and basal area, decreased sapling and shrub abundance, and higher herbaceous cover. Compositional differences on charcoal hearths included decreased importance of several Quercus species and ericaceous shrubs and increased importance of Liriodendrontulipifera L. Results of this study indicated that the initial effect of charcoal production was the prevention of stump sprouting and a delay in recolonization following disturbance due to extreme soil physical and chemical properties. Failure of hearth seedlings to recruit into larger size classes, age–diameter relationships of Liriodendrontulipifera L. trees, and the failure of calcifuge species to reestablish similar cover on charcoal hearths suggested that unfavorable properties of charcoal soils continue to negatively affect long-term productivity. Relative to nonhearth soils, large, significant differences in soil pH, cation exchange capacity, base saturation, and exchangeable Ca, Mg, and K indicated that continuing inhibition of woody plants on charcoal hearths may be related to alterations in soil chemistry that have persisted for 110 years.

Description: The effects of defoliation by western spruce budworm (Choristoneuraoccidentalis (Freeman)), on Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) radial growth at breast height and tree mortality are given. Four hundred and twenty trees were marked in an 81-year-old stand, and their defoliation levels were recorded annually from 1970 to 1980 in an outbreak that lasted from 1970 to 1974, inclusive. Forty-one trees were felled and dissected in 1977, 3 years after recovery began. The number of stems per hectare was reduced by 39.3% and basal area by 11.6% through mortality, most occurring among the small diameter, suppressed, and intermediate trees. Relationships were established between mortality and defoliation. Radial increments were examined, and the presence of four outbreaks during the life of the stand was detected. The combined effect of these infestations amounted to a loss of about 12% of the estimated potential diameter had not the insects been active. The most recent outbreak (1970–1974) caused a total of 10 years of subnormal growth, including 5 years due to defoliation and 5 years of recovery. The relationship between radial increment losses and defoliation intensity and duration is studied and quantified.

Description: Copper, nickel, and cobalt solutions were added to a variety of substrates to test the effects of these metals on the germination and radicle elongation of two deciduous and five coniferous woody species native to eastern North America. For species grown on filter paper, germination was little affected by metal concentrations of up to 100 ppm. Filter-paper tests showed that radicle elongation was reduced by 25% at concentrations that ranged from 1 to 5 ppm for Betulapapyrifera Marsh, to as much as 50 to 100 ppm for Pinusstrobus L. Concentrations causing similar effects on mineral and organic soil substrates were, respectively, 10 and 100 times greater than those for filter paper. For all species, toxicity followed the pattern Ni 〉 Cu 〉 Co for filter paper and [Formula: see text] for mineral and organic soils. Deciduous species were more readily damaged by these metals than were coniferous species.

Description: The vegetative phenology of Piceaglauca (Moench) Voss and P. mariana (Mill.) B.S.P. was determined in 1979 based on four ramets selected from each of 14 clones of each species located at a seed orchard in northern Ontario. The time of flushing of the leaders and four lateral branches was determined by a qualitative index of bud and shoot development; time of growth cessation was scored as the date at which 95% of shoot growth was complete. The flushing of the vegetative buds of white spruce lasted for a 10-day period compared with only 6 days for black spruce. Although the average date of flushing for white spruce clones was 9 days ahead of the average date for black spruce clones, the latest white spruce clone flushed only 3 days before the earliest black spruce clones. As well, degree-day requirements for flushing were significantly different for clones within each of the two species. These results suggest that the selection of late-flushing white spruce trees for seed orchard stock has the potential to decrease spring frost damage in this species in northern Ontario. Date of budbreak was not correlated with date of growth cessation for either white or black spruce; however, early-flushing clones of black spruce produced significantly greater leader extension than late-flushing clones.

Description: Ocular and shoot-count defoliation estimation techniques were compared for accuracy and precision at the levels of branches and crown position within trees, whole trees, plots, and stands. A shoot-count estimate of defoliation for a midcrown branch had the best relative accuracy (±7%), while the best ocular estimate was for the whole tree by an experienced observer (accuracy ±12%). Ocular estimates were biased towards ovcrestimation at low defoliation levels (error 20–30% defoliation), and previous defoliation caused the ovcrestimation of current defoliation by 30–40% on trees that had been previously severely defoliated. Observers were found to be consistent in their rating, but biased by about ±10%; experienced observers were about 5–10% more accurate than inexperienced observers. Intertree variance in defoliation was greater than intratree variance or variance between plots in a stand. It was concluded that ocular estimation of defoliation is a viable technique that can give accuracy within the limits required for surveys and many research applications, if the influence of observer experience, observer bias, and previous defoliation arc recognized, and adjusted for when necessary.

Description: The photosynthetic capacity of different needle age-classes of black spruce (Piceamariana (Mill) B.S.P.) was studied using 14C labelling on whole branches at a site near Fairbanks, Alaska. Black spruce had highest photosynthetic rates in the 1-year-old tissue with the four most current age-classes showing similar high rates before declining with age. Older needles were found to maintain 40% of maximum photosynthetic rates after 13 seasons. Highest level of nitrogen was found in current needles with the first eight age-classes maintaining high levels before declining to 70% of maximum values in the oldest needles. Phosphorus levels were much higher in current tissue with a gradual decline after the 1-year-old tissue to a value of 55% of maximum values in the oldest tissue. Nutrient use efficiency was found to be highest in the 1-year-old tissue and declined with needle age. The loss of nutrient use efficiency may be due to the use of older tissue as aboveground nutrient stores, a decline in the efficiency of the photosynthetic apparatus of the needles, or an increase in the leaf specific weight. Black spruce has adapted to the low nutrient availability with low photosynthetic rates and low nutrient contents. Greater longevity of the needles would maximize the photosynthetic return per unit nitrogen invested in the needles.

Description: Twenty-four specimens of six boreal tree species were excavated: eight Pinusbanksiana Lamb., five Populustremuloides Michx., four Piceaglauca (Moench) Voss, three Piceamariana (Mill.) B.S.P., two Abiesbalsamea (L.) Mills., and two Lara laricina (Du Roi) K. Koch. Root systems were described, and percent biomass determined for above- and below-ground components for half these specimens. Tree ages ranged from 3 to 120 years. Horizontally spreading lateral roots dominated the root systems of all species and occurred within 3– 15 cm of the ground surface. Nutrient and moisture absorption appear to be the principal functions of lateral roots. Maximum vertical root growth occurred near the tree stump as: tap-, heart, sinker, and oblique lateral roots. Vertical root morphology is influenced by site conditions. In addition to providing mechanical support, sinker and taproots may be important adaptations for deep-water utilization on xeric sites. Our data suggest that roots may be important in boreal succession processes through two related mechanisms: (i) nutrient and water deprivation occurring through preemptive growth of tree roots from climax species over roots of serai species, and through interception by mosses; and (ii) niche partitioning occurring below ground between serai and climax, and among climax tree species, by vertical separation of the root systems.

Description: The impact of Hurricane David on the forests of Dominica was measured 40 days after the hurricane struck the island on August 29, 1979, with winds averaging 92 km/h which lasted 10.2 h. Sixteen 0.1-ha plots were studied. They were located on a variety of slope and exposure conditions, representing three life zones and 11 plant associations. Measurements included tree diameter at breast height (dbh), total height, wood volume, and percent canopy closure of stand. Species and damage conditions were noted. The hurricane caused severe damage, particularly to forests on the southern half of the island. Forty-two percent of the standing timber volume in the study areas was damaged at an average intensity of 27 m3/ha. About 5.1 × I06 timber trees were damaged in an area of 246 km2. "Complex" vegetation was more resistant to hurricane damage than "simpler" vegetation. The climax Dacryodesexcelsa Vahl associations suffered the least hurricane damage, while the palm brake suffered the most damage. Only one species (Richeriagrandis Vahl) exhibited significantly higher hurricane damage. Trees in larger diameter classes tended to uproot with more frequency than smaller diameter trees, which tended to snap and break. Regrowth of seedlings and saplings was rapid on wet areas of the damaged sites. We found more species on regenerating plots than on the undisturbed forest plots. The damage caused by Hurricane David is the most extensive reported to date anywhere, and damage to vegetation by hurricanes appears to be more extensive than damage by earthquakes and landslides. Owing to their high frequencies in the Caribbean, hurricanes induce cyclic plant successions.

