ALBERT

Description: Changes in tree form and taper over time, as affected by changes in tree, stand, and site factors for interior lodgepole pine (Pinuscontorta var. latifolia Engelm.) were investigated using detailed stem analysis data from interior British Columbia. It was found that tree shape and taper change along the stem at one time and over time with changes in tree and stand factors, particularly the diameter at breast height to total tree height ratio, crown length, and crown ratio, and with predicted quadratic mean diameter at age 50 years, a stand density measure. At young ages, the trees were parabolic in shape from ground to top. However, as they increased in size over time, different portions of the stem took different shapes because of unequal growth in diameter along the stem. Changes in tree shape and taper over time were closely related to the crown size, which is related to stand density.

Description: Estimates of individual-tree narrow-sense heritability and additive genetic coefficient of variation of seven traits of forest trees were compiled from 67 published papers. Distributions of the values for each trait were characterized and compared by calculating medians and running Kolmogorov–Smirnov and Wilcoxon signed-rank tests. Generalizations are possible about at least some of the traits examined. Heritability of wood specific gravity was almost always above 0.3 (median 0.48). Heritabilities for other traits tended to be low: medians ranged from 0.185 to 0.26, and individual values generally ranged from 0.1 to 0.4. Evidence that heritabilities of form traits tend to be higher than those of growth traits was weak. The analysis of additive genetic coefficients of variation suggested that specific gravity tends to have lower values than other traits (median 5.1%), while height and diameter (medians 8.5 and 8.6%, respectively) had lower values than straightness (median 11.65%). Individual-tree volume showed the highest levels of additive genetic coefficient of variation (median 20.3%). The levels of additive genetic variation and heritabilities suggest that reasonable levels of genetic gain can be achieved by screening relatively low numbers of trees.

Description: By measuring incident precipitation, throughfall, and stemflow chemistry, the roles of coniferous- and deciduous-dominated forest canopies as a source of and sink for ions in precipitation were examined. A regression technique for distinguishing between external (dry deposition) and internal (canopy leaching) sources of ions in the throughfall flux was evaluated. The effect of seasonal changes in the forest canopy on throughfall and stemflow chemistry was also examined. Throughfall comprised 74 and 84%, respectively, of the hydrologic flux at the coniferous and deciduous sites. Sulphate fluxes were highest at the coniferous site during both growing and dormant seasons, suggesting either a higher scavenging efficiency of the needles for atmospheric SO42−, or higher SO42− leaching from the foliage. The deciduous site neutralized acidic inputs, as demonstrated by its net negative H+ flux year round. The buffering capacity of the coniferous forest was exceeded by the higher amount of acid interception by the canopy. Nitrate behaved conservatively and base ions were exported from the canopy. Stemflow contributions of ions, although low, were generally higher than the contribution of stemflow to the hydrologic flux (2–3%). Independent dry deposition measurements for the growing season, when compared with net SO42− flux, overestimated dry deposition collected by the deciduous canopy, but were comparable to the flux at the coniferous site. These data suggest that dry SO2−SO42− deposition may be responsible for all SO42− enrichment seen in throughfall at these sites. A regression technique for separating internal and external ion sources in throughfall yielded inconsistent results, and attributed virtually all ion enrichment to internal sources. Problems with false assumptions and spurious correlations are discussed. We conclude that this method is not satisfactory for separating ion sources. Seasonal patterns in throughfall chemistry are present. During the growing seasons bases exchange for H+ and are exported similarly with SO42−. Hydrogen retention mirrors SO42− export. Base cations (particularly K+) are leached from the canopy primarily during senescence, but from the stem of the tree primarily during the dormant period. This was most evident at the deciduous site. Chloride behaved in a similar manner, while NH4+ and H+ were retained during the senescent period.

Description: A simple system for the estimation of stem volume is presented based on the compatible stem profile and volume equations. This system can directly predict the stem volume above breast height from measurements of stem diameter at breast height and at an another point along the upper stem, and does not require any sample data for determining a parameter of volume equation. In comparison with the prediction accuracy of existing volume equations from the literature, using data from Cryptomeriajaponica D. Don, Chamaecyparisobtsusa Endl., and Pseudotsugamenziesii (Mirb.) Franco, this system has the advantage of reducing prediction error.

Description: Thirty years of cone production records for subalpine fir (Abieslasiocarpa (Hook.) Nutt.) and mountain hemlock (Tsugamertensiana (Bong.) Carr.) (two sites each) in the Cascade Mountains of Washington and Oregon were compared with basal area increment and weather records to determine relationships among weather, radial growth, and cone crop. Results show that the size of subalpine fir cone crops was negatively related to large crops and positively related to radial growth in the previous 2 years. Mountain hemlock cone crops were negatively related o a large cone crop and positively related to July or August temperature in the previous year. Radial growth in heavy cone years was inhibited more for subalpine fir than for mountain hemlock. Results are explained by differences in the location of cone production between species. It is concluded that global climate warming could result in fewer and more irregular cone crops for these species.

Description: We describe a visual survey technique for evaluating acorn production. In contrast with previously proposed methods, our technique yields ratio-level data on annual productivity that are analyzable with standard statistics and, by sampling the same trees each year, data on the reproductive patterns of individual trees. We compared this technique with two independent sets of acorn-trap data acquired on oaks of three species at Hastings Reservation in central coastal California. Correlations between acorns counted by the visual surveys and collected from acorn traps under the same trees were significant for all three species. Most scatter in the data appeared to be attributable to three causes: (1) sampling error, especially among trees with very small crops, (2) finite counting speed, leading to a lack of discrimination among trees with very large crops by the visual surveys, and (3) arboreal acorn removal by animals. This latter factor can be particularly large, rendering visual surveys more reliable than the use of traps. Furthermore, only the high efficiency of visual surveys allows for the practical assessment of samples large enough to accommodate high within-population variation and detect widespread geographic variation in acorn production. Visual surveys offer a method of assessing the fruit or cone crops of many hardwood and conifer species that is not only more efficient but also more accurate than the use of traps.

