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1.
Analysis of the impacts of forest management and climate change on the European forest sector carbon budget between 1990 and 2050 are presented in this article. Forest inventory based carbon budgeting with large scale scenario modelling was used. Altogether 27 countries and 128.5 million hectare of forests are included in the analysis. Two forest management and climate scenarios were applied. In Business as Usual (BaU) scenario national fellings remained at the 1990 level while in Multifunctional (MultiF) scenario fellings increased 0.5–1% per year until 2020, 4 million hectare afforestation program took place between 1990 and 2020 and forest management paid more attention to current trends towards more nature oriented management. Mean annual temperature increased 2.5 °C and annual precipitation 5–15% between 1990 and 2050 in changing climate scenario. Total amount of carbon in 1990 was 12 869 Tg, of which 94% in tree biomass and forest soil, and 6% in wood products in use. In 1995–2000, when BaU scenario was applied under current climatic conditions, net primary production was 409 Tg C year−1, net ecosystem production 164 Tg C year−1, net biome production 84.5 Tg C year−1, and net sequestration of the whole system 87.4 Tg C year−1 which was equal to 7–8% of carbon emissions from fossil fuel combustion in 1990. Carbon stocks in tree biomass, soil and wood products increased in all applied management and climate scenarios, but slower after 2010–2020 than that before. This was due to ageing of forests and higher carbon densities per unit of forest land. Differences in carbon sequestration were very small between applied management scenarios, implying that forest management should be changed more than in this study if aim is to influence carbon sequestration. Applied climate scenarios increased carbon stocks and net carbon sequestration compared to current climatic conditions.  相似文献   

2.
We used national scenario analyses to examine the effects of harvesting intensity on the development of forest resources, timber supply, carbon balance, and biodiversity indicators of Finnish forestry in nine 10-year simulation periods (90-year simulation period) under the current climate. Data from the 11th National Forest Inventory of Finland were used to develop five even-flow harvesting scenarios for non-protected forests with the annual harvest ranging from 40 to 100 million m3. The results show that the highest annual even-flow harvest level, which did not decrease the growing stock volume over the 90-year simulation period, was 73 million m3. The total 90-year timber production, consisting of harvested volume and change in growing stock volume, was maximized when the annual harvest was 60 million m3. Volume increment increased for several decades when harvested volume was less than the current volume increment. The total carbon balance of forestry was the highest with low volume of harvested wood. Low harvested volume increased the values of biodiversity indicators, namely volume of deciduous trees, amount of deadwood and area of old forest.  相似文献   

3.
The aim of the presented research project is to fit a site index model capable for predicting changes in site-productivity in a changing climate. A generalized additive model is used to predict site index as a function of soil and climate variables. The climate parameter values are estimated using the regional climate model WETTREG, based on global climate simulations with the global circulation model ECHAM5/MPI-OM for the reference period from 1961 to 1990. The climate values are further regionalized on a 200 m × 200 m grid. The generalized additive model quantifies the partial linear and non-linear effects of the predictor variables on site index. The model is parameterized for Norway spruce (Picea abies (L.) Karst.) and common beech (Fagus sylvatica L.) in Lower Saxony, Germany. Two case studies investigate the model's ability to generate information in order to support forest management planning decisions under a changing climate. One example analyzes the possible shift in site index of spruce along a precipitation gradient under the International Panel on Climate Change (IPCC) emission scenario A1B in the period from 2041 to 2050. The other case study shows possible future changes in site index of beech along a temperature gradient.  相似文献   