Description: Extensions of a basic allometric equation applied in predicting total foliage of individual trees were developed to estimate foliage and woody components of individual branches in western hemlock (Tsugaheterophylla (Raf.) Sarg.), Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), and grand fir (Abiesgrandis (Dougl. ex D. Don) Lindl.). Nine initial equations were fitted on both nonlinear and log-transformed scales to data collected in the western Cascade Mountains of Washington. In all cases, the logarithmic form of each equation provided the best fit to the data based on a modified likelihood criterion and residual patterns. Branch diameter was the overall best predictor of branch foliage and woody mass; however, significant (p = 0.05) improvements in fit were obtained when other structural and positional variables were included in the equations (e.g., foliated branch length and depth into crown). The effects of fertilization and site (locality) differences were explored using indicator variables for western hemlock branches. Significant site effects were observed for intercept terms for all three branch components (total foliage area, total foliage mass, and total woody mass), while fertilization effects were observed in interaction with relative height above crown base for both foliage components.

Description: A field experiment was established between 1989 and 1993 to study the effects of (i) the age of clearcuts on damage by pine weevils (Hylobiusabietis L.) and (11) competing vegetation on the survival and growth of planted Norway spruce (Piceaabies (L.) Karst.). On each of four sites Norway spruce seedlings were planted on 0 to 4-year-old clearcuts. Effects of mounding, herbicide and mowing, removal of slash, and seedling stock type were also investigated. As many seedlings suffered severely from a drought that affected southern Sweden in 1992, this study reports a separate analysis of mortality due to drough. From the middle of May until the beginning of July 1992, only negligible precipitation was recorded on all four sites. The biomass of ground vegetation was correlated with the age of the clearcut. On fresh and 1-year-old clearcuts, only negligible amounts of vegetation were found, whereas about 2 Mg•ha−1 of ground vegetation were found on 2- and 3-year-old clearcuts. Low soil water potentials were recorded on 2- and 3-year-old clearcuts but not on fresh clearcuts. There was no effect of the slash removal treatment on soil water potential, but there was a significant effect of the soil and vegetation treatments. Mounding and herbicide treatments increased the soil water potentials compared with untreated controls and mowed plots. Mortality by drought was higher for seedlings planted on old clearcuts than for seedlings planted on fresh ones. Mortality was reduced by mounding, but late planting increased the number of dead seedlings significantly. The mortality of containerized seedlings was considerably less than that of bare-root seedlings. On old clearcuts growth of seedlings planted on plots with no vegetation control (untreated control and mown plots) was less than that of seedlings planted on plots where transpiration by ground vegetation was reduced (herbicide and mounding).

Description: A probabilistic two-step method of analysis is described that overcomes the problems associated with using a single model to analyze data drawn from a two-state system. The two steps of the analysis are (i) to determine the probability that an observation with given characteristics falls in each of the two states of the system and (ii) to estimate the response of the dependent variable in each of the two states as a function of characteristics of observations. Estimating cull volume in standing trees provides an example. This analysis results in two component models that more closely describe the process of interest than is possible with any single model. Statistically sound approximations to confidence intervals and tests of hypotheses for the parameters of each of the component models may be computed.

Description: Measurements of aboveground biomass and nitrogen (N) nutrition were made during July 1993 in 50-, 130-, and 380-year-old stands of Larixgmelinii (Rupr.) Rupr. in eastern Siberia. Constituting six forest types based on understorey plants, the stands were representative of vegetation throughout the Yakutsk region. Average tree height, diameter, and density ranged from 2 m, 23 mm, and 50 800 stems/ha in the 50-year-old stand to 11 m, 160 mm, and 600 stems/ha in the oldest stand. Aboveground biomass in the 50-year-old stand was 4.4 kg•m−2, and the aboveground N pool was 1.1 mol•m−2. This was slightly higher than the N pool in a 125-year-old stand with a Ledum understorey (1.0 mol•m−2), despite its higher biomass (7.2 kg•m−2). The highest observed aboveground biomass in a 125-year-old stand (characterized by the N2-fixing understorey plant Alnasterfruticosa) reached 12.0 kg•m−2, but the corresponding N pool was only 1.6 mol•m−2. In the oldest stand, aboveground biomass was 8.9 kg•m−2 and the N pool was 1.1 mol•m−2. There was thus a relatively constant quantity of N in the aboveground biomass of stands differing in age by almost 400 years. We postulate that N sets a limit on carbon accumulation in this boreal forest type. Trees were extremely slow growing, and there was essentially no aboveground biomass accumulation between the ages of 130 and 380 years because of a lack of available N. This conclusion was supported by graphical analysis indicating that the self-thinning process in our stands was not governed by the availability of radiation according to allometric theory. Much of the available N was used in the production of tree stems where 86% of the aboveground N (and 96% of aboveground biomass) was immobilized in the oldest stand. N in wood of the old stand exceeded the N pool in the litter layer and was 20% of the N pool in the Ah horizon. The processes of carbon and N partitioning were further explored by the estimation of carbon and N fluxes during three periods of forest development. We calculated a loss of ecosystem N during the period of self-thinning, while in the mature stands the N cycle appeared to be very tight. The immobilized N is returned from the wood into a plant-available form only by a recurrent fire cycle, which regenerates the N cycle. Thus fire is an essential component for the persistence of the L. gmelinii forest.

Description: Riparian forests are often identified as prime habitat for wildlife because of the presence of particular plant communities and edges creating a highly developed and diversified vegetation structure. However, in the northeastern boreal forests of Canada, where narrow land–water ecotones with abrupt edges are quite common, the relative habitat value of riparian forests remains to be demonstrated. We compared bird communities of eight pairs of riparian and nonriparian plots, similar in vegetation structure and composition, to verify the relative value for breeding birds of typical coniferous riparian forest stands of the southern boreal region of eastern Quebec. Bird abundance (P = 0.02), richness (P = 0.03), and diversity (P = 0.02) were significantly higher in the riparian stands, where the spatial sequence of three distinct habitats (a balsam fir (Abiesbalsamea (L.) Mill.)–northern white cedar (Thujaoccidentalis L.) forest, a narrow alder (Alnusrugosa (Du Roi) Spreng.) - grass wetland, and water) created high horizontal vegetation diversity. In riparian stands median bird richness and density were, respectively, 23.5 species and 437.5 territories/km2 compared with 19.0 species and 348.2 territories/km2 for interior stands. Nine species were observed exclusively in riparian plots. In addition to the species usually found in the studied nonriparian forests, the riparian plots were used by species typically related to the water edge such as the Northern Waterthrush (Seiurusnoveboracensis Gmelin) and Rusty Blackbird (Euphaguscarolinus Miiller) as well as species associated with the shrub and grass wetland such as the American Robin (Turdusmigratorius L.), the Veery (Catharusfuscescens Stephens), and the Common Yellowthroat (Geothlypistrichas L.). The shrub-foraging guild showed higher abundance in riparian stands. The tree-foraging and tree-bole foraging guilds, however, were comparable in both groups of stands. In this study, the natural conditions prevailing along he riparian sites appeared mostly positive for the breeding-bird community; it created what is perceived as being an "edge effect." The edge effect can be defined, in this case, as being the additional density and number of species induced by the added horizontal vegetation diversity created by the close association of three extremely different ecosystems: a forest stand, an aquatic ecosystem, and a narrow but distinct shrub-grass wetland. This also confirms the necessity of distinguishing natural edges that are permanent features of the landscape from induced edges created by human activity.