Description: Geostatistics provides tools to model, estimate, map, and eventually predict spatial patterns of tree size and growth. Variogram models and kriged maps were used to study spatial dependence of stem diameter (DBH), basal area (BA), and 10-year periodic basal area increment (BAI) in an old-growth forest stand. Temporal variation of spatial patterns was evaluated by fitting spatial stochastic models at 10-year intervals, from 1920 to 1990. The study area was a naturally seeded stand of southwestern ponderosa pine (Pinusponderosa Dougl. ex Laws. var. scopulorum) where total BA and tree density have steadily increased over the last decades. Our objective was to determine if increased stand density simply reduced individual growth rates or if it also altered spatial interactions among trees. Despite increased crowding, stem size maintained the same type of spatial dependence from 1920 to 1990. An isotropic Gaussian variogram was the model of choice to represent spatial dependence at all times. Stem size was spatially autocorrelated over distances no greater than 30 m, a measure of average patch diameter in this forest ecosystem. Because patch diameter remained constant through time, tree density increased by increasing the number of pine groups, not their horizontal dimension. Spatial dependence of stem size (DBH and BA) was always much greater and decreased less through time than that of stem increment (BAI). Spatial dependence of BAI was close to zero in the most recent decade, indicating that growth rates in 1980–1990 varied regardless of mutual tree position. Increased tree crowding corresponded not only to lower average and variance of individual growth rates, but also to reduced spatial dependence of BAI. Because growth variation was less affected by intertree distance with greater local crowding, prediction of individual growth rates benefits from information on horizontal stand structure only if tree density does not exceed threshold values. Simulation models and area estimates of tree performance in old-growth forests may be improved by including geostatistical components to summarize ecological spatial dependence.

Description: Application of base-cation fertilizers has been shown to increase tree growth and vigour in declining sugar maple (Acersaccharum Marsh.) stands in southern Quebec but little is known about the effects of such fertilizers on litter quality or decomposition. Sugar maple foliage litters from fertilized and unfertilized plots on a base-poor site and from a naturally base-rich site were incubated in litterbags of 1- and 3-mm mesh sizes on fertilized and unfertilized plots at the base-poor site. Mass loss of unfertilized litter was slower in fertilized than in unfertilized plots, suggesting a negative effect of fertilization on the decomposer community. Faster mass loss of fertilized than unfertilized litter incubated in the same plot indicated that changes in litter quality brought about by fertilization enhanced decomposition. Mass loss of fertilized litter on fertilized plots did not differ from that of unfertilized litter on control plots, indicating that although decomposition processes are affected by fertilization the overall effect on decomposition is negligible. Mass loss was significantly, but only slightly, higher in large mesh than in small mesh bags indicating that larger soil fauna play a limited role in litter decomposition in this forest.

Description: Radial growth patterns, canopy recruitment characteristics, and disturbance histories were examined in a shade-tolerant species, Nyssasylvatica Marsh., and a shade-intolerant species, Liriodendrontulipifera L., to determine the influence of canopy gaps in species with contrasting life histories. Tree cores of these co-occurring species were taken from three mixed-Quercus forests in northern Virginia. Most N. sylvatica individuals became established prior to 1850 and experienced multiple release and suppression periods coinciding with logging during the late 1800s and early 1900s. Many L. tulipifera became established during the early 1900s following logging, and only a few individuals experienced prolonged suppression periods. Regardless of site, L. tulipifera grew faster than N. sylvatica (average radial growth 〉1.70 mm/year for L. tulipifera vs. 2 mm (15–37 years for L. tulipifera vs.

Description: We test one of the fundamental assumptions of most dendroclimatological research, that the radial growth response of trees to climate does not vary with age once the biological growth trend has been removed. Piceaglauca (Moench) Voss from three sites in the western Northwest Territories, Canada, are disaggregated into age-classes, and their response to climate examined through response function and linear regression analyses. These data are then used in multiple regression analyses to estimate June-July temperatures at Norman Wells, N.W.T., from 1909 to 1989 using both age-dependent and standard (age-independent) models. The response function and regression analyses suggest that the response of Piceaglauca radial growth to climate differs between trees greater than 200 years old and less than 200 years old. These results suggest that the assumption of an age-invariate climate–growth function is therefore invalid at these sites. These apparent age-dependent responses are site specific and may reflect physiological changes related to aging. One possible causal factor of age dependence is that the trees are becoming increasingly moisture stressed with age owing to a reduction in the efficiency of water and nutrient translocation mechanisms. The estimation of June–July temperatures based on an age-dependent model produced improved calibration and verification statistics as compared with a reconstruction based on standard dendroclimatic modelling. If present, age-dependent climate–growth relationships may result in less accurate reconstructions of past climate, particularly during the early portions. However, age-dependent responses could also be used to increase the number of tree-ring based predictor variables for dendroclimatic reconstructions.

Description: The reliability of a leaf-disk assay to assess resistance of Populusdeltoides Bartr. to Melampsoramedusae Thuëm. f.sp. deltoidae, the causal agent of poplar leaf rust, was evaluated. Leaf disks of eight host genotypes were inoculated in a spore settling tower with 11 isolates of the pathogen in all possible combinations, and the latent period, infection probability, sporulation, and progeny/parent ratio were recorded. Correlations were established between these measures and measures derived from field epidemics, namely the relative area under the disease progress curve, the apparent rate of infection, the final disease severity, and the number of days before defoliation. Four genotypes were highly resistant to all 11 isolates tested with the leaf-disk assay and to the local inoculum in field tests. Three genotypes were highly susceptible in inoculation assays and were also susceptible in the field. One genotype was highly resistant in inoculation assays but had intermediate resistance in the field. Significant correlations (p 〈 0.05) were found between all leaf-disk and all field parameters.

Description: A combination of antiaggregation and aggregation pheromones was tested for protecting stands of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) at high risk for infestation by the Douglas-fir beetle (Dendroctonuspseudotsugae Hopkins). The antiaggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), was applied in a bubble capsule formulation to the perimeter of 1-ha circular plots at a rate of 60 g/plot. Treated plots also had three or four clusters of four Lindgren funnel traps baited with frontalin, seudenol, 1-methylcyclohex-2-en-1-ol, and ethanol located outside of the plot but within 160 m of the boundary. Mean (±SE) accumulated catches in all traps per plot were 73 658 ± 19 721 Douglas-fir beetles and 12 892 ± 2 513 Thanasimusundatulus (Say), a predator of the Douglas-fir beetle. The mean percentage of Douglas-fir trees ≥20 cm DBH that were mass attacked was reduced by 80% within the treated plots compared with the untreated plots. However, there was an eightfold increase in the percentage of trees mass attacked in the area outside the treated plots in the vicinity of the funnel traps. The net effect of the treatment was to concentrate mass-attacked trees within a limited area outside of the protected stand. Our results indicate that Douglas-fir beetle antiaggregation and aggregation pheromones can be used effectively to reduce the probability of infestation in small, high-value stands.

Description: Subalpine fir (Abieslasiocarpa (Hook.) Nutt.) regeneration following fire was studied at two locations that burned in 1902 northeast of Mount Rainier, Washington. Tree establishment dates were compared with local climatic records using multiple and logistic regression to identify potential relationships between seasonal climate and annual tree establishment. The influence of microsite features on forest regeneration was also explored. Little regeneration occurred in the first 30 years after the fires, and most trees established in the 1950s, 1977, 1983, and 1989. The dominance of trees

Description: This study presents an individual tree height prediction model for white spruce (Piceaglauca (Moench) Voss) and trembling aspen (Populustremuloides Michx.) grown in boreal mixed-species stands in Alberta. The model is based on a three-parameter Chapman–Richards function fitted to data from 164 permanent sample plots using the parameter prediction method. It is age independent and expresses tree height as a function of tree diameter, tree basal area, stand density, species composition, site productivity, and stand average diameter. This height-prediction model was fitted by weighted nonlinear regression for spruce and unweighted nonlinear regression for aspen. Almost all estimates of parameters were significant at α = 0.05 and model R2-values were high (0.9192 for white spruce and 0.9087 for aspen). No consistent underestimate or overestimate of tree heights was evident in plots of studentized residuals against predicted heights. The model was also tested on an independent data set representing the population on which the model was to be used. Results showed that the average prediction biases were not significant at α = 0.05 for either species, indicating that the model appropriately described the data and performed well when predictions were made.

Description: Beech bark disease occurs when either Nectriagalligena Bres., or Nectriacoccinea var. faginata Lohman, Watson, and Ayers kills bark that is or has been infested and altered by the beech scale, Cryptococcusfagisuga (Lind.). Introduced to Nova Scotia around 1890, this insect now occurs as far southwest as Ohio, West Virginia, Virginia, and North Carolina. I determined the relative occurrence of the two pathogens in forests affected for varying times and the temporal changes in their relative occurrence in recently affected stands of the Monongahela National Forest, West Virginia (MNF). Stands in the Canadian Maritimes, New England, New York, and Pennsylvania were sampled in 1985–1986; and in the Catskill Park, New York in 1988 and 1991. Stands on the MNF were sampled in 1982, 1983, 1984, 1986, 1988, and 1991. The following trends were indicated: N. galligena dominated recently affected stands in Pennsylvania and West Virginia, and N. coccinea var. faginata dominated long-affected stands in Canada, New England, and New York. On the MNF, only N. galligena was isolated in 1982; by 1988, N. coccinea var. faginata was isolated from 8 of 16 stands and from all 16 stands in 1991. Stands where N. galligena persisted had higher proportions of tree species highly susceptible to N. galligena than stands dominated quickly by N. coccinea var. faginata. Once present, however, N. coccinea var. faginata eventually will replace N. galligena as the dominant pathogen.

Description: The problem of fitting height–diameter curves for repeated measurements on growth plots is addressed. The context of the problem is fitting historical data with varying sampling protocols and varying measurement accuracy. A key consideration is obtaining good estimates of top height and top-height increment. A particular model and objective function for fitting are presented. The model has two parameters for each measurement and one common parameter; limited crossovers in the height–diameter curves for the various measurements are allowed. The objective function minimizes errors in predicted height and in predicted change in height. The programming is described, and the availability of code is announced. Examples show both the strengths and weaknesses of this approach.

Description: Reciprocal cross pollinations between western larch (Larixoccidentalis Nutt.) and alpine larch (L. lyallii Parl.) were done in Spring, 1991. The cross to alpine larch females was highly successful; 63% of the seeds developed mature embryos and 79% germinated. However, the cross to western larch females resulted in only 4% filled seed of which 68% germinated. Open-pollinated western larch and alpine larch averaged 26 and 32% filled seed with 48 and 44% germination, respectively. Less than 1% of the alpine larch hypocotyls were reddish in color; most of them were green. About 15% of the western larch and about 17% of the hybrids from alpine larch females had reddish hypocotyls, whereas hybrids from western larch females were intermediate between western larch and alpine larch. Hybrid seed began germinating before the parental types and initial height growth exceeded that of the parental types. However, 4 months following germination, western larch seedlings were ca. four times taller than the hybrids and 10 times taller than alpine larch. Stems of hybrids were significantly thicker than those of either western larch or alpine larch. Hybrid seedlings are robust, stocky, and may be useful in revegetating cold, moist sites between the elevational ranges of alpine and western larch.

