Effects of Management on Carbon Sequestration in Forest Biomass in Southeast Alaska

The Tongass National Forest (Tongass) is the largest national forest and largest area of old-growth forest in the United States. Spatial geographic information system data for the Tongass were combined with forest inventory data to estimate and map total carbon stock in the Tongass; the result was 2.8 ± 0.5 Pg C, or 8% of the total carbon in the forests of the conterminous USA and 0.25% of the carbon in global forest vegetation and soils. Cumulative net carbon loss from the Tongass due to management of the forest for the period 1900–95 was estimated at 6.4–17.2 Tg C. Using our spatially explicit data for carbon stock and net flux, we modeled the potential effect of five management regimes on future net carbon flux. Estimates of net carbon flux were sensitive to projections of the rate of carbon accumulation in second-growth forests and to the amount of carbon left in standing biomass after harvest. Projections of net carbon flux in the Tongass range from 0.33 Tg C annual sequestration to 2.3 Tg C annual emission for the period 1995–2095. For the period 1995–2195, net flux estimates range from 0.19 Tg C annual sequestration to 1.6 Tg C annual emission. If all timber harvesting in the Tongass were halted from 1995 to 2095, the economic value of the net carbon sequestered during the 100-year hiatus, assuming $20/Mg C, would be $4 to $7 million/y (1995 US dollars). If a prohibition on logging were extended to 2195, the annual economic value of the carbon sequestered would be largely unaffected ($3 to $6 million/y). The potential annual economic value of carbon sequestration with management maximizing carbon storage in the Tongass is comparable to revenue from annual timber sales historically authorized for the forest.     

全球森林生态系统碳储量、固碳能力估算及其区域特征

从气候地带性和地理区域分布两方面对森林生态系统碳储量及固碳能力,以及土地利用变化对森林固碳的影响和森林固碳估算不确定性的原因进行综述.据估算,全球森林生态系统碳储量为652～927 Pg C,固碳能力达到4.02 Pg C·a^-1.各气候地带森林碳储量表现为热带最大(471 Pg C),寒带次之(272 Pg C),温带(113～159 Pg C)最小,固碳能力表现为热带(1.02～1.3 Pg C·a^-1)最大,温带次之(0.8 Pg C·a^-1),寒带(0.5 Pg C·a^-1)最小;各地理区域森林碳储量表现为南美洲(187.7～290 Pg C)最大,其次是欧洲(162.6 Pg C)、北美洲(106.7 Pg C)、非洲(98.2 Pg C)和亚洲(74.5 Pg C),而大洋洲(21.7 Pg C)最小,固碳能力为南美洲热带(1276 Tg C·a^-1)和非洲热带(753 Tg C·a^-1)较大,其次是北美洲(248 Tg C·a^-1)和欧洲(239 Tg C·a^-1),而东亚(98.8～136.5 Tg C·a^-1)较小.为进一步减少森林生态系统固碳估算的不确定性,今后应综合运用连续长期观测技术、样地清查、遥感分析和模型模拟等方法.     

Vegetation carbon sequestration in Chinese forests from 2010 to 2050

Forests store a large part of the terrestrial vegetation carbon (C) and have high C sequestration potential. Here, we developed a new forest C sequestration (FCS) model based on the secondary succession theory, to estimate vegetation C sequestration capacity in China's forest vegetation. The model used the field measurement data of 3161 forest plots and three future climate scenarios. The results showed that logistic equations provided a good fit for vegetation biomass with forest age in natural and planted forests. The FCS model has been verified with forest biomass data, and model uncertainty is discussed. The increment of vegetation C storage in China's forest vegetation from 2010 to 2050 was estimated as 13.92 Pg C, while the average vegetation C sequestration rate was 0.34 Pg C yr^?1 with a 95% confidence interval of 0.28–0.42 Pg C yr^?1, which differed significantly between forest types. The largest contributor to the increment was deciduous broadleaf forest (37.8%), while the smallest was deciduous needleleaf forest (2.7%). The vegetation C sequestration rate might reach its maximum around 2020, although vegetation C storage increases continually. It is estimated that vegetation C sequestration might offset 6–8% of China's future emissions. Furthermore, there was a significant negative relationship between vegetation C sequestration rate and C emission rate in different provinces of China, suggesting that developed provinces might need to compensate for undeveloped provinces through C trade. Our findings will provide valuable guidelines to policymakers for designing afforestation strategies and forest C trade in China.     

Biomass carbon stocks in China’s forests between 2000 and 2050: A prediction based on forest biomass-age relationships

China’s forests are characterized by young forest age, low carbon density and a large area of planted forests, and thus have high potential to act as carbon sinks in the future. Using China’s national forest inventory data during 1994–1998 and 1999–2003, and direct field measurements, we investigated the relationships between forest biomass density and forest age for 36 major forest types. Statistical approaches and the predicted future forest area from the national forestry development plan were applied to estimate the potential of forest biomass carbon storage in China during 2000–2050. Under an assumption of continuous natural forest growth, China’s existing forest biomass carbon (C) stock would increase from 5.86 Pg C (1 Pg=10¹⁵ g) in 1999–2003 to 10.23 Pg C in 2050, resulting in a total increase of 4.37 Pg C. Newly planted forests through afforestation and reforestation will sequestrate an additional 2.86 Pg C in biomass. Overall, China’s forests will potentially act as a carbon sink for 7.23 Pg C during the period 2000–2050, with an average carbon sink of 0.14 Pg C yr⁻¹. This suggests that China’s forests will be a significant carbon sink in the next 50 years.     

中国国家森林公园碳储量及固碳速率的时空动态

森林生态系统在调节气候变化和维持碳平衡中具有重要作用。国家森林公园是森林保护的主要载体,探明其碳储量和固碳速率的变化对于森林生态系统的固碳能力评估和可持续经营管理具有重要意义。本研究采用生态系统过程模型CEVSA2模型,模拟了1982—2017年中国881处国家森林公园的碳密度、碳储量和固碳速率的空间分布特征。结果表明: 国家森林公园平均碳密度为255.18 t C·hm^-2,高于中国森林生态系统平均碳密度。2017年,国家森林公园总碳储量为3.56 Pg C,占全国森林生态系统总碳储量的11.0%~12.2%。1982—2017年国家森林公园平均固碳速率达到0.45 t C·hm^-2·a^-1,各地区国家森林公园固碳速率都在0.30 t C·hm^-2·a^-1以上。东北和西南地区国家森林公园的总碳储量最高。东北地区国家森林公园的土壤有机碳固碳速率最高,而华东和中南地区国家森林公园的植被碳固碳速率最高。国家森林公园面积占中国森林总面积的5.8%,在森林碳汇管理中占据着重要地位。准确评估国家森林公园的森林生长状况、固碳潜力和碳吸收特征,可为我国森林公园生态系统服务功能的总体评估提供借鉴和参考。     

Soil carbon stocks,deforestation and land‐cover changes in the Western Ghats biodiversity hotspot (India)

Habitat loss and soil organic carbon (SOC) stock variations linked to land‐cover change were estimated over two decades in the most densely populated biodiversity hotspot in the world, in order to assess the possible influence of conservation practices on the protection of SOC. For a study area of 88 484 km², 70% of which lie inside the Western Ghats Biodiversