ALBERT

Beschreibung: The effects of climate on the growth of sugar maple (Acersaccharum Marsh.) were studied at five sites along an 800-km acidic deposition gradient from Cook County, Minnesota, to Oceana County, Michigan. Fifty increment cores were taken from 25 dominant and codominant individuals at each site in the spring of 1990. Annual ring widths (1940–1989) were measured to 0.01 mm, standardized by taking the first logarithmic differences, and averaged into chronologies using the biweight mean. The five resulting chronologies were then related to climate using least squares regression techniques. The analyses indicate that temperature is associated with sugar maple growth to a greater degree than precipitation, though there were differences in the relationships among the five study sites. Growth was also found to be significantly affected by prior growing season conditions. No evidence of an overall decline or increase in sugar maple growth rates was observed over the 50-year study period.

Beschreibung: Calamagrostiscanadensis (Michx.) Beauv. is a widely distributed rhizomatous grass that can seriously inhibit growth of white spruce (Piceaglauca (Moench) Voss) seedlings in the boreal forests of North America. We review the dynamics of this grass during four successional stages: the colonization of disturbed sites; dominance of the site by the grass a few years after disturbance; gradual loss of dominance with overstory development; and maintenance of the grass at low levels in the understory of the mature forest. We also describe C. canadensis in relation to recruitment from clonal growth and seed, environmental conditions for growth, the effects of grass litter buildup on conifer seedling microclimate, and overall competitive abilities. Control strategies for C. canadensis are as follows. If the grass is found in nearly every square metre in the understory prior to logging, there will be rapid spread when the stand is clear-cut unless clones are killed using herbicides or a deep burn. Large spruce seedlings, planted on large soil scalps or mounds, coupled with release by way of herbicides or sheep grazing, may be necessary for plantation establishment under conditions of encroachment by C. canadensis. Alternatively, the shade provided by a partial canopy may inhibit the grass sufficiently to allow spruce seedlings to establish. If grass is not abundant in the understory, we recommend (i) minimizing forest floor disturbance to reduce sites for grass seedling colonization or (ii) a slash burn with the hope of encouraging colonization by herbaceous species that have less impact on conifer seedlings.

Beschreibung: High-resolution analysis of macroscopic charcoal in sediment cores from Little Lake was used to reconstruct the fire history of the last 9000 years. Variations in sediment magnetism were examined to detect changes in allochthonous sedimentation associated with past fire occurrence. Fire intervals from ca. 9000 to 6850 calendar years BP averaged 110 ± 20 years, when the climate was warmer and drier than today and xerophytic vegetation dominated. From ca. 6850 to 2750 calendar years BP the mean fire interval lengthened to 160 ± 20 years in conjunction with the onset of cool humid conditions. Fire-sensitive species, such as Thuja plicata Donn ex D. Don, Tsuga heterophylla (Raf.) Sarg., and Picea sitchensis (Bong.) Carr., increased in abundance. At ca. 4000 calendar years BP, increases in allochthonous sedimentation increased the delivery of secondary charcoal to the site. From ca. 2750 calendar years BP to present, the mean fire interval increased to 230 ± 30 years as cool humid conditions and mesophytic taxa prevailed. The Little Lake record suggests that fire frequency has varied continuously on millennial time scales as a result of climate change and the present-day fire regime has been present for no more than 1000 years.

Beschreibung: In an open-pollinated progeny trial of Pinusradiata D. Don, stem diameter assessments were cross-referenced for 410 families for ages 5, 10, and 17 years from planting. Also cross-referenced were Cyclaneusma needle cast (CYCLA) and wood density (PILO) measured by Pilodyn needle penetration. Estimated narrow-sense heritability for stem diameter declined mildly from 0.34 at age 5 to 0.25 at age 17. Estimated heritability of family means, however, only declined from 0.59 to 0.55. CYCLA and PILO gave, respectively, narrow-sense heritability estimates of 0.32 and 0.40, with repeatabilities of family means of 0.57 and 0.67. The genetic age-age correlations for stem diameter were all positive and somewhat higher than phenotypic (family-mean) age–age correlations. Such correlations indicated comparable or slightly slower rank changes among progeny families than had been reported previously for diameter, basal area, or stem volume in P. radiata and Pinustaeda L., but faster rank changes than the literature reports for tree height. A considerable contribution of CYCLA to rank changes in stem diameter was evident from path coefficients and partial correlations. PILO made no evident contribution to rank changes. Predicted gains for stem diameter at age 17 were almost maximal using year-10 data, while using CYCLA as an auxiliary selection criterion enhanced expected gain, particularly with selection at year 5. Predicted gains for stem diameter, with age–age correlations extrapolated according to the Lambeth relationship, indicated maximal gains per annum with selection at 7–8 years for rotations of 25–30 years.

Beschreibung: Each day, forest fire managers must deploy airtankers at initial attack bases to minimize initial attack response times. They must decide how many airtankers to deploy at each base and the initial attack range of each airtanker. We develop a daily airtanker simulation model and use it to investigate how airtanker system performance varies as a function of initial attack range, fire arrival rates, and time of day. Our results indicate that the optimal initial attack range decreases as the daily fire load increases. Fire managers can use this information to design airtanker dispatch policies that will minimize initial attack response times.

Beschreibung: Bulk density of forest soils from nine locations in New England was closely and inversely related to the organic fraction of the soil. Measured data over the whole range of organic fractions followed the theoretical relationship Db = DbmDbo/[FoDbm + (1 − Fo)Dbo] where Db is the bulk density (Mg/m3), Fo is the organic fraction (kgo/kg), Dbo is the bulk density when Fo = 1, and Dbm is the bulk density when Fo = 0. The relation arises from assuming that (i) Dbo, the bulk density of "pure" organic matter, and Dbm, the bulk density of "pure" mineral matter, are constant and (ii) in a mixture, the volumes occupied by the organic mass and the mineral mass are additive. For forest soils on coarse-textured till in New England, Dbo = 0.11 Mg/m3 and Dbm varied from 1.45 Mg/m3 for sandy loams to 2.19 Mg/m3 for silt loams. When these parameters are known, Db can be estimated from Fo, which is more easily measured. When Fo is greater than 0.1 kgo/kg, the organic mass per unit soil volume (FoDb), or organic density, is approximately constant at 0.1 Mgo/m3. For many nutrients, separate evaluation of the organic density and the amount of nutrient per unit organic mass may facilitate intersite comparisons for studies of nutrient availability and leaching.

Beschreibung: Boles of quaking aspen (Populustremuloides Michx.), white spruce (Piceaglauca (Moench) Voss), red pine (Pinusresinosa Ait.), and jack pine (Pinusbanksiana Lamb.) were sampled after decomposing for 11–17 years. Mass loss and changes in chemical composition were determined. Density decreased by 40–73%, and the decomposition constant (k) decreased in the order aspen 〉 spruce 〉 red pine 〉 jack pine. Although the decomposition rate was strongly species dependent, it did not differ between the two sites. The decomposition constant was weakly related to lignin and phosphorus concentration in the original stems (r2 = 0.44 and 0.49, respectively) and not significantly related to original nitrogen concentrations. Nutrient concentration increased during decomposition, particularly for nitrogen and phosphorus. Nitrogen content increased during decomposition, and potassium content decreased. Calcium and magnesium content changed little during decomposition, whereas phosphorus content increased or decreased, depending on species. In general, species with the lowest initial nutrient contents had the greatest nutrient increases during decomposition. Nutrient content of boles of all species became similar during decomposition.

Beschreibung: The internal transport of carbon dioxide by water flow has until now been omitted when interpreting measurements of photosynthesis and respiration. Theoretical and empirical analyses of the behaviour of carbon dioxide within a tree show that the consideration of dissolved carbon transportation may be important when estimating the respiration rate, but not so important when considering photosynthetic production.

Beschreibung: Tree-ring analysis was used to study historical patterns of basal area increment (BAI) by healthy (0–5% dieback) and declined (greater than 30% dieback) overstory sugar maples (Acersaccharum Marsh.) in four stands in Pennsylvania. The objectives were to establish if and when BAI decreased in healthy and declined trees and to identify causal factors associated with decreased BAI. Reduction in BAI of declined compared with healthy trees was first evident following a series of defoliations and summer droughts in the mid-1960s and early 1970s. These stresses were followed by repeated damage by pear thrips (Taeniothripsinconsequens Uzel) in the 1980s and a drought in 1988, during which large reductions in BAI occurred for both declined and healthy trees in all stands. Foliar nutrient analysis of two stands suggested deficiency of Mg and Ca. Other factors hypothesized to be associated with this sugar maple decline as either predisposing or inciting factors include unusually warm winter temperatures in the 1980s and air pollution.

Beschreibung: Three southern Appalachian stands with sparse and unproductive pine–hardwood overstories and dense Kalmialatifolia L. understories were treated to restore productivity and diversity on steep slopes. An adaptation of the fell and burn practice was applied in summer and fall 1990. About one-half of the woody fuels were consumed at each site. A range of fire intensities was observed. Flame temperatures approached 800 °C, but the heat pulse into the forest floor only reached 60 °C at 5 cm. Humus and charred leaf litter remained on most of the surface after burning. Evidence of soil erosion was spotty and related to points of local soil disturbance. No soil left the sites. At the end of the first growing season, 23% of the burned surfaces were covered by growing plants and 62% by residual forest floor and woody debris. Felling and burning reduced evapotranspiration so that soil in the treated areas remained moister than under adjacent uncut stands. Opening the sites increased soil temperatures 2 to 5 °C at 10 cm during the first 16 months after treatment.

Beschreibung: Radial growth following a shelterwood seed cut in a 174-year-old stand of white spruce (Piceaglauca (Moench) Voss) in interior Alaska was compared with growth in an adjacent undisturbed stand of the same age. After a 2-year lag, radial growth of residual trees accelerated an average of 27% in 5 of the next 6 years. Net mean increase in growth after 8 years was 164%. Basal area growth of individual shelterwood trees increased 26.8% over the 14-year posttreatment period, while control trees increased 16.5%.

Beschreibung: The hardening of hydroponically cultured Scots pine (Pinus sylvestris L.) seedlings and their recovery after freezing was studied at the end of the second growing season (LD), after 3 weeks of short day treatment (SD), after a gradual decrease in temperature to 5°C over 4 weeks (H1), and after 4 weeks at 5°C (H2). Frost hardiness was determined by several methods and the recovery as survival of the seedlings. The highest frost hardiness was achieved in the distal parts of needles (-21 to -27°C) and in the proximal parts of needles (-18 to -25°C), followed by woody roots (-7 to -9°C), the 1-year-old and current stem (-8°C), and the fine roots (-5°C), all at the end of H2. Hardening of needles was induced by SD, but the stem and woody roots started to harden later, as a response to low temperature. As a result of frost treatment during LD and SD, potential plasma membrane roman H+-ATPase activity of roots decreased as electrolyte leakage increased and extracellular resistance decreased, but this relationship was lost during H1 and H2. The present study demonstrates the lack of hardening capacity in the fine roots of Scots pine seedlings at nonfreezing temperatures and the increased mortality of the young seedlings having frost damage on roots.

Beschreibung: Three paired watersheds treated with a fell and burn prescription were studied to determine the effects on soil, soil water, and stream water. Soil nitrification and mineralization were measured by in situ closed-core incubation. Soil water was collected with porous cup lysimeters placed at 30 and 60 cm depths, and water samples were collected from streams draining control and burned areas on one of the three sites. All data were collected for 6 months prior to and 12 months after treatment. Soil ammonium (NH4+) content increased significantly in all three sites after burning, but the magnitude differed greatly among sites. However, there was no change in soil nitrate (NO3−) content. In situ measurements of net mineralization showed increased rates with increasing burn severity. Net nitrification displayed no treatment response. Slight and nonsignificant increases in soil water NO3− concentration occurred after burning in two of the three sites. Stream water NO3− concentrations increased in the one stream sampled. Thus, while prescribed burning increased available soil N, there was little change in N transformation rates or movement of dissolved inorganic N off site during the first year after burning.

Beschreibung: A series of experiments on field-grown seed-derived trees between 2 and 17 years old demonstrated that the growth regulator paclobutrazol could be used to reduce vegetative growth and enhance flower-bud production in Eucalyptusglobulus Labill. and Eucalyptusnitens (Dean & Maid.) ex Maid. Responses to high levels of trunk injection and collar drenching persisted for up to six growing seasons, yielding both increases in frequency of flowering and heaviness of bud crop. Growth responses were expressed in the immediate growing season, but flowering responses were not evident for another year. Foliar spray treatments reduced vegetative growth in young trees of both species for one growing season, but only the E. globulus showed an associated flowering response. Assessment of seed yield per capsule and subsequent germination tests showed no deleterious effects on seed development or quality. Choice of application method will vary with objective and size of tree. Collar drenching shows the most promise for treating large numbers of seed orchard trees because application time is substantially independent of tree size and weather conditions.

Beschreibung: This paper describes a decision support system that forest managers can use to help evaluate short-term, site-specific silvicultural operating plans in terms of their potential impact on long-term, forest-level strategic objectives. The system is based upon strategic and tactical forest-level silvicultural planning models that are linked with each other and with a geographical information system. Managers can first use the strategic mathematical programming model to develop broad silvicultural strategies based on aggregate timber strata. These strategies help them to subjectively delineate specific candidate sites that might be treated during the first 10 years of a much longer planning horizon using a geographical information system and to describe potential silvicultural prescriptions for each candidate site. The tactical model identifies an annual silvicultural schedule for these candidate sites in the first 10 years, and a harvesting and regeneration schedule by 10-year periods for aggregate timber strata for the remainder of the planning horizon, that will maximize the sustainable yield of one or more timber species in the whole forest, given the candidate sites and treatments specified by the managers. The system is demonstrated on a 90 000 - ha area in northeastern Ontario.

Beschreibung: Biomass allocation to roots was studied in holm oak (Quercusilex L.), a dominant evergreen tree in broad-leaved sclerophyllous Mediterranean forests. The root systems of 32 single-stemmed holm oaks growing in shallow soils on largely unfissured bedrock were excavated in a mesic site and a xeric site in the Montseny Mountains (northeast Spain). Individual root:shoot biomass ratios (roots with diameter

Beschreibung: The responses of CO2 assimilation rate (A), transpiration rate (E), and leaf conductance (g) to increasing leaf to air water vapor concentration difference (ΔW) were investigated (i) using excised shoots from mature trees of Abiesalba, Abiescephalonica, Abiesmarocana, and Abiesnordmanniana and (ii) in situ on a mature tree of Abiesbornmulleriana. Gas-exchange responses to increasing soil drought were also studied in plants of A. bornmulleriana, A. cephalonica, and Cedrusatlantica. Stable carbon isotope composition measurements were carried out on annual growth rings of A. bornmulleriana to estimate the time-integrated values of the ratio of intercellular leaf (Ci) to ambient (Ca) CO2 concentration. Increasing ΔW around the shoots reduced A and g in such a way that either Ci remained constant or its decrease was not pronounced enough for the changes in A to be accounted for by changes in g only. This suggests a direct effect of ΔW on photosynthesis. The different Abies species showed clear differences in water-use efficiency. Abiescephalonica and A. marocana had lower water costs of CO2 assimilation (E/A) than A. nordmanniana and A. alba. It has also been shown that A. cephalonica and A. marocana are characterized by an optimal stomatal control of leaf gas exchange. Stomata closed very rapidly in A. bornmulleriana in response to water supply being withheld, even prior to there being any important decrease in leaf predawn water potential. The stomatal response in C. atlantica was more gradual. In A. bornmulleriana, drought adaptation appears to be linked to the ability to avoid internal water stress, whereas drought adaptation in C. atlantica involves the ability to tolerate internal water stress. The high stomatal sensitivity mA. bornmulleriana is also supported by the isotopic carbon composition data, as shown by the substantial interannual variations in the estimates of Ci/Ca, ranging from 0.48 for the dryest years to 0.61 for the rainy years.

Beschreibung: Seedlings of four geographically diverse paper birch (Betula papyrifera Marsh.) populations native to British Columbia were grown under low and high levels of water and nitrogen in a greenhouse for 3 months to examine the relative sensitivity of each population to water and nutrient availability. Nine sequential measurements on height and basal diameter growth were made, and then the seedlings were harvested for final biomass measurements. Under optimal conditions the highest elevation population ceased height growth, while the low-elevation coastal population continued to increase in height under all treatment conditions. Plants of all populations grown under high N conditions grew faster and had larger total biomass and lower root/shoot ratios than plants grown under low N conditions. Relative growth rate was significantly correlated with shoot and foliage biomass, leaf area, and root weight ratio. All populations generally responded more to low N level than to low moisture level in terms of height growth, relative growth rate, total biomass, and root/shoot ratio. This suggests that the populations observed in this study are better adapted to drought than poor soil nutrient availability. Therefore, consideration of site quality, which includes soil moisture regime and soil nutrient regime, should be a primary concern when allocating birch seed lots in a planting program.