4.
We simulated loblolly pine (Pinus taeda L.) net canopy assimilation, using BIOMASS version 13.0, for the southeastern United States (1° latitude by 1° longitude grid cells) using a 44-year historical climate record, estimates of available water-holding capacity from a natural resource conservation soils database, and two contrasting leaf area indices (LAI) (low; peak LAI of 1.5 m2 m−2 projected, and high; 3.5 m2 m−2). Median (50th percentile) available water-holding capacity varied from 100 to 250 mm across the forest type for a normalized 1.25 m soil profile. Climate also varied considerably (growing season precipitation ranged from 200 to 1600 mm while mean growing season temperature ranged from 13° to 26°C). Net canopy assimilation ranged from 9.3 to 19.2 Mg C ha−1 a−1 for high LAI and the 95th percentile of available water-holding capacity simulations.We examined the influence of soil available water-holding capacity, and annual variation in temperature and precipitation, on net canopy assimilation for three cells of similar latitude. An asymptotic, hyperbolic relationship was found between the 44-year average net canopy assimilation and soil available water-holding capacity. Shallow soils had, naturally, low water-holding capacity (<100 mm) and, subsequently, low productivity. However, median available water-holding capacity (125–150 mm) was sufficient to maintain near maximum production potential in these cells.Simulations were also conduced to examine the direct affects of soil available water on photosynthesis (PN) and stomatal conductance (gS) on net canopy assimilation. In the absence of water limitations on PN and gS, net canopy assimilation increased by only 10% or less over most of the loblolly pine region (when compared to simulations for median available water-holding capacity with water influences in place). However, the production differences between high and low LAI, at the median soil available water-holding capacity, ranged from 30% to 60% across the loblolly pine range. Vapor pressure deficit was found to dramatically reduce productivity for stands of similar LAI, incident radiation, rainfall, and available water-holding capacity. Thus, these simulations suggest that, regionally, loblolly pine productivity may be more limited by low LAI than by soil available water-holding capacity (for soils of median available water-holding capacity or greater). In addition, high atmospheric forcing for water vapor will reduce net assimilation for regions of otherwise favorable available water and LAI.  相似文献   

5.
Interspecific variation in water-induced fluctuations in stem girth demonstrates the mechanisms promoting coexistence in seasonally dry tropical forest. In addition, these fluctuations are a potential, but unevaluated, source of bias in measurements of annual tree growth rates. To examine diurnal and seasonal patterns of stem diameter change, tree girth was measured over 2 years (1997–1999), using dendrometer bands, for three species (Celtis mildbraedii, C. zenkeri and Strombosia glaucescens) in semi-deciduous forest in Ghana. Soil matric potential was measured concurrently at 15 cm depth. In addition, measurements of all trees >20 cm dbh on three, 1 ha plots were made at the beginning and middle of the 1998/1999 dry season. During the severe 1997/1998 dry season, soil matric potential declined below −1.5 MPa and two species showed significant stem shrinkage. For the evergreen species, C. mildbraedii, there was a significant positive effect of tree diameter on stem shrinkage, and shrinkage was greater in the second, compared to the first, half of the dry season. For the deciduous species, C. zenkeri, shrinkage was reduced during the second half of the dry season, following leaf fall. During 1998/1999, soil matric potential, did not decline below −1.5 MPa, and rates of girth change remained positive for all species. There were no significant effects of size or phenology on the rate of girth change in the plot-based study. Deviations in annual increment calculated over successive monthly intervals indicate that a 10-fold difference in soil water availability between measurement occasions can lead to a 4% bias in estimates of annual growth. Measurements of forest plots should be made when inter-annual variation in soil water availability is low. In this forest, measurements should, therefore, be made during the wet season, contrary to published recommendations.  相似文献   

6.

A process-based model was used to simulate biomass production of Norway spruce under both current climate and climate change scenarios. The model was parameterized for Nordmoen in south-east Norway using real climate data for the period 1987-1989. The model was applied to predict the biomass production responses to three climate change scenarios. The results showed that net primary production (NPP) increased by 7% under an elevated annual mean air temperature of 4°C from the current 10.1 t dry mass ha -1 yr -1 . A doubled current ambient CO 2 concentration significantly increased NPP by 36%. The scenario of both elevated temperature and elevated CO 2 concentration led to an increase in the NPP of 49%, higher than the sum of the two effects acting singly. The results also showed that forest production responses to climate change depend on the conditions of climate used for reference.  相似文献   

