摘要:

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.

ISSN:0045-5067    

DOI:10.1139/x98-033

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Measurements of radiation and energy balances were made over two forests, 12.8 km apart, in eastern Ontario during three summers, 1989-1991. The two sites were AECL, a primarily deciduous forest with fine sandy soils, and PNFI, a mixed forest over a thin sandy-loam soil. The objective of the study was to investigate spatial heterogeneity in energy fluxes in a mixed forest landscape by examining interannual variations in radiation and energy balance components between the sites. The two sites showed small differences in albedo and net radiation. Total heat storage was not different between the two sites, yet there were some differences in the relative magnitudes of the storage components. The largest between-site differences were in energy partitioning between the convective fluxes of sensible heat,QH, and latent heat,QE. TheQHwas usually larger at PNFI andQEwas usually larger at AECL. Thus, Bowen ratios were almost always smaller at AECL. The magnitude of these differences was controlled by soil moisture stress, with moisture stress frequently observed at PNFI but not at AECL. The implications of these results for regional-scale surface-vegetation-atmosphere climate modelling are discussed.

ISSN:0045-5067    

DOI:10.1139/x98-016

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Spatial distribution and species composition of the boreal forest are expected to change under predicted climate change scenarios. Current research indicates that water limitations control the southern boundary of the central Canadian boreal forest and temperature limitations control the northern boundary. As part of Boreal Ecosystem - Atmosphere Study (BOREAS), we examined this idea by comparing annual variation in tree-ring widths and carbon isotope ratios ( delta13C) of tree-ring cellulose with annual climatic parameters in the northern and southern boreal forest. Contrary to expectations, climate correlations with ring widths at the northern and southern sites were similar in black spruce (Picea mariana(Mill.) BSP). Annual growth was favored by cooler and wetter conditions. For jack pine (Pinus banksianaLamb.), increased temperature and spring precipitation favored annual growth at both sites. In the north, annual growth was negatively correlated with winter precipitation. The delta13C - climate correlations inPinus banksianafollowed current distribution theories. In the south, potential evapotranspiration explained significant annual delta13C variation, whereas in the north, winter and growing season precipitation influenced annual delta13C variations. Our data support the concept that moisture limits the southern range ofPinus banksianaand cold soil temperatures limit the northern extent. However, colder, wetter conditions favored growth ofPicea marianathroughout its range. These observations strengthen the concept that species respond individually to climate change, not as a cohesive biome.

ISSN:0045-5067    

DOI:10.1139/x98-018

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Quantification of the components of ecosystem respiration is essential to understanding carbon (C) cycling of natural and disturbed landscapes. Soil respiration, which includes autotrophic and heterotrophic respiration from throughout the soilprofile, is the second largest flux in the global carbon cycle. We measured soil respiration (soil CO2 emission) at an undisturbedmature jack pine (Pinus banksiana Lamb.) stand in Saskatchewan (old jack pine, OJP), and at a formerly continuous portionof the stand that was clear-cut during the previous winter (clear-cut, CC). Tree harvesting reduced soil CO2 emission from ~22.5 to ~9.1 mol CO2 cdot m-2 for the 1994 growing season. OJP was a small net sink of atmospheric CO2, while CC was a net source of CO2. Winter emissions were similar at both sites. Reduction of soil respiration was attributed to disruption of the soil surface and to the death of tree roots. Flux simulations for CC and OJP identify 40% of CO2 emission at the undisturbed OJP site as near-surface respiration, 25% as deep-soil respiration, and 35% as tree-root respiration. The near-surface component was larger than the estimated annual C input to soil, suggesting fast C turnover and no net C accumulation in these boreal uplands in 1994.

ISSN:0045-5067    

DOI:10.1139/x98-023

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The impact of increasing the number of crosses per parent (k) on the efficiency of roguing seed orchards (backwards selection, i.e., reselection of parents) was examined by using Monte Carlo simulation. Efficiencies were examined in light of advanced-generation Douglas-fir (Pseudotsuga menziesii(Mirb.) Franco) tree improvement programs where information is available from previous generations, seed orchards have reduced genetic variation as a result of selection, and dominance variation is small compared with additive variation. Both the efficiency of reselection and its associated variance leveled off after two or three crosses per parent. The information from previous generations did not significantly increase reselection efficiency.