Beschreibung: We studied radial growth reduction in American beech (Fagusgrandifolia Ehrh.) in relation to the level of defect induced by beech bark disease, in second-growth and old-growth northern hardwoods stands in New Hampshire. In the second-growth stand at Moose Mountain (n = 243 trees), 1989–1990 radial growth declined significantly with increasing severity of external symptoms. The severity of external symptoms increased significantly with DBH. To examine temporal trends, internal defect induced by the disease was quantified as the percentage of growth sheath cankered in each year, by cross-sectioning a subsample of 40 trees. Internal defect first appeared in 1950, increased through 1969, then declined until a major pulse of infection in the period 1983–1987. Sectioned trees were divided into infection classes based on a cumulative measure of internal defect. Growth of severely infected trees first fell below that of uninfected trees in 1965, and was consistently lower after 1972. The growth ratio of severely infected to uninfected trees generally declined from 1960 to 1990; by 1990, growth of severely infected trees was reduced by more than 40% relative to healthy trees. This decline in the growth ratio corresponded well to the increase in cumulative internal defect in the stand, suggesting that disease stress had cumulative effects on tree vigor. The relation between beech bark disease and growth was also examined on an individual-tree basis; recent growth decline was significantly greater for trees with higher levels of internal defect. Internal defect was a better predictor of growth trends than was external defect. External defect was only moderately correlated with internal defect (r2 = 0.503). In the old-growth stand at Bartlett, N.H. (n = 40 trees) infection was quantified from external symptoms only. As in the second-growth stand, the growth of severely infected trees in the old-growth stand fell significantly below that of uninfected trees. However, significant differences in growth between uninfected and severely infected trees occurred earlier in the old-growth stand, first appearing in 1949. Delayed growth reductions in the second-growth stand may be associated with changes in shade and moisture affecting the beech scale, changes in tree physiological stress after selective logging, or changes in the density of large trees. Beech may survive long periods of infection by beech bark disease. However, our results demonstrate clearly that beech bark disease has reduced the growth of American beech in both second-growth and old-growth northern hardwoods stands for several decades.

Beschreibung: The renewal of boreal fir stands after harvesting is related to the abundance of fir advanced regeneration. The objective of this study was to compare the advanced regeneration in 45-years-old balsam fir stands of second growth to determine if ecological site conditions could explain some regeneration problems noted in the balsam fir – white birch ecoclimatic domain. Seven ecological phases were studied; these are among the most common in the Laurentians north of Québec. On the basis of fir seedling densities (2 years old and more), three groups could be distinguished using a cluster analysis method for grouping means. Dry balsam fir – herb-and-moss type on well drained tills formed a first group characterized with very high seedling densities (〉 60 000 seedlings/ha). A second group, characterized with high seedling densities (25 000 – 40 000 seedlings/ha), was constituted of three phases with an important moss cover:the mesic balsam fir – moss-and-herb type on moderately well drained tills, the humid balsam fir – moss-and-herb type on imperfectly drained tills with seepage, and the humid balsam fir – moss type on imperfectly drained tills. A third group, with low seedling densities (

Beschreibung: Stratum-based timber harvest schedules must be disaggregated into operational plans prior to implementation. In most cases this is an expensive and time-consuming manual task that does not ensure consistency between the long-term harvest schedule and short-term operational activities. This paper presents the results of applying the CRYSTAL algorithm, which automates the disaggregation and allocation of a stratum-based harvest schedule into harvest blocks, to a small forest in New Brunswick. The results indicate that it is possible to use a set of allocation guidelines to quickly delineate harvest blocks in a consistent, reproducible manner. We also discuss how the algorithm is used in conjunction with a Monte Carlo integer programming model to estimate the potential losses in timber harvest volumes attributable to deviations from the stratum-based schedule and the addition of adjacency constraints.

Beschreibung: Stand tables from forest inventories representing more than 22 × 106 ha of forests in tropical Asia were used to estimate aboveground biomass (point and 99% confidence interval). The mean inventory-based biomass for moist forests (225 Mg/ha) was lower than that reported by direct measurements for mature forests in the same region (350 Mg/ha), whereas the mean inventory-based biomass for dry forests (82 Mg/ha) was higher than estimates based on direct measurements (55 Mg/ha). Our analyses demonstrated that human use of the forests in tropical Asia is intense, leading to degradation. Between two national forest inventories of Peninsular Malaysia in 1972 and 1981, the total area and biomass of forests declined by 18 and 28%, respectively. Modeling land-use changes and carbon dynamics of tropical Asian forests must take into consideration human impact on vegetation because such use of forests reduces their biomass and may stimulate forest growth and carbon uptake.

Beschreibung: The response of trace gas fluxes (CO2, CH4, and N2O) and litter decomposition to increased soil temperature was evaluated in a northern hardwood forest. Four experimental plots (10 × 10 m) had heating cables installed within the forest floor. Temperatures at 5 cm were increased 2.5, 5.0, or 7.5°C in individual heated plots during the field season in 1993 and 1994. The fourth plot was a cabled, nonheated reference. Trace gas fluxes were monitored using closed chambers. Soil moisture was monitored using tensiometers and time domain reflectometry. Changes in leaf litter decomposition were quantified using litter bags for American beech (Fagus grandifolia Ehrh.) and sugar maple (Acer saccharum Marsh.) litter. Fluxes of CO2 increased exponentially with increased soil temperatures within treatments and were higher in heated plots than in the reference plot. Temperature coefficients (Q10) and mass remaining of American beech leaf litter decreased with the level of heating, suggesting a nonlinear microbial response to elevated temperatures. Soil water content exhibited the most influence on CH4 and N2O flux in the second season. The experimental manipulations showed the importance of evaluating the influence of soil temperature coupled with effects of N and moisture availability.

Beschreibung: Measuring the mass of snow on cut branch tips soon after snowfalls during two winters provided comparisons of catch by Engelmann spruce (Piceaengelmannii Parry), subalpine fir (Abieslasiocarpa (Hook.) Nutt.), and lodgepole pine (Pinuscontorta var. latifolia Engelm.). Analysis of these and other reported measurements confirmed (i) snow bridging by cohesion, (ii) bouncing of snow crystals by elastic rebound, and (iii) branch bending as mechanisms that determine the sigmoidal growth curves characterizing snow interception relative to snowfall. The fraction of snowfall intercepted by the branches was largest when storm accumulations were 3–4 mm water equivalent, with low specific gravity (0.04–0.07). Percent catch in snowfalls with 10 mm water and low specific gravity was near 50% for Engelmann spruce and about 45% for subalpine fir and lodgepole pine, but values decreased to near 30% in 20-mm storms. Catch was inversely proportional to the density of snow accumulations in the specific gravity range 0.04–0.13. Average branch catch was only about 10% of a storm with 10 mm water equivalent at 0.13 specific gravity. Meteorological conditions were more important than branch growth form in determining snow interception amounts on the conifers tested. The results suggest, as a hypothesis, a computational function for the fraction of snowfall caught on conifer crowns.

Beschreibung: Identifying the factors that influence foresters to adopt management innovations is essential for developing models that accurately forecast the rate at which new technology will be adopted. Models were developed to evaluate the impact of sociodemographic characteristics, attitudes, and structural–external variables on New Hampshire foresters' decisions to adopt three distinct soil information sources. The soil information sources studied were County Soil Surveys, Important Forest Soils Groups, and Leak's Habitat Classification System. Discriminant analytic models were developed and evaluated for each information source. Information on use and other variables were collected by a mail survey with a response rate of approximately 60%. The results reveal that structural variables exerted the greatest influence on adoption decisions, while sociodemographic characteristics were the least important. College and noncollege sources of information about the innovations were the most important variables in the discriminant models. Other significant structural variables included employer, prior use of soils information, and participation in continuing education. All three models correctly classified more than 75% of the respondents, with one model classifying more than 90%. The difference in accuracy may be attributed to differences in information access among the three soils information sources.

