摘要:

Two hundred thirteen potential sawlog trees from 22- to 34-year-oldEucalyptusregnansF. Muell. andEucalyptusdelegatensisR.T. Baker regrowth forests from four sites in southern Tasmania were felled, dissected, and assessed for discolouration and decay. Of the aboveground origins, branches accounted for more than half of the discolouration and decay both in terms of incidence and volume. Stem-boring insects and branch crotches were the source of most of the remaining aboveground decay. Butt rots accounted for only 7% of the columns of discolouration and decay, but their incidence showed considerable local variation such that on some plots they accounted for more than 20% of the total volume of discolouration and decay in the bottom 6 m of the stem. Decay in individual trees was 0 to 17.5% of total volume, with a mean of 1.3%. Only 12% of the trees were completely free of discolouration and decay, while 25% of the trees had discolouration and decay in more than 1.5% of the total stem volume. Whilst both the incidence and percent volume of decay showed considerable, and often statistically significant, variation both among sites and locally, among plots within sites, the greatest proportion of the variation was tree to tree. Our ability to limit future timber losses resulting from decay will require that those site, stand, and most importantly, tree factors that influence the prevalence of, and susceptibility to, decay in eucalypts are identified.

ISSN:0045-5067    

DOI:10.1139/x26-001

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Site-index curves derived from stem analysis of trees with dominant height at the time of selection will underestimate dominant height of young trees and thus overestimate the performance and yield expectations of young stands. A simple model-based adjustment procedure is presented and tested on two artificial populations and two data sets from repeatedly measured plots. To recover a less biased height–age curve of dominant trees, estimates are needed of age–age correlations and the sampling intensity (standardized height difference) applied to the selection of site trees for stem analysis. Adaptation to different definitions of dominant height is possible. Results confirmed that the recovery procedure is very effective in reducing the relative bias. Bias reduction in excess of 40% can be expected during the first half of a rotation. Small but insignificant increases in bias were encountered during the second half of a rotation.

ISSN:0045-5067    

DOI:10.1139/x26-002

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The effects of single-season tropospheric ozone (O3) exposures on growth, leaf abscission, and biomass of trembling aspen (PopulustremuloidesMichx.) rooted cuttings and seedlings were studied. Plants were grown in the Upper Peninsula of Michigan in open-top chambers with O3exposures that ranged from 7 to 92 ppm-h. Depending on the genotype, total seasonal O3exposure in the range of 50–92 ppm-h had negative impacts on stem, retained leaf, and root biomass accumulation and on diameter growth. Leaf abscission generally increased with increasing O3exposure and was the principal cause of the decrease in leaf biomass of the O3-treated plants. Considerable genetic variation in O3responses occurred, as shown by differences in sensitivities among clones and among seedlings. However, the responses to O3of rooted cuttings and seedlings were similar when seedling means were compared with clonal means for leaf abscission, diameter growth, retained leaf biomass, and root biomass. Comparison of a single square-wave treatment (52 ppm-h) with 70 and 92 ppm-h episodic exposures suggested that the plant response to the square-wave exposure was similar to the response to the highest episodic exposure even though the 92 ppm-h episodic exposure was almost twice the square-wave exposure. Our results are consistent with previous studies that show thatP.tremuloidesis highly responsive to O3exposure and this response has a strong genetic component.

ISSN:0045-5067    

DOI:10.1139/x26-003

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

This study compared the effects of sampling metrics (basal area and density of trees) on cluster analyses of oak woodland vegetation. Minimum-variance clustering was used to define communities within oak woodlands. Communities derived from basal area data were more distinct and more homogeneous than communities derived from density data. Consistent with previous research, minimum-variance clustering of basal area data produced groups of approximately equal size. In contrast, minimum-variance clustering of density data did not result in similar-sized groups. Formation of similar-sized groups, which is generally reported to be an advantage of minimum-variance clustering, apparently is dependent on the sampling metric employed.

