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1.
We used pine (Pinus elliottii Engelm.) forests located along a short urban–rural gradient in Nanchang, China to study nitrogen (N) cycling responses to urbanization. Annual average rates of nitrification and net N-mineralization in soils (0–15 cm depth) measured from February 2007 to January 2009 increased from rural (8 and 37 kg ha−1 year−1) to suburban (69 and 79 kg ha−1 year−1) and urban sites (114 and 116 kg ha−1 year−1) (P < 0.05). Soil nitrate and mineral N pools exhibited the same spatial patterns in response to urban location. In comparison to rural sites, urban and suburban sites experienced soil microbial biomass N that increased by 98% and 38%, sucrase activity that increased by 40% and 26%, and urease activity that decreased by 35% and 25%, respectively. Soil microbial biomass C:N and free amino acids varied little along the urban–rural gradient. Foliar N concentrations and N resorption proficiencies were higher in urban (12.3 and 4.8 g kg−1) and suburban (12.3 and 6.2 g kg−1) than in rural (9.9 and 3.6 g kg−1) sites, while N resorption efficiencies (from 58% to 72%) were not statistically different. These results indicate that forests in suburban and especially in urban areas are moving rapidly towards a state of “N saturation” and increased potential N loss most likely attributable to higher N deposition to these sites.  相似文献   

2.
Dissolved inorganic nitrogen (DIN) (as ammonium nitrate) was applied monthly onto the forest floor of one old-growth forest (>400 years old, at levels of 50, 100 and 150 kg N ha−1 yr−1) and two young forests (both about 70 years old, at levels of 50 and 100 kg N ha−1 yr−1) over 3 years (2004–2006), to investigate how nitrogen (N) input influenced N leaching output, and if there were differences in N retention between the old-growth and the young forests in the subtropical monsoon region of southern China. The ambient throughfall inputs were 23–27 kg N ha−1 yr−1 in the young forests and 29–35 kg N ha−1 yr−1 in the old-growth forest. In the control plots without experimental N addition, a net N retention was observed in the young forests (on average 6–11 kg N ha−1 yr−1), but a net N loss occurred in the old-growth forest (−13 kg N ha−1 yr−1). Experimental N addition immediately increased DIN leaching in all three forests, with 25–66% of added N leached over the 3-year experiment. At the lowest level of N addition (50 kg N ha−1 yr−1), the percentage N loss was higher in the old-growth forest (66% of added N) than in the two young forests (38% and 26%). However, at higher levels of N addition (100 and 150 kg N ha−1 yr−1), the old-growth forest exhibited similar N losses (25–43%) to those in the young forests (28–43%). These results indicate that N retention is largely determined by the forest successional stages and the levels of N addition. Compared to most temperate forests studied in Europe and North America, N leaching loss in these seasonal monsoon subtropical forests occurred mainly in the rainy growing season, with measured N loss in leaching substantially higher under both ambient deposition and experimental N additions.  相似文献   

3.
The carryover effects of N fertilization on five coastal Pacific Northwest Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) plantations were studied. “Carryover” is defined as the long-term impact of N fertilizer added to a previous stand on the growth of a subsequent stand. Average height and diameter at 1.3 m above-ground (DBH) of 7–9-year-old Douglas-fir trees and biomass and N-content of understory vegetation were assessed on paired control (untreated) and urea-N-fertilized plots that had received cumulative additions of 810–1120 kg N ha−1 to a previous stand. Overall productivity was significantly greater in the fertilized stands compared to the controls. In 2006, the last growth measurement year, mean seedling height was 15% greater (p = 0.06) and mean DBH was 29% greater (p = 0.04) on previously fertilized plots compared to control plots. Understory vegetation biomass of fertilized plots was 73% greater (p = 0.005), and N-content was 97% greater (p = 0.004) compared to control plots. These results show that past N fertilization markedly increased seedling growth in these plantations as well as biomass and N-content of understory vegetation in a subsequent rotation. These findings suggest that N fertilization could potentially increase site productivity of young Douglas-fir stands found on low quality sites in the Pacific Northwest 15–22 years after application by a carryover effect. These plantations have not yet reached the age where marketable materials can be harvested from them, and the growth of trees should be monitored over a longer time period before potential impacts on older stands, if any, can be determined.  相似文献   

