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1.
Development trends of Russian forests and their impact on the global carbon budget were assessed at the national level on the basis of long-term forest inventory data (1961–1998). Over this period, vegetation of Russian forest lands are estimated as a carbon sink, with an annual average level of carbon sequestration in vegetational organic matter of 210 ± 30 Tg C · yr–1 (soil carbon is not considered in this study), of which 153 Tg C · yr–1 were accumulated in live biomass and 57 Tg C · yr–1 in dead wood. The temporal variability of the sink is very large; for the five-year averages used in the analysis, the C sequestration varies from about 60 to above 300 Tg C· yr–1. It is shown that long-term forest inventory data could serve as an important information base for assessing crucial indicators of full carbon accounting of forests.  相似文献   

2.
Forest inventories and remote sensing are the two principal data sources used to estimate carbon (C) stocks and fluxes for large forest regions. National governments have historically relied on forest inventories for assessments but developments in remote sensing technology provide additional opportunities for operational C monitoring. The estimate of total C stock in live forest biomass modeled from Landsat imagery for the St. Petersburg region was consistent with estimates derived from forest inventory data for the early 1990s (272 and 269 TgC, respectively). The estimates of mean C sink in live forest biomass also agreed well (0.36 and 0.34 Mg C ha–1 yr–1). Virtually all forest lands were accumulating C in live biomass, however when the net change in total ecosystem C stock was considered, 19% of the forest area were a net source of C. The average net C sink in total ecosystem biomass is quite weak (0.08 MgC ha–1 yr–1 and could be reversed by minor increases in harvest rates or a small decline in biomass growth rates.  相似文献   

3.
Forest inventories and remote sensing are the two principal data sources used to estimate carbon (C) stocks and fluxes for large forest regions. National governments have historically relied on forest inventories for assessments but developments in remote sensing technology provide additional opportunities for operational C monitoring. The estimate of total C stock in live forest biomass modeled from Landsat imagery for the St. Petersburg region was consistent with estimates derived from forest inventory data for the early 1990s (272 and 269 TgC, respectively). The estimates of mean C sink in live forest biomass also agreed well (0.36 and 0.34 Mg C ha–1 yr–1). Virtually all forest lands were accumulating C in live biomass, however when the net change in total ecosystem C stock was considered, 19% of the forest area were a net source of C. The average net C sink in total ecosystem biomass is quite weak (0.08 MgC ha–1 yr–1 and could be reversed by minor increases in harvest rates or a small decline in biomass growth rates.  相似文献   

4.
The study reports estimates of above ground phytomass carbon pools in Indian forests for 1992 and 2002 using two different methodologies. The first estimate was derived from remote sensing based forest area and crown density estimates, and growing stock data for 1992 and 2002 and the estimated pool size was in the range 2,626–3,071 Tg C (41 to 48 Mg C ha???1) and 2,660–3,180 Tg C (39 to 47 Mg C ha???1) for 1992 and 2002, respectively. The second methodology followed IPCC 2006 guidelines and using an initial 1992 pool of carbon, the carbon pool for 2002 was estimated to be in the range of 2,668–3,112 Tg C (39 to 46 Mg C ha???1), accounting for biomass increment and removals for the period concerned. The estimated total biomass increment was about 458 Tg over the period 1992–2002. Removals from forests include mainly timber and fuel wood, whereby the latter includes large uncertainty as reported extraction is lower than actual consumption. For the purpose of this study, the annual extraction values of 23 million m3 for timber and 126 million m3 for fuel wood were used. Out of the total area, 10 million ha are plantation forests with an average productivity (3.2 Mg ha???1 year???1) that is higher than natural forests, a correction of 408 Tg C for the 10 year period was incorporated in total estimated phytomass carbon pool of Indian forests. This results in an estimate for the net sink of 4 Tg C year???1. Both approaches indicate Indian forests to be sequestering carbon and both the estimates are in agreement with recent studies. A major uncertainty in Indian phytomass carbon pool dynamics is associated with trees outside forests and with soil organic carbon dynamics. Using recent remote-sensing based estimates of tree cover and growing stock outside forests, the estimated phytomass carbon pool for trees outside forests for the year 2002, is 934 Tg C with a national average tree carbon density of 4 Mg C ha???1 in non-forest area, in contrast to an average density of 43 Mg C ha???1 in forests. Future studies will have to consider dynamics in both trees outside forests and soil for total terrestrial carbon dynamics.  相似文献   