7.
Reforestation and afforestation have been suggested as an important land use management in mitigating the increase in atmospheric CO2 concentration under Kyoto Protocol of UN Framework Convention on climate change. Forest inventory data (FID) are important resources for understanding the dynamics of forest biomass, net primary productivity (NPP) and carbon cycling at landscape and regional scales. In this study, more than 300 data sets of biomass, volume, NPP and stand age for five planted forest types in China (Larix, Pinus tabulaeformis, Pinus massoniana, Cunninghamia lanceolata, Pouulus) from literatures were synthesized to develop regression equations between biomass and volume, and between NPP and biomass, and stand age. Based on the fourth FID (1989–1993), biomass and NPP of five planted forest types in China were estimated. The results showed that total biomass and total NPP of the five types of forest plantations were 2.81 Pg (1 Pg = 1015 g) and 235.65 Mg ha−1 yr−1 (1 Mg = 106 g), respectively. The area-weighted mean biomass density (biomass) and NPP of different forest types varied from 44.43 (P. massoniana) to 146.05 Mg ha−1 (P. tabulaeformis) and from 4.41 (P. massoniana) to 7.33 Mg ha−1 yr−1 (Populus), respectively. The biomass and NPP of the five planted forest types were not distributed evenly across different regions in China. Larix forests have the greatest variations in biomass and NPP, ranging from 2.7 to 135.37 Mg ha−1 and 0.9 to 10.3 Mg ha−1 yr−1, respectively. However, biomass and NPP of Populus forests in different region varied less and they were approximately 50 Mg ha−1 and 7–8 Mg ha−1 yr−1, respectively. The distribution pattern of biomass and NPP of different forest types closely related with stand ages and regions. The study provided not only with an estimation biomass and NPP of major planted forests in China but also with a useful methodology for estimating forest carbon storage at regional and global levels.  相似文献   

8.
Tree encroachment into rough fescue (Festuca campestris) grassland has been identified as an ecological concern on the Cypress Hills plateau in southeastern Alberta, Canada. A combination of field sampling (109 transects), a dendrochronological assessment (1361 trees), and a time series analysis of remotely sensed images from five different time periods (1950–2002) were used to determine the extent and rate of tree encroachment and forest development. Tree cover increased by 768 ha (～51%) between 1950 and 2007, representing 10% of the study area, from 1502 ha of pre-1950 forest. Post-1950 tree invasion also created an ingress zone of 750 ha (～10% of study area) based on field transects. Forest cover increased at a consistent rate of 14.3 ha/year. Lodgepole pine (Pinus contorta var. latifolia) was the most common tree species associated with encroachment. Invasion based on the number of established trees occurred at an exponential rate of 3.1%/year after 1890, with density increased by filling spaces adjacent to and between trees within the grassland vegetation. The rate of tree establishment increased to 4.4%/year after 1980, suggesting a change occurred in environmental conditions. Annual atmospheric temperatures increased 0.55 °C from 1929 to 2005 (P < 0.001), with winter (December–February) and spring (March–May) temperatures accounting for most of the increase (P < 0.001), whereas summer (June–August) temperatures slightly decreased (P < 0.050, 0.34 °C) and precipitation increased (P < 0.005, 30 mm). Cattle and elk (Cervus elaphus) grazing was not considered a primary factor for explaining tree encroachment. Based on multidimensional scaling, lodgepole pine establishment was associated with warmer spring temperatures and greater fall (October–November) precipitation. A landscape devoid of wildfires, combined with greater moisture availability, and a longer frost-free season is likely conducive to the sustained establishment of coniferous trees and forest development within the Cypress Hills fescue grassland ecosystem. Long-term conservation of the fescue grasslands could be possible by reintroducing fire.  相似文献   

9.
Climate warming is already influencing plant migration in different parts of the world. Numerous models have been developed to forecast future plant distributions. Few studies, however, have investigated the potential effect of warming on the reproductive output of plants. Understorey forest herbs in particular, have received little attention in the debate on climate change impacts.This study focuses on the effect of temperature on sexual reproductive output (number of seeds, seed mass, germination percentage and seedling mass) of Anemone nemorosa L., a model species for slow colonizing herbaceous forest plants. We sampled seeds of A. nemorosa in populations along a 2400 km latitudinal gradient from northern France to northern Sweden during three growing seasons (2005, 2006 and 2008). This study design allowed us to isolate the effects of accumulated temperature (Growing Degree Hours; GDH) from latitude and the local abiotic and biotic environment. Germination and seed sowing trials were performed in incubators, a greenhouse and under field conditions in a forest. Finally, we disentangled correlations between the different reproductive traits of A. nemorosa along the latitudinal gradient.We found a clear positive relationship between accumulated temperature and seed and seedling traits: reproductive output of A. nemorosa improved with increasing GDH along the latitudinal gradient. Seed mass and seedling mass, for instance, increased by 9.7% and 10.4%, respectively, for every 1000 °C h increase in GDH. We also derived strong correlations between several seed and seedling traits both under field conditions and in incubators. Our results indicate that seed mass, incubator-based germination percentage (Germ%Inc) and the output of germinable seeds (product of number of seeds and Germ%Inc divided by 100) from plants grown along a latitudinal gradient (i.e. at different temperature regimes) provide valuable proxies to parameterize key population processes in models.We conclude that (1) climate warming may have a pronounced positive impact on sexual reproduction of A. nemorosa and (2) climate models forecasting plant distributions would benefit from including the temperature sensitivity of key seed traits and population processes.  相似文献   