4.
We measured the change in above- and below-ground carbon and nutrient pools 11 years after the harvesting and site preparation of a histic-mineral soil wetland forest in the Upper Peninsula of Michigan. The original stand of black spruce (Picea mariana), jack pine (Pinus banksiana) and tamarack (Larix laricina) was whole-tree harvested, and three post-harvest treatments (disk trenching, bedding, and none) were randomly assigned to three Latin square blocks (n = 9). Nine control plots were also established in an adjoining uncut stand. Carbon and nutrients were measured in three strata of above-ground vegetation, woody debris, roots, forest floor, and mineral soil to a depth of 1.5 m. Eleven years following harvesting, soil C, N, Ca, Mg, and K pools were similar among the three site preparation treatments and the uncut stand. However, there were differences in ecosystem-level nutrient pools because of differences in live biomass. Coarse roots comprised approximately 30% of the tree biomass C in the regenerated stands and 18% in the uncut stand. Nutrient sequestration, in the vegetation since harvesting yielded an average net ecosystem gain of 332 kg N ha−1, 110 kg Ca ha−1, 18 kg Mg ha−1, and 65 kg K ha−1. The likely source for the cations and N is uptake from shallow groundwater, but N additions could also come from non-symbiotic N-fixation and N deposition. These are the only reported findings on long-term effects of harvesting and site preparation on a histic-mineral soil wetland and the results illustrate the importance of understanding the ecohydrology and nutrient dynamics of the wetland forest. This wetland type appears less sensitive to disturbance than upland sites, and is capable of sustained productivity under these silvicultural treatments.  相似文献   

5.
Information on soil carbon sequestration and its interaction with nitrogen availability is rather limited, since soil processes account for the most significant unknowns in the C and N cycles. In this paper we compare three completely different approaches to calculate carbon sequestration in forest soils. The first approach is the limit-value concept, in which the soil carbon accumulation is estimated by multiplying the annual litter fall with the recalcitrant fraction of the decomposing plant litter, which depends on the nitrogen and calcium content in the litter. The second approach is the N-balance method, where carbon sequestration is calculated from the nitrogen retention in the soil multiplied with the present soil C/N ratio in organic layer and mineral topsoil. The third approach is the dynamic SMART2 model in combination with an empirical approach to assess litter fall inputs. The comparison is done by first validating the methods at three chronosequences with measured C pools, two in Denmark and one in Sweden, and then application on 192 intensive monitoring plots located in the Northern and Western part of Europe. Considering all three chronosequences, the N-balance method was generally most in accordance with the C pool measurements, although the SMART2 model was also quite consistent with the measurements at two chronosequences. The limit-value approach generally overestimated the soil carbon sequestration. At the intensive monitoring plots, the limit-value concept calculated the highest carbon sequestration, ranging from 160 to 978 kg ha−1 year−1, followed by the N-balance method which ranged from 0 to 535 kg ha−1 year−1. With SMART2 we calculated the lowest carbon sequestration from −30 to 254 kg ha−1 year−1. All the three approaches found lower carbon sequestration at a latitude from 60 to 70° compared to latitudes from 40 to 50 and from 50 to 60. Considering the validation of the three approaches, the range in results from both the N-balance method and SMART2 model seems most appropriate.  相似文献   

6.
Several studies have reported different estimates for forest biomass carbon (C) stocks in China. The discrepancy among these estimates may be largely attributed to the methods used. In this study, we used three methods [mean biomass density method (MBM), mean ratio method (MRM), and continuous biomass expansion factor (BEF) method (abbreviated as CBM)] applied to forest inventory data to estimate China's forest biomass C stocks and their changes from 1984 to 2003. The three methods generated various estimates of the biomass C stocks: the lowest (4.0–5.9 Pg C) from CBM and the highest (5.7–7.7 Pg C) from MBM, with an intermediate estimate (4.2–6.2 Pg C) from MRM. Forest age class is a major factor responsible for these method-induced differences. MBM overestimates biomass for young-aged forests, but underestimates biomass for old-aged forests; while the reverse is true for MRM. Further, the three methods resulted in different estimates of biomass C stocks for different forest types. For temperate/subtropical mixed forests, MBM generated a 92% higher estimate than CBM and MRM generated a 14% lower than CBM. The degree of the overestimates is closely related with the proportion of young-aged forest within total area of each forest type.  相似文献   

