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1.
The aim of this study was to quantify 5-year growth, yield and mortality responses of 9- to 13-year-old naturally regenerated, even-aged paper birch ( Betula papyrifera Marsh.) stands to pre-commercial thinning in interior British Columbia. The study included four residual densities (9902–21,807 stems ha −1 (unthinned control), 3000, 1000 and 400 stems ha −1) and four sites with 3-fold within-site replication in a randomised block design. The largest, straightest, undamaged trees were selected to leave during thinning. Thinning reduced stand basal area from 5.90 m 2 ha −1 in the control to 2.50, 1.53 and 0.85 m 2 ha −1 in the three thinning treatments, representing 42, 26 and 15% of control basal area, respectively. After 5 years, total stand volume per plot remained lower in the three thinning treatments than the control (50.20, 30.07, 18.99 and 11.86 m 3 in the control, 3000, 1000 and 400 stems ha −1 treatments), whereas mean stand diameter, diameter increment, height, and height increment were increased by thinning, and top height (tallest 100 trees ha −1) was unaffected. When a select group of crop trees (largest 250 trees ha −1) in the thinning treatments was compared with the equivalent group in the control, there was a significant increase in mean diameter, diameter increment, basal area, basal area increment, and volume increment. Mean height, height increment, top height, and total volume were unaffected by thinning. Crop tree diameter increment was the greatest following thinning to 400 stems ha −1 for all diameter classes. Thinning to 1000 stems ha −1 resulted in lower diameter increment than thinning to 400 stems ha −1 but tended to have higher volume increment. Dominant trees responded similarly to subdominant trees at 400 stems ha −1, but showed the greatest response at 3000 stems ha −1. Results suggest that pre-commercial thinning of 9–13-year-old stands to 1000 stems ha −1 would improve growth of individual trees without seriously under-utilising site resources. 相似文献
2.
A model to project forest growth in the Terra Firme forests of the eastern Amazon is described. It is based on 12–17 years measurements from experimental plots at Jarí and Tapajós. Forest stands are represented by cohorts of species group, diameter, and defect. There are 54 species groups, with a robust diameter increment function fitted to each, tables of mortality by crown and defect status, and recruit lists by disturbance level and locality. Stand level functions partition trees by crown status, and modify growth for stand density. Recruitment is a function of basal-area losses. Evaluation compares model performance with two experiments involving heavy felling in Tapajos State Forest. At one site, total bole volume growth of all species over 45 cm DBH was 2.56 m 3 ha −1 year −1 over 17 years, whereas the model projected 3.13 m 3 ha −1 year −1. At the other site, actual growth over 12 years was 0.39 m 3 ha −1 year −1, with the model giving an identical result. Both felled and control plots are compared in the study and accurately simulated. Some weaknesses in the model are discussed. 相似文献
3.
Management scenarios with rotation lengths of 20 and 30 years were developed for different site qualities (high, medium and low) under two different management options (high individual tree growth versus high stand growth) for teak ( Tectona grandis L.f.) in Costa Rica. The scenarios are based on data collected in different regions in Costa Rica, representing different site conditions, offering a variety of possible management options for high-quality teak yield. Three competition indices were used for modeling the competition and for the definition of intensities and the plantation age at thinning. The maximum site occupation (MSO) and the Reineke density index (RDI) provide conservative stand density management limits, resulting in the need to execute several thinning frequently. The competition factor (CF) matches the field observations and seems to be more appropriate for the growth characteristics of the species. Final stand densities varied between 120 and 447 trees ha−1, with mean diameter at breast height (dbh) of 24.9–47.8 cm, and mean total heights between 23.0 and 32.4 m, depending on rotation length and site quality. The mean annual increment of total volume (MAIVol) at the end of the rotation varied from 11.3 to 24.9 m3 ha−1 year−1, accumulating a total volume over rotation of 268–524 m3 ha−1. The most suitable scenario for teak plantations for high-quality sites is the 30-year-rotation scenario with five thinnings of intensities between 20 and 50% (of the standing trees) at the ages of 4, 8, 12, 18 and 24 years. After the sectioning of the merchantable stem in 4-m length logs, the merchantable volume varied between 145 and 386 m3 ha−1, with an estimated heartwood volume of 45–195 m3 ha−1, both depending on rotation length and site quality. 相似文献
4.