10.
Studies of growth rates of trees in managed neotropical forests have rarely employed complete botanical identification of all species, while published information for Central American lowland rain forests largely concerns forests free of recent disturbance. We studied diameter increments of trees in a managed Costa Rican rain forest. The Pentaclethra macroloba-dominated forest was located on low hills with Ultisols in Holdridge's Tropical Wet Forest life zone. The 540 m × 540 m (29.2 ha) experimental area was lightly logged during 1989–1990. The 180 m × 180 m (3.24 ha) experimental plots comprised a 100 m × 100 m (1.0 ha) central permanent sample plot (PSP) with a 40-m wide buffer strip. Post-harvest silvicultural treatments were liberation/refinement (in 1991) and shelterwood (in 1992), applied under a complete randomized block design with three replicates, using logged but untreated plots as controls. All live trees ≥10 cm DBH in the PSPs, were identified to species; data reported are for 1993–1996. Cluster analysis was used to group species on the basis of the median and quartiles of their diameter increment distributions, separating data by silvicultural treatments; five diameter increment groups were established and subdivided on the basis of the adult height of each species (four categories), giving 17 species groups in the final classification. Adult height and silvicultural treatment made a significant contribution to growth rate variation. Median annual increments of the slowest-growing species groups, which featured many under- and middle story species, were ca. 1 mm; those for the fastest growing species, which were mainly canopy and emergents, were ca. 16 mm. All species in the groups of very fast growth were pioneers, whether short or long-lived, though many other pioneer species did not show fast growth. The proportions of species found in groups of moderate, fast or very fast growth were greater in the silviculturally treated plots than in the controls, and one complete diameter increment group, of fast growth, was only represented in the treated plots. Crown form, crown illumination and presence of lianas in the crown, showed significant correlations with diameter increments, though the importance of these latter two variables varied with silvicultural treatment. The very fast growth groups differed from the others in having higher proportions of trees with well-formed, well-illuminated crowns and an irregular diameter distribution with relatively few individuals in the smallest DBH class. Comparison with data from other neotropical forest sites shows that long-lived pioneers such as Vochysia ferruginea and Jacaranda copaia grow fast or very fast at all sites, while non-commercial canopy and emergent species of Chrysobalanaceae and Sapotaceae appear to be uniformly slow-growing. Growth data for the majority of species are, however, published for the first time.  相似文献   

11.
China has been implementing the world's most ambitious afforestation and forest conservation programs and undergoing rapid forest expansion since 1990s, thus, understanding the forest dynamics in China has global implications for sustainable forest management. Through analyzing forest area, biomass dynamics, and factors influencing deforestation and forest restoration, we found that the natural disasters and economic development drove forest dynamics and transition in China. The growth of the economy and population drove up demand for forest products, facilitating deforestation. The booming economy also boosted government's investment in forest restoration and conservation programs. Natural disasters damaged and frequently destroyed forests, but they also served as stimuli for the authorities to adopt remedy forestry policies and programs that ultimately led to forest increase. Nationwide, increasing peaks of annual afforestation were observed in the late 1950s, early 1980s, and early 2000s, and the newly increased area closed for forest restoration reached the peak in 1998. All these peaks were closely associated with peaks of natural disasters (i.e., floods, drought, and dust storm events). Based on the dynamics of forest area, biomass and forest consumption over the past 40 years, forest transition occurred during the late 1980s to the early 1990s, and it also strengthened the carbon (C) sink function of forests in China (with an increasing rate of 0.137 Pg C yr.−1 during 1994–2008). Overall, our study highlighted the influences of natural disasters and economic development on the forestry policies and forest C dynamics in the newly industrialized country.  相似文献   