Beschreibung: The southern edge of the boreal forest in central Saskatchewan, Canada, has had its forest composition changed in the first decades of this century, primarily by logging and escaped fires from adjacent agricultural clearance. Three timber berths were established in 1884 within and immediately adjacent to the present southern half of Prince Albert National Park (established in 1927). These timber berths were selectively logged for saw timber between 1900 and 1918. Between 1907 and 1918, an average of 70 trees per hectare were removed by selective logging. Most of these trees were white spruce (Picea glauca (Moench) Voss). Since logging companies were required to remove all merchantable trees with a basal diameter greater than 25 cm, it is estimated that between 28 and 54% of the canopy trees were removed. Between 1883 and 1942, 81% of the timber berths were burned two or more times by crown fires that spread through the study area from adjacent agricultural clearances 30 km or more away. By 1945, agricultural clearance was largely complete and the clearance-caused fires stopped. The changes in tree composition were determined by transition probabilities between forest surveys taken in 1883 and 1994. Forests subjected to short-interval, clearance-caused fires but no logging were significantly reduced in their abundance of sexually reproducing trees such as white spruce, but increased in trees with either vegetative reproduction (i.e., underground stems, not just basal sprouts) or serotinous cones, such as aspen (Populus tremuloides Michx.) and jack pine (Pinus banksiana Lamb.), respectively. Transition probabilities for forests experiencing both short-interval, clearance-caused fires and logging reveal an even more marked compositional change in this direction.

Beschreibung: Three experiments were conducted to examine the effects of Calamagrostis canadensis (Michx.) Beauv. on the growth of Populus tremuloides Michx. Containerized seedlings of P. tremuloides were transplanted into large pots and subjected to (1) three soil temperatures (20, 12, and 6°C), (2) root competition with C. canadensis, or (3) presence or absence of C. canadensis litter, each at two nutrient regimes. In the first experiment, significant differences (p = 0.0001) in pre- and neo-formed leaf area and root and shoot dry weights were observed for plants subjected to the three different soil temperatures. In experiment two, the presence of C. canadensis significantly (p 〈 0.001) reduced total biomass, plant height, and root collar calliper of P. tremuloides. In the third experiment, a significant interaction (p = 0.027) between C. canadensis litter and nutrient regime was observed, with the greatest inhibitory effect on P. tremuloides growth resulting from litter at the low nutrient regime. Low soil temperature had the strongest negative effect on P. tremuloides of the four factors investigated. However, direct competition with C. canadensis, low nutrient conditions, and C. canadensis litter likely would add to the growth suppression of P. tremuloides by this grass. The results of this study have significant implications for the management of P. tremuloides after harvesting.

Beschreibung: Western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings from four dormancy induction treatments (DIT) (i.e., long-day dry, long-day wet, short-day dry, short-day wet) were planted on a coastal reforestation site in British Columbia and monitored for physiological response and morphological development over the first growing season. Seedlings in all DIT showed a similar net photosynthetic, needle conductance, and shoot water potential response to seasonal low temperature, non droughty, and late summer drought conditions. Pressure–volume analysis at the beginning of the growing season (late February) showed short-day wet seedlings to have lower saturated and turgor loss point osmotic potentials than other DIT, while at the end of the growing season (October) there was no osmotic potential difference between DIT. At the end of the growing season, short-day wet seedlings had a much lower maximum modulus of elasticity than other DIT, indicating their shoots were still elongating. Morphological assessment 1 month after field planting showed short-day DIT seedlings had less needle damage and greater root development in response to continuous low temperature exposure. Four months after planting, long-day wet seedlings had the greatest shoot (i.e., height, root collar diameter) and root development in response to mild temperatures and high soil moisture conditions. Eight months after planting, survival was between 95 and 97% for all DIT. Long-day DIT seedlings had the greatest height and all DIT had similar root collar diameter and root development. Short-day DIT seedlings had the best shoot/soil roots ratio. Short-day wet seedlings had the least number of stem units per centimetre of new shoot development throughout the growing season. Results are discussed in reference to stock quality assessment presented in the first paper of this series.

Beschreibung: Test plantations were established in western Washington and Oregon to compare tree growth at six initial planting densities ranging from 300 to 2960 trees/ha (120 to 1200/acre). A size-density relation was visually apparent 3 to 4 years after planting. Inventory data from the oldest 11 trials (5 or 6 years after planting) showed that initial spacing strongly influenced early growth of coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii). Average height and diameter at breast height were progressively larger as planting density increased; at the widest spacing (lowest stand density), average height was 75% and average diameter at breast height was 67% of that at the closest spacing. We have no firm explanation for the early faster tree growth at close spacings. Trees planted at 2960 trees/ha (1200 trees/acre) attained breast height (1.3 m) 2 years earlier than trees planted at a density of 300/ha (120/acre). This finding has practical significance to current efforts to achieve early establishment of plantations.

Beschreibung: The reactions of sessile oak (Quercuspetraea (Mattuschka) Liebl.) to drought were studied under natural conditions in a 32-year-old stand near Nancy (northeastern France) during the summers of 1989 (strongly rain deficient) and 1990. A plot of five trees was subjected to imposed water shortage, while a group of irrigated trees was used as a control. Measurements of xylem sap flows and water potential enabled the computation of plot transpiration, canopy conductance, and specific hydraulic conductance in the soil–tree continuum. Stomatal conductance was measured directly with a porometer. Specific hydraulic conductance of our oaks was of the same order of magnitude as that reported for other species. It decreased significantly during spring because of a time lag between cambial growth and leaf area expansion. Measured transpiration was close to potential evapotranspiration, except during days with high vapor pressure deficits, which promoted stomatal closure in the absence of soil water deficits. Imposed drought caused predawn leaf water potentials to reach values as low as −2.0 MPa and a progressive decline in hydraulic conductance, which was probably attributable to modifications in hydraulic properties at the soil–root interface. This gradual decline in conductance was attributed to their deep rooting (1.40 m). This study revealed that Q. petraea may be considered as drought tolerant because of adaptations like deep rooting, efficient and safe xylem sap transport, maintenance of significant stomatal conductance, and significant transpiration, even during strong drought stress.

Beschreibung: The frequency and intensity of large-scale watershed disturbances (e.g., clearcuts and wildfires) is increasing in northwestern Ontario. Timber harvesting and wildfires have been shown to alter water quantity and quality in stream ecosystems. Unfortunately, scientific studies of these impacts on lakes are considerably rarer. Using paleolimnological techniques, we examined the remains of scaled chrysophytes in sediment cores from four lakes that have had the majority of their watersheds clearcut, two lakes that have had large forest fires in their watersheds, and two lakes that have had minimal watershed disturbance. Lakes in this study showed minor changes in the composition of scaled chrysophytes at a temporal resolution of 2-4 years, despite removal of over 90% of the forest. Furthermore, temporal variability in the species assemblages were similar in all lakes. A gradual change in the species assemblages of all lakes suggested a regional influence may have been responsible. We hypothesize that hydrological changes brought about by a regional drought from 1970 to 1990 may have exerted an overriding influence on lakes over this time period.

Beschreibung: This review presents information on the occurrence, persistence and nontarget effects of Bacillusthuringiensis Berliner (B.t.) in soil, with particular emphasis on forest ecosystems. Both field and laboratory studies have confirmed that B.t. is able to survive for several years after spraying, but studies on long-term persistence and possible accumulation of spores in soils are inadequate. The ecological role of B.t. in the soil ecosystem is poorly understood; we do not even know where and under what conditions B.t. multiplies in nature. Information on the effects of B.t. on soil microflora is contradictory, with studies variously suggesting that B.t. caused an increase, a decrease, or did not affect indigenous bacterial populations. Toxicity of B.t. to species of several invertebrate taxa (Acarina, Nematoda, Collembola, Annelida, Hymenoptera) inhabiting the soil has been demonstrated, but only rarely is it possible to relate dosage information to field situations, and in many cases the B.t. subspecies tested are not currently used for pest control in North America. There is an urgent need for further research to elucidate the relationships between B.t. and the natural soil microflora and fauna.