Fast growth tree plantations and secondary forests are considered highly efficient carbon sinks. In northwest Patagonia, more than 2 million ha of rangelands are suitable for forestry, and tree plantation or native forest restoration could largely contribute to climate change mitigation. The commonest baseline is the heavily grazed gramineous steppe of Festuca pallescens (St. Yves) Parodi. To assess the carbon sequestration potential of ponderosa pine ( Pinus ponderosa (Dougl.) Laws) plantations and native cypress ( Austrocedrus chilensis (Don) Flor. et Boutl.), individual above and below ground biomass models were developed, and scaled to stand level in forests between 600 and 1500 annual rainfall. To calculate the carbon sequestration baseline, the pasture biomass was simulated. Also, soil carbon at two depths was assessed in paired pine-cypress-pasture sample plots, the same as the litter carbon content of both forest types. Individual stem, foliage, branch and root log linear equations adjusted for pine and cypress trees presented similar slopes ( P>0.05), although some differed in the elevations. Biomass carbon was 52.3 Mg ha −1 (S.D.=30.6) for pine stands and 73.2 Mg ha −1 (S.D.=95.4) for cypress forests, given stand volumes of 148.1 and 168.4 m 3 ha −1, respectively. Soil carbon (litter included) was 86.3 Mg ha −1 (S.D.=46.5) for pine stands and 116.5 Mg ha −1 (S.D.=38.5) for cypress. Root/shoot ratio was 19.5 and 11.4%, respectively. The low r/s value for cypress may account for differences in nutrient cycling and water uptake potential. At stand level, differences in foliage, taproot and soil carbon compartments were highly significative ( P<0.01) between both forest types. In pine stands, both biomass and soil carbon were highly explained by the rainfall gradient ( r2=0.94). Nevertheless, such a relationship was not found for cypress, possibly due to stand and soil disturbances in sample plots. The carbon baseline estimated in pasture biomass, including litter, was 2.6 Mg ha −1 (S.D.=0.8). Since no differences in soil carbon were found between pasture and both forest types, additionality should be accounted only by biomass. However, the replacement of pasture by pine plantations may decrease the soil carbon storage, at least during the first years. On the other hand, the soil may be a more relevant compartment of sequestered carbon in cypress forests, and if pine plantation replaces cypress forests, soil carbon losses could cause a negative balance. 相似文献
5.
Annual litter fall of Acacia mangium in the period of September 1995 to August 1996 was estimated at 5939 kg ha −1 year −1 and from September 1995 to August 1996 at 6048 kg ha −1 year −1, with the highest seasonal production in the dry season. The litter fall was dominated mainly by leaves, 4446 kg (75%) and 4137 kg (68%), respectively. Seed production in the litter fall was estimated at 42.4 kg ha −1 year −1 (4.1 million seeds ha −1) and 39 kg ha −1 year −1 (3.8 million seeds ha −1), with the highest in the dry season from June to October. The accumulated litter fall in the forest floor together with shrubs and grass provide a high fuel load, increasing fire risk. 相似文献
6.