12.
【目的】探讨川西亚高山地区各海拔生境处岷江冷杉和紫果云杉径向生长对气候因子的响应,为进一步揭示当地森林对气候变化的响应机制提供依据。【方法】分别获取王朗自然保护区中海拔与高海拔生境处岷江冷杉和紫果云杉的标准年表,分析年表同气候因子间的关系。【结果】中海拔生境处岷江冷杉生长在1990年后与年均气温存在一定程度的“分离效应”;中海拔生境处岷江冷杉和紫果云杉生长与上年生长季(上年7月和8月)气温和上年生长季末(上年10月)降水量显著负相关( P <0.05),岷江冷杉生长与当年9月气温和降水量显著负相关( P <0.05),紫果云杉生长与当年2、6月月均最低气温显著正相关( P <0.05);高海拔生境处岷江冷杉和紫果云杉生长均与当年生长季前(上年11月、当年1月、当年2月)、当年生长季(当年7月)和上年生长季(上年6月)气温显著正相关( P <0.05),岷江冷杉生长还与当年6月份的降水量及上年8月份的气温显著负相关( P <0.05);滑动相关分析和年表特征年气候分析结果充分印证了各年表对月气候因子响应的可靠性。【结论】上年生长季气温的“滞后效应”对中海拔生境处的岷江冷杉、紫果云杉以及高海拔生境处的岷江冷杉生长均有显著影响;近几十年来,上年生长季末降水对中海拔生境处的岷江冷杉、紫果云杉以及高海拔生境处的紫果云杉生长都具有稳定而显著的抑制作用。  相似文献   

13.
In this study we investigate the implications of reaching the 2 °C climate target for global woody biomass use by applying the Global Biosphere Management Model (GLOBIOM) and the recently published SSP-RCP scenario calculations. We show that the higher biomass demand for energy needed to reach the 2 °C target can be achieved without significant distortions to woody biomass material use and that it can even benefit certain forest industries and regions. This is because the higher woody biomass use for energy increases the demand for forest industry by-products, which makes forest industry final products production more profitable and compensates for the cost effect of increased competition over raw materials. The higher woody biomass use for energy is found to benefit sawnwood, plywood and chemical pulp production, which provide large amounts of by-products, and to inhibit fiberboard and mechanical pulp production, which provide small amounts of by-products. At the regional level, the higher woody biomass use for energy is found to benefit material production in regions, which use little roundwood for energy (Russia, North-America and EU28), and to inhibit material production in regions, which use large amounts of roundwood for energy (Asia, Africa and South-America). Even if the 2 °C target increases harvest volumes in the tropical regions significantly compared to the non-mitigation scenario, harvest volumes remain in these regions at a relatively low level compared to the harvest potential.  相似文献   

14.
The annual course of daily transpiration and the hydrological balance of a Tabor oak forest were determined. The study was done in a representative forest within the natural geographical range of the species in the lower Galilee region of Israel. The climate is sub-humid with a rainless dry season from May to October. A partial water balance of a 0.1 ha area supporting an average of 14 trees was calculated from: (a) soil water content (SWC) measured by a Neutron Probe at depths of from 0.2 to 8 m, and (b) daylight transpiration rate measured with sap flow sensors by the heat pulse technique.Soil–bedrock complex water content (%) in the first 2 m of the profile fluctuated strongly between 5 and 20% depending on the season. The water content increased with depth from about 10% at 2.0 m depth to more than 20% at 5.0 m depth. For depths exceeding 5.5 m seasonal fluctuations in water content were negligible and water content ranged from 30 to 35%. After a dry winter, water content generally decreased within the main root zone down to about 2.0 m depth. Monthly changes in water content (mm) were greatest at depths of 0.35–1.0 m. Only minor changes in the soil–bedrock complex water content were recorded at greater depths. After a very rainy winter (2002/2003), decreases in soil–bedrock complex water content in the upper 2 m were much larger than after a dry winter. Fluctuations of soil–bedrock complex water content in deeper regions were larger in the wetter year, probably the result of drainage.Sap velocity was measured at six depths in the sapwood, from 4 to 44 mm, at 8 mm intervals. Sap velocity declined with depth, hence, sap flux density too.Based on sap velocity measurements performed during 4 years, the annual average daily transpiration (T) was 0.796 mm/day. This sums up to 239 mm during ∼300 days of leaf carriage, i.e. 41.3% of the 578 mm average annual rainfall for the area in the last 50 years. In a relatively dry year (rainfall of 432.7 mm) total water withdrawal from the 8 m soil–bedrock profile was 81% of the annual rainfall; of this amount 69% were transpired by the oak trees (239.0 mm), or 55% of the annual rainfall. In a relatively wet year (annual rainfall 801.4 mm) total water withdrawal was 67%; of this amount 45% would be transpired by the oak trees, or 30% of the annual rainfall.  相似文献   