Beschreibung: Seedlings of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), lodgepole pine (Pinuscontorta Dougl.), and white spruce (Piceaglauca (Moench) Voss) were grown in a container nursery from February to July 1988 and then exposed to three temperatures and three levels of drought stress applied factorially during mid-July to October 1988. Seedlings were retained in a shelter house until January 1989, when they were cold-stored until early May. Measurements of stomatal conductance (gs), transpiration (E), and specific leaf area (SLA) were made at the end of the treatment period in September 1988 and again after growth the following year at the end of June. Root growth capacity (RGC) was tested in early May 1989. Results were considered in conjunction with performance of other samples of the same plants that had been planted in sand beds in April 1989, where irrigation was regulated to provide three levels of moisture stress. Low temperature (13 °C) generally reduced gs and E, which were adjusted for xylem pressure potential, and SLA in all species by the time nursery treatment was completed at the end of September. No effect of nursery temperature treatment on gs and E could be detected when new needles were measured in June and July (after 9 to 12 weeks of growth), but SLA of lodgepole pine increased with nursery temperature treatment, and SLA of white spruce decreased with nursery temperature treatment. RGC was higher for the 13 °C treatment than for the 16 and 20 °C treatments. Survival of outplanted seedlings was mainly inversely related to nursery temperature. Low nursery temperature reduced gs, E, and SLA and increased RGC. SLA of planted lodgepole pine increased with level of nursery drought treatment, and severe nursery drought increased gs under stress, when measured in June. No other effects of drought were detected, although drought treatment was effective in increasing survival of planted seedlings.

Beschreibung: Development of humus layer soil microbial biomass C (Cmic) and N (Nmic), fungal biomass (as soil ergosterol content), microbial respiration activity, and the soil organic C (Corg) and N (Ntot) were determined in coniferous forest soils that had received a single prescribed fire treatment at different times over a period of 45 years. The ratio of soil respiration rate to microbial biomass C (qCO2) and the Cmic/Corg and Nmic/Ntot percentages were derived from the measurements taken. All the measured biomass indicators reacted identically to show recovery from prescribed burning within 12 years. A raised metabolic quotient (qCO2) was detected in soils over the first 2 years following the fire treatment, but after the third year it had decreased to a stable level. These observations suggest that during the first few years after fire the soil microflora can be characterized on the basis of simple substrate–decomposer relationships. The first 12 years were characterized by increasing Cmic/Corg and Nmic/Ntot percentages, which then stabilized at mean values of 1.3 and 5.5%, respectively. The observed rise in the Cmic within a large pool of Corg suggested increasing availability of energy-rich C sources. These C sources are probably derived from the organic C input resulting from postfire plant succession.

Beschreibung: During a 3-year study, soil microbial biomass C and N, length of the fungal hyphae, soil respiration, and the percent mass loss of needle litter were recorded in coniferous forest soil humus layers following a prescribed burning (PB) treatment or a forest fire simulation (FF) treatment (five plots per treatment). Unburned humus from adjacent plots served as controls (PC and FC, respectively). Prescribed burning was more intensive than the forest fire, and this was reflected in all the measurements taken. The amounts of microbial biomass C and N, length of fungal hyphae, and soil respiration in the PB area did not recover to their controls levels, whereas unchanged microbial biomass N and recovery of the length of the fungal hyphae to control levels were observed in the FF area. The mean microbial C/N ratio was approximately 7 in all the areas, which reflected the C/N ratio of the soil microbial community. Deviation from this mean value, as observed during the first three samplings from the PB area (3, 18, and 35 days after fire treatment), suggested a change in the composition of the microbial community. Of the two treated areas, the decrease in soil respiration (laboratory measurements) was much more pronounced in the PB area. However, when the humus samples from both areas were adjusted to 60% water holding capacity, no differences in respiration capacity were observed. The drier humus, due to higher soil temperatures, of the PB area is a likely explanation for the low soil respiration. Lower soil respiration was not reflected in lower litter decomposition rates of the PB area, since there was a significantly higher needle litter mass loss during the first year in the PB area followed by a decline to the control level during the second year. Consistently higher mass losses were recorded in the FC area than in the FF area.

Beschreibung: Nitrogen (N) mineralization and nitrification were compared among ecosystems representing a primary successional sequence on the Tanana River floodplain of interior Alaska. These processes displayed marked seasonality, were closely related to substrate chemistry, and reflected the impact of vegetation clearing. The highest rates of N mineralization were encountered in the June to July incubation periods, and rates generally declined during the remainder of the summer. The early season period (June to July) was the interval of most favorable litter and mineral soil temperature and most available energy supply for microbial mineralization of detrital materials. Minimal rates were encountered during the winter. Litter layer N mineralization rates were highest in the early-successional poplar–alder (Populusbalsamifera–Alnustenuifolia (Nutt.) stage and declined with advancing succession in poplar (Populusbalsamifera) and mature white spruce (Piceaglauca) (Moench) Voss) stands. The poplar–alder stage displayed the highest rate of nitrification. Nitrate constituted 98% of the mineralized N in early-successional poplar–alder forest floors but fell to 4 and 0% in poplar and white spruce forest floors, respectively. Nitrogen mineralization was closely related to significant increases in the lignin/N ratio across the sequence of vegetation types. The rate of surface mineral soil net N mineralization increased with succession in response to higher soil organic matter content. The range of average total seasonal net N mineralization (260–1600 mg N•m−2) for litter layer plus mineral soil among successional stages in this study was generally lower than the 1200–8400 mg N•m−2 reported by investigators for other studies in temperate latitudes. Vegetation clearing increased the magnitude of temporal fluxes as well as total annual mineral N production. The most consistent increases were encountered in the poplar–alder vegetation type. The average seasonal total net N mineralization for forest floor plus mineral soil in this vegetation type increased from 1500 to 3264 mg N•m−2 as a result of clearing. Soil temperature declined with advancing succession and generally increased as a consequence of clearing. However, these changes were not as closely correlated with N mineralization as were the changes in substrate chemistry encountered across this successional sequence.

Beschreibung: Variation in diameter, height, and stem volume of 57-year-old Douglas-fir (Pseudotsugamenziesii var. menziesii (Mirb.) Franco) was related to distance of these trees from a 27 m wide strip in the same Douglas-fir plantation that had been interplanted with red alder (Alnusrubra Bong.). Within the interplanted strip and despite its greater total stand density, bole volume of dominant and codominant Douglas-fir averaged 1.27 m3 compared with 0.55, 0.45, 0.46, or 0.49 m3 in trees 15, 30,45, or 60 m, respectively, from the edge of the mixed stand. Some positive influence of nitrogen-fixing red alder apparently extended about 15 m beyond the edge of the mixed stand at this poor quality site in southwest Washington. We infer that similar ribbonlike distributions of naturally regenerated red alder could be retained to improve growth of nearby conifers on nitrogen-deficient sites.

Beschreibung: Allometric equations were developed for mature trees of 10 deciduous species (Acer rubrum L., Betula lenta L., Carya spp., Cornus florida L., Liriodendron tulipifera L., Oxydendrum arboreum (L.) DC., Quercus alba L., Quercus coccinea Muenchh., Quercus prinus L., and Quercus rubra L.) at the Coweeta Hydrologic Laboratory in western North Carolina, U.S.A. These equations included the following dependent variables: stem wood mass, stem bark mass, branch mass, total wood mass, foliage mass, total biomass, foliage area, stem surface area, sapwood volume, and total tree volume. High correlation coefficients (R2) were observed for all variables versus stem diameter, with the highest being for total tree biomass, which ranged from 0.981 for Oxydendrum arboreum to 0.999 for Quercus coccinea. Foliage area had the lowest R2 values, ranging from 0.555 for Quercus alba to 0.962 for Betula lenta. When all species were combined, correlation coefficients ranged from 0.822 for foliage area to 0.986 for total wood mass, total tree biomass, and total tree volume. Species with ring versus diffuse/semiring porous wood anatomy exhibited higher leaf area with a given cross-sectional sapwood area as well as lower total sapwood volume. Liriodendron tulipifera contained one of the highest foliar nitrogen concentrations and had consistently low branch, bark, sapwood, and heartwood nitrogen contents. For a tree diameter of 50 cm, Carya spp. exhibited the highest total nitrogen content whereas Liriodendron tulipifera exhibited the lowest.