Description: The effects of DiPel® 176, a commercially available Bacillusthuringiensis Berliner subsp. kurstaki (B.t.k.) formulation, on microbially mediated carbon and nitrogen mineralization processes, and the persistence of B.t.k. following application of DiPel® 176 to an acidic, coniferous forest soil were evaluated in the laboratory using simple microcosms. Litter (L) and fermentation–humus (FH) material were exposed to DiPel® at the recommended field application rate (FA), DiPel® at 1000× the field application rate (1000× FA), or left untreated. Respiration, substrate induced respiration (SIR), microbial biomass C, metabolic quotients (qCO2), NH4-N, NO3-N, cellulose decay, and B.t.k. viability were monitored regularly over 8 weeks. The FA treatment had no significant impact on soil processes in either the L or FH. The 1000× FA treatment increased SIR and biomass C and decreased qCO2 consistently in both the L and FH. No other effects of the 1000× FA treatment were evident in the L, while in the FH this treatment stimulated respiration initially, then reduced it below control levels; it enhanced cellulose decay; and it inhibited ammonification and nitrification after 8 weeks incubation. In both the L and FH there was no significant loss in viability of B.t.k. in either of the DiPel® treatments over 8 weeks. The microcosms used in this study were simple, inexpensive, and effective, with respiration, SIR, biomass C, and qCO2 being the least variable measurements and the most sensitive to perturbation. This approach is recommended for ecotoxicological and fate testing as outlined in the GuidelinesforRegistrationofNaturallyOccurringMicrobialPestControlAgents.

Description: Microbial isolates from conifer foliage and strawberry were evaluated for biocontrol of Botrytiscinerea Pers.:Fr. in container-grown seedlings of black spruce (Piceamariana (Mill.) B.S.P.). In growth room assays, seedlings were environmentally predisposed to the pathogen and coinoculated with the isolates and B. cinerea. Sporulation incidence of the pathogen was later estimated on needle segments that were cut from the seedlings and incubated on paraquat–chloramphenicol agar medium. The isolates suppressed sporulation by 0–100%. Those of Alternaria, Cladosporium, Epicoccum, yeasts, and bacteria were of low to moderate effectiveness, but those of Gliocladium, Myrothecium, Trichoderma, and Trichothecium were moderately to highly suppressive. In two greenhouse tests, spore suspensions of Gliocladium roseum Link:Bainier and of Myrotheciumverrucaria (Alb. & Schw.) Ditm. ex Stendel. (applied three times) at 2- to 3-week intervals suppressed incidence of B. cinerea by 50–69% and 42–60%, respectively, and were at least as effective as recommended fungicide treatments. Two or three additional applications of the antagonists did not further suppress the pathogen. Isolates of Fusarium sp. and Penicillium sp. were generally ineffective in the greenhouse tests. The four fungi ranked similarly in biocontrol effectiveness in the growth room and greenhouse. It is concluded that the growth room assay provided a strong indication of biocontrol performance in the greenhouse and that G. roseum and M. verrucaria have potential for managing B. cinerea in black spruce in greenhouses.

Description: Four species of boreal forest conifers share a similar southern limit of natural distribution in the three Prairie Provinces of western Canada. The southern boundaries of boreal forest and aspen parkland were compared with geographic patterns of several climate variables to provide a preliminary assessment of how global climate change could affect forest distribution in the future. Forest zonation corresponded most closely with climatic moisture regimes (annual precipitation minus potential evaporation). In contrast, thermal characteristics of climate (mean July and annual temperature, growing degree-days) showed an inconsistent relationship with forest zonation. It is postulated that moisture limitations prevent conifer regeneration south of the present limit of natural distribution. Alternatively, the more arid climates south of the boreal forest may have promoted higher fire frequencies historically, thus preventing conifers from achieving sufficient longevity to regenerate. The driest areas of boreal forest in the region occur at low elevations in west-central Manitoba, throughout Saskatchewan and Alberta, and the southwestern Mackenzie District, Northwest Territories; these areas may be most vulnerable to increased climatic dryness. Climatically induced losses of forest cover from these low-elevation areas could eventually lead to the fragmentation of the boreal forest in western Canada.

Description: Parent and preflight-adult Douglas-fir beetles (Dendroctonuspseudotsugae Hopk., Coleoptera: Scolytidae) were collected from felled Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) trees. Fungi isolated from the beetles included blue-stain fungi, such as Ophiostomapseudotsugae (Rumbold) von Arx, Leptographiumterebrantis Barras & Perry, and Leptographiumabietinum (Peck) Wingfield; other ascomycetes, such as Graphium spp. and Leptographium spp.; yeasts; and unidentified basidiomycetes. All fungal cultures derived from parent beetles, preflight adults, beetle eggs, larvae, frass, and bark from galleries had yeasts present. Ophiostomapseudotsugae was isolated from 67% of the parent females, 19% of the parent males, and 100% of the preflight adults of both sexes collected from their pupal cells. Rinsing the beetles with 70% ethanol prior to fungus isolations reduced the frequency of all fungi, except yeasts. Parent and preflight adult beetles (of both sexes) were examined with a scanning electron microscope, where spores of O. pseudotsugae were visible in shallow pits on the elytra of both male and female beetles. Spores of other fungi were observed in shallow pits on elytra and in much smaller but deeper pits on the scutellum of both sexes. The results indicate a close association between Douglas-fir beetles and fungi, accompanied by anatomical differentiation on the beetles that allows the dissemination of blue-stain fungi to new Douglas-fir hosts and substrates.

Description: The biochemical bases of water-stress tolerance in a pedigree consisting of black cottonwood (Populustrichocarpa Torr. & Gray female) and eastern cottonwood (Populusdeltoides Bartr. male) parental clones and four hybrid progeny were investigated. Trees were grown outdoors in pots; well-watered trees (soil water potential greater than −0.03 MPa) were kept moist in trays, and stressed trees (soil water potential less than −2.0 MPa) were subjected to repeated cyclical stress of 1 or 2 days duration over the 14-week study. Analysis of the major metabolites and ions in fully expanded leaves demonstrated that the greatest degree of osmotic adjustment was displayed by male hybrid 242, the P. deltoides male parent, and male hybrid 239 to a lesser extent. Osmotic adjustment in leaves of both hybrid 242 and the P. deltoides male parent was primarily constituted by malic acid, K, sucrose, and glucose, with the same metabolites also increasing in fine roots of hybrid 242, the only clone to display osmotic adjustment in roots. Female clone 240 and P. deltoides displayed organic solute-based adjustments to water stress that were offset by declines in inorganic ions, particularly Na and Mg. Given that the P. trichocarpa female parent did not display osmotic adjustment in either tissue, the hybrids' capacity for adjustment was likely conferred by the P. deltoides male parent.