15.
The current work adopted the Biome-BioGeochemical Cycle model to simulate the net primary productivity (NPP) of a subalpine forest (Picea crassifolia forest) under four representative concentration pathway (RCP) scenarios in the Qilian Mountains of northwest China. This study also investigated the responses of forest’s NPP to different combinations of climatic changes and CO2 concentration increase. Results showed that (1) under the RCP scenarios, greater increases in temperature, precipitation, and CO2 concentration caused larger increments in forest NPP; (2) the effect of CO2 concentration (increased NPP from 19.9% to 21.7%) was more significant than that of climate change (increased NPP from 7.5% to 17.1%); (3) the simultaneous increments in climatic change and atmospheric CO2 concentration led to a remarkable increase in P. crassifolia forest NPP (ranging from 33.1% to 41.3%), with the combination of the two exerting strong interactive effects on forest NPP; and (4) the response of the forest’s NPP to future global change was more intense at high elevations than at low ones, with the temperature being the main factor controlling forest NPP variation at the high-elevation regions. These valuable predictions can help clarify how subalpine forest ecosystems respond to simultaneous or independent changes in climate and CO2 concentration.  相似文献   

16.
Human induced changes in global environmental conditions are expected to influence or, as it is hypothesised in this study, have already influenced the biomass and growth of forest ecosystems. In this study, we reconstruct the history of tree growth and quantify the standing biomass along a chronosequence of six Norway spruce stands (Picea abies [L.] Karst; 16–142 years old) on acid soils in a mountainous region with high nitrogen deposition. The inventories of the study sites, as well as the historical stem growth of the sample trees were compared with common yield tables, representing growing conditions before 1960, to find out if and when significant changes in growth of trees had occurred. The growth at tree level (0.003–0.030 m3 yr−1) was about 150–350% higher than predicted by the yield tables, independent of tree age. Because of low stand densities due to early thinning, the increase of stem growth at stand level (90% higher than yield table predictions) and the stand volume (35% higher than yield table predictions) were not as high as the increase of growth at tree level. Total biomass at stand level (including stems, branches, twigs, needles and roots) ranged between 35 and 180 t C ha−1. Net primary productivity varied between 6 and 13 t C ha−1 yr−1. Intensive tree thinning activities probably stimulated growth of remaining trees, but the observed growth rates were beyond what would be expected from these activities exclusively. Thus it is assumed that the fertilisation effects of increased nitrogen deposition and CO2 concentration, and improved climatic conditions due to ongoing climate change, have contributed to the observed changes in stem growth and that the thinning activities were synergetic with changing environmental conditions. The implications for carbon sinks as accountable under the Kyoto Protocol are probably small, because changes in environmental conditions are not accountable under the Kyoto Protocol and most of the observed changes in growth took place before 1990, the baseline for the Kyoto Protocol. Additionally, it is assumed that impacts on the carbon balance of forest stands due to changes in the thinning regime after 1990, which would be accountable according to article 3.4 of the Kyoto Protocol, are very small without any synergetic changes in environmental conditions.  相似文献   

17.
论述了青藏高原植被净初级生产力(NPP)的空间分布和时间变化动态,以及NPP与气候因子的关系和对未来气候变化的响应。总结出了以下结论:①青藏高原年均NPP为0.3Pg Ca-1,由东南向西北逐渐递减,与该地区的水热条件和植被类型的地带性分异规律一致;②近年来,青藏高原的植被生产力在波动中呈上升趋势,年增加速率约为0.7%;③温度是影响青藏高原生物生长的主导因子,青藏高原净初级生产力随着气温和降水的增加而增加;④未来气候变化影响青藏高原植被NPP,在IPCC预测的B1、A1B和A2气候变化情景下,青藏高原的NPP均呈增加的趋势。  相似文献   