Although the northeastern US includes extensive areas of aggrading forest, uncertainty regarding the intensity and pattern of forest harvesting hampers an understanding of important ecological processes and characteristics such as carbon and nitrogen storage, habitat quality, and forest dynamics, and impedes regional conservation and management planning. Due to the complex ownership pattern dominated by thousands of non-industrial private forest (NIPF) owners and the difficulty of detecting selective logging using remote sensing, details of the harvesting regime remain largely unknown to the scientific and policy communities. To examine the value of statewide regulatory data for Massachusetts as a unique source of this critical information, we analyzed 17 years of timber harvest data gathered for regulatory purposes for a 168,000 ha forested landscape in Massachusetts that is the focus of concerted conservation planning and intensive study of landscape and ecosystem pattern and process. The North Quabbin Region is heavily wooded with a complicated ownership pattern dominated by over 2500 NIPF owners, three state agencies, and diverse conservation and municipal holdings. The extent and intensity of harvesting were surprising, with an annual disturbance rate of 1.5% and a mean intensity of 44.7 m3 ha−1 (approximately one-fourth of average stand volume). The predominant form of harvesting was selective removal of commercially valuable tree sizes, grades and species (e.g., Quercus rubra and Pinus strobus). The spatial pattern of logging was random with regards to major physical, biological, or cultural factors. However, logging was strongly related to landowner class. NIPF owners control 60% of the forest area and were responsible for 64.1% of harvest area, but the highest logging intensity (volume per area harvested; 69.3 m3 ha−1) among major landowners was conducted by the state agency responsible for managing southern New England’s largest conservation property, the watershed of Boston’s drinking reservoir. This regime of chronic disturbance is occurring over the entire landscape and exerting a major influence on forest composition, dynamics, and habitat quality. However, dispersed selective harvesting is largely unnoticed by residents, is routinely overlooked by ecologists and conservationists, and would remain unrecognized in the absence of this previously unused regulatory data. These results identify the value of regional regulatory spatial information to estimate ecological trends and to assist in conservation planning. Given similarities among ownership and forest patterns for much of the northeastern US, we expect that the broad findings of this study to have regional application. 相似文献
7.
Annual net primary production (NPP) and N uptake were estimated for lysimeter-grown basket willows ( Salix viminalis L.) during 3 years after planting. The willows were grown in a stand structure and continuously supplied with water and liquid fertilizer through drip tubes. The lysimeters contained either clay from the site or washed quartz sand. Shoot growth and leaf litter were measured and fine-root dynamics observed in minirhizotrons. Destructive samples were taken annually in late autumn and entire root systems were washed out. Dry mass and N content of all plant parts were determined. Fine-root production was estimated by two methods, based on destructive samplings and observations in minirhizotrons. The proportion of biomass allocated below ground increased considerably when estimates based on accumulated NPP were compared with those based on standing dry mass. In the first year, 49 and 58% of annual NPP in willows grown in clay and sand, respectively, was belowground. In subsequent years the proportions were 36–38% and 33–40%. Most belowground production was fine roots. Relatively more N was used belowground in the first year than subsequently, but no substrate-induced differences were observed in the allocation pattern. Both annual NPP and N uptake was always higher in plants in clay than in those in sand: in the final 2 years, 21–22 tonnes DM ha−1 year−1 and 190 kg N ha−1 year−1 in clay, and 9–10 tonnes DM ha−1 year−1 and 100 kg N ha−1 year−1 in sand. 相似文献
8.
Biomass burning in tropical forests – the normal practice to prepare land for agriculture and ranching – has been a major source of CO 2 emitted to the atmosphere. Mass transformations by burning are still little studied in the tropics. The present study estimated parameters, such as the stock of carbon contained in the biomass, burning efficiency and the formation of charcoal and ashes in a tropical moist forest. Two sets of plots arranged in the form of ‘stars' (720 m 2 total) were installed in a 3.5 ha area of forest that had been felled for planting pasture at Fazenda Nova Vida, Ariquemes, Rondônia. Each ‘star' had six rays measuring 2 m × 30 m; alternating rays were designated for pre-burn and post-burn measurements. All above-ground biomass present in the plots was weighed directly before the burn in the pre-burn rays and after the burn in the post-burn rays. Pieces of wood with diameter ≥10 cm also had their biomasses estimated from volume estimates, using line-intersect sampling (LIS) in order to increase the area of sampling and to allow volume loss to be estimated as an increment based on individual pieces measured before, and after, the burn at the same point (as opposed to inferring change as a difference between independent estimates of stocks). The initial above-ground biomass (dry weight) before the burn was estimated at 306.5 ± 48.6 (mean ± SE) Mg ha −1, with an additional 4.5 Mg ha −1 for trees left standing. Carbon stock in the initial biomass (including trees left standing) was 141.3 (Mg C) ha −1. After burning, carbon stock was reduced by 36.8% (burning efficiency). The stocks of charcoal and ash formed in the burn were, respectively, 6.4 ± 2.7 and 5.7 ± 1.0 Mg ha −1. The destructive and nondestructive (LIS) methods did not differ significantly ( t-test, p > 0.05) in estimating post-burn stocks of wood and charcoal. The results of this study contribute to improving the estimates of parameters needed for global carbon calculations and point to ways in which estimates of these parameters could be further improved. 相似文献
9.