Description: Some physical, thermal, and chemical properties of bark of 16 tree species native to the central hardwood region were measured to determine their potential to protect the vascular cambium from damage by fire. The relationship between DBH and bark thickness for each of 16 species was determined. For purposes of monitoring seasonal trends, two species (Quercusmacrocarpa Michx. and Acersaccharinum L.) were sampled periodically during one growing season. Temperature response to bark surface heating of 11 species was monitored at the cambial layer during simulated fires conducted in the field. Bark samples were analyzed for moisture content, specific gravity, dry weight, volatile matter content, and time until ignition. Overall, during simulated fires, temperature gradients were decreased and maximum cambial temperatures were reduced as bark thickness increased. Thick-barked species had lower maximum cambial temperatures, longer times to reach peak temperatures, slower rates of heat loss, and shorter time until surface ignition. Populusdeltoides Marsh, was the most heat resistant among species tested, while Acersaccharinum was the least. Higher specific gravities were associated with higher rates at which cambial temperatures rose as well as with increased time required for surface ignition.

Description: We tested the hypothesis that naturally occurring nitrogen (N) isotope ratios in foliage (from plants that do not symbiotically fix atmospheric N2) are an indicator of soil N dynamics in forests. Replicate plots were established at eight locations ranging in elevation from 615 to 1670 m in Great Smoky Mountains National Park in eastern Tennessee, U.S.A. The locations selected ranged from N-poor (low-elevation) to N-rich (high-elevation) forest stands. Soils were sampled in June 1992; plants, forest floors, and upper mineral soils were sampled in August 1992. Net N mineralization and net nitrification potentials for surface mineral soils and organic matter layers at each site were determined by aerobic laboratory incubations. Soils and organic layers from high-elevation sites had greater net N mineralization and nitrification potentials than soils from low-elevation sites. There were significant (P ≤ 0.05) differences between study sites in soil 15N abundance. Therefore, we examined correlations between measures of soil N availability and both mean foliar δ15N values and mean enrichment factors (εp−s = δ15Nleaf − δ15Nsoil). In evergreens, maples, and ferns, mean foliar δ15N values and mean enrichment factors were positively correlated with net N mineralization and net nitrification potentials in soil. The observed relationships between natural 15N abundance in plant leaves and soil N availability were explained by a simple model of soil N dynamics. The model predicts how the isotopic composition of plant N is affected by the following factors: (i) varying uptake of soil NH4-N and NO3-N, (ii) the isotopic composition of different soil N pools, and (iii) relative rates of soil N transformations.

Description: A 1992 study of serotiny in lodgepole pine (Pinuscontorta Dougl. ex Loud. var. latifolia Engelm.) in Yellowstone National Park asked four questions: (i) are there morphological characteristics that can be used to estimate pre-fire proportion of serotinous trees in forests that burned in 1988?; (ii) at what spatial scale does percent serotinous trees vary across the landscape?; (iii) which environmental factors are correlated with serotiny?; and (iv) what is the relationship between prefire serotiny and postfire lodgepole pine seedling density? We first sampled cone characteristics in serotinous and nonserotinous trees along four 2950-m transects in unburned forests, and examined burned trees nearby. Results indicated that asymmetrical cones and an acute angle of cone attachment to the branch were reliable indicators of serotiny even in burned trees. We then sampled nine patches of lodgepole pine forest that had burned in 1988, and varied in size from 1–3600 ha. We sampled serotiny at varying intervals along two perpendicular transects that crossed in the center of each patch. At each sample point, the 12 nearest canopy lodgepole pines were classified as serotinous or nonserotinous. We concluded that the percentage of serotinous trees is most variable at intermediate scales of 1–10 km, and is relatively homogeneous at both fine scales (

Description: Silvicultural practices such as thinning and fertilization can affect both canopy foliage quantity and distribution, altering stand growth. The objectives of this research were to quantify the effects of tree size and silvicultural treatment on the vertical distribution of foliage of individual trees of loblolly pine (Pinustaeda L.) and to estimate foliage quantity and distribution using easily measured tree data. In three stands sampled in North and South Carolina, fertilization and (or) thinning treatments had been applied 2 years prior to sampling. A fourth stand was untreated. Nonlinear and linear regression models were developed to test the effects of silvicultural treatment on individual branch foliage biomass and whole tree foliage biomass. Vertical distributions of foliage and branches were modelled using a Weibull probability density function. Analyses indicated that individual branch foliage biomass was positively related to branch size but negatively related to distance from the top of the tree. Fertilization with nitrogen and phosphorus, or thinning, increased the foliage biomass carried by a given sized branch. Silvicultural treatment effects on individual branches translated into whole-tree foliage biomass with thinning and fertilization increasing the crown size of individual trees. Though treatment affected crown size, the distribution of foliage (and branches) remained unaffected. Because silvicultural treatments change the size of crowns for trees of given dimensions, any estimation of loblolly pine crown biomass must be site and treatment specific.

Description: The level of genetic diversity of natural populations of eastern white pine (Pinusstrobus L.) from Quebec was estimated from allozyme variants of 18 loci coding 12 enzyme systems. On average, a white pine population was polymorphic at 50.6% of loci, had 1.96 alleles and 1.22 effective alleles per locus, and observed and expected heterozygosities of 0.176 and 0.180, respectively. The level of genetic diversity was lower in the populations of the St. Lawrence lowlands than in those of western Quebec. This observation will help in guiding the selection program of the eastern white pine improvement program under way in Quebec. Genetic differentiation among sampled populations was weak and accounted for only 2% of the total diversity. The estimate of gene flow was very high, resulting in low values for genetic distances among populations. Only one locus showed a heterogeneity of allelic frequencies among populations after the Bonferroni procedure was applied for simultaneous statistical tests. A cluster analysis based on genetic distances among populations revealed that the Anticosti and Abitibi populations, located at the limit of the natural range of white pine, were similar to populations from regions that were geographically the most distant.