ISSN:0045-5067    

DOI:10.1139/x26-004

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

We summarize three existing conceptual frameworks for forest regeneration in northeastern North America and suggest that none consider both a range of disturbance characteristics and a range of forest conditions at the time of disturbance. We offer a more general conceptual model, within which the existing models can be seen as special cases. We propose that the abundance of characteristic seed–bank, pioneer species, such asPrunuspensylvanicaL.f. andRubusspp. (oftenRubusallegheniensisT.C. Porter,RubushispidusL., orRubusodoratusL.), is dependent on propagule availability, which in turn is determined by forest age and size. Specifically, following disturbance, large tracts of forest and older forests (ca. >125 years) are predicted to have very low densities of the above pioneers. As a result, population, community, and ecosystem parameters may be substantially different in the regenerating forest than in the familiar cases of regeneration in secondary forests. Indeed, the presettlement forest of much of northeastern North America may have experienced a notable scarcity of pioneers after disturbances, in areas far enough inland for hurricanes to be unimportant. Our hypothesis makes predictions of seed-bank abundance that are well supported in a variety of forest types; we also provide support for our hypothesis with data on regeneration following catastrophic windthrow in Allegheny National Forest, Pennsylvania, and elsewhere. Finally, our hypothesis also predicts that the potential regeneration in much of the secondary forest of northeastern North America should profoundly shift as stands age from roughly 100 to 130 years.

ISSN:0045-5067    

DOI:10.1139/x26-005

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Hydrologic drainage criteria that describe the position of the water table between adjacent ditches are commonly used to assess the initial effectiveness of peatland drainage projects for tree growth improvement. However, these criteria do not reflect the soil conditions that regulate tree growth and performance after drainage. The effect of three drainage ditch spacings (30, 40, and 50 m) on the spatial variability of soil water conditions at three drained boreal Alberta peatlands was studied. Soil water content (0–30 cm depth) was found to be insensitive (p = 0.686) to drainage ditch spacing several years after drainage. Greater variation was observed between different sampling locations (p = 0.024) relative to the position of the ditch edge within similar ditch spacings. Spatial distribution of soil water in the unsaturated zone was found to be inversely related to the degree of water table lowering. Spatial patterns of soil water content were strongly associated with changes to substrate bulk density resulting from post-drainage peatland subsidence.

ISSN:0045-5067    

DOI:10.1139/x26-006

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Using isoenzymes as gene markers and spatial autocorrelation analysis as a tool to detect spatial patterns, we studied the spatial distribution of genotypes in a naturally regenerated uneven-aged Norway spruce (Piceaabies(L.) Karst.) stand on the eastern Italian Alps. In most cases we found a random distribution of genotypes in space; in the whole data set less than 11% of genotype pairs showed positive associations for the first (10 m) distance class. Extensive gene flow, due to long distance dispersal of pollen and seeds inP.abies, may account for the observed spatial patterns. A few genotypes (GotB-22,LapB-23,LapB-24,SkdB-12, andMnrB-12) showed a significant clumped distribution over a small spatial scale. We suggested that selection processes driven by environmental variability might have produced significant clumping of these genotypes. However, the role of factors linked to the breeding system, and of chance events, in determining the population spatial structure cannot be excluded in our study.