7.
Uncertainties in biomass estimates in Amazonian forests result in a broad range of possible magnitude for the emissions of carbon from deforestation and other land-use changes. This paper presents biomass equations developed from trees directly weighed in open forest on fertile soils in the southern Amazon (SA) and allometric equations for bole-volume estimates of trees in both dense and open forests. The equations were used to improve the commonly used biomass models based on large-scale wood-volume inventories carried out in Amazonian forest. The biomass estimates from the SA allometric equation indicate that equations developed in forests on infertile soils in central Amazonia (CA) result in overestimates if applied to trees in the open forests of SA. All aboveground components of 267 trees in open forests of SA were cut and weighed, and the proportion of the biomass stored in the crowns of trees in open forest was found to be higher than in dense forest. In the case of inventoried wood volume, corrections were applied for indentations and hollow trunks and it was determined that no adjustment is needed for the form factor used in the RadamBrasil volume formula. New values are suggested for use in models to convert wood volume to biomass estimates. A biomass map for Brazilian Amazonia was produced from 2702 plots inventoried by the RadamBrasil Project incorporating all corrections for wood density and wood volume and in factors used to add the bole volume of small trees and the crown biomass. Considering all adjustments, the biomass map indicates total biomass of 123.1 Gt (1 Gt = 1 billion tons) dry weight (aboveground + belowground) for originally forested areas in 1976 in the Brazilian Legal Amazon as a whole (102.3 Gt for aboveground only) at the time of the RadamBrasil inventories, which were carried out before intensive deforestation had occurred in the region. Excluded from this estimate are 529,000 km2 of forest lacking sufficient RadamBrasil inventory data. After forest losses of 676,000 km2 by 2006 – not counting 175,000 km2 of this deforested area lacking RadamBrasil data – the estimated dry biomass stock was reduced to 105.4 and 87.6 Gt (aboveground + belowground and only above-ground). Thus, in 2006 the carbon storage in forested areas in Brazilian Amazonia as a whole will be around 51.1 Gt (assuming 1 Mg dry biomass = 0.485 Mg C). Biomass estimates by forest type (aggregated into 12 vegetation classes) are provided for each state in the Brazilian Legal Amazon.  相似文献   

8.
The purpose of this study was to compare carbon sequestration between moso bamboo (Phyllostachys heterocycla) and China fir (Cunninghamia lanceolata) forests. The study site was located in the lower mountain area of central Taiwan, where both moso bamboo and China fir were rich. In addition, moso bamboo and China fir forests were surveyed on 12 and 19 plantations, respectively. We predicted carbon sequestration based on the allometric model for moso bamboo and China fir forests and compared the relationships between characteristics of bamboo forests and elevation. The results showed that mean diameter at breast height (DBH), culms per hectare and aboveground biomass were not clearly affected by elevation, whereas a negative correlation (R = −0.600, p = 0.039) between mean DBH and stand density was found for moso bamboo forests. Moreover, the aboveground carbon storage was higher for China fir forests than for moso bamboo (99.5 vs. 40.6 Mg ha−1). However, moso bamboo is an uneven-aged stand which is only composed of 1-5-year-old culms, while China fir is an even-aged stand and the age range is from 15 to 54 years, such that, per year, the mean aboveground carbon sequestration is 8.13 ± 2.15 and 3.35 ± 2.02 Mg ha−1 for moso bamboo and China fir, respectively. On the other hand, the mean carbon sequestration of China fir decreases with increasing the age class. Furthermore, the ratio of moso bamboo to China fir is 2.39 and a T-test showed that the aboveground carbon levels were significantly different between these two species; thus, moso bamboo is a species with high potential for carbon sequestration.  相似文献   