Following the tree harvest, the biogeochemistry of a catchment is modified by changes in soil temperature and moisture, and nutrient cycling. We monitored soil-solution and stream-water chemistry, and soil properties in a Pinus radiata D. Don plantation in New Zealand before and after clear-cutting and replanting in 1997. The annual rainfall during the study was 1440–1860 mm. The soil was a 1800-year-old pumice soil of high natural N status; the catchment had received large inputs of volcanic N in rain, probably over the 1800 years since the pumice had been deposited. The leaching loss of nitrate-N was 28 kg ha −1 yr −1 in 1996, and then decreased sharply after clear-cutting to 3 kg ha −1 yr −1 in 1998 and <1 kg ha −1 yr −1 in 1999. Weed growth and soil microbial biomass increased during this time, and would have removed much of the N from soil solution in the upper soil layers. Although the catchment was small (8.7 ha), there was a 2-year lag until N decreased in stream-water; the losses of dissolved organic N to stream-water were low. There was no change in soil pH over the 4 years, but spring-water pH appeared to increase, which was consistent with the increase in bicarbonate that accompanied grass/weed growth. The export of cations (mmol c l −1) in the spring-water was Na>Ca>Mg=K as expected for rhyolitic pumice, and the total concentration was probably controlled by the accompanying anions. The export of anions was NO 3=Cl>SO 4=HCO 3 before harvest and HCO 3=Cl>SO 4=NO 3 after harvest. 相似文献
10.
We estimated the required sample sizes for estimating large-scale soil respiration (for areas from 1 to 2 ha) in four ecosystems (primary and secondary forests, and oil palm and rubber plantations) in Malaysia. The soil respiration rates were 769 ± 329 mg CO 2 m −2 h −1 in the primary forest (2 ha, 50 sample points), 708 ± 300 mg CO 2 m −2 h −1 in the secondary forest (2 ha, 50 points), 815 ± 363 mg CO 2 m −2 h −1 in the oil palm plantation (1 ha, 25 points), and 450 ± 178 mg CO 2 m −2 h −1 in the rubber plantation (1 ha, 25 points). According to our sample size analysis, the number of measurement points required to determine the mean soil respiration rate at each site with an error in the mean of no more than 10% ranged from 67 to 85 at the 95% probability level. These results suggest that evaluating the spatial heterogeneity of soil respiration rates in the tropics may require more measurement points than in temperate forests. 相似文献
11.
Managed forests often differ substantially from undisturbed forests in terms of tree structure and diversity. By altering the forest structure, management may affect the C stored in biomass and soil. A survey of 58 natural stands located in the south-westernmost limit of European beech forests was carried out to assess how the C pools are affected by the changes in tree structural diversity resulting from past management. The mean tree density, basal area and the number of large trees found in unmanaged forests were similar to those corresponding to virgin beech forests in Central Europe, whereas large live trees were totally absent from partially cut stands. Analysis of the Evenness index and the Gini coefficient indicated high structural diversity in the three stand types. The results of the Kolmogorov–Smirnov test used to compare the diameter distributions of each group revealed significant differences between stand types in terms of distributions of total tree species and of Fagus sylvatica. The mean C stocks in the whole ecosystem – trees, litter layer and mineral soil – ranged from 220 to 770 Mg ha−1 (average 380 Mg ha−1). Tree biomass (above and belowground), which averaged 293 Mg C ha−1, constituted the main C pool of the system (50–97%). The statistical test (Kolmogorov–Smirnov) revealed differences in the distribution of C pools in tree biomass between unmanaged and partially cut stands. As a consequence of the presence of large trees, in some unmanaged stands the C stock in tree biomass was as high as 500–600 Mg C ha−1. In the partially cut stands, most of the C was mainly accumulated in trees smaller than 20 cm dbh, whereas in unmanaged stands the 30% of tree C pool was found in trees larger than 50 cm dbh. Furthermore, many unmanaged stands showed a larger C pool in the litter layer. The C content of mineral soils ranged from 40 to 260 Mg C ha−1 and it was especially high in umbrisols. In conclusion, the implementation of protective measures in these fragile ecosystems may help to maintain the highly heterogeneous tree structure and enhance the role of both soils and trees as long-term C sinks. 相似文献
12.