18.
We used a combination of data from USDA Forest Service inventories, intensive chronosequences, extensive sites, and satellite remote sensing, to estimate biomass and net primary production (NPP) for the forested region of western Oregon. The study area was divided into four ecoregions differing widely in climatic conditions and management regime. The forest age distributions (as derived from inventory data) differed by ecozone with fewer old stands in the Coast Range and the East Cascades, and a relatively uniform distribution of ages from 0 to 815 in the Cascade Mountains. Age distributions also differed by land ownership, with fewer old stands on non-federal lands than on national forest lands. Estimated biomass increased rapidly in early stand development and tended to stabilize after about 200 years. Peak biomass in the semi-arid East Cascades was about one-third that of the other ecoregions (median biomass at asymptote ∼9 and ∼25 kg C m−2, respectively). The timing and magnitude of maximum net primary production also varied by ecoregion, with the high productivity Coast Range forests reaching a maximum NPP before 30 years of age (median ∼1 kg C m−2 y−1), and the low productivity East Cascades reaching a maximum NPP between 80 and 100 years (median ∼0.3 kg C m−2 y−1). Productivity was generally lower in older stands with the exception of the East Cascades ecoregion where, contrary to the paradigm of age-related decline in forest growth, the oldest stands had the highest NPP. The East Cascades also differed from the other ecoregions in that the proportion of NPP allocated belowground decreased rather than increased with stand age. This study demonstrates the value of combining data from intensive and extensive measurement sites for improved estimates of carbon stocks and fluxes as well as improved parameterization of process models used in scaling carbon flux over broad regions.  相似文献   

19.
Loblolly pine (Pinus taeda L.) is a highly plastic species with respect to growth responses to forest management. Loblolly pine is the most planted species across the southern United States, a region with the most expansive and intensively managed forest plantations in the world. Management intensity, using tools such as site preparation and fertilization, is increasing greatly in scope over time. To better define to the productive potential of loblolly pine under intensive management, the influence of 6 years of management with weed control (W), weed control plus irrigation (WI), weed control plus irrigation and fertigation (irrigation with a fertilizer solution) (WIF), or weed control plus irrigation, fertigation, and pest control (WIFP) since plantation establishment on stand productivity in loblolly pine was examined. The site is located near Bainbridge, GA (30°48′N latitude and 84°39′W longitude) and is of medium quality (site index=18 m, base age 25). Increasing management intensity greatly accelerated stand development and biomass accumulation. At age 6 total production (above plus belowground) was nearly doubled from 50 to 93 Mg ha−1 in WIFP stands compared to W stands, and standing stem biomass increased from 24 Mg ha−1 in W stands to 48 Mg ha−1 in response to WIFP treatment. Stem current annual increment (CAI) peaked at age 5 in the WIF and WIFP stands at 17–18 Mg ha−1 per year at a basal area between 18 and 21 m2 ha−1. Year to year variation in CAI was better explained by previous-year leaf area index (LAI) than current-year LAI. Maximum stemwood production in loblolly pine was achieved through large increases in LAI and small decreases in allocation to woody roots (tap+coarse roots) versus woody shoots (stem+branches) associated with intensive treatments.  相似文献   

20.
Wood volume yield and stand structure were investigated for Norway spruce understorey growing at 1500 trees ha−1 under birch shelters of two different densities, 300 and 600 trees ha−1, and Norway spruce growing without shelter, in a field trial in the boreal coniferous forest, 56 years after the establishment of the stand and 19 years after establishment of the trial.Wood volume yield in sheltered spruce (mean annual increments of 1.87 and 1.78 m3 ha−1 year−1 under the dense and sparse shelterwoods, respectively) was significantly lower than that of unsheltered spruce (mean annual increment 2.43 m3 ha−1 year−1). The loss in wood volume yield for sheltered spruce was more than compensated for by the additional wood volume yield in the shelterwoods (mean annual increments 3.26 and 1.88 m3 ha−1 year−1 for the dense and sparse shelterwood respectively).Shelterwood density did not produce any significant differences in inequality of the understorey stands, measured as skewness and the Gini coefficient for the wood volume distributions. This implies that two-sided competition for nutrients and water was more significant than competition for light.Immediately after trial establishment, trees in the no shelterwood treatment (i.e. where all overstory trees had been removed) showed a marked increase in diameter growth. Over time, the growth rate of unsheltered Norway spruce was reduced to a level comparable to that of sheltered spruce. The difference in average diameter has persisted during the trial period. There was no similar effect on height growth, resulting in an increased slenderness index (h/d) with increased shelterwood density for the understorey trees.  相似文献   

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