Description: A variety of evergreen and deciduous forests in the taiga of interior Alaska were studied over a 5-year period to examine how the chemical quality of forest-floor organic matter affected its rate of decomposition and mineral cycling within and outside the tree vegetation. Litterbag and respiration studies were used to monitor decomposition. Natural forest-floor substrates and others altered by addition of N, P, and K fertilizer and glucose as a carbon source were studied in the laboratory and field for rates of weight loss and O2 consumption. Forest floors differing in C/N ratios, including those deficient in N, were used to measure substrate quality influences on seedling growth, nutrient content, and tannin content. Microbial (bacteria and fungi) biomass was measured across a range of forest types along with pH, base saturation total pool sizes of N and P, and annual mineralization of organic matter per square metre. Under identical moisture and temperature conditions average respiration rates in evergreen forest-floor L, F, and H substrates were 1.8, 2.8, and 2.0 times less than in the corresponding deciduous forest horizons, respectively. Birch L and F horizons had respiration rates 11.5 times higher than the corresponding black spruce layers. Weight losses in birch L, F, and H horizons were 6, 3, and 2 times higher, respectively, than in the corresponding black spruce substrates. Substrates had a quality-dependent decay rate which did not change when they were relocated within or between sites indicating that measured field climatic differences were not as influential on decay rates as substrate quality components. Fungal biomass was significantly correlated with the quantity of organic matter in all sites (n = 15, r = 0.62) but correlations were better for deciduous (n = 9, r = 0.89), and evergreen (n = 6, r = 0.82) forests separately. Strong correlations exist also between grams of organic matter decayed per square metre per year and fungal biomass (n = 13, r = 0.86), and fungal biomass and grams of N and P mineralized per square metre per year (n = 14, r = 0.95) and (n = 11, r = 0.94, respectively). Seedlings on mineral-deficient substrates produced more tannins than the controls, and seedlings on substrates with widening C/N ratios had successively less tissue with lower N content, and proportionally more roots. Nitrogen content of litter fall in increasingly nitrogen-poor forest floors was correspondingly lower. Nitrogen content of litter fall on N rich forest floors and N fertilized forest floors was proportionately higher. Nitrogen withdrawal in leaves at senescence was inversely correlated with grams N mineralized per square metre per year in forest floors. Fertilization did not influence microbial processes in the field, though lab studies indicated a negative influence of NH4, P, and K on microbial respiration. Glucose added in the laboratory and field markedly increased forest-floor microbial respiration. In vitro glucose-induced increases in respiration were not influenced by addition of ammonium nitrate and were significantly depressed by addition of P and K. In the field, fertilization had no effect on either glucose-induced respiration or microbial biomass.

Description: An old, merchantable, low-site class black spruce (Piceamariana (Mill.) B.S.P.) stand growing on a Lithic Humo-Ferric Podzol overlying a granite bedrock, and a younger but merchantable low-site class jack pine (Pinusbanksiana Lamb.) stand growing on a Ferro-Humic Podzol overlying a deep coarse sand near Baie Comeau, P.Q., were analysed for stand biomass and macronutrient contents of both stand and soil. The magnitude of the depletions of macronutrients from the site, in full-tree and tree-length methods of logging, are compared with their available and total quantities in the soil. The range of values from the literature for nutrient inputs are presented and discussed in relation to logging losses. The results suggest that full-tree logging in the dry jack pine stand could cause a severe loss of potentially mineralizable N supply; P, K, and Mg deficiency problems owing to export are not apparent, but a Ca balance problem is apparent. The implication is that full-tree logging should be avoided on such sites.

Description: The advance regeneration often present following clear-cutting in black spruce (Piceamariana (Mill.) B.S.P.) stands is generally composed of individuals of various heights. This initial height difference is hypothesized to affect the yield of the future stand. Height of the advance regeneration at time of release was determined on several black spruce trees within 33 stands distributed across the boreal forest of the province of Quebec, Canada. From these data, a regeneration structure index was developed and used to explain a part of the variation in subsequent stand yield. Dominant trees of stands developing for 38 to 65 years since clear-cutting generally originated from the tallest advance regeneration at time of release. Stands with the tallest regeneration at time of release produced the largest yields for a given site quality and number of years since harvesting. A 3-m increase in advance-regeneration height resulted in a similar yield gain as a 3-m increase in site index. Site indices calculated from age-height relationships of dominant trees originating from tall advance regeneration were less than those calculated from trees that have undergone a relatively short period of suppression. These results suggest that traditional management tools developed for fire-origin black spruce stands, i.e., stands mainly composed of seed-origin trees established after perturbation, should be adjusted for clearcut-origin stands that largely develop from advance regeneration.

Description: Seven units (about 2 ha each) of black spruce – feather moss forest were experimentally burned over a range of fuel moisture conditions during the summer of 1978. Surface woody fuels were sparse and the principal carrier fuel was the forest floor (largely mosses and their decomposition products). Forest floors after burning comprised a small-scale mosaic of unburned, scorched, lightly burned, moderately burned, and heavily burned (organic materials entirely consumed) conditions. Percentage of the unit area in the moderately and heavily burned condition ranged from 11.2 to 77.2% and percent decrease in forest-floor thickness varied from 27.4 to 63.1% in the seven units. Forest-floor consumption was most closely correlated with the moisture content of lower moss (01 horizon) and lower duff layers (022 horizon) at the time of burning. For the first 3 years after fire, biomass production was greater on heavily burned than on lightly burned sites (58 vs. 37 g/m2 on an annual basis). Heavily burned sites were completely dominated by the invading species Epilobiumangustifolium L., Ceratodonpurpureus (Hedw.) Brid., and Marchantiapolymorpha L., whereas lightly burned plots were occupied by sprouting species such as Calamagrostiscanadensis (Michx.) Beauv., Vacciniumuliginosum L., and Ledumgroenlandicum Oeder. Soil pH and amounts of total P and available P in the forest floor increased significantly as a result of burning; and in all cases, increases reached a maximum in moderately and heavily burned areas. Total N in the forest floor increased significantly in moderately burned, but decreased slightly in heavily burned areas. Total N and total P showed smaller increases in the surface mineral soil as a result of burning. Supplies of available P in the mineral soil increased almost 4-fold in moderately burned and over 16-fold in heavily burned areas.

Description: Radial stem wood sections of fertilized (at age 14 years) and unfertilized loblolly pine (Pinustaecla L.) trees were analyzed 5 and 9 years after treatment to establish if xylem nitrogen (N) can be used for a diagnostic nitrogen test. The percentage of xylem nitrogen in wood formed since fertilization was greater in fertilized than in unfertilized trees. The 2 years of wood growth near the cambium had a higher percent N than older wood, but differences between treatments were less pronounced than in older wood. Concentrations of N for fertilized and unfertilized trees were nearly constant for 2- to 9-year-old wood indicating that a sampling technique to determine the N status of loblolly pine could be developed by increment coring.

Description: The ability of seedlings of Eucalyptustereticornis Smith to accumulate 137Cs and 90Sr, characteristic radioisotopes of nuclear fallout, from contaminated growth medium was tested. All seedlings were grown for 3 months in 165 cm3 of sphagnum peat moss–perlite (1:1 v/v) in a growth chamber before treatment with an isotope. After 1 month of exposure, seedlings had accumulated 31.0% of the 137Cs and 11.3% of the 90Sr originally present in the growth medium, with bioconcentration ratios of 54:1 for 137Cs and 13:1 for 90Sr. Accumulation of 137Cs and 90Sr in plant tissue was correlated curvilinearly with increasing time of exposure and with increasing concentration of radioisotope in the growth medium. Because seedlings of E. tereticornis accumulate these radioisotopes rapidly, they may be valuable in remediation of contaminated soils.

Description: Allometric regressions for estimating red maple (Acerrubrum L.) biomass did not differ by stand age and site index. Significant differences were found only in terms of error variance, not in terms of regression slope or intercept. These trends suggest a single predictive model is valid for regional estimates. More attention should be given to regional sampling procedures and predictive relations that are valid for a wide range of stand and site conditions in developing weight tables and conducting biomass inventories.