5.
Tropical deforestation and atmospheric carbon dioxide   总被引：4，自引：0，他引：4  
Recent estimates of the net release of carbon to the atmosphere from deforestation in the tropics have ranged between 0.4 and 2.5 × 1015 g yr–1. Two things have happened to require a revision of these estimates. First, refinements of the methods used to estimate the stocks of carbon in the vegetation of tropical forests have produced new estimates that are intermediate between the previous high and low estimates of carbon stocks. When these revised estimates were used here to calculate the emissions of carbon from deforestation, the new range was 1.0–2.0 × 1015 g C.Second, the previous range of estimates of flux was based on rates of deforestation in 1980. Myers' recent estimate of the rates of tropical deforestation in 1989 is about 90% higher than the rates just 10 years ago. When these recent rates were used to calculate the current net flux of carbon to the atmosphere, the range was between 1.6 and 2.7 × 1015 g C.Other uncertainties expanded this range, however, to 1.1–3.6 × 1015 g C yr–1. Three factors contributed about equally to the expanded range: rates of deforestation, the fate of deforested lands (permanent or temporary clearing), and carbon stocks of forests, including anthropogenic reductions of carbon stocks within forests (thinning or degradation).  相似文献   

6.
The aim of this study was to close the carbon budget and reduce uncertainty in annual C balances for Scots pine (Pinus sylvestris) forests in The Netherlands. This was done by comparing estimates of the Net Ecosystem Exchange (NEE) as assessed by two different methods. The inventory based carbon budgeting method estimated the average NEE for 1997 – 2001 at 202 g C m–2 yr–1 (a sink) with a confidence interval of 138 – 271 g C m–2 yr–1. The estimate obtained by the eddy covariance method was 295 g C m–2 yr–1 on average for the same period, with a confidence interval of 224 – 366 g C m–2 yr–1. Uncertainties in the eddy covariance method were mostly related to gap filling of the data. Main uncertainties in the inventory-based method are related to the soil and the root compartment. The difference in NEE as obtained by two independent methods indicates that it is not straightforward to design a sound National System for monitoring and reporting of the total land area and for accounting of changes in forest area under the Kyoto Protocol, and that more effort is required in this field.  相似文献   

7.
Jian Ni 《Climatic change》2002,55(1-2):61-75
The BIOME3 model was used to simulate the distribution patterns and carbon storage of the horizontal, zonal boreal forests in northeast and northwest China using a mapping system for vegetation patterns combined with carbon density estimates from vegetation and soils. The BIOME3 prediction is in reasonable good agreement with the potential distribution of Chinese boreal forests. The effects of changing atmospheric CO2 concentration had a nonlinear effect on boreal forest distribution, with 3.5–10.8% reduced areas for both increasing and decreasing CO2. In contrast, the increased climate together with and without changing CO2 concentration showed dramatic changes in geographic patterns, with 70% reduction in area and disappearance of almost boreal forests in northeast China. The baseline carbon storage in boreal forests of China is 4.60 PgC (median estimate) based on the vegetation area of actual boreal forest distribution. If taking the large area of agricultural crops into account, the median value of potential carbon storage is 6.92 PgC. The increasing (340–500 ppmv) and decreasing CO2 concentration (340–200 ppmv) led to decrease of carbon storage, 0.33 PgC and 1.01 PgC respectively compared to BIOME3 potential prediction under present climate and CO2 conditions. Both climate change alone and climate change with CO2 enrichment (340–500 ppmv) reduced largely the carbon stored in vegetation and soils by ca. 6.5 PgC. The effect of climate change is more significant than the direct physiological effect of CO2 concentration on the boreal forests of China, showing a large reduction in both distribution area and carbon storage.  相似文献   