Description: Crown class, site class, and breast-height age were incorporated into Kozak's variable-exponent taper equation (A. Kozak. 1988. Can. J. For. Res. 18: 1363–1368) for three species: Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), western red cedar (Thujaplicata Donn), and aspen (Populustremuloides Michx.). For lodgepole pine (Pinuscontorta Dougl.), crown ratio, breast-height age, and quadratic mean diameter were incorporated into Kozak's taper equation. The effects of adding these variables to the exponent part of the taper equation on the prediction abilities of the taper model were assessed for prediction of diameter inside bark along the stem, total tree volume, and tree merchantable height. It was found that apart from the use of crown ratio for lodgepole pine, the additional variables resulted in only marginal improvements to the published version of Kozak's taper function. Therefore, the cost of measuring these additional variables is not justifiable.

Description: This study investigated the effect of different cold storage conditions on (i) root freezing tolerance of Norway spruce (Piceaabies (L.) Karst.) and Scots pine (Pinussylvestris L.) and (ii) the vitality of seedlings that suffered freezing injury to roots prior to storage. Container-grown seedlings, 1 year old, were stored from the end of October to April in three environments with different root temperatures: outdoor storage (−0.5 to 11.0 °C), cool storage (0.7 to 3.7 °C), or frozen storage (−5.0 to −3.8 °C). Root freezing tolerance was determined prior to storage in October and during storage in January and March. Maximum root freezing tolerance for both species occurred in January, when over 50% of spruce and pine seedlings survived 2 h exposure to −25 and −20 °C, respectively. At this time, roots of frozen-stored spruce were significantly more freezing tolerant than outdoor-stored seedlings, whereas storage environment had no significant effect on pine. Freezing tolerance in roots of both species decreased from January to March in all test environments but to a lesser extent at the subzero temperatures in the frozen storage. Root freezing to −10, −15, or −20 °C in late October before storage resulted in reduced poststorage survival of seedlings in April. Pine was more adversely affected (0–13% survival) than spruce (0–85% survival). Freezing of roots prior to storage caused the lowest survival with frozen storage.

Description: The crown development of red pine (Pinusresinosa Ait.) plantations originating from different initial spacings was studied between 13 and 33 years of age. First, the effect of spacing on models used to predict crown width and crown ratio from diameter at breast height (DBH) and height was examined. Models for trees of different ages that included all the spacings were found to predict crown growth measures as well as separate models derived for each spacing. Second, the following crown relative growth measures were studied: crown width/crown length (crown shape ratio), crown surface/crown volume, and foliage biomass/crown volume. The way such measures changed over time under different initial spacings was studied; these findings were compared with changes in relative growth rate (RGR), which can be used to evaluate the effect of competitive stress. Crown shape ratio decreased with an increase in DBH in the absence of severe competition, and increased with DBH under severe competitive stress. The other two crown relative growth measures were always negatively correlated with DBH; this shows that large trees use their aerial growing space less efficiently than small trees at all stages of stand development. Only crown shape ratio changed in the same way as RGR.

Description: Age structures and growth curves were used to determine the origin and to follow the development of 17 balsam fir (Abiesbalsamea (L.) Mill.) stands in the middle of the Boreal Zone in the north of Lake Saint-Jean, Quebec. Every growth curve from the studied sites presented a more or less long period of suppression in the early growth of the balsam fir, followed by a marked release synchronous between the trees of a given site. Generally, a balsam fir cohort established just before the growth release. Characteristic growth releases generally occurred after the formation of exceptionally narrow rings, which took place around 1952, 1914, and between 1860 and 1890 in the sampled trees. Unimodal even-aged stands regenerated from balsam fir advanced growth following spruce budworm (Choristoneurafumiferana (Clem.)) outbreaks that rapidly defoliated the trees and caused openings, sometimes associated with blowdown; these outbreaks occurred between 1944 and 1953 (one stand), between 1909 and 1923 (six stands), and possibly between ca. 1860 and 1900 (seven stands). Bimodal and uneven-aged stands were associated with two spruce budworm outbreaks. In one stand, some of the trees regenerated from the spruce budworm outbreak that occurred between 1909 and 1923, but the 1944–1953 outbreak was intense enough to cause important defoliation and mortality, which released a second cohort. Finally, two stands regenerated from the possible spruce budworm outbreak that occurred around 1860–1900 and from the 1909–1923 outbreak. The presence of a fir cohort and associated growth release between 1860 and 1890 strongly suggests that an outbreak occurred at that time in the studied region. Every sampled stand from the Boreal Zone north of Lake Saint-Jean regenerated from a balsam fir seedling bank following a spruce budworm outbreak that affected the mature balsam fir canopy. These results are in good agreement with the hypothesis that spruce budworm outbreaks and balsam fir forests form an interdependent self-regulating system. Our study shows the drastic effect of spruce budworm outbreaks in the boreal forest, where black spruce (Piceamariana (Mill.) B.S.P.) dominates.

Description: Water-stress tolerance of six clones in a pedigree consisting of black cottonwood (Populustrichocarpa Torr. & Gray, female) and eastern cottonwood (Populusdeltoides Bartr., male) parental clones and four hybrid progeny was investigated. Trees were grown outdoors in pots; well-watered trees were kept moist (soil water potential greater than −0.03 MPa), and stressed trees (soil water potential less than −2.0 MPa) were subjected to repeated cyclical stress of 1 or 2 days duration over the 14-week study. Male P. deltoides and the male clone 242 displayed the greatest degree of stress tolerance, as evidenced by greater osmotic adjustment at saturation (0.25 MPa) and maintenance of relative growth rate of the main stem under water stress at 100 and 69% of that of well-watered trees, respectively, compared with reductions to 50–58% for the other hybrid clones. However, differences in total plant dry weight under water stress were less obvious, with female clones allocating more carbon to branch production under well-watered conditions, which was further increased under water stress. Three of the four hybrids displayed some degree of osmotic adjustment at saturation after bud set, which was likely conferred by male P. deltoides. Screening clones of Populus for drought tolerance should take into account the segregating tendency of hybrids to allocate carbon to lateral meristems under stress.