Description: This study characterized the height growth and crown form of 14-year-old balsam fir regenerated naturally under a light gradient varying from 3 to 83% of photosynthetic photon flux density (PPFD). After 14 years, total height growth was correlated with percent PPFD (R2 = 0.766; p 

Description: A linear mixed-effects model that accounts for the covariances among repeated measurements and for random plot effects is developed. A continuous-time autocorrelation error structure permits the model to be applied to irregularly spaced, unbalanced data. A strategy for fitting this model and diagnostic tools for assessing its goodness of fit are presented and demonstrated. The model is fitted to two permanent-plot data bases and shows marked improvement compared with models that do not account for the error structure.

Description: We studied the wood structure of eastern larch (Larixlaricina (Du Roi) K. Koch) affected by a larch sawfly (Pristiphoraerichsonii (Htg.)) infestation that occurred in 1939 in the Lac à l'Eau-Claire and Rivière-aux-Mélèzes areas, subarctic Quebec. The objective was to document variation in wood characteristics in relation to defoliation at three study sites. Lumen diameter of tracheids and cell wall thickness were measured from thin sections representing the 1931–1955 period. Significant changes in the wood structure of larch was noticed only at the Atkinson Island site, where the radial growth pattern was typical of the insect activity. A light ring was formed the 1st year of the infestation (1939). During the 2nd year (1940), the size of tracheids (lumen) decreased abruptly along with radial growth, while the proportion of latewood increased. The variation in wood anatomy among the three study sites paralleled that in radial growth. Wood structure appears to be a good indicator of the end of an infestation.

Description: A nonlinear model that yields logical predictions for tree crown ratio is presented. The model is based on data from permanent experimental plots located in even-aged Scots pine (Pinussylvestris L.) stands in southern and central Finland. Regressor variables in the model are stand dominant height, stand basal area, tree diameter, and tree height. The effect of thinning on tree crown ratio is modelled by incorporating a thinning response variable into the model. Thinning effect is dependent on thinning intensity and time elapsed from thinning, the latter of which is represented by the difference between current stand dominant height and dominant height at the time of thinning.

Description: Modeling both road construction and land management activities as 0–1 variables greatly enhances the spatial aspect of linear programming models dealing with harvest scheduling and transportation planning. In previous work we developed a heuristic procedure that modeled only road construction as 0–1 variables. We have expanded this past procedure to also consider land management decisions as 0–1 variables. This paper outlines the heuristic procedure developed for modeling both road building and land management decisions as integer variables in light of adjacency constraints. The heuristic procedure allows economic or physical objectives to be maximized or minimized. A wide variety of side constraints can be accommodated and these constraints can include both road construction and land management decision variables. These heuristic procedures have performed well on models tested thus far.

Description: The relationships of root attributes and tree, stand, and site factors to root contact between second-growth Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) were studied in excavated root systems. Type 1 contacts (tenuous) were positively related to root length and inversely related to root volume. Type 2–3 contacts (with slight to severe root deformation) were positively related to number of roots. Type 4 contacts (apparent grafts) were positively related to root number and cross-sectional area. Differentiation among groups containing no contacts. Type 1 contacts only or all contact types showed that intertree distance, tree diameter, rooting depth, soil gravel content, and percent slope were significant in determining probability of root contact.

Description: In response to concerns about the effects of slash removal on natural regeneration, a microenvironment study was conducted in logging slash using weighed full-tree (FT) and tree-length (TL) slash loads, and no slash (control), in the first summer after harvesting a mixed stand in New Brunswick. Significantly higher temperatures at the litter surface occurred in control and FT plots than in TL plots. Potentially lethal temperatures for new conifer germinants were recorded 18 times in FT and control plots combined, and once in TL plots. Differences among treatments in temperature peaks diminished in prolonged droughty weather. There were no differences in soil moisture tension at 10 cm depth, apparently because of restricted drainage. An average of 95% of full solar radiation (W/m2, response range of measuring device 0.35–2.5 μm) was measured in FT slash and 66% in TL slash. No significant differences in mortality or height growth of established coniferous advance growth (Picea spp. and Abiesbalsamea (L.) Mill., mean height = 28.5 cm) occurred, but significantly less mortality and significantly greater height growth of small AcerrubrumL. seedlings (mean height = 7 cm) occurred in the FT and control treatments than in the TL treatment. Results suggest that harvesting methods that involve slash removal could result in increased mortality of small conifer seedlings from direct heat damage and in increased competition from pioneering hardwoods.

Description: Seed size was examined as a possible explanation for variation in the size of containerized loblolly pine (Pinustaeda L.) seedlings. Under laboratory conditions of minimal environmental stress, larger seed were found to germinate more quickly and produce a larger germinant after 28 days of growth. In a similar experiment conducted under greenhouse growing conditions, large seed produced the largest seedlings. Size differences among seedlings in both experiments resulted from differences in the rate of germination unique to each seed size class. Consequently, seedling size and possibly uniformity of growth were considered to be a function of germination patterns which were strongly influenced by seed size and weight.

Description: A 24-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) stand was treated with various levels and combinations of nitrogen fertilization and thinning. Over a period of 5–9 years after treatments, trees were sampled to determine effects on foliage quantity and sapwood characteristics at different stem heights together with their relationships. Sapwood width remained relatively constant up the stem where heartwood was present, but the number of annual rings it contained decreased with height. The sapwood width at breast height (bh) increased with stem diameter; treatments had little effect on percent sapwood at bh. The ratio of foliage mass to sapwood cross-sectional area changed for different portions of the crown and was lower when based on sapwood area at bh than at base of live crown. Significant linear relationships of foliage mass and area to sapwood area at bh were found, but relationships of foliage to basal area (bh) were just as close for all treatments; treatments significantly affected these relationships with control trees having the lowest regression slopes.

Description: Tomato mosaic tobamovirus (ToMV) was detected by enzyme-linked immunosorbent assay in the roots of red spruce (Picearubens Sarg.) on Whiteface Mountain, New York. Both virus incidence and concentration in the roots of red spruce vary by site and were greater in trees with little to moderate crown dieback than in trees with severe dieback. There was no significant association between virus incidence or concentration in the roots of red spruce and elevation on Whiteface Mountain. Multiple regression analysis of virus concentration in the roots, as the dependent variable, was performed against nine selected crown and root variables. In the final regression model, the number of live second-order nonwoody roots per length of first-order nonwoody root and length of the live crown were positively and negatively correlated, respectively, with virus concentration in the roots. These results suggest a complex epidemiology and a potentially significant impact of ToMV infection on the growth of red spruce on Whiteface Mountain.

Description: The allocation of biomass and nutrients (N, P, K, Ca, Mg) was measured from August 1976 to September 1978 in a young, second-growth Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) stand in the Oregon Coast Range. Tree biomass comprised 78–79% of the total standing crop of organic matter with the remainder allocated as follows: soil organic matter, 17%; forest floor, 4%; and fungi, 2%. Bole biomass accounted for 64–66% of the total tree standing crop; the remainder was apportioned among: nonmycorrhizal roots, 17–18%; branches, 7–8%; mycorrhizae, 6%; and foliage, 4%. Nutrient stocks in aboveground tree components exceeded those in belowground components by one to nine times. For all nutrients except Ca, roots and mycorrhizae contained larger stocks than either the forest floor or fungi; amounts of Ca in the forest floor and in fungi were twice those in roots and mycorrhizae. Return of organic matter to the soil by fine roots and mycorrhizae ranged from 84 to 78% of total tree return. About 73% of total net primary production was invested in growth and maintenance of roots and mycorrhizae. Return of N, P, and K to the soil by mycorrhizae comprised 83–87% of total tree return and 25–51% of Ca and Mg return. Return by mycorrhizae of N, P, and K was four to five times greater than that of roots, nearly equal for Ca, and three times less for Mg.