8.
Tropical forests are responsible for a large proportion of the global terrestrial C flux annually for natural ecosystems. Increased atmospheric CO2 and changes in climate are likely to affect the distribution of C pools in the tropics and the rate of cycling through vegetation and soils. In this paper, I review the literature on the pools and fluxes of carbon in tropical forests, and the relationship of these to nutrient cycling and climate. Tropical moist and humid forests have the highest rates of annual net primary productivity and the greatest carbon flux from soil respiration globally. Tropical dry forests have lower rates of carbon circulation, but may have greater soil organic carbon storage, especially at depths below 1 meter. Data from tropical elevation gradients were used to examine the sensitivity of biogeochemical cycling to incremental changes in temperature and rainfall. These data show significant positive correlations of litterfall N concentrations with temperature and decomposition rates. Increased atmospheric CO2 and changes in climate are expected to alter carbon and nutrient allocation patterns and storage in tropical forest. Modeling and experimental studies suggest that even a small increase in temperature and CO2 concentrations results in more rapid decomposition rates, and a large initial CO2 efflux from moist tropical soils. Soil P limitation or reductions in C:N and C:P ratios of litterfall could eventually limit the size of this flux. Increased frequency of fires in dry forest and hurricanes in moist and humid forests are expected to reduce the ecosystem carbon storage capacity over longer time periods.  相似文献   

9.
The dynamics of terrestrial ecosystems depends on interactions between carbon, nutrient and hydrological cycles. Terrestrial ecosystems retain carbon in live biomass (aboveground and belowground), decomposing organic matter, and soil. Carbon is exchanged naturally between these systems and the atmosphere through photosynthesis, respiration, decomposition, and combustion. Human activities change carbon stock in these pools and exchanges between them and the atmosphere through land-use, land-use change, and forestry.In the present study we estimated the wood (stem) biomass, growing stock (GS) and carbon stock of Indian forests for 1984 and 1994. The forest area, wood biomass, GS, and carbon stock were 63.86 Mha, 4327.99 Mm3, 2398.19 Mt and 1085.06 Mt respectively in 1984 and with the reduction in forest area, 63.34 Mha, in 1994, wood biomass (2395.12 Mt) and carbon stock (1083.69 Mt) also reduced subsequently. The Conifers, of temperate region, stocked maximum carbon in their woods, 28.88 to 65.21 t C ha−1, followed by Mangrove forests, 28.24 t C ha−1, Dipterocarp forests, 28.00 t C ha−1, and Shorea robusta forests, 24.07 t C ha−1. Boswellia serrata, with 0.22 Mha forest area, stocked only 3.91 t C ha−1. To have an idea of rate of carbon loss the negative changes (loss of forest area) in forest area occurred during 1984–1994 (10yrs) and 1991–1994 (4yrs) were also estimated. In India, land-use changes and fuelwood requirements are the main cause of negative change. Total 24.75 Mt C was lost during 1984–1994 and 21.35 Mt C during 1991–94 at a rate of 2.48 Mt C yr−1 and 5.35 Mt C yr−1 respectively. While in other parts of India negative change is due to multiple reasons like fuelwood, extraction of non-wood forest products (NWFPs), illicit felling etc., but in the northeastern region of the country shifting cultivation is the only reason for deforestation. Decrease in forest area due to shifting cultivation accounts for 23.0% of the total deforestation in India, with an annual loss of 0.93 Mt C yr−1.  相似文献   

10.
Increased Carbon Sink in Temperate and Boreal Forests   总被引：6，自引：0，他引：6  
An intense search is under way to identify the `missing sink' in the world carbon budget of perhaps 2 Pg year–1 (petagrams, or billiontonnes) of carbon, but its location and mechanism have proved elusive. Here we use a new forest inventory data set to estimate the carbon sink and the carbon pool of woody biomass in 55 countries that account for nearly all temperate or boreal forests and approximately half the world's total forest area. In each country there was a net accumulation of biomass; together, the carbon sink of woody biomass was 0.88 Pg year–1 during the 1990swith estimated uncertainty from 0.71 to 1.1 Pg year–1. Thisestimate, already about half of the missing sink, would probably be even larger if carbon accumulation in soil and detritus were also accounted for, but we are unable to quantify that additional sink. The sink is twice that estimated for the woody biomass of these forests a decade ago due to higher estimates for tree growth throughout the region and decreased timber harvests in Russia. In contrast, the new data indicate a carbon pool that is smaller than earlier estimates because of improved data for Russia and Australia.  相似文献   