Description: Woody vegetation was surveyed in 58 forest stands in northern Virginia to examine the effects of previous land-use history on past and present-day forest composition and dynamics. Stands were separated using detrended correspondence analysis (DCA) and overstory importance values into three forest groups: (i) white oak (Quercusalba L.)–tulip-poplar (Liriodendrontulipifera L.) (ii) white oak–scarlet oak (Quercuscoccinea Muenchh.) and (iii) Virginia pine (Pinusvirginiana Mill.) The first DCA axis represents a successional continuum from more recently disturbed areas containing young pine forests to less disturbed mature oak stands, and is negatively correlated with stand age and species diversity. White oak and red oak (Quercusrubra L.) dominated presettlement forests in the area. Following European settlement, forests experienced intense logging associated with the charcoal iron industry, large-scale clearing for agriculture, and subsequent land abandonment. By coupling radial growth analysis with age–diameter figures, we evaluated the responses of stands to disturbances associated with various land-use practices. This analysis indicated that many Virginia pine stands resulted from agricultural abandonment during the early 1900s, while a majority of oak stands experienced peak recruitment and radial growth following periodic logging disturbances in the 1800s. Canopy closure, forest protection, and reduced fire and logging disturbance this century led to increases in dogwood (Cornusflorida L.) and blackgum (Nyssasylvatica Marsh.) in area forests. The oldest stands exhibited a lack of tall oak regeneration; however, they also contained a scarcity of potential oak replacement species. Therefore, oak will seemingly share future dominance with several mixed-mesophytic species, although the exact successional status of these stands is unresolved.

Description: This paper reports the nuclear DNA content estimates obtained by flow cytometry for a group of twelve Eucalyptus species and five fast-growing hybrids that includes those most widely planted throughout the world. Estimates of nuclear (2C) DNA content for the species surveyed ranged from 0.77 pg/2C for Eucalyptuscitriodora Hook. (subgenus Corymbia) to 1.47 pg/2C for Eucalyptussaligna Smith (subgenus Symphyomyrtus). This range corresponds to a haploid genome size range of 370–700 megabase pairs. The average physical equivalent of a 1 cM distance could be as low as 200 kilobase pairs in Eucalyptus, an attractive feature for positional cloning efforts in woody plants. The closer the species were in phylogenetic relationship the more similar were their nuclear DNA content values. All the interspecific hybrids surveyed displayed a nuclear DNA content in the expected intermediate range between the respective parental species, with the exception of one originating from Rio Claro, Brazil, whose exact parentage is unknown. No evidence of polyploidy was observed in any of the hybrids. The flow cytometry procedure employed in this study is an efficient method for investigating ploidy levels of high yielding hybrids of Eucalyptus.

Description: The productivity of trees under short-rotation intensive culture is influenced by herbaceous competition and drainage conditions. During the first year of establishment of Salixdiscolor Mühl. and Salixviminalis L., four weed-suppression treatments were applied to two sites showing different drainage conditions, one well drained and the other is poorly drained. On the well-drained site, the productivity of the trees increased in all the plots under treatment, whereas on the poorly drained site, only the use of a plastic mulch increased the biomass production. The mean productivity on the well-drained site was always superior to the productivity measured on the poorly drained site except when the vegetation was controlled by the use of a plastic mulch. The analyses related to nutrition revealed that the trees on the well-drained site absorbed more nutrients than those on the poorly drained site. Salixdiscolor showed a higher uptake of potassium and S. viminalis, a higher concentration of calcium. Our results indicate that weed suppression is essential to the establishment of trees in short-rotation intensive culture and that the use of a plastic mulch proved to be particularly profitable on marginal sites.

Description: Canopy nutrition, leaf chlorophyll concentration, and leaf CO2 assimilation capacity (Amax) were examined in sugar maple (Acersaccharum Marsh.) trees exhibiting symptoms of crown dieback in four stands on acid soils (pH ≈ 4.0) in northern Vermont. Leaf CO2 assimilation capacity was measured on foliage from detached and rehydrated branches harvested from the upper portion of the canopy. Leaf calcium (Ca) and magnesium (Mg) concentrations were among the lowest reported for sugar maple in its natural range. Total leaf chlorophyll concentrations of canopy leaves were lowest on the sites exhibiting the lowest leaf nitrogen (N) and Ca, and CO2 assimilation capacity was correlated with chlorophyll concentration among canopy leaves from all sites. Strong linear relationships were observed between leaf CO2 assimilation capacity per unit leaf mass and leaf N (r2 = 0.60) as well as leaf Ca (r2 = 0.51) among the four sites. On the basis of the observed strong correlation between leaf Ca and leaf N (r2 = 0.64) and the lack of clear enhancement of leaf CO2 assimilation capacity in trees fertilized with base cations (K, Ca, and Mg), it appears that leaf CO2 assimilation capacity and leaf Ca may not necessarily be functionally related. However, since low leaf CO2 assimilation capacity and photosynthetic N-use efficiency were common in unfertilized trees with low Ca (Ca 〈 0.6%), CO2 assimilation processes in sugar maple on acid soils may be limited by N and Ca × Mg interactions. The strongly acidic nature of the soils in these stands and the magnitude of acidic deposition in the region may precondition sugar maple trees on some sites to levels of cation deficiency that may be associated with low CO2 assimilation in the forest canopy.