Description: This work reports and discusses data gathered during soil solution monitoring that was part of an experiment conducted in the Duchesnay Experimental Forest (Quebec, Canada) to study the effects of induced deep frost, superficial frost, and superficial frost plus drought on mature sugar maple trees (Acersaccharum Marsh.). Frost treatment was applied by preventing snow from accumulating under the canopy. Soil solution chemistry was modified when mature sugar maple trees declined after exposure to a severe deep frost. The first vegetation period after treatment showed that losses of NO3− below the rooting zone were greatly increased under affected trees. The leaching rate of NO3− and basic cations was directly related to the level of change in canopy dieback and transparency. A mean NO3− concentration of 630 μmolc•L−1 (53 times the controls; max. 4500 μmolc•L−1) was measured in soil solution under the deep frost treated trees. The leaching rate of K+ (18×, relative to the control) and Mn2+ (11×) was higher than that of Mg2+ (5×) and Ca2+ (2.6×). Acidification of the soil solution (50% more H+) as a result of intense nitrification caused an increase in aluminum concentration (5×) and a decrease in SO42−. The acidification during the year after treatment was equivalent to decades of atmospheric acid deposition. The seasonal mean of SO42− did not differ between treatments, but there was evidence of a significant correlation between pH and SO42− in soil solution. Concentration of NH4+ was also enhanced but to a lesser degree (10×) than that of NO3−. Specific conductivity was a good predictor of NO3−, Ca2+, Mg2+, and total Al in soil solution. The ion balance shifted from an anion deficit to a strong cation deficit when NO3− concentrations were high. Superficial frost with or without induced summer drought did not cause any significant change in soil solution chemistry compared with the controls. These results indicated the necessity to consider perturbations induced by extreme climate conditions, like deep soil frost, for the interpretation of soil solution chemistry data in the context of acid deposition studies and forest health.

Description: The influence of spruce budworrn (Choristoneurafumiferana (Clem.)) defoliation was analysed at different stem heights by counting the number of latewood tracheids and measuring tree-ring width. The total height of the tree was divided into three different equal parts: the lower, the middle, and the upper sections of the total stem length. However, only the results of the lower and the upper sections will be presented in this paper. The reduction of ring widths started in the upper part for the living crown and continued downwards to the stem base (0 m) with a delay of 1–2 years. The number of latewood tracheids generally showed a reduction 1 year earlier than the ring widths, particularly in the crown, but also in the other parts of the stem. Considering this, we think that the reduction of the number of latewood tracheids may date the beginning of spruce budworm defoliation more accurately and present a better characterization of the first impact of spruce budworm than the measuring of the ring widths. This parameter will be particularly helpful (when expensive equipment, such as a densitometer or an image analysis system cannot be used) in detecting past outbreaks in the tree-ring records, especially when defoliation records are missing and when the reduction of the ring widths is not very pronounced.

Description: The root density and depth patterns of four boreal forest age sequences were analyzed for successional trends. Rooting depths increased with age on sandy substrates which supported aspen (Populustremuloides Michx.) and jack pine (Pinusbanksiana Lamb.) communities. Rooting depth did not change in an aspen series on fine-textured substrates or in a black spruce (Piceamariana (Mill.) BSP) series growing on organic substrates. Plant communities growing on mineral soils showed a decrease in near-surface root densities and understory vascular plant cover with increasing age. Maximum rooting was deepest on sandy substrates and shallowest on organic deposits. Roots in all stands were concentrated near the ground surface. In most cases 50% of all roots were located within 15 cm of the forest floor. Root densities in this zone ranged from 11 000 to 30 000 roots m−2 of vertical surface. Densities were approximately 4300 roots m−2 for the overall rooting zone.

Description: Analysis of dead boles of Piceasitchensis (Bong.) Carr. and Tsugaheterophylla (Raf.) Sarg. in open- and closed-canopy forests of the Olympic Peninsula Washington, U.S.A., revealed that hemlock mortality in both forest types was due mainly to windthrow, whereas spruce typically died upright. The open forest contained 120 t/ha of dead bole wood; the closed forest contained 161 t/ha. Hemlock boles decayed more rapidly than the larger spruce boles, although both showed considerable variability. On a per-hectare basis, 146–223 kg of N, 147–197 kg of Ca. 39–61 kg of K, 18–29 kg of Mg, 6–14 kg of Na, and 17–29 kg of P were contained in dead boles of the open- and closed-canopy forests, respectively. Except for N and Mg, the nutrient concentrations of the wood were not significantly different after 33–68 years of bole decay. The N:P ratios increased with increasing decay for both species.

Description: The biomass of 76 jack pine (Pinusbanksiana Lamb.) trees (29 stands) and 72 red pine (P. resinosa Ait.) trees (28 stands) from throughout the northern Lake States was determined. All trees were from even-aged, unthinned plantations ranging from 20–61 years old; site indexes represented nearly the complete range for these species. Individual tree component weights (foliage, live branches, dead branches, stem wood, and stem bark) were regressed against dbh and tree height using the nonlinear form Bt = aDbHc. Stand biomass was also estimated with stand basal area and mean height of dominant and codominant trees using the equation form Bs = a + b(B) + c(Hs) or a + b(B)(Hs). The equations were tested in two additional stands of red pine and two of jack pine and by comparison with literature values. Individual tree equations were most accurate for estimating bole components and the total tree and less accurate for foliage and branches. The standard error of the estimate divided by mean weight ranged from 0.06 to 0.17 for bole components, from 0.21 to 0.28 for live crown components, and from 0.43 to 0.49 for dead branches. For all components, jack pine equations were slightly less precise than those for red pine. The individual tree equations appear to be applicable over a wide geographical area and usable for both natural stands and plantations. The equations appear to be valid for the majority of unthinned stands in the age range of 20–50 years. The stand equations, while less precise than individual tree estimates, should give reasonably accurate estimates of stand biomass components in most situations.

Description: This paper is a comprehensive review of operational research studies in forest fire management during the years 1961 through 1981. It includes a brief discussion of fire management decision making, summaries of and comments regarding the practical merits of the work that has been done, and suggestions concerning future efforts in this field.

Description: The growth, biomass allocation, crown architecture, and leaf morphology of 50 to 200 cm tall Betulapubescens Ehrh. and Betulapendula Roth seedlings growing under eight Scots pine (Pinussylvestris L.) stands varying in age from 7 to 105 years were studied in southern Finland. The main objective of the study was to assess the degree of morphological plasticity of birch in response to understory conditions in stands of varying structure. In each of these stands, the light, water, and nutrient availability were measured. No clear trend in nutrient and water availability was found from the 7- to 105-year-old stands. Light availability decreased from the 7-year-old stands (45% and 82% of full sunlight in nongap and gap locations, respectively) to the 20-year-old stands (5% and 12% of full sunlight), and then increased to the mature stands (21% and 26% of full sunlight). Relative branch growth rate and height increment decreased with increasing shade. The ratios of leaf area to branch length and to branch weight did not vary significantly among the eight stands. The ratios of height to diameter and fine-root biomass to leaf biomass were the highest under the most shaded stands (20-year-old). Increase in shading decreased leaf thickness and increased specific leaf weight. No major differences were found in any of the growth parameters measured between the two birch species, indicating that they do not differ in their juvenile stage. These results indicate that these two birch species have relatively little morphological plasticity in response to shade. They appear to be able to persist in shade by minimizing carbon demand for growth and by modifying leaf morphology to presumably optimize photosynthesis.

Description: Retranslocation from leaves was investigated as a means of retaining nutrients in stands of Quercusprinus L. on two sites in southern Illinois, where wind rapidly moves litter downslope. Foliage samples were collected from late summer until leaf fall to describe the trends of leaf dry weight and nutrient concentration (N, K, P, Ca) changes. Free-falling rain and throughfall were collected to estimate foliar leaching. Foliar concentrations of N, K, and P decreased markedly during senescence while Ca concentrations increased. The pattern of concentration change was unique for each element, and the change in N concentration was closely correlated with change in leaf color. For the study sites as a whole, leaf dry weight decreased to 70% of the original value. Of 84.2 kg N/ha in green foliage, only 22.6% was returned to the site as litter. The canopy gained 0.3 kg N/ha (0.4%) from rainfall. The 78.5% N unaccounted for is attributed to retranslocation. Similarly, from 51.4 kg K/ha; 8.2, P; and 47.8, Ca in green foliage, 9.8, 1.3, and 3.3%, respectively, were removed by leaching; 27.4, 43.7, and 85.1% were returned to the site in litter. The remaining 63.0% K, 55.0% P, and 11.5% Ca unaccounted for is attributed to retranslocation. Retranslocation and leaching of nutrients was greater on the site of higher quality. But on both sites it appears that retranslocation is an important means of retaining and conserving N, K, and P countering the effect of annual litter removal.