11.
Application of nitrate fertilizers on two types of forest soils led to a marked increase in the NO emission rate indicating a large potential for NO production in these soils. The largest fluxes on the fertilized plots were up to 60 ng NO–N m–2 s–1. About 0.35% of the applied nitrogen was lost as NO within about 14 days after fertilization. The fluxes from the unfertilized forest soils were in the range 0.1 to 0.8 ng NO–N m–2 s–1 with a median value of 0.3 ng NO–N m–2 s–1. If this value, obtained during June and August to September, is representative for the growing season (150 days), it corresponds to an annual emission of 0.04 kg NO–N ha–1. This is about 30% of the value obtained for an unfertilized agricultural soil. Because of the large areas occupied by forests in Sweden the flux of NO from forest soils represents a significant contribution to the total flux of NO from soils in Sweden.Earlier observations of equilibrium concentrations for NO have been verified. These were found to range from 0.2 to 2 ppbv for an unfertilized forest soil and up to 170 ppbv for a fertilized soil. At the rural site in Sweden where these measurements were performed the ambient concentrations where found to be less than this equilibrium concentration, and consequently there was generally a net emission of NO.There are still large uncertainties about the global flux of NO from soils. Using direct measurements on three different types of ecosystems and estimates based on a qualitative discussion for the remaining land areas, a global natural source for NO of the order of 1 Tg N a–1 was obtained. If 0.35% of the total annual production of fertilizer nitrogen is lost as NO, fertilization of soils may contribute with 20% to the natural flux from soils.  相似文献   

12.
Nitrous oxide (N2O) fluxes for south-easternAustralia have been estimated using a combination ofthe in situ N2O and radon (Rn) measurementsmade at the Cape Grim Baseline Air Pollution Station,in north-west Tasmania. The average N2O fluxesfrom the south-eastern mainland of Australia and fromTasmania over the nine years of record analysed (1985–1993) have beenfound to be 130 ± 30 kgN km-2yr-1 and 160 ± 45 kgN km-2yr-1respectively. These fluxes are larger than expectedand a significant dependence of the flux on rainfallis observed, with greater fluxes in the spring (October–December) andduring periods of positive SouthernOscillation Index. A large flux (1,300 ± 500kgN km-2 yr-1) from a nearby island (KingIsland) was also estimated from the data record,indicating a strong source, although the small size ofthe island means that it is not a significant sourcefor Australia.  相似文献   

13.
Net greenhouse gas (GHG) emissions from Canadian crop and livestock production were estimated for 1990, 1996 and 2001 and projected to 2008. Net emissions were also estimated for three scenarios (low (L), medium (M) and high (H)) of adoption of sink enhancing practices above the projected 2008 level. Carbon sequestration estimates were based on four sink-enhancing activities: conversion from conventional to zero tillage (ZT), reduced frequency of summerfallow (SF), the conversion of cropland to permanent cover crops (PC), and improved grazing land management (GM). GHG emissions were estimated with the Canadian Economic and Emissions Model for Agriculture (CEEMA). CEEMA estimates levels of production activities within the Canadian agriculture sector and calculates the emissions and removals associated with those levels of activities. The estimates indicate a decline in net emissions from 54 Tg CO2–Eq yr–1 in1990 to 52 Tg CO2–Eq yr–1 in 2008. Adoption of thesink-enhancing practices above the level projected for 2008 resulted in further declines in emissions to 48 Tg CO2–Eq yr–1 (L), 42 TgCO2–Eq yr–1 (M) or 36 Tg CO2–Eq yr–1 (H). Among thesink-enhancing practices, the conversion from conventional tillage to ZT provided the largest C sequestration potential and net reduction in GHG emissions among the scenarios. Although rates of C sequestration were generally higher for conversion of cropland to PC and adoption of improved GM, those scenarios involved smaller areas of land and therefore less C sequestration. Also, increased areas of PC were associated with an increase in livestock numbers and CH4 and N2O emissions from enteric fermentation andmanure, which partially offset the carbon sink. The CEEMA estimates indicate that soil C sinks are a viable option for achieving the UNFCCC objective of protecting and enhancing GHG sinks and reservoirs as a means of reducing GHG emissions (UNFCCC, 1992).  相似文献   