ISSN:0045-5067    

DOI:10.1139/x26-007

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Two types of scarification (cone and disk) were applied at two intensities (simple and double passes), in a randomized complete block design, established alongside buffer stands of spruce protective of water courses, that provided a natural seed source. Treatment effects on seedbed evolution, natural seeding of black spruce (Piceamariana(Mill.) BSP), competing vegetation, and soil physical and chemical properties were examined over a 3-year period. In situ nitrogen mineralization was also studied, using the buried-bag method. All scarification treatments created a surface horizon (0–10 cm) with 80% less organic matter content than the control treatment. However, treatments tended to loosen the exposed deep layers, creating microsites whose compactness appeared adequate for root development (1.07–1.22 Mg/m3). The organic matter loss mainly decreased exchangeable K and Mg in the surface 20 cm of scarified microsites. Scarification had little impact on total N of sampled profiles and clearcutting did not increase N mineralization with regard to the forest, during the first year after disturbance. The weak soil warming and the stability of temperatures under the unscarified humus suggest that clearcutting did not significantly enhanced microbial activity on the site. However, removal of the insulating humus layer allowed a significant summer soil warming in the furrows. Despite this, scarified microsites were characterized by N immobilization during the first growing season after treatment. However, net N production was positive during the winter period, presumably because of a N-flux phenomenon. Scarification improved black spruce regeneration by natural seeding. Three years after treatment, stocking levels reached 40 to 51% in the scarified sectors while they reached 31% in the controls, this gap being mainly attributed to the second germination year. The difference can be explained by the improved receptivity of bare mineral soil, well-decomposed humus, and mixed mineral–organic seedbeds that covered 12–20% of the scarified areas immediately after treatment. Generally, results indicate that microsites created by a light scarification are as receptive as microsites created by a severe perturbation. Finally, every scarification treatment efficiently controlled the ericaceous shrub cover during the first 3 years after treatment.

ISSN:0045-5067    

DOI:10.1139/x26-008

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Eight-year-old Norway spruce (Piceaabies(L.) Karst.) and 6-year-old red oak (QuercusrubraL.) trees planted directly into the soil were enclosed in open-top chambers and exposed to either 350 or 700 μmol•mol−1of CO2for three growing seasons. During the third year a natural drought was allowed to develop, reducing the predawn leaf water potential to between −0.80 and −1.15 MPa. Intensive gas-exchange measurements were performed before, during, and after the drought. CO2response curves revealed mesophyll limitation to photosynthesis in drought-stressed trees grown in elevated levels of CO2. The water-use efficiency was greater for trees grown at elevated CO2, but less so during drought in red oak and the same between treatments for drought-stressed spruce. Diurnal measurements showed that enhancement of assimilation rates of trees grown at 700 μmol•mol−1depended upon the time of day that measurements were made. There was an acclimation to increased CO2in both species that could not be explained by leaf area differences, available soil for roots, nutrient limitation, or starch accumulation.

ISSN:0045-5067    

DOI:10.1139/x26-009

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Seedling stands of loblolly pine (PinustaedaL.) and sweetgum (LiquidambarstyracifluaL.) were grown in monoculture or mixed stands for two growing cycles in controlled-environment chambers. Treatments consisted of ambient (408 ppm) and elevated (806 ppm) CO2, concentrations, water-stressed and well-watered conditions, and low (20 kg N/ha) and high (215 kg N/ha) nitrogen application rates. Photosynthesis rates were measured under ambient and elevated cuvette CO2concentrations for both whole stands and individual seedlings from these stands. Significant interactions between CO2and water suggested that elevated CO2concentration compensated for low water availability in individually measured loblolly pine and in whole seedling stands regardless of stand type. Expressing photosynthesis on a soil area versus a leaf-mass basis influenced the photosynthetic rankings of the three stand types relative to one another. Net photosynthetic rates per unit leaf mass were 390 and 880% higher in individually measured seedlings than in whole monoculture stands for loblolly pine and sweetgum, respectively. Lower photosynthetic contributions from lower canopy leaves in whole seedling stands compared with the upper canopy leaves used in individual-seedling measurements were thought to be responsible for lower photosynthetic rates in seedling stands. These results suggest that photosynthetic response is influenced by canopy dynamics that are unaccounted for by individual-seedling measurements of photosynthesis. Differences in photosynthetic response between loblolly pine and sweetgum stands and individuals are thought to be largely due to species-specific differences in canopy light extinction characteristics.

ISSN:0045-5067    

DOI:10.1139/x26-010

出版商:NRC Research Press    

年代:1996

数据来源: NRC