ISSN:0045-5067    

DOI:10.1139/x98-019

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The leaves ofCryptomeria japonicaD. Don collected near an electrochemical plant (on Yakushima Island) had more wax (approximately 10% higher in 1-year leaves) and less chlorophyll (approximately 50 and 30% lower in 0- and 1-year leaves, respectively) than those from a reference area, although the trees showed no symptoms of decline. In the Kanto Plain around Tokyo (Saitama and Ibaraki), whereC. japonicais declining (dieback and (or) defoliation), the amount of epicuticular wax in current-year leaves and the leaf chlorophyll content were almost equivalent to those of healthy plants in mountainous areas, but the wax eroded more rapidly (approximately 1.5 times faster). Although the C and O contents and the C/O ratio of epicuticular wax were approximately equivalent irrespective of the levels of decline, the cuticular transpiration rate, especially in 1-year leaves, was higher in Saitama (water loss: 0.92 ± 0.21%/h) and to some extent in Ibaraki (0.66 ± 0.08%/h) than in the mountainous area (0.60 ± 0.12%/h). This excessive transpiration, probably resulting from a degraded wax layer and the partial malfunctioning of stomata due to deposited aerosols, may be a significant factor causing the decline ofC. japonica. Dry atmospheric conditions (e.g., rain factor <100), which have prevailed since the 1950s due to urbanization, may have inflicted additional stress on the tr

ISSN:0045-5067    

DOI:10.1139/x98-021

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The hardening of hydroponically cultured Scots pine (Pinus sylvestrisL.) 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.

ISSN:0045-5067    

DOI:10.1139/x98-022

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

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 biformisHook.) 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.

ISSN:0045-5067    

DOI:10.1139/x98-028

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

An old-growth and a mature stand, each of fire origin and similar in drainage, slope, and exposure, were selected at each of two sites. Soil cores were collected in spring and fall for 2 years in each stand. Ectomycorrhizae were separated into types based on detailed examination of morphology and anatomy. All root tips were separated and counted. Sixty-nine morphological types were distinguished. Nineteen accounted for >1% of the 17 500 root tips examined, and 14 types were found in>5% of the 120 soil cores. Only three types were found in>20% of the cores. Total richness was approximately 100 fungi. Nine codominant mycosymbionts each colonized 2.8–24% of all tips and together colonized 67% of all tips.Cenococcum geophilumFr. was the most abundant, followed by aRhizopogon vinicolorFr.-like species, an unidentifiedPiloderma-like species,Lactarius rubrilacteusHesler & Smith,Piloderma fallax(Libert) Stalpers, and four unidentified species. Old-growth and mature stands had similar richness and diversity of ectomycorrhizal types. There was no evidence that any types were more abundant or frequent in one age-class than in the other

ISSN:0045-5067    

DOI:10.1139/x98-026

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

We examined temporal changes in the forest floor across a zonal chronosequence represented by four stages of stand development: stand initiation ( <= 7 years after disturbance), stem exclusion ( ±40-year-old stands), understory reinitiation ( ±60-year-old stands), and old-growth (>350-year-old) stands. All stages, except the old-growth, had a similar history of disturbance: clear-cutting without subsequent burning and silvicultural treatments. Considering thickness and chemical and biotic properties of the LF and H horizons, the most dissimilar stages were the stand initiation and old-growth, and the most similar stages were the stem exclusion and understory reinitiation. Compared with the old-growth stage, the stand initiation stage had about the same thickness of LF and H horizons and bacterial biomass but lower acidity, C:N ratio, fungal biomass, and soil fauna density and higher N mineralization. The stem exclusion and understory reinitiation stages had, in general, properties intermediate between the stand initiation and old-growth stage, with a gradual increase in acidity, C:N ratio, and fungal and faunal populations. After clear-cutting, the forest floor showed inevitable qualitative and quantitative alterations in response to the open-area climate. At the same time, it showed resilience, as most faunal groups of the old-growth stage were present in the stand initiation stage.

ISSN:0045-5067    

DOI:10.1139/x98-027

出版商:NRC Research Press    

年代:1998

数据来源: NRC