Russian forests are of high importance for the Russian economy, the European wood market, for nature conservation, and for carbon sequestration. However, the ongoing changes in forest management and administration in Russia led to uncertainty about forest ownership, wood harvesting levels, and long-term impacts of alternative management plans. Therefore, better insight in their current and future state is highly desirable. We present a study for the Leningrad region forests in which alternative management regimes for wood production and nature conservation values are balanced in varying ways. The total forest land area in the Leningrad region forest fund is 4.8 million ha. Coniferous species dominate and due to the natural succession occurring, the forests are divers in vertical structurally. A timber assessment model was used to project the forest until 2040. Five forest management scenarios were run. Special attention was paid to a scenario that simulates recovery of the Russian forest sector in combination with the incorporation of a ‘set-aside for nature conservation’ policy. All scenarios showed that recovery of the forest sector in the Leningrad region is biologically feasible. A sustainable continuous annual production of 10.6 million m3 per year (2.8 m3 ha−1 per year) by 2040 was found. The ‘Recovery with Nature Conservation’ scenario showed that recovery of the forest sector in combination with the establishment of set-aside areas is very well feasible. It was possible to set aside 28% of the forest area for nature conservation while still developing a forest sector to a production level higher than that achieved in the late eighties. The timber assessment model applied was not specifically designed to incorporate nature-oriented forest management. We, therefore, discuss ways of improving the required methodology to analyse long-term effects of nature-oriented forest management in Europe. 相似文献
13.
We examined whether N-fertilization and soil origin of Douglas-fir [ Psuedotsuga menziesii (Mirb.) Franco] stands in western Washington state could affect C sequestration in both the tree biomass and in soils, as well as the flux of dissolved organic carbon (DOC) through the soil profile. This study utilized four forest sites that were initially established between 1972 and 1980 as part of Regional Forest Nutrition Research Project (RFNRP). Two of the soils were derived from coarse-textured glacial outwash and two from finer-textured volcanic-source material, primarily tephra, both common soil types for forestry in the region. Between 1972 and 1996 fertilized sites received either three or four additions of 224 kg N ha −1 as urea (672–896 kg N ha −1 total). Due to enhanced tree growth, the N-fertilized sites (161 Mg C ha −1) had an average of 20% more C in the tree biomass compared to unfertilized sites (135 Mg C ha −1). Overall, N-fertilized soils (260 Mg C ha −1) had 48% more soil C compared to unfertilized soils (175 Mg C ha −1). The finer-textured volcanic-origin soils (348 Mg C ha −1) had 299% more C than glacial outwash soils (87.2 Mg C ha −1), independent of N-fertilization. Soil-solution DOC collected by lysimeters also appeared to be higher in N-fertilized, upper soil horizons compared to unfertilized controls but it was unclear what fraction of the difference was lost from decomposition or contributed to deep-profile soil C by leaching and adsorption. When soil, understory vegetation and live-tree C compartments are pooled and compared by treatment, N-fertilized plots had an average of 110 Mg C ha −1 more than unfertilized controls. These results indicate these sites generally responded to N-fertilization with increased C sequestration, but differences in stand and soil response to N-fertilization might be partially explained by soil origin and texture. 相似文献
14.