14.
The ecosystem carbon (C) and nitrogen (N) simulations recently implemented in the Canadian Land Surface Scheme (CLASS) are presented. The main calculations include plant photosynthesis, autotrophic respiration, root N uptake, litterfall, plant growth, and soil heterotrophic respiration. Model experiments are made on two boreal forest ecosystems, deciduous (aspen) and conifers (black spruce). Simulated plant, soil, and ecosystem CO2 exchanges are analysed on half-hourly, daily, and annual time scales and compared with tower eddy correlation flux measurements and estimates from various authors. Modeled daily ecosystem CO2 exchange explained86% and 54%, respectively, of the observed variance of eddy correlationflux at the aspen site and at the black spruce site. Annual results show that the aspen ecosystem was simulated as a C sink in both 1994 (+164 g Cm–2) and 1996 (+142 g C m–2), and the black spruce ecosystem wassimulated as a C sink in 1994 (+39 g C m–2) and 1995 (+25 g Cm–2), but as a C source in 1996 (–27 g C m–2).  相似文献   

15.
A study has been undertaken to understand some of the aspects of carbon-dioxide exchange between the atmosphere and Indian plant biota. The net primary production and the total pool of carbon in forests, cultivated land, and grassland during 1980 is estimated. The flux of carbon dioxide due to deforestation and the consumption of firewood is also estimated. The total pool of carbon in a forest ecosystem shows a very low value when compared with the size and climate of the country. On the other hand, carbon-dioxide emission due to firewood combustion shows a very high value.  相似文献   

16.
The U.K. has extensive databases on soils, land cover and historic land use change which have made it possible to construct a comprehensive inventory of the principal terrestrial sources and sinks of carbon for approximately the year 1990, using methods that are consistent with, and at least as accurate as, the revised 1996 guidelines recommended by IPCC where available – and including categories which are not currently considered under the UN Framework Convention on Climate Change. This country inventory highlights issues concerning methodology, uncertainty, double counting, the importance of soils and the relative magnitude of sources and sinks which are reported to the UNFCCC relative to other sources and sinks. The carbon sinks (negative values in MtC a-1) for categories reported to the UNFCCC, based on the IPCC categories, were estimated to be: forest trees and litter (–2.1), U.K. forest products (–0.5, ignoring imports and exports), non-forest biomass (–0.3), forest soils (–0.1) and soils on set-aside land (–0.4). The carbon sources (positive values) reported under the UNFCCC were estimated to be: losses of soil organic carbon resulting from cultivation of semi-natural land (6.2) and from urbanization (1.6), drainage of peatlands (0.3) and fenlands (0.5), and peat extraction (0.2). A range of other sources and sinks not covered by the IPCC guidelines were also quantified, namely, the accumulation of carbon in undrained peatlands (–0.7, ignoring methane emission), sediment accretion in coastal marshes (–0.1), the possible U.K. share of the CO2 and N fertilization carbon sink (–2.0) and riverine organic and particulate carbon export to the sea (1.4, which may be assumed to be a source if most of this carbon is released as CO2 in the sea). All sinks totalled –6.2 and sources 10.2, giving a net flux to the atmosphere in 1990 of 4.0 MtC a-1. Uncertainties associated with categories, mostly based on best guesses, ranged from ±15% for forest biomass and litter to ±60% for CO2 and N fertilization.  相似文献   

17.
Estimates of carbon emissions from the forest sector in Mexico are derived for the year 1985 and for two contrasting scenarios in 2025. The analysis covers both tropical and temperate closed forests. In the mid-1980s, approximately 804,000 ha/year of closed forests suffered major perturbations, of which 668,000 ha was deforestation. Seventy-five percent of total deforestation is concentrated in tropical forests. The resulting annual carbon balance from land-use change is estimated at 67.0 × 106 tons/year, which lead to net emissions of 52.3 × 106 tons/year accounting for the carbon uptake in restoration plantations and degraded forest lands. This last figure represents approximately 40% of the country's estimated annual total carbon emissions for 1985–1987. The annual carbon balance from the forest sector in 2025 is expected to decline to 28.0 × 106 t in the reference scenario and to become negative (i.e., a carbon sink), 62.0 × 106 t in the policy scenario. A number of policy changes are identified that would help achieve the carbon sequestration potential identified in this last scenario.  相似文献   