Description: Seedlings of six Alaskan taiga tree species and one tall shrub were grown in sand at three phosphate levels. There was a positive correlation between the growth rate of a species at the high-phosphate level in sand culture and its productivity in the natural environment. Poplar (Populusbalsamifera L.), which had highest growth rate under high phosphate, was most sensitive to reduction in phosphate supply, followed by birch (Betulapapyrifera (Reg.) Fern, and Raup) and aspen (Populustremuloides Michx.), whereas growth of conifers (larch (Larixlaricina (Du Roi) K. Koch), white spruce (Piceaglauca (Moench) Voss), and black spruce (P. mariana (Mill.) B.S.P.)) from late successional sites was slow and unaffected by phosphate supply. Similarly, when birch and white spruce seedlings were transplanted into natural forest stands, the maximum growth rate of birch was greater than that of white spruce, but birch growth was curtailed more by unfavorable conditions than was that of white spruce. We conclude that a slow growth rate reduces nutrient requirement and therefore minimizes nutrient stress on infertile sites, whereas a rapid growth enables nutrient-demanding species to dominate fertile sites.

Description: The effects of CO2 enrichment on root proliferation of loblolly pine (Pinus taeda L.) and sweetgum (Liquidambar styracijlua L.) seedlings were studied under varied water and nitrogen (N) regimes and in competitive interaction. Seedlings of each species were grown from seed as monocultures or as 50:50 pine-sweetgum mixtures in 22-L pots filled with forest soil. Seedlings were exposed to either ambient (400 ppm) or CO2-enriched (ambient plus 400 ppm) air for 32 weeks in continuously stirred tank reactors. Detailed sampling of very fine roots (〉0.5 mm diam.) showed a general increase (up to 2-fold) in root length density (RLD, cm · m-3 with elevated CO2; however, the effects of CO2 on RLD differed according to species, culture type, water, and N availability. In monoculture, low water with low N conditions produced the largest RLD responses to elevated CO2: 75% increase for sweetgum and 31% increase for pine. In mixed culture, by contrast, the largest RLD responses to CO2 were observed under high water, high N regimes: pine showed a 110% increase and sweetgum a 96% increase. The total RLD of the standing crop in mixture under elevated CO2, high water, and high N was 2.6 cm · m-3 compared with 1.6 cm · m-3 in ambient CO2, with sweetgum accounting for 〉75% of the total RLD in both cases. These findings suggest that resource-rich rather than resource-poor soil environments could be th.e circumstances under which belowground interference from sweetgum would intensify in pine-sweetgum mixtures with rising atmospheric CO2.

Description: Studies to develop equations for upper stem taper, volume, and weight require observed values of upper stem volume. Tree volumes up to various upper stem diameters calculated using Smalian's formula throughout the stem length on 4- to 8-ft (1 ft = 0.30 m) bolts may overestimate true volumes by 1 to 4%. Calculating the butt bolt's volume with Newton's formula improves the estimates considerably. A new approach that uses Newton's formula on successive overlapping pairs of bolts produces even more improvement and still gives volume estimates for each bolt. The overlapping bolts method on 6-ft bolts is equally as precise as the conventional non-overlapping method on 4-ft bolts and would result in a 33.3% savings in sampling effort.

Description: Annual net N mineralization in the 0–10 cm mineral soil zone of nine forest stands on silt–loam soils was measured using a series of insitu soil incubations from April 1980 through April 1981. Differences in soil organic matter (SOM) dynamics among sites were shown with net N mineralization ranging from 0.54 to 2.10 mg N mineralized•g SOM−1•year−1. This variation was not related to percent N in SOM. Net N mineralization varied seasonally with maximum rates in June and very low rates in winter. Nitrification rates were constant from May through September despite fluctuations in soil ammonium pools. Nitrification was greater than 50% of annual net N mineralization at all sites. N uptake by vegetation, as estimated by net N mineralization plus mineral N inputs via precipitation, with minor corrections for mineralization below the incubation depth and for mineral N losses to groundwater, ranged from 40.3 to 119.2 kg N•ha−1•year−1. Annual leaf and needle litter production ranged from 2.12 to 4.17 Mg•ha−1•year−1 and was strongly correlated with N uptake (r = 0.938, P 

Description: Vegetation, forest productivity, and soils of 23 forest stands in the taiga of interior Alaska are described. The stands are arranged on an environmental gradient from an aspen (Populustremuloides Michx.) stand on a dry, steep south-facing bluff, to open black spruce (Piceamariana (Mill.) B.S.P.) stands underlain by permafrost on north-facing slopes. The coldest site is a mixed white spruce (Piceaglauca (Moench) Voss) and black spruce woodland at the treeline. Mesic upland sites are represented by successional stands of paper birch (Betulapapyrifera Marsh.) and aspen, and highly productive stands of white spruce. Several floodplain stands represent the successional sequence from productive balsam poplar (Populusbalsamifera L.) and white spruce to black spruce stands underlain by permafrost on the older terraces. The environmental gradient is described by using two soil factors: soil moisture and annual accumulated soil degree days (SDD), which range from 2217 SDD for the warmest aspen stand to 480 SDD for the coldest permafrost-dominated black spruce site. Soils vary from Alfie Cryochrepts on most of the mesic sites to Histic Pergelic Cryochrepts on the colder sites underlain by permafrost. A typical soil profile is described for each major forest type. A black spruce stand on permafrost has the lowest tree standing crop (15806 g•m−2) and annual productivity (56 g•m−2•year−1) whereas a mature white spruce stand has the largest tree standing crop (24 577 g•m−2) and an annual productivity of 540 g•m−2•year−1, but the successional balsam poplar stand on flood plain alluvium has the highest annual tree increment (952 g•m−2•year−1). The study supports the hypothesis that black spruce is a nutrient poor, unproductive forest type and that its low productivity is primarily the result of low soil temperature and high soil moisture.

Description: Mature dominant and codominant sugar maples (Acersaccharum Marsh.) at the Duchesnay Experimental Forest (Quebec, Canada) were subjected to deep soil freezing (DF), superficial freezing (SF), and superficial freezing with drought (SFD) during the 1990–1991 and 1991–1992 seasons. Soil temperatures below the DF trees reached lows of −6 °C at 20 cm depth and were significantly lower than the controls. Compared with the controls, unfrozen soil water content was lower (10%, v/v) below the DF trees. During the dry summer of 1991, soil water content remained high below the DF trees at 30% (v/v); controls reached 10% (v/v). Deep frost treated trees had significantly lower sap flow rates, total sap volume, and less total sugar per tree than other treatments for at least 2 years after treatment. These lower values were likely related to the condition of the DF trees (increased canopy transparency; branch dieback). Percent sugar was significantly higher in the DF trees in 1992. Drought did not seem to have a significant effect on sap flow rate as values obtained for 1991 to 1993 followed the same pattern as that for the control trees. Sap in SF trees tended to flow more than in control trees in 1991. Sap in DF-treated trees that did not show visual symptoms of dieback had a lower flow rate than control trees. Soil freezing, which is concomitant with severe reductions in soil water availability, had a negative effect on spring sap flow. A sufficient source of soil water at the moment of stem recharge seems to be critical during the conditioning period to maintain stem pressure and sap flow.

Description: We quantified stand leaf area index and vertical leaf area distribution, and developed canopy extinction coefficients (k), in four mature hardwood stands. Leaf area index, calculated from litter fall and specific leaf area (c2•g−1), ranged from 4.3 to 5.4 m2•m−2. In three of the four stands, leaf area was distributed in the upper canopy. In the other stand, leaf area was uniformly distributed throughout the canopy. Variation in vertical leaf area distribution was related to the size and density of upper and lower canopy trees. Light transmittance through the canopies followed the Beer–Lambert Law, and k values ranged from 0.53 to 0.67. Application of these k values to an independent set of five hardwood stands with validation data for light transmittance and litter-fall leaf area index yielded variable results. For example, at k = 0.53, calculated leaf area index was within ± 10% of litter-fall estimates for three of the five sites, but from −35 to + 85% different for two other sites. Averaged across all validation sites, litter-fall leaf area index and Beer-Lambert leaf area index predictions were in much closer agreement ( ± 7 to ± 15%).