In many forests of the Alps, permanent forest cover and, therefore, its continuous renewal is the main silvicultural goal. Regenerating these forests must be based on a sound understanding of the ecology of the tree species in question. The regeneration of silver fir ( Abies alba Mill.) and Norway spruce ( Picea abies (L.) Karst.) in the upper montane zone of the southern central Alps has so far received little attention. The aim of this study was, therefore, to characterize the ecological niche for the establishment and growth of silver fir and Norway spruce seedlings in this zone. The study was conducted as a case study on a plot of 1.5 ha in the upper montane zone of southern Switzerland, at an altitude of 1380 m. The basal area of the mixed Norway spruce–silver fir stand was 43.7 m 2 ha −1. Seedlings were censused on 375 plots of 1.0 m 2 area. Seedling density was 1.30 ± 4.25 m −2 (mean ± standard deviation) for Norway spruce and 0.87 ± 1.50 m −2 for silver fir. Logistic regression models were used to test the effect of microsite characteristics on seedling occurrence, and general linear models for effects on seedling height growth and biomass increment. Most seedlings received less than 10% light (photosynthetic photon flux density) as compared to values in the open. Silver fir occurrence was positively related to microsites at the edge of canopy trees, but unrelated to ground cover type, light and micro-relief. Norway spruce occurrence was only, and positively, related to the presence of mosses. Height growth and biomass increment of seedlings of both species were only loosely correlated with microsite conditions. Seedlings without canopy cover grew faster than those under canopy cover, probably as a result of light and moisture limitations under the canopy of adult trees. Diffuse radiation was positively correlated with average annual biomass increment of silver fir, but not of Norway spruce seedlings. In general, the results suggest that silver fir seedlings have less specific microsite requirements than Norway spruce seedlings in terms of ground cover. They are also more shade tolerant, and therefore, grow faster than Norway spruce in low-light environments of the upper montane zone of the southern Alps. While the microsite concept can be helpful in designing silvicultural operations, it has limitations when only patch characteristics that are easy to assess are used, and others neglected. Finally, our study suggests that counting the number of green shoots is a promising method to quickly and non-destructively estimate the biomass of a great number of small seedlings. 相似文献
15.
Data from the Swedish Forest Inventory was used to calculate mass balances for base cations Ca, Mg and K for Swedish forests. Using lysimeter and forest survey soil analyses to estimate present base cation leaching from the root zone reveals that weathering plus base cation deposition is not sufficient to support both, the present base cation leaching rate and the present rate of uptake caused by stem growth. Calculations suggest that 96% of the productive forested area may have higher rates of removal than supply for one or more base cation. Under a best-case scenario, assuming less pollution, the present growth rate and 100% efficiency in uptake of available nutrients, the area with more removal than supply would still be at least 30% of the total area. Forest soils are being depleted at a rate where the exchangeable reservoirs have high risk of being severely depleted in the next few decades in central and southern Sweden. During 1983–1985 the depletion rate is calculated to be, on the average, 0.33 keq ha −1 year −1. The weathering rate and present base cation deposition can sustain growth at a level where (80–85)×10 6m 3 stemwood year −1 can be harvested. Any harvested growth beyond this volume must be sustained by artificial means. For whole-tree harvesting without base cation return, the calculations indicate that it would significantly increase the base saturation depletion rate to an average of 0.62 keq ha−1 year−1, and risk depletion of the soil in less than one-to-two rotation periods almost anywhere in Sweden. The calculations stress the importance that sustainable forest management must include the management of nutrient fluxes and reservoirs. 相似文献
16.