9.
Four forest stands each of twenty major forest types in sub-tropical to temperate zones (350 m asl–3100 m asl) of Garhwal Himalaya were studied. The aim of the study was to assess the stem density, tree diversity, biomass and carbon stocks in these forests and make recommendations for forest management based on priorities for biodiversity protection and carbon sequestration. Stem density ranged between 295 and 850 N ha−1, while total biomass ranged from 129 to 533 Mg ha−1. Total carbon storage ranged between 59 and 245 Mg ha−1. The range of Shannon–Wiener diversity index was between 0.28 and 1.75. Most of the conifer-dominated forest types had higher carbon storage than broadleaf-dominated forest types. Protecting conifer-dominated stands, especially those dominated by Abies pindrow and Cedrus deodara, would have the largest impact, per unit area, on reducing carbon emissions from deforestation.  相似文献   

10.
Data on the biomass and productivity of southeast Asian tropical forests are rare, making it difficult to evaluate the role of these forest ecosystems in the global carbon cycle and the effects of increasing deforestation rates in this region. In particular, more precise information on size and dynamics of the root system is needed. In six natural forest stands at pre-montane elevation (c. 1000 m a.s.l.) on Sulawesi (Indonesia), we determined above-ground biomass and the distribution of fine (d < 2 mm) and coarse roots (d > 2 mm), estimated above- and below-ground net production, and compared the results to literature data from other pre-montane paleo- and neotropical forests. The mean total biomass of the stands was 303 Mg ha−1 (or 128 Mg C ha−1), with the largest biomass fraction being recorded for the above-ground components (286 Mg ha−1) and 11.2 and 5.6 Mg ha−1 of coarse and fine root biomass (down to 300 cm in the soil profile), resulting in a remarkably high shoot:root ratio of c. 17. Fine root density in the soil profile showed an exponential decrease with soil depth that was closely related to the concentrations of base cations, soil pH and in particular of total P and N. The above-ground biomass of these stands was found to be much higher than that of pre-montane forests in the Neotropics, on average, but lower compared to other pre-montane forests in the Paleotropics, in particular when compared with dipterocarp forests in Malesia. The total above- and below-ground net primary production was estimated at 15.2 Mg ha−1 yr−1 (or 6.7 Mg C ha−1 yr−1) with 14% of this stand total being invested below-ground and 86% representing above-ground net primary production. Leaf production was found to exceed net primary production of stem wood. The estimated above-ground production was high in relation to the mean calculated for pre-montane forests on a global scale, but it was markedly lower compared to data on dipterocarp forests in South-east Asia. We conclude that the studied forest plots on Sulawesi follow the general trend of higher biomasses and productivity found for paleotropical pre-montane forest compared to neotropical ones. However, biomass stocks and productivity appear to be lower in these Fagaceae-rich forests on Sulawesi than in dipterocarp forests of Malesia.  相似文献   

11.
A substantial portion of the carbon (C) fixed by the trees is allocated belowground to ectomycorrhizal (EM) symbionts, but this fraction usually declines after fertilization. The aim of the present study was to estimate the effect of optimal fertilization (including all the necessary nutrients) on the growth of EM fungi in young Norway spruce forests over a three year period. In addition, the amount of carbon sequestered by EM mycelia was estimated using a method based on the difference in δ13C between C3 and C4 plants. Sand-filled ingrowth mesh bags were used to estimate EM growth, and similar bags amended with compost made from maize leaves (a C4 plant) were used to estimate C sequestration. Fertilizers had been applied either every year or every second year since 2002 and the estimates of EM growth started in 2007. The application of fertilizer reduced EM growth to between 0% and 40% of the growth in the control plots at one site (Ebbegärde), while no significant effect was found at the other three sites studied. The effect of the fertilizer was similar in sand-filled and maize-compost-amended mesh bags, but the total production of EM fungi was 3-4 times higher in maize-compost-amended mesh bags. The fertilizer tended to reduce EM growth more when applied every year than when applied every second year. The amount of C sequestered in maize-compost-amended mesh bags collected from unfertilized treatments was estimated to be between 0.2 and 0.7 mg C g sand−1 at Ebbegärde and between 0.2 and 0.5 mg C g sand−1 at Grängshammar. This corresponds to between 300 and 1100 kg C per ha, assuming a similar production in the soil as in the mesh bags. Fertilization at the Ebbegärde site reduced carbon sequestration, which confirmed the results based on estimates of fungal growth (ergosterol levels). A correlation was found between fungal biomass and δ13C in mesh bags amended with maize compost. Based on this, it was estimated that a fungal production of 1 μg ergosterol corresponded to 0.33 mg of sequestered carbon. In conclusion, the effect of the fertilizer on EM growth seemed to be dependent on the effect of the fertilizer on tree growth. Thus, at Ebbegärde, were tree growth was less stimulated by the fertilizer, EM growth was reduced upon fertilization. At other sites, where tree growth was more stimulated, the fertilizer did not influence EM growth. The large amounts of carbon sequestered during the experiment may be a result of fungal residues remaining in the soil after the death of the hyphae.  相似文献   