Beschreibung: The net annual flux of carbon from south and southeast Asia as a result of changes in the area of forests was calculated for the period 1850 to 1985. The total net flux ranged from 14.4 to 24.0 Pg of carbon, depending on the estimates of biomass used in the calculations. High estimates of biomass, based on direct measurement of a few stands, and low estimates of biomass, based on volumes of merchantable wood surveyed over large areas, differ by a factor of almost 2. These and previous estimates of the release of carbon from terrestrial ecosystems to the atmosphere have been based on changes in the area of forests, or rates of deforestation. Recent studies have shown, however, that the loss of carbon from forests in tropical Asia is greater than would be expected on the basis of deforestation alone. This loss of carbon from within forests (degradation) also releases carbon to the atmosphere when the products removed from the forest burn or decay. Thus, degradation should be included in analyses of the net flux of carbon from terrestrial ecosystems. Degradation may also explain some of the difference between estimates of tropical forest biomass if the higher estimates are based on undisturbed forests and the lower estimates are more representative of the region. The implication of degradation for estimates of the release of carbon from terrestrial ecosystems is explored. When degradation was included in the analyses, the net flux of carbon between 1850 and 1985 was 30.2 Pg of carbon, about 25% above that calculated on the basis of deforestation alone (with high estimates of biomass), and about 110% above that calculated with low estimates of biomass. Thus, lower estimates of biomass for contemporary tropical forests do not necessarily result in lower estimates of flux.

Beschreibung: One-year-old Cornusflorida L. seedlings were randomly assigned to four treatments of simulated rain (pH 2.5, 3.5, 4.5, and 5.5) in two greenhouse–laboratory studies in 1989 and 1990. After 10 applications over a 42-day period, the seedlings were moved to a temperature-controlled laboratory, placed in plastic bags, humidified, and sprayed with a spore suspension of five Disculadestructiva isolates. About 30 days later, the seedlings were examined for percentage of leaves exhibiting anthracnose symptoms and disease severity on affected leaves. Both trials showed that as the acidity of the simulated rain increased, the incidence and severity of anthracnose leaf symptoms increased. The 1989 study included a soil lime treatment that showed the same trend but the overall occurrence and severity of symptoms was higher.

Beschreibung: Survey records of spruce budworm (Choristneura fumiferana Clem.) defoliation in Ontario, taken annually since 1941, were analysed using geographic information systems (GIS), spatial statistics, and time-series methods. Cumulative frequency maps indicated that the 41 × 106 ha of Ontario that had been defoliated in at least one year since 1941 could be split into three zones of frequent defoliation separated by two approximately 100 km wide, longitudinally oriented corridors of lower frequency. Analysis of annual records of the total area defoliated showed that the fluctuations in this time series are the result of a basic oscillation of approximately 36 years, which is modified by secondary fluctuations and occasionally by sharp drops. The secondary fluctuations are at least partially due to asynchrony in otherwise remarkably similar long-wave oscillations in the eastern (25.5 × 106 ha) and western (9.6 × 106 ha) zones of frequent defoliation. Analysis of this asynchrony showed that outbreaks in the eastern zone occurred 5 or 6 years before outbreaks in the central (6.6 × 106 ha) and western zones, which were synchronous. These observations contradict previous reports of the large-scale spread of outbreaks from west to east.

Beschreibung: Drainage of peatlands for forestry causes the water level to draw down, which results in subsidence of peat surface and increased peat bulk density (Db). Later on, an accelerated rate of organic matter decomposition and the pressure of the growing tree stand further compacts the peat. We measured the peat Db (0-80 cm) in 180 undrained and 209 drained (ca. 60-year-old) peatland sites representing three nutrient levels of pine fens and five macroclimatic regions from southern to northern Finland. Db was affected by climatic conditions, nutrient status, and the tree stand volume of the site. Db was significantly higher in drained than in undrained sites in all regions and site types: the mean (±SD) Db in the whole material was 82 ± 23 kg ·m-3 for the undrained sites and 133 ± 22 kg ·m-3 for the drained sites. The increase in Db was significant in all regions down to a depth of 60 cm and in southern Finland, even deeper than 80 cm. When the increase in carbon concentration was taken into consideration, the average postdrainage increase in the Db of the 0-80 cm layer equalled the amount of carbon in the 54-cm layer in average undrained peat. As the reported subsidences of peat surface in forest drainage areas in Finland are usually below this limit, the carbon storage of peat is likely to increase after drainage.

Beschreibung: Phenotypic variation in defoliation of ponderosa pine, Pinusponderosa Laws., by the pine sawfly, Neodiprionfulviceps, is reported. Two field and one laboratory bioassays of paired phenotypically resistant and susceptible trees consistently indicated that sawfly egg, larval, and total survival were 5–14% lower on resistant trees. A suite of host-plant traits were assayed on resistant and susceptible trees including anatomical characteristics of the needles and concentration of terpene and nitrogen. Resistant trees had thicker outer cell layers, more fiber cells, higher toughness, and lower soluble nitrogen than susceptible trees. Resistant and susceptible trees were not distinguished by differences in terpenes. Generational survival of N. fulviceps was inversely related to foliage toughness and number of fiber cells.

Beschreibung: Studies on tree allometry have often focused on the average tree of a representative stand across an age gradient. Another dimension of change in tree form is the variation caused by differences in competitive status, evident between trees of one stand or between stands of comparable age but different stocking densities. This study compares the structural relationships of dominant Scots pine (Pinus sylvestris L.) trees over a wide age range with those in young trees of similar age but different competitive status. Allometric relationships are developed between biomass components and diameter, and crown structure is analysed in terms of crown allometry, pipe model relationships, and foliage density. The differences in allometry seem to be largely due to the rise of the crown base, which is positively correlated with size in the age series and negatively correlated with size in the cross-sectional data. The allometric relationships of the crown are less variable, but differences are found in the crown size to foliage biomass ratios between the two data sets. In the age series, foliage biomass is proportional to crown surface area, while in the cross-sectional data, it is proportional to crown volume. It is concluded that the reaction to competition for light is twofold: (1) to allocate new foliage higher up and, consequently, to lift the crown base, and (2) to grow sparser crowns.

Beschreibung: Measurements of the spatial mean values of global irradiance, photosynthetic photon flux density, and the downward longwave irradiance under a 26-year-old, second-growth Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) forest canopy on a 26° south-facing slope were made with a tramway system, which scanned a 20-m transect in 12 min. The diffuse solar irradiance under the canopy was measured with a stationary pyranometer equipped with a shadow band. The extinction coefficients for the direct, global, and photon components were derived as functions of the solar incident angle over the range of 15° to 85°. The extinction coefficient for the diffuse radiation was found to correlate well with the ratio of the direct to diffuse irradiance above the canopy. Complete diurnal cycles of the downward longwave irradiance were simulated with a simple model based on the air temperature inside the stand. Analyses of the measurements of all the shortwave and longwave components were made using an effective leaf area index, which was derived from the measurements of the direct irradiance above and below the stand. It was found that the distribution of the leaf inclination angle of a Douglas-fir canopy has strong planophile characteristics, and that in the case of a forest stand on a slope, it is critical to obtain the characteristics of the light transmission through the canopy over the entire incident angle range before effective leaf area index is calculated. Warren Wilson's 57.5° approximation did not hold for the Douglas-fir canopy, which had distinct foliage clumping features.

Beschreibung: Nitrification and denitrification were measured in a 120-year-old Piceaglauca (Moench) Voss forest in southwestern Alberta. Nitrifying activity could not be detected using short-term incubations of F–H and upper mineral soil horizons. Long-term incubations for nitrifying potential indicated that nitrifying organisms were present. The results suggest that the population of nitrifying organisms must have been small, their activity was limited, or the microhabitat necessary for their activity was not adequately simulated by the soil slurries in the short-term incubations. Low rates of denitrification were detected but probably did not represent a substantial loss of N from the soil–plant system. Low rates of denitrification may have been due to a lack of substrate (NO3−), reflecting the low rates of nitrification.

Beschreibung: The nutritional requirements of Eucalyptusgrandis Hill ex Maiden seedlings were studied in glasshouse pot experiments. Nitrogen (N), phosphorus (P), and potassium (K) demand was assessed by bioassays, in which the uptake of tracers (15N, 32P, or 86Rb) by roots excised from the seedlings grown at different levels of nutrient supply was measured. A pilot study showed that there was an inverse relationship between nutrient supply and influx. The measured influx was affected by the length of time that the roots were stored before the bioassay was applied. In a 33 N, P, and K factorial nutrient experiment, growth was primarily influenced by N. Maximum growth occurred at the highest level of supply of each of the three nutrients. N and K influx in the root bioassay was inversely related to foliar N and K concentration, but P uptake was not related to foliar P concentration. These results indicate that the root bioassays are more sensitive determinants of nutrient limitation than. foliar analysis. Interactions between N and P and between N and K alter the stem:leaf ratio, which may be of importance in optimizing wood production.