The cultural practices associated with Euro-American settlement in the United States have altered forest structure and ultimately changed fundamental ecosystem processes. Coarse woody debris (CWD) and canopy cover are recognized as having great importance for many wildlife species and ecological processes. Little information is available from forests on historical levels of canopy cover and CWD before European settlement. A great deal of uncertainty exists concerning the long-term role of fire and the dynamics of CWD, especially in forests that once experienced frequent, low-moderate intensity fire regimes. The objective of this study was to quantify CWD and forest canopy cover in an area where harvesting has never occurred and limited fire suppression began in the 1970s. This study was done in Jeffrey pine-mixed conifer forests in the Sierra San Pedro Martir (SSPM) in northwestern Mexico. Canopy cover, canopy closure, and CWD were sampled on a grid of plots. Average canopy cover was 26.8%, average canopy closure was 40.1%. A total of 102 CWD pieces were measured, and nearly half of the plots (45.7%) had no CWD present. Average CWD density, percent cover, volume, and weight were 108 pieces ha −1, 1.5%, 47.5 m 3 ha −1, and 15.7 tonnes ha −1, respectively. All of the CWD sampled were in the later stages of decay. Less than average values for CWD density, percent cover, volume, and weight were recorded in 57%, 64%, 67%, and 69% of the plots, respectively. CWD dynamics in forests that experience frequent, low-moderate intensity fires are fundamentally different than those having long-interval, high-severity fires. There was a large amount of variability in all CWD and forest canopy cover measurements taken from Jeffrey pine-mixed conifer forests in the SSPM. Spatial heterogeneity in forest structure should be included in the desired conditions of xeric, pine-dominated forests in the United States that once experienced frequent, low-moderate intensity fire regimes. It should be noted that heterogeneity by itself may not lead to sustainable forests unless that heterogeneity includes stand structures that are resistant/resilient to high-severity fire, drought, insects, and disease. 相似文献
17.
Carbon stocks and stock changes in a chronosequence of 24 red spruce ( Picea rubens Sarg.) dominated stands in Nova Scotia, Canada, were compared against predictions from the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3). Regression analysis of the observed versus simulated total ecosystem C stocks indicates the model's predictions accounted for 81.1% of the variation in the observed biomass data and for 63.2% of the variation in total ecosystem C data; however, the simultaneous F-test for bias was significant. Discrepancy between the observed and simulated total ecosystem C data was primarily caused by differences in dead organic matter C pool estimates, with the model consistently predicting higher soil C throughout stand development. Changes to model parameters were not warranted however, as the field data measured only a portion of the mineral soil profile represented in the model. Clear-cut and partial-cut harvesting scenarios for red spruce stands were simulated to examine the impacts of clear-cut and partial-cut harvesting on C stocks. Total ecosystem C increased in the partial-cut stand throughout the 240-year simulation from 308.9 to 327.3 Mg C ha−1, while it decreased in the clear-cut stand to 305.8 Mg C ha−1. Enhanced C sequestration in the partial-cut stand was a consequence of the residual standing biomass providing a continuous source of litterfall and reducing decomposition rates of the forest floor. Choice of harvest system clearly affects forest ecosystem C stocks, but also affects the amount of C removed from forests to meet society's needs. Over the period of the simulation, partial cutting provided 115.6 Mg C ha−1 of merchantable timber, while clear-cutting provided 132.4 Mg C ha−1. Strategies aimed at using forest management to mitigate atmospheric C increases need to assess both the direct impacts on the forest ecosystem and the indirect impacts through product and energy substitution associated with the use and storage of harvested biomass. 相似文献
18.
Tree vegetation and size structure was sampled in a miombo woodland area in E Tanzania and related to environmental factors, particularly soil and disturbance history. A total of 86 tree species was found. Four plant communities were distinguished through multivariate classification. Community 1 was dominated by Brachystegia boehmii, Brachystegia bussei and Julbernardia globiflora, and community 2 by B. boehmii and Brachystegia spiciformis. Community 1 was found on grey, eroded soil and community 2 on red, residual soil, a fact that opens up possibilities to use soil signals of satellite data for vegetation mapping. Community 3 is heavily disturbed miombo woodland near villages and community 4 was found on more clayey soil where miombo woodland is not expected. At our 42 sampled sites, density ranged from 74 to 1041 individuals ha−1 and basal area from 3.9 to 16.7 m2 ha−1. Regeneration is generally good but large sized trees are less prominent in communities 3 and 4 due to harvesting. With reduced disturbance miombo species may rapidly resume dominance in community 3. A higher than expected representation by the size class 30–40 (−50) cm dbh in community 2 is probably related to disturbance history. Prevalence of certain species (Pseudolachnostylis maprouneifolia, Pterocarpus angolensis and Diplorhynchos condylocarpon) may be related to frequent fires. Selective logging will soon cause extinction of Dalbergia melanoxylon, whereas Pterocarpus angolensis still has good regeneration, possibly because individuals below logging size have a good seed set. A way to get an easy overview of size classes in all species in an area using PCA is discussed. 相似文献
19.