12.
The effects of historical land use changes on the global C cycle have mainly been studied by means of bookkeeping models. Here, we investigate with such models the impact of afforestation and deforestation on soil organic carbon (SOC) stocks. This approach, using field-based estimates of the response of SOC upon land use changes, is applied to a pilot area in the Belgian Ardennes over one and a half century (1868–2005). After a small initial decline during the 1868–1888 period due to deforestation for agricultural use, mean SOC stocks increased steadily up to 1990, due essentially to the conversion of deciduous to coniferous forests (in the study area, deciduous forests stored less SOC than coniferous) and the reclamation of heathland, which occurred both at the turn of the 19th and 20th centuries. Simulations showed that SOC stocks decreased recently (1990–2005) because of the slow down of sequestration in coniferous forests and a reversion of some of the coniferous plantations to deciduous forests. Over the entire period, afforestation resulted in a net sequestration of carbon (0.16 t C ha−1 year−1). Monte Carlo simulations demonstrated that the model was highly sensitive to its inputs (initial SOC stocks for each land use) both in term of predicted SOC stocks and rates of SOC stocks change. However, the sensitivity of the model was not large enough to revert the main trends of SOC changes observed. Compared to the amount of carbon sequestered in the biomass, the contribution of soils to the C sink in forest is small. Despite several sources of errors, a detailed reconstruction of land use changes combined with realistic SOC response curves upon land use conversion are required to be able to quantify the contribution of soils to terrestrial carbon fluxes.  相似文献   

13.
Acacia plantation establishment might cause soil acidification in strongly weathered soils in the wet tropics because the base cations in the soil are translocated rapidly to plant biomass during Acacia growth. We examined whether soils under an Acacia plantation were acidified, as well as the factors causing soil acidification. We compared soils from 10 stands of 8-year-old Acacia mangium plantations with soils from 10 secondary forests and eight Imperata cylindrica grasslands, which were transformed into Acacia plantations. Soil samples were collected every 5–30 cm in depth, and pH and related soil properties were analyzed. Soil pH was significantly lower in Acacia plantations and secondary forests than in Imperata grasslands at every soil depth. The difference was about 1.0 pH unit at 0–5 cm and 0.5 pH unit at 25–30 cm. A significant positive correlation between pH and base saturation at 0–20 cm depth indicated that the low pH under forest vegetation was associated with exchangeable cation status. Using analysis of covariance (ANCOVA), with clay content as the covariate, exchangeable Ca (Ex-Ca) and Mg (Ex-Mg) stocks were significantly lower in forested areas than in Imperata grasslands at any clay content which was strongly related to exchangeable cation stock. The adjusted average Ex-Ca stock calculated by ANCOVA was 249 kg ha−1 in Acacia plantations, 200 kg ha−1 in secondary forests, and 756 kg ha−1 in Imperata grasslands at 0–30 cm. Based on a comparison of estimated nutrient stocks in biomass and soil among the vegetation types, the translocation of base cations from soil to plant biomass might cause a decrease in exchangeable cations and soil acidification in Acacia plantations.  相似文献   