Description: The effects of self-pollination in white spruce, Piceaglauca (Moench) Voss, were examined in 20 trees in three populations. The most drastic effect is the increased frequency of empty seeds which averages over 90%, and is 5 to 22 times higher than that from comparable cross-pollinations. The average numbers of embryonic lethal equivalents, although highly variable for individual trees, averaged 8.0, 9.1, and 12.9 for the three populations. Self-pollination also resulted in slightly lower germination and reduced survival. The total number of lethal equivalents affecting seed yield, germination, and survival to age 17 years is estimated as 12.6. The effect of selfing on growth becomes evident at age 2 years and increases to age 17 years when seedlings from self-pollinations averaged 44.5% shorter and 63.7% smaller diameter than seedlings from unrelated matings.

Description: The influence of mechanical and architectural properties of trees on growth rates, mortality rates, and relative probabilities of snapping and uprooting were examined on Barro Colorado Island, Republic of Panama. Of 310 fallen trees, 70% snapped, 25% uprooted, and 5% broke off at ground level. Stepwise discriminant analysis between snapped and uprooted trees indicated that of the variables measured, wood properties were the most important factors determining the type of death in trees. Uprooted trees tended to be larger, shorter for a given stem diameter, and to have denser, stiffer, and stronger wood than snapped trees. There were no significant differences between trees that snapped and trees that uprooted in the extent of buttress development or in the slope of the ground upon which they grew. Trees with low density wood grew faster in stem diameter than those with high density wood but also suffered higher mortality rates. After damage, many of the snapped trees sprouted; small trees sprouted more frequently than large trees. Sprouting is proposed as a means by which weak-wooded fast-growing trees partially compensate for being prone to snapping.

Description: Bald cypress (Taxodiumdistichum (L.) Rich.) seedlings from two sources in Louisiana were tested for a possible difference in salt tolerance. The study was conducted in rhizotrons under controlled environmental-conditions. Seedlings were subjected to a control (no flood or salt) and three combinations of flooding salinity: flooding only, flooding plus 68 mol•m−3 salt (4 ppt), and flooding plus 136 mol•m−3 salt (8 ppt). Both populations survived the flooding and salinity treatments for the duration of the study. However, gas exchange and net biomass production were reduced in both populations as salinity of floodwater increased from 0 to 136 mol•m−3. The gas exchange and biomass data indicated that plants from the freshwater source had higher growth rates than the brackish plants. This superiority was also maintained under all the treatments except the highest salinity treatment. Significantly greater net photosynthetic capacity per unit area of leaf was found for the freshwater population than for the brackish population in 68 mol•m−3 salt. In addition, greater root porosity, height growth, and biomass production (shoot, root) were found for the freshwater population than for the brackish population under different treatments. The data indicate that there is a potential for population differentiation in bald cypress, as shown primarily by differences in growth traits. However, the data do not support the hypothesis that bald cypress plants from the brackish source have a capacity to survive and grow better in saltwater than plants from the freshwater source. In fact, combined flooding and salinity treatments resulted in significant reductions in net photosynthesis as compared with the control in both sources.

Description: The effects of reduced stand density on (i) water status of jarrah (Eucalyptusmarginata Donn ex Sm.) and (ii) growth rate of artificially induced lesions of Phytophthoracinnamomi Rands in phloem of E. marginata were examined. Plots in the high ( 〉 1100 mm•year−1), intermediate (900–1100 mm•year−1), and low ( 

Description: The effect of red alder (Alnusrubra Bong.) on soil phosphorus (P) availability in conifer forests of the Pacific Northwest has been the focus of several recent studies. One study at the Thompson Research Center in Washington State, found Bray No. 2 extractable P to be lower in soils under pure alder than in soils under adjacent stands of pure conifer. The Thompson study, and others in forests of the Northwest, have also found that the quantity of P in aboveground litter fall is greater for conifer stands mixed with alder than in adjacent pure conifer stands, suggesting equal or greater soil P availability under the influence of alder. We assessed the effect of low densities of red alder on soil P, using a modified Hedley sequential P fractionation scheme, in a Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) plantation in coastal Oregon. We determined that soils under plots with 190 alder stems/ha and 740 Douglas-fir stems/ha had greater inorganic P availability than pure Douglas-fir plots (740 stems/ha). Inorganic P fractions, sequentially extracted from soils at 0–0.15 m depths by anion exchange resins, by sodium hydroxide, and by hydrochloric acid, were 65–225% greater in plots with alder. Soil phosphatase activity was nearly three times greater in plots mixed with alder. No significant pH differences between the treatments were found. We conclude that red alder appears to increase the availability of soil P at our site, but note that increased P supplies may not prevent a P limitation on productivity for either alder or conifers.

Description: Sprouting of sugar maple (Acersaccharum Marsh.) was investigated in the first growing period following conventional, commercial clear-cutting in the Nashwaak Experimental Watershed Project, in New Brunswick. The number of sprouts and the height of the tallest sprout on 296 stumps from dormant-period cuts were recorded. A regression equation was developed from standing trees in adjacent uncut areas to predict dbh from diameter at stump height. The percentage of stumps which bore sprouts decreased with increasing dbh greater than 15 cm. The relationships between dbh and number of sprouts per stump, and between dbh and height of the tallest sprout per stump were bimodal with frequency peaks occurring at 10 and 65 cm. The number of clumps of sprouts per stump was relatively constant in all dbh classes except for an apparent increase in the 65-cm dbh class.

Description: Spatial and temporal variations in photosynthetic photon flux density (PPFD) at 1 m above the forest floor were measured under and between dominant pines and in 21- to 52-m2 gaps under developing Scots pine (Pinussylvestris L.) stands in southern Finland. For each stand, PPFD data were collected continuously every 10-s and then averaged for every 5-min period during 4-6 days under completely clear and overcast sky conditions. Measurements were made during 102 consecutive days within two different areas in each of 10 different Scots pine stands ranging in age from 7 to 105 years. Mean daily percent PPFD in the understory varied from 7.5% in the 20-year-old stands to 38% in the 7-year-old stands, and did not differ significantly between completely clear and overcast sky conditions. Mean daily percent PPFD did not vary significantly between the different sensor locations within closed pine stands, indicating that at high latitudes mean daily percent PPFD does not vary much spatially under closed Scots pine forests. Measurements of PPFD made at different periods during the day under clear sky conditions, one of the main approaches used in the literature, were not representative of the whole-day conditions. Two different results suggest that PPFD can be better characterized under completely overcast sky conditions. First, the 5-min percent PPFD in the understory was fairly constant between 06:00 and 20:00 for all stand ages under completely overcast sky conditions. Second, there was an almost perfect 1:1 relationship of the mean daily percent PPFD measured at 40 different locations in the 10 stands between clear and overcast sky conditions. These two results suggest that an instantaneous measure of percent PPFD obtained under completely overcast sky conditions is representative of the mean daily percent PPFD for both sky conditions. These results provide the basis for a quick and efficient method of estimating the mean daily percent PPFD in the understory of closed forests.

Description: Balsam fir (Abiesbalsamea (L.) Mill.) mortality caused by the last spruce budworm (Choristoneurafumiferana (Clem.)) outbreak (1970–1987) was studied in 624 sites belonging to a complex natural forest mosaic originating from different fires in northwestern Quebec. Multiple regression analyses were used to assess the respective effects of stand structure, species composition, site characteristics, and the forest composition surrounding the stand on observed stand mortality. Mortality was observed to increase in relation to diameter of the trees, basal area of balsam fir, and the number of stands dominated by conifers in the forest mosaic. All of these factors showed significant independent effects, but 60% of the variance remained unexplained. Site characteristics, however, did not show a significant relationship to stand mortality. The results suggest that forest composition at both the stand and the forest mosaic levels may be responsible for differing degrees of defoliation that result in differences in stand mortality. Forest management strategies that favor the presence of mixed compositions both at the stand level and at the mosaic level may contribute to decreased stand vulnerability.