Beschreibung: Forest floors and mineral soils from early (open willow), middle (poplar–alder), and late (white spruce) floodplain primary successional stages were examined for nitrogen fixation and denitrification. The acetylene-reduction and acetylene-inhibition techniques were used separately and in combination to measure nitrogenase and denitrification activities, both in laboratory and field studies. In situ N2O production was undetectable at all sites and during all sampling periods. Denitrifying activity measured in the field with acetylene amendments was low to undetectable, except after a brief flood in the open willow stand when N2O production ranged from undetectable to 34 ng N•cm−2•h−1 within the newly deposited alluvium–old mineral soil interface. Intact core assays also had low to undetectable denitrification activities; the highest activities (259 ng N•g−1 h−1) were measured in the poplar–alder forest floor in the fall. Laboratory studies showed that potential denitrification enzyme activity (DEA) was also greatest in the poplar–alder forest floor (4332 ng N•g−1•h−1), once again occurring in the fall. In early and midsuccessional stages, the interactive effects of temperature, carbon, and NO3− limited denitrification, yet even with the addition of the limiting amendments, low to undetectable DEA was observed in mineral soils. The later white spruce successional stage also had low to undetectable DEA, increasing only with the addition of the full DEA media and independent of temperature changes. Nonsymbiotic nitrogenase activities were highly variable, ranging from undetectable to 30 ng N•cm−2•h−1. Highest activities were seen in the open willow, newly deposited alluvium–old mineral soil interface immediately after a flood and approximately 1 month after the flood on the newly deposited silt surface. Only the white spruce forest floor had measurable nonsymbiotic nitrogenase activity at all sampling times. Alder root nodule nitrogenase activity showed no significant differences between sampling periods. The estimated annual nitrogen fixation rate of 164 kg N•ha−1 for alder root nodules is a substantial N contribution to the alder stand and to the floodplain ecosystem in general.

Beschreibung: Eighteen natural second-growth stands of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) from a wide range of stand densities and stocking levels were measured for stand leaf area index (LAI) from allometric relationships (direct LAI) and the LI-COR LAI-2000 plant canopy analyzer (indirect LAI). LAI was based on one-half total leaf area (m2) per square metre of ground surface area, normal to any slope. The LAI-2000 underestimated direct LAI by 62%. The underestimate of LAI was due to the confinement of needles within branches (74%) and nonrandom branch distribution (26%). In effect, the branches behaved like big leaves. The LAI-2000 can be used to estimate LAI across a variety of stand density and stocking levels by using a single stand clumping factor of 2.63.

Beschreibung: The effect of convection column air temperature and live needle moisture content on ignitability of tree branches was verified and quantified by exposing branches of three conifer species to a hot-air convection column, at temperatures between 400 and 640 °C, and measuring time to ignition. The three species were ponderosa pine (Pinusponderosa Laws.), Douglas-fir (Pseudotsugamenziesii var glauca (Beissn.) Franco), and lodgepole pine (Pinuscontorta Dougl.). The experiment was repeated monthly over the course of a year, taking advantage of the natural fluctuation of live needle moisture content. Three multiple regression equations for the prediction of time to ignition with air temperature and needle moisture as the independent variables were developed.

Beschreibung: Seven different tree-ring parameters (total ring width, earlywood width, latewood width, maximum latewood density, minimum earlywood density, average earlywood density, and average latewood density) were obtained from pink pine (Halocarpus biformis Hook.) at one chronology site in New Zealand (NZ). The chronologies were analyzed individually and then compared with each other. The relationships between the different tree-ring parameters and climate data (NZ average and local climate data) are also presented. There were more significant climate response functions in the NZ national average climate series than that of local climate data series. Earlywood-related parameters (earlywood width, minimum density, and average earlywood density) were more sensitive to climate than those of latewood. Temperature during the NZ growth season (November-March) was found to be the most strongly related to tree growth. This study demonstrates that the use of both ring width and ring density data can increase the climate information obtained from ring widths and should lead to improved paleoclimate reconstructions in New Zealand.

Beschreibung: Sampling of 24-, 34-, and 44-year-old patch cuts (324–2400 m2) in the Bartlett Experimental Forest, New Hampshire, was undertaken to assess the effect of gap size and location within a gap on tree species abundance (relative basal area and relative density). Shade-tolerant species, especially eastern hemlock (Tsugacanadensis (L.) Carr.) and American beech (Fagusgrandifolia Ehrh.), were relatively more abundant in small gaps and gap edges and generally decreased with increasing gap size. Shade-intolerant species, including paper birch (Betulapapyrifera Marsh.) and pin cherry (Prunuspensylvanica L.f.), were relatively more abundant in large gaps and gap centers and increased with increasing gap size. Intermediately shade-tolerant species, especially yellow birch (Betulaalleghaniensis Britt.) and red maple (Acerrubrum L.), were relatively more abundant in gap centers. Striped maple (Acerpensylvanicum L.) was relatively more abundant in gap edges. Many of these relationships were complex due to interactions with gap age and slope. Sugar maple (Acersaccharum Marsh.) relative abundance was not associated with gap size or location within a gap. Analyses isolating irradiance as a factor influencing species composition were inconclusive. Instead, other effects of gap disturbance and characteristics associated with different locations in the gap, such as soil conditions and root competition, may play an important role in the gap dynamics of this northern hardwoods forest. Gap age had a strong effect on species relative abundances and these patterns reflected typical successional sequences in northern hardwood forests. The gap disturbances increased species richness and diversity in this forest. Gaps contained species not present in the old-growth forest, and the species compositional variations among different gap sizes suggest that a forest with a range of gap sizes will have high diversity. Competitive exclusion appeared to be prevented by the gap disturbances, a likely consequence of the release of previously unavailable resources.

Beschreibung: The temporarily increased fire hazard that is believed to result from the process of thinning is included in a single-stand model for assessing the economic benefits of juvenile spacing. Formulas for the expected net present value and the land expectation value are given along with methods for determining the age of financial maturity and the optimal rotation age. A numerical example is given to illustrate the degree of loss due to the increased fire risk. The problem of commercial thinning when the risk of fire is present is addressed using continuous-time models. It is shown how, when the fire hazard is exogenous to the thinning activity, the problem reduces to one of deterministic optimal control with the discount rate adjusted upward by an amount equal to the fire hazard rate. In the case when the fire hazard increases whenever thinning is taking place, it is shown that in general the optimal thinning policy is qualitatively different from that which is optimal in the no-risk case and involves periods of thinning at the maximum rate interspersed with periods of no thinning activity.

Beschreibung: This effort to improve prediction of forest snowpack evaporation was aimed at understanding differences in winter snowpack among forested aspects. Theoretical arguments combined air temperature, humidity, wind speed, and radiation into a sublimation index. Monitoring weather factors and the mass of a 65-cm-diameter pan of snow set in a forest snowpack provided calibration of the index. Changes in snow surface structure caused a decrease with time in the empirical ratio of snowpack-to-index sublimation. This decrease was proportional to total sublimation since snowfall. We applied the model to compute daily snowpack sublimation on two adjacent forested slopes in central Colorado, U.S.A., during a 40-d accumulation period in March and April 1996. The estimate for both slopes combined was 0.52 mm/d, with sublimation from a south slope snowpack (0.61 mm/d) averaging 1.2 times that from an adjacent north-facing slope (0.43 mm/d). Extending the average difference of 0.18 mm/d through a winter season (150 d) would account for a 27-mm difference in snowpack water between the two aspects. Sublimation of 78 mm in a snow season, estimated from the combined average daily rate, represents about 20% of the normal peak water equivalent of these snowpacks. Effects of surface structure on snowpack sublimation should also apply to surfaces of snow intercepted by canopies.

Beschreibung: The factors and processes that regulate Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) natural regeneration in southwestern Argentina are unknown. We investigated (i) the germination responses of P. menziesii seeds to variations in the radiation and thermal environments imposed by canopy cover and litter, (ii) the effects of litter on seedling emergence, and (iii) the effects of understory vegetation on seedling performance and seed and seedling predation. Seed germination was high in darkness and under canopies. Under a combination of canopy types and litter covers, germination showed a negative correlation with temperature between 23 and 40°C. Germination was not altered by changes in red/far-red ratio. These results suggest that the presence of an overstory canopy promotes P. menziesii seed germination compared with a no-canopy situation (e.g., a clearcut). Litter inhibited seedling emergence by reducing water availability and by acting as a mechanical barrier. Understory vegetation (established saplings) reduced seedling growth and survival. However, our results suggest that direct competition between seedlings and understory vegetation is not the principal force regulating regeneration; indirect effects appear to be of paramount importance because P. menziesii seed and seedling consumption (presumably by rodents) is greatly encouraged by the presence of dense vegetation patches in the understory.