14.
In regions of Australia of low–medium rainfall (500–800 mm/year), there is growing community and land-owner support for re-planting trees to achieve multiple environmental objectives, particularly amelioration of soil salinity. Sequestration of carbon by newly established trees is not only another important environmental benefit, but also a potential commercial benefit. To obtain estimates of carbon sequestered by species of commercial potential in such regions, we calibrated the carbon (C) accounting model FullCAM to Eucalyptus cladocalyx and Corymbia maculata plantations. This was achieved by harvesting trees of a range in sizes to determine the allometric relationships that most accurately predict biomass and stem density from measures of stem diameter. Predictions of stem diameter were obtained from a forest growth model (3-PG) previously calibrated for these two species. By applying these predictions of changes in stem diameter as the stand matures in our allometric relationships, we estimated changes in partitioning of biomass (between stem, branches, bark, foliage and roots) and stem wood density as the stand matures under scenarios of 500, 600 and 750 mm mean annual rainfall. We found that for both species, regardless of annual rainfall, throughout the rotation 37–50% of carbon sequestered in the total tree biomass was in the stem, 18–27% in both branches and roots, and the remainder in foliage or bark. However, rate of accumulation of carbon was dependent on annual rainfall, with average annual rate of sequestration of carbon in tree biomass and litter during the first rotation of E. cladocalyx (or C. maculata) increasing from 3.68 (or 4.17) to 4.72 (or 4.86) Mg C ha−1 yr−1 as annual rainfall increased from about 500 to 750 mm. Although it was predicted that decomposition negated any accumulation of debris between successive rotations, carbon was predicted to accumulate in sawlog products, given that assumed rates of product decomposition were slightly less than their rate of accumulation. This resulted in a slight increase (<8 Mg C ha−1) in predicted total sequestration of carbon between successive rotations.  相似文献   

15.
Infestations of Essigella californica following the installation of post-thinning fertilizer trials in Pinus radiata plantations provided an opportunity to examine the impact of repeated defoliation over a period of 8 years (1997–2005). Replicated treatments (n = 4) of nil fertilizer (control), N (300 kg ha−1) as urea, P (80 kg ha−1) and S (45 kg ha−1) as superphosphates were applied immediately after thinning at three sites and this was followed by a second application of NPS fertilizers 6 years later with N applied at 300 kg ha−1 as urea and ammonium sulphate and P at 80 or 120 kg ha−1. Defoliation of untreated P. radiata gradually increased to 50% over a period of 8 years. Basal area growth was negatively correlated with average defoliation for two consecutive post-fertilizer periods of 6 and 2 years. Growth responses to fertilizer varied considerably between sites but the largest improvement in growth was due to NPS fertilizer, this increased basal area by 30–80%. Application of N fertilizer raised total N levels in foliage and increased defoliation with a commensurate loss in growth under conditions of deficiencies of S or P. Repeated infestations gradually increased the percentage of trees with severe defoliation (>80% loss of foliage) indicating that nutrient-deficient trees have a reduced capacity for foliage recovery between episodes of peak infestation. In contrast, treatment with N fertilizer in combination with S- and P-corrected deficiencies of these nutrients, raised levels of total N in foliage and reduced defoliation to approximately 20%. Basal area growth responses to NPS fertilizers reflected improved nutrition as well as reduced insect damage. The reduction in defoliation under conditions of balanced tree nutrition was most likely due to enhanced needle retention following correction of P deficiency as well as greater availability of nutrients enabling a more vigorous recovery of P. radiata after an episode of E. californica activity. Treatment with fertilizer therefore reduced the long-term impact of aphid damage and improved growth of P. radiata.  相似文献   