Description: Dispersal gradients of conidia of Sirococcusclavigignenti-juglandacearum Nair, Kostichka, and Kuntz, the causal agent of butternut canker, were studied in the forest for various rainfall dates. During rain, large numbers of conidia from branch cankers were carried in runoff water down the tree trunks of butternut (Juglanscinerea L.), causing infections that resulted in trunk cankers. Conidia also were dispersed in small droplets or aerosols and disseminated up to 40 m from a cankered tree during rainfall. Concentrations of conidia in the air decreased exponentially with increasing distances from the inoculum source. Dispersal gradients were influenced by stand composition and (or) size of the inoculum source, with steeper gradients associated with a dense forest canopy and a small area source of inoculum. Weather conditions, excluding the necessity for rain, had little influence in altering dispersal gradients within the same stand for different rainfall dates.

Description: Deer browsing and interference from forest weeds, particularly hayscented fern (Dennstaedtiapunctilobula (Michx.) Moore), New York fern (Thelypterisnoveboracensis L.), and short husk grass (Brachyelytrumerectum Schreb.), influence the establishment of Allegheny hardwood reproduction. We determined the independent interference by deer and weeds after a seed cut and a removal cut in a two-cut shelterwood sequence. Weeds, particularly the ferns, caused significant interference with germination, survival, and growth of desirable species following both cuttings. Deer browsing had no direct effect on desirable species because they did not grow enough to emerge from the herbaceous cover. Deer browsing did affect growth ofRubus, yellow and black birch (Betulaalleghaniensis Britt, and Betulalento L.), and pin cherry (Prunuspensylvanica L.) that grew above the herbaceous cover. Browsing of Rubus may be a serious problem in some stands because substantial reduction in fern and grass coverage occurred as the Rubus developed.

Description: Changes in foliar production caused by spruce budworm (Choristoneurafumiferana (Clem.)) defoliation and patterns of volume increment of surviving trees during and after the outbreak were determined in 20 mature balsam fir (Abiesbalsamea (L.) Mill.) stands on Cape Breton Island, Nova Scotia. Following the cessation of defoliation, the number of shoots increased 4-fold and mean shoot length doubled, resulting in a 12-fold increase in needle biomass. Average specific volume increment declined from 0.17–0.25 to 0.02–0.04 cm3•cm−2•year−1 after 4 years of severe defoliation; maximum increment reduction was 74–92%. Periodic radial increment and volume increment reduction (percent of mean increment in the previous decade) were both significantly related to cumulative (summed current annual) defoliation; a logistic regression equation explained 77% of the variation in volume loss. Differences in growth recovery among trees were determined by the temporal patterns of defoliation, with a 1-year lag before the beginning of volume increment recovery. Following 5 to 8 years of recovery, surviving trees had regained 48–82% of their predefoliation increment; however, absolute volume losses during the outbreak averaged 12–33 dm3/tree, or 32–48%.

Description: The influence of N fertilizer on soil mineral N fluxes, canopy development, and tree growth was studied in a thinned 11-year-old Pinusradiata D. Don plantation. Ammonium sulphate and single superphosphate were applied in an incomplete factorial design, but only the main effects of N application at 0 (control) or 200 kg N•ha−1 are considered here. Spring application of fertilizer increased the quantity of mineral N in the forest floor plus surface soil (0–0.30 m) from 1.2 to 194 kg•ha−1. Within 51 weeks this had fallen to 8.3 kg•ha−1, and after 89 weeks had returned to prefertilizer levels. In the unfertilized soil, rates of net mineralization were low with little seasonal variation. Nitrogen fertilizer increased N mineralization; over the 2 years of measurement fertilized and unfertilized soils mineralized 155 and 77 kg N•ha−1, respectively. There was no net immobilization of fertilizer N. There was no leaching of mineral N from the unfertilized soil whereas 149 kg N•ha−1 was leached below 0.30 m during the 2 years after fertilizer application. Nitrogen uptake increased from 71 kg•ha−1 in the control to 203 kg•ha−1 in the fertilized treatment. Fifty-one percent (103 kg•ha−1) of N uptake by trees in the fertilized treatment occurred within 20 weeks of fertilizer application. Fertilized trees took up 58% of the available N (N added as fertilizer plus N mineralized), while 42% was leached. Ammonium dominated the soil mineral N pool and mineral N fluxes, with nitrate generally accounting for less than 10% of mineral N in both fertilized and unfertilized soils. Leaching of mineral N from the fertilized soil (Nleach, kg•ha−1•week−1) was highly correlated (r2 = 0.92) with soil mineral N content (Nstart, kg•ha−1) and effective rainfall (rainfall minus evaporation, Reff, mm•week−1) according to the relationship Nleach = aNstart + bReff, while N uptake (kg•ha−1•week−1) was highly correlated (r2 = 0.91) with soil mineral N content and N mineralization (Nmin, kg•ha−1•week−1) according to the relationship Nuptake = aNstart + bNmin. Fertilizer increased needle N concentrations and content by 52 and 87%, respectively, after 58 weeks, and resulted in a 17% increase in leaf area index after 71 weeks. These differences were reflected by an increase in basal area increment of 23% during the 2 years since fertilizer application. The rapid uptake of N fertilizer was associated with storage in existing biomass. Uptake of fertilizer N should, therefore, increase with plantation biomass. Consequently, it should be possible to increase the uptake of N fertilizer, and minimize leaching, by applying fertilizer before, rather than after, thinning. Such a strategy may be particularly appropriate for soils that have a low capacity to retain applied N.

Description: Seasonal patterns of biomass, nitrogen (N), and phosphorus (P) were determined for major plant parts of the deciduous shrub Vacciniumuliginosum L. and the evergreen shrub Ledumgroenlandicum Oeder. in a black spruce (Piceamariana (Mill.) B.S.P.) forest in interior Alaska. New growth comprised 52 ± 7% of aboveground biomass in Vaccinium compared with the evergreen Ledum for which a maximum of 38 ± 3% of aboveground biomass was new growth. In Vaccinium the spring decline in leaf N and P concentration was due to dilution by increasing leaf biomass, whereas the autumn decline in N and P concentration was due to retranslocation, at which time 68–72% of leaf N and P was retranslocated from leaves. In contrast, the entire decline in N and P concentration of new growth in Ledum was due to dilution by increasing leaf biomass. Uptake contributed 60–68% of the maximum N and P requirement for aboveground growth of Vaccinium, with the remainder coming from stored reserves. Ledum supported 71–79% of its aboveground nutrient requirement by direct uptake from soil and may have been less dependent upon stored nutrient reserves. Vaccinium and Ledum together comprised only 0.8–2.8% of the standing crop of aboveground vascular biomass and N and P pools at Washington Creek but contributed 16% of vascular aboveground production and 19–24% of the N and P cycled annually by vascular plants. The importance of understory shrubs is due to their small support structure and rapid turnover of biomass and nutrients (34–43% of aboveground pools annually) relative to that of the trees (2–5% annually). Understory shrubs at Washington Creek and in other evergreen forests are much more important in nutrient cycling than their small biomass would suggest.

Description: We compared growth with soil and foliar elemental composition in seven stands of sugar maple (Acersaccharum Marsh.) in northern Vermont characterized by high or low incidence of crown dieback over the period 1989–1992. In stands with low-quality crown conditions, such as elevated crown dieback, long-term basal area growth rates were approximately half of those in stands with higher crown quality. Average annual basal area growth was 17.5 cm2 for dominant trees in these stands during the period 1953–1992 compared with 32.3 cm2 for trees in higher quality stands. The occurrence of elevated crown dieback was apparently unrelated to stand characteristics such as stand age, basal area, stem density, elevation, or aspect among the stands sampled. Stands with elevated crown dieback were found on soils characterized by low pH (