18.
Transpiration of a 7 m-high Stika spruce forest was investigated using measurments of net radiation, sensible heat and ground heat fluxes in an energy balance to give latent heat flux, and hence canopy resistance from the Penman-Monteith equation. Sensible heat flux was measured by the eddy-correlation method using a Fluxatron circuit.During six consecutive days of measurement in July/August, canopy resistance typically followed a decreasing trend from high values (150 s m-) at dawn to around 40 s m–1 at midday and then returning steadily to > 100 s m–1 at sunset. Transpiration was 3 mm day–1 on average over the period studied and changes in the rate within the day were significantly correlated with changes in net radiation.Comparisons are drawn with published data from other forest sites and the conclusion is reached that it is imprudent to generalise about transpiration rates and canopy resistances of different species at different sites from results gathered at one or two places.  相似文献   

19.
There is considerable uncertainty as to whether interannual variability in climate and terrestrial ecosystem production is sufficient to explain observed variation in atmospheric carbon content over the past 20–30 years. In this paper, we investigated the response of net CO2 exchange in terrestrial ecosystems to interannual climate variability (1983 to 1988) using global satellite observations as drivers for the NASA-CASA (Carnegie-Ames-Stanford Approach) simulation model. This computer model of net ecosystem production (NEP) is calibrated for interannual simulations driven by monthly satellite vegetation index data (NDVI) from the NOAA Advanced Very High Resolution Radiometer (AVHRR) at 1 degree spatial resolution. Major results from NASA-CASA simulations suggest that from 1985 to 1988, the northern middle-latitude zone (between 30 and 60°N) was the principal region driving progressive annual increases in global net primary production (NPP; i.e., the terrestrial biosphere sink for carbon). The average annual increase in NPP over this predominantly northern forest zone was on the order of +0.4 Pg (1015 g) C per year. This increase resulted mainly from notable expansion of the growing season for plant carbon fixation toward the zonal latitude extremes, a pattern uniquely demonstrated in our regional visualization results. A net biosphere source flux of CO2 in 1983–1984, coinciding with an El Niño event, was followed by a major recovery of global NEP in 1985 which lasted through 1987 as a net carbon sink of between 0.4 and 2.6 Pg C per year. Analysis of model controls on NPP and soil heterotrophic CO2 fluxes (Rh) suggests that regional warming in northern forests can enhance ecosystem production significantly. In seasonally dry tropical zones, periodic drought and temperature drying effects may carry over with at least a two-year lag time to adversely impact ecosystem production. These yearly patterns in our model-predicted NEP are consistent in magnitude with the estimated exchange of CO2 by the terrestrial biosphere with the atmosphere, as determined by previous isotopic (13C) deconvolution analysis. Ecosystem simulation results can help further target locations where net carbon sink fluxes have occurred in the past or may be verified in subsequent field studies.  相似文献   

20.
    
The spatial and temporal variability of land carbon flux over the past one hundred years was investigated based on an empirical model directly calculating soil respiration rate. Our model shows that during 1901–1995, about 44-89 PgC (equals to 0.5, 0.9 PgC/yr respectively) were absorbed by terrestrial biosphere. The simulated net ecosystem productivity (NEP) after the 1930s was close to the estimated value of “ missing C sink” from deconvolution analysis. Most of the total carbon sink happened during 1951–1985 with the estimated value of 33–50 PgC. Three major sinks were located in the tropics (10°S–10°N), Northern mid-latitudes (30°–60°N) and Southern subtropics (10°–40°S). During 1940s-mid-1970s, carbon sinks by terrestrial ecosystem increased with time, and decreased after the mid-1970s. These may be due to the changing of climate condition, as during the 1940s–1970s, temperature decreased and precipitation increased, while after the mid-1970s, an opposite climate situation occurred with evident increasing in temperature and decreasing in precipitation. Usually, warmer and dryer climate condition is not favor for carbon absorption by biosphere and even induces net carbon release from soil, while cooler and wetter condition may induce more carbon sink. Our model results show that the net carbon flux is particularly dependent on moisture / precipitation effect despite of temperature effect. The changing of climate in the past century may be a possible factor inducing increases in carbon sink in addition to CO2 and N fertilizer. This research was funded by CAS One Hundred Talents project and Knowledge Innovation Project of CAS(KZCX2-201).  相似文献   

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