In the Murray-Darling basin, irrigation of tree crops is being evaluated as an alternative method for the disposal of municipal effluent. A study was carried out at Wodonga in which seven tree species were irrigated with effluent for a period of 4 years. Irrigation was calculated weekly on the basis of pan evaporation and rainfall during the preceding week. Annual irrigation varied between 1190 mm and 1750 mm with a total input over the 4-year-period of 4940 mm. Height and diameter growth varied significantly between species. At age 4, mean dominant height of Eucalyptus grandis, E. saligna and Populus deltoides × P. nigra ranged from 14.3 to 15.0 m compared with 6.6 to 9.8 m for Casuarina cunninghamiana, E. camaldulensis, P. deltoides and Pinus radiata. Wood production of the faster-growing species (E. grandis and E. saligna) was approximately 130 m3 ha−1, or around 32 m3 ha−1 year−1 over a 4-year period. This was nearly three-fold the production of the other native species and twice that of Pi. radiata. Volume growth of P. deltoides × P. nigra (85 m3 ha−1) was significantly greater than that of P. deltoides (42 m3 ha−1). Accumulation of nutrients in the above-ground biomass varied significantly between species and ranged from 24 to 41 g m−2 for N, 2.6 to 5.9 g m−2 for P, 0.5 to 9.2 g m−2 for Na, 12 to 27 g m−2 for K, 7 to 52 g m−2 for Ca and 3.1 to 7.9 g m−2 for Mg. Nutrient accumulation was generally greater in species with a comparatively large crown biomass relative to stem size such as C. cunninghamiana and E. camadulensis. Average nutrient accumulation by trees as a percentage of input from effluent was estimated at 19% for N, 9% for P, 1% for Na, 14% for K, 52% for Ca and 32% for Mg. Results of this study indicate the importance of selecting species on the basis of not only growth but also nutrient accumulation to optimise renovation of wastewater by tree plantations. 相似文献
20.
The profitability of growing a naturally emerged birch ( Betula pendula Roth or Betula pubescens Ehrh.) overstory in a young Norway spruce ( Picea abies (L.) Karst.) plantation was examined with empirical stand structure, growth and yield, logging cost, and logging damage models. In the projected alternatives, an overstory of either birch species was thinned to 200–1000 stems per ha at the age of 15 years and retained for another 15 years. Development of the remaining spruce stand was simulated up to rotation age (70–85 years). Alternative treatments included removing the overstory completely at 15 years, and managing a pure spruce stand that was kept free of birch throughout. Growing a birch overstory of 200–1000 stems per ha up to age 30 years resulted in a 61–93 m3 ha−1 or 9.1–16.8% yield loss for the spruce stand due to growth retardation, and a mortality of 382–498 out of 1900 stems per ha through logging damage. This was compensated for or exceeded by the additional yield of the birch (54–173 m3 ha−1) except for the lowest stocking (200–400 stems per ha) alternatives with B. pubescens. Treatment regimes with a birch overstory were clearly the most profitable alternatives, yielding up to 151% (B. pendula) and 113% (B. pubescens) of the net present value of the pure spruce alternative, at 4% interest rate. Removing the birch overstory already at 15 years was the least profitable alternative with 79 and 83% net present values, respectively. The most profitable treatment with current technology, price, and cost structure appears to be to grow 500–800 birch per ha up to about age 40 years for B. pendula and 45–50 years for B. pubescens. 相似文献
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