Beschreibung: An aseptic technique was used to collect 227 sap samples from 84 tapholes, including several initial and successive collections, of 27 sugar maples (Acersaccharum Marsh.) over six sap flow seasons (mid-February to late April). In this technique, all material used is sterilized, and the bark as well is sterilized with alcohol. Of the 227 sap samples, 62.5% were sterile or essentially sterile (0–10 colony forming units of microorganisms per millilitre), and of the 74 sap samples from initial collections, 83.8% were sterile or essentially sterile, in contrast with successive collections from the same taphole (P = 0.001). The 35 composite sap samples collected from 1800 nonaseptically tapped tapholes on 900 trees, which were our control, were all contaminated with greater than 800 colony forming units of microorganisms per millilitre. Sap obtained with the aseptic tapping technique produced 92.8% light amber grade syrup and 7.2% medium amber grade syrup. Sap obtained with the traditional tapping technique produced 61.8% light amber syrup, 11.8% medium amber syrup, 14.7% dark amber syrup, and 11.8% syrup that was darker than the dark amber grade. The grade was determined both visually and by a spectrophotometric method. We have substantiated that maple sap is sterile in maple xylem. If sap microbial contamination is minimized and cold sap storage is used, lighter color grade syrup than what is achieved with traditional practices (P = 0.001) can be produced to the end of the season. To avoid the usage of a chemical taphole sanitizer, we recommend cleaner ways for tapping maple trees.

Beschreibung: Height and lateral growth, biomass distribution, leaf morphology, and crown architecture were studied in yellow birch (Betula alleghaniensis Britton), sugar maple (Acer saccharum Marsh.), and beech (Fagus grandifolia Ehrh.) seedlings growing under 1-50% of above-canopy light in a sugar maple stand, in Quebec. All three species showed increasing growth with increasing light, but growth of yellow birch was higher and more responsive than that of sugar maple and beech. All three species showed typical sun-shade morphological responses, such as decreasing specific leaf area and leaf area ratio, and increasing leaf area index, with increasing light availability. Sugar maple was morphologically more plastic than the other species. It showed variations in biomass allocation to leaves and branches, a decrease in branch length to seedling height ratio, and a marked increase in the ratio of leaf area to stem length. Although our results clearly demonstrate the ability of these three species to modify several of their morphological features in response to variations in light, they do not show a clear relationship between species shade tolerance and morphological response to light variations. We suggest that species-specific developmental patterns may act as important constraints to morphological acclimation to light variation.

Beschreibung: Fluxes of nitrous oxide (N2O) and nitric oxide (NO) were measured on a drained and forested peatland in 1992-1995. Net mineralization and nitrification were studied in situ in 1993-1994. Nitrogen additions in 1992 as KNO3, NH4Cl, or urea (100 kg N ·ha-1) were used to study the fate and transformations of N in peat. The mean N2O emissions during the growth season in 1993 were 1.9, 2.6, 3.3, and 3.5 mg N ·m-2·day-1in the control soil, KNO3, NH4Cl, and urea-treated soils, respectively. Mean NO fluxes during the growth season in 1993 averaged 0.3, 0.4, 0.7, and 0.6 mg N ·m-2·day-1in the control soil, KNO3, NH4Cl, and urea treatment, respectively. Annual net N mineralization was 87 kg N ·ha-1in the control soil and 107, 129, and 91 kg ·ha-1in the KNO3, NH4Cl, and urea-treated soils, respectively. Added N increased the fluxes of N oxides at least for a year after the treatments. The study showed that forests on drained N-rich peat soils may be significant sources of N2O and NO and that their production of nitrogenous trace gases is enhanced by additional N.

Beschreibung: We studied the effects of weak and extremely low frequency magnetic fields on the growth and germination of spruce seedlings (Picea abies (L.) Karst.) that were exposed simultaneously to different pH levels. The experiments showed that a weak, sinusoidal magnetic field (50 Hz, 26 and 105 µT, stimulation 12 h/day), which was computer controlled and generated by a system of Helmholtz-like coils, slightly reduced the length of the seedlings and delayed germination at low pH levels. A 26- µT magnetic field at 50 Hz slightly reduced the length of the seedlings at pH 2, delayed germination between pH 2 and 3, and caused no effects or were even stimulatory at pH 6 and 7. At a higher magnetic flux density (105 µT) the length, fresh weight, and germination were reduced mostly at pH 2 and 3 and with a higher statistical significance than at 26 µT. Germination was influenced during the first days of germination, and later the effect diminished rapidly. A 10- µT magnetic field at 46 Hz stimulated only the length of the seedlings. This phenomenon corresponds to the observations made by some other authors, namely that biological systems during various phases of intensive growth and (or) in suboptimal environmental conditions (physiological stress) are prone to exhibit greater sensitivity to extremely low frequency fields.

Beschreibung: A system of three conditioned equations is used to describe whole-tree taper for western hemlock (Tsugaheterophylla (Raf.) Sarg.). Geometric attributes of the system are predicted as empirical functions of DBH and total height. This allows for a wide range of predicted stem profiles without risk of illogical profile predictions for any tree size. Fitting is by multivariate nonlinear regression, where the dependent variables are inside-bark diameters at 12 points on each sample tree. Residual analysis shows that the system does mimic the data in the prediction of different profiles for various combinations of DBH and height. The resultant system can produce analytically tractable estimates of volume. The goodness of fit of the compatible volume estimator is comparable with that of the best whole-tree volume equations. A product of the analysis is a multivariate description of the error distribution; this could have application in the development of profile prediction systems that utilize diameter measurements at multiple heights.

Beschreibung: Increasing needle chlorosis at a declining Piceaabies (L.) Karst. site in northeast Bavaria, Germany, as well as in other declining P. abies stands in southern Germany, was associated with a decrease in the concentrations of both chlorophyll a and b, and, to a lesser extent, of carotenoids. Needle chlorosis related more to a decrease in the chlorophyll concentration than to a decrease in the ratio of total chlorophyll to carotenoids. In forests growing on relatively acidified soils, concentrations of both chlorophyll a and b, and of carotenoids in chlorotic needles were related only to foliar magnesium concentration. In forests growing on more alkaline soils, chlorophyll concentration increased with potassium and phosphorus concentrations and decreased with calcium and magnesium concentrations. Green needles from a declining site in northeast Bavaria were also compared with those from a nearby healthy site. The chlorophyll concentrations in needles increased more at the healthy site than at the declining site during the growing season and with increasing needle age as predicted by a nutritional disharmony model. The use of foliar chlorophyll and nutrient analyses of needles representing a range in severity of chlorosis is proposed as a quick method of identifying the soil processes which, in some areas, cause forest decline.

Beschreibung: Simulated annealing is a stochastic approach to solving large combinatorial problems. This approach was used to model a harvest scheduling problem having block size constraints (no limit, 100–200, and 200–400 ha), a 20-year adjacency delay, and objectives to meet harvest volume targets on the minimum area possible. Spatially explicit harvest schedules complying with the constraints were successfully generated on test data sets of 6148 and 27 548 forest stands.

Beschreibung: Growth and foliar characteristics of red spruce (Picea rubens Sarg.) seedlings produced from somatic embryos (SS) from cell lines representing three genotypes, zygotic embryos (ZS) germinated in vitro, and normal seed (NS) germinated in a greenhouse were compared after 8 months of growth in the greenhouse. NS and SS were similar in terms of height, diameter, root to shoot ratio, and total plant dry mass, but ZS grew significantly more. The root to shoot ratio of ZS was only one half that of SS and NS. Foliar characteristics such as needle dry mass and specific leaf area were also similar between SS and NS and appeared to be distinctly juvenile, but were the most juvenile in ZS. Net photosynthesis, stomatal conductance, and total chlorophyll content were lowest in the ZS, even though they grew the most. After 2 years of growth in pots outdoors, the stem diameter of ZS was still significantly greater than that of SS or NS, although height growth was no longer significantly different. There was no evidence that SS showed signs of accelerated maturation. The possibility that the unexpectedly greater growth of ZS is due to environmental variation during seed set and early germination that affects subsequent seedling growth and development is discussed.