16.
In the climate change discussion, the possibility of carbon sequestration of forests plays an important role. Therefore, research on the effects of environmental changes on net primary productivity is interesting. In this study we investigated the influence of changing temperature, precipitation and deposition of sulphur and nitrogen compounds on forest growth. The database consisted of 654 plots of the European intensive monitoring program (Level II plots) with 5-year growth data for the period 1994–1999. Among these 654 plots only 382 plots in 18 European countries met the requirements necessary to be used in our analysis. Our analysis was done for common beech (Fagus sylvatica), oak (Quercus petraea and Q. robur), Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). We developed an individual tree growth model with measured basal area increment of each individual tree as responding growth factor and tree size (diameter at breast height), tree competition (basal area of larger trees and stand density index), site factors (soil C/N ratio, temperature), and environmental factors (temperature change compared to long-term average, nitrogen and sulphur deposition) as influencing parameters. Using a mixed model approach, all models for the tree species show a high goodness of fit with Pseudo-R2 between 0.33 and 0.44. Diameter at breast height and basal area of larger trees were highly influential variables in all models. Increasing temperature shows a positive effect on growth for all species except Norway spruce. Nitrogen deposition shows a positive impact on growth for all four species. This influence was significant with p < 0.05 for all species except common beech. For beech the effect was nearly significant (p = 0.077). An increase of 1 kg N ha−1 yr−1 corresponds to an increase in basal area increment between 1.20% and 1.49% depending on species. Considering an average total carbon uptake for European forests near 1730 kg per hectare and year, this implies an estimated sequestration of approximately 21–26 kg carbon per kg nitrogen deposition.  相似文献   

17.
The carbon sequestration potential in living biomass and soil organic matter under the Grain for Green Program (GGP) in Yunnan Province, one of the most important target provinces of the GGP in China, was estimated in this paper using empirical curves and factors. The area of tree species planted during 2000–2007 was collected, and four scenarios for the annual area of GGP-stands to be planted during 2008–2010 and harvest options were schemed. Empirical growth curves for different tree species were developed based on data about the growth of existing plantation in Yunnan Province from National Forestry Inventory, and were used for the estimation of the carbon stocks in the tree biomass pools by incorporating with basic wood density, biomass expansion factors and carbon fraction. Empirical factors were introduced to estimate the stock change in soil organic carbon (SOC) under the GGP. The results show that the carbon stock in the GGP-stands in Yunnan Province will increase by 12.474–12.608 TgC, 33.016–35.161 TgC, 38.119–47.100 TgC, 43.057–53.626 TgC and 49.918–56.621 by the year 2010, 2020, 2030, 2040 and 2050, respectively. The annual carbon stock change in the GGP-stands will peak at 2.342–2.536 TgC per year in 2013, followed by a gradual decrease. The estimated potential carbon sequestration by GGP-stands amounts to 10.82–12.27% of the carbon stocks of forest ecosystems in Yunnan province in the 1990s.  相似文献   

18.
Live aboveground biomass (AGB) is an important source of uncertainty in the carbon balance from the tropical regions in part due scarcity of reliable estimates of live AGB and its variation across landscapes and forest types. Studies of forest structure and biomass stocks of Neotropical forests are biased toward Amazonian and Central American sites. In particular, standardized estimates of aboveground biomass stocks for the Brazilian Atlantic forest are rarely available. Notwithstanding the role of environmental variables that control the distribution and abundance of biomass in tropical lowland forests has been the subject of considerable research, the effect of short, steep elevational gradients on tropical forest structure and carbon dynamics is not well known. In order to evaluate forest structure and live AGB variation along an elevational gradient (0–1100 m a.s.l.) of coastal Atlantic Forest in SE Brazil, we carried out a standard census of woody stems ≥4.8 cm dbh in 13 1-ha permanent plots established on four different sites in 2006–2007. Live AGB ranged from 166.3 Mg ha−1 (bootstrapped 95% CI: 144.4,187.0) to 283.2 Mg ha−1 (bootstrapped 95% CI: 253.0,325.2) and increased with elevation. We found that local-scale topographic variation associated with elevation influences the distribution of trees >50 cm dbh and total live AGB. Across all elevations, we found more stems (64–75%) with limited crown illumination but the largest proportion of the live AGB (68–85%) was stored in stems with highly illuminated or fully exposed crowns. Topography, disturbance and associated changes in light and nutrient supply probably control biomass distribution along this short but representative elevational gradient. Our findings also showed that intact Atlantic forest sites stored substantial amounts of carbon aboveground. The live tree AGB of the stands was found to be lower than Central Amazonian forests, but within the range of Neotropical forests, in particular when compared to Central American forests. Our comparative data suggests that differences in live tree AGB among Neotropical forests are probably related to the heterogeneous distribution of large and medium-sized diameter trees within forests and how the live biomass is partitioned among those size classes, in accordance with general trends found by previous studies. In addition, the elevational variation in live AGB stocks suggests a large spatial variability over coastal Atlantic forests in Brazil, clearly indicating that it is important to consider regional differences in biomass stocks for evaluating the role of this threatened tropical biome in the global carbon cycle.  相似文献   