Description: One of the most common ways to account for investment risk is to add a risk premium to the risk-free discount rate when computing present values of expected revenues which are uncertain. Using certainty-equivalent analysis, we show that the correct risk premium for short-term investments can easily be in the commonly used 7-percentage-point range. But for such risk premiums to be appropriate for long-term forestry investments, the necessary certainty-equivalent conditions often seem to be unreasonably restrictive. Results suggest that the appropriate risk premium may decline with lengthening payoff period for many forest investments. Limited empirical data provide tentative support, but more research is needed to resolve the issue. We review policy implications and suggest areas for further research.

Description: Quantitative assessments of the incidence and severity of Mycosphaerella leaf disease were made on nine provenances (encompassing the four subspecies) of Eucalyptusglobulus Labill. over three seasons in 1990 in a trial in Victoria, Australia. Defoliation was also assessed and tree height and diameter measured. Mycosphaerella leaf disease increased rapidly from winter to spring with disease incidence reaching 100% in most provenances by summer. There were highly significant differences in disease severity among provenances, with provenances from E. globulus ssp. globulus Kirkpatrick and E. globulus ssp. bicostata (Maid, et al.) Kirkpatrick being the most severely affected, while provenances from E. globulus ssp. maidenii (F. Muell.) Kirkpatrick and E. globulus ssp. pseudoglobulus Kirkpatrick were only slightly affected. There were also highly significant differences among provenances within E. globulus ssp. globulus and E. globulus ssp. pseudoglobulus. There was a high correlation between disease severity in summer and defoliation, suggesting that Mycosphaerella leaf disease was the main causal agent in leaf fall. There was also a high negative correlation between disease severity and growth rate. This study shows the potential benefits of selecting resistant provenances of E. globulus to maximise production from plantations in areas where Mycosphaerella leaf disease is a problem.

Description: We used a new technique to examine the response of the trunk and structural roots of white spruce (Piceaglauca (Moench) Voss) to an increase in wind exposure. Ring widths were measured in the roots and trunks of trees located within a 120-year-old, boreal mixedwood stand (control) and at the edge of a road built through the stand 16 years before sampling (released). The observed ring widths were divided by widths predicted from regression to produce ring indices. Response indices were produced by subtracting the ring indices of control trees from those of released trees. Allocation indices were produced by subtracting the ring indices of trunks from those of roots. A final index, quantifying the change in allocation to the root and trunk after road clearing, was produced by subtracting allocation indices of control trees from those of released trees. Following the road clearing, the rate of trunk diameter growth remained unchanged for 3–9 years, while root diameter growth increased. These observations suggest that trunk growth may be suppressed for some years following road clearing as a result of increased root growth. The increase in root growth may help stabilize trees after exposure to increased wind stress by increasing the amount of root wood anchoring and supporting them.

Description: A common-garden study of Populustrichocarpa Torr. & Gray was initiated in 1985 when clonal material from 128 trees was collected from sites distributed along two mesic (Hoh and Nisqually) and two xeric (Dungeness and Yakima) river valleys. This material was grown for 1 year at Puyallup, Wash. In spring 1986, cuttings from this material were used to establish two replicate plantations, one at Puyallup and one at Wenatchee, Wash. Over the 2 year period, trees were assessed for survival, damage, and growth. Two-year survival was 86% at Puyallup and 59% at Wenatchee; survival was higher for mesic-origin trees at both sites. At Wenatchee, mortality was mainly due to a droughty soil and hot, dry climate in the first year, and damage was due to the tarnished plant bug (Lygus spp.), field voles (Microtus spp.), and grasshoppers (Family Acrididae). At both locations, Melampsoraoccidentalis Jacks. leaf rust was found mainly on trees originating from Yakima. Mean 2-year height and diameter at Puyallup were 457 cm and 40 mm, respectively; corresponding values at Wenatchee were 320 cm and 29 mm. At Puyallup, 2-year stem volume (diameter2 × height) decreased significantly in this order: Nisqually (13 500 cm3) = Hoh 〉 Dungeness 〉 Yakima (4700 cm3). Within the Nisqually trees, clones from lower, milder climate elevations grew more than those from the upper elevations. The reverse was true for the Yakima trees, presumably because the lower elevation trees are adapted to an arid climate and are very susceptible to Melampsora rust. At Wenatchee, high microsite heterogeneity masked much of the genetic variation. The genetic variance component (among rivers, sites, and clones) for stem volume at Puyallup increased from 27 to 51% over the second year. In analyses of each river valley, genetic components (elevational group and clone) were also high at 27–63%; however, for the Yakima trees, the elevational group variance (40%) was much larger than for the other valleys (0–7%) and suggests a steep selection gradient midway along the river transect.

Description: Field exclosure studies have shown that mammalian browsers such as white-tailed deer (Odocoileusvirginianus) can have pervasive effects on forest dynamics in eastern North America. Direct experimental tests of the effects of browsing on growth and survival of a wide range of tree species, however, have yielded conflicting results. This study was designed to assess the effects of variation in the frequency, seasonal timing, and intensity of browsing (simulated by mechanical clipping) on the growth and mortality of three of the major tree species of the Hudson Valley, New York. The clipping treatments were applied to seedlings grown under two different light regimes (full sun and 8% of full sun) to examine seedling responses under different levels of shade-induced carbon stress. Our results demonstrate that even 2 successive years of heavy winter clipping (75% of new shoot growth removed) has little immediate effect on growth or survival of any of the three species. It is possible that winter browsing only has significant negative effects when seedlings are browsed repeatedly over long periods of time. However, comparable levels of summer browsing for only 2 years significantly reduced both growth and survival of all three species. While most natural browsing occurs in the dormant season, our results suggest that it is the less frequent browsing during late spring and early summer that has the greatest immediate effect on tree seedlings. Shading reduced growth and increased mortality in all three species; however, there was only a limited interaction between light level and the simulated browsing treatments. The effects of browsing on survival were similar in all three species; however, the effects of browsing on cumulative height and annual growth varied enough among the species to suggest that browsing could cause significant variation among these species in their rate of invasion in old fields and rights of way, and their rate of regeneration following logging or disturbance of forests.