19.
We compared different potential indicators of nitrogen (N) availability across 50 beech forests growing on a wide range of soils in northeastern France. Among the 50 sites measured, high elevation acidic soils had the highest potential net N mineralization in the A horizon (PNM0–5 cm), while low elevation neutral and calcareous soils had the lowest (PNM0–5 cm). We found that (PNM0–5 cm) was negatively correlated with soil pH (R2 = 0.47***) and positively correlated with microbial C/N (R2 = 0.34***). However, when high elevation sites were excluded from analyses, the relationship between PNM0–5 cm and soil pH as well as microbial C/N became weaker (R2 = 0.23*** for both variables). We found no relationship between PNM0–5 cm and organic N concentration, soil C/N, or vegetation-based indices for N availability (Ellenberg N and Ecoplant C/N). Bivariate linear regression analyses showed that 69% of the variability in percent nitrification (%Nitrif) was explained by both soil pH (0–5 cm) and soil C/N. Percent nitrification was strongly correlated with vegetation-based indices for N availability. The Ellenberg N and R (pH index) values together explained 74% of the variation in %Nitrif. No relationship was found between %Nitrif and soil δ15N (natural abundance in 15N). Of the 76 plant species evaluated, the probability of presence of 61 plant species was significantly correlated with %Nitrif while the probability of presence of 27 plant species only was correlated with PNM0–5 cm. From these results, we believe that the use of plant community composition or the combination of soil pH and C/N are robust indicators of N availability.  相似文献   

20.
The effects of global change on ecosystem productivity and water resources in the southern United States (SUS), a traditionally ‘water-rich’ region and the ‘timber basket’ of the country, are not well quantified. We carried out several simulation experiments to quantify ecosystem net primary productivity (NPP), evapotranspiration (ET) and water use efficiency (WUE) (i.e., NPP/ET) in the SUS by employing an integrated process-based ecosystem model (Dynamic Land Ecosystem Model, DLEM). The results indicated that the average ET in the SUS was 710 mm during 1895–2007. As a whole, the annual ET increased and decreased slightly during the first and second half of the study period, respectively. The mean regional total NPP was 1.18 Pg C/yr (525.2 g C/m2/yr) during 1895–2007. NPP increased consistently from 1895 to 2007 with a rate of 2.5 Tg C/yr or 1.10 g C/m2/yr, representing a 27% increase. The average WUE was about 0.71 g C/kg H2O and increased about 25% from 1895 to 2007. The rather stable ET might explain the resulting increase in WUE. The average WUE of different biomes followed an order of: forest (0.93 g C/kg H2O) > wetland (0.75 g C/kg H2O) > grassland (0.58 g C/kg H2O) > cropland (0.54 g C/kg H2O) > shrubland (0.45 g C/kg H2O). WUE of cropland increased the fastest (by 30%), followed by shrubland (17%) and grassland (9%), while WUE of forest and wetland changed little from the period of 1895–1950 to the period of 1951–2007. NPP, ET and WUE showed substantial inter-annual and spatial variability, which was induced by the non-uniform distribution patterns and change rates of environmental factors across the SUS. We concluded that an accurate projection of the regional impact of climate change on carbon and water resources must consider the spatial variability of ecosystem water use efficiency across biomes as well as the interactions among all stresses, especially land-use and land-cover change and climate.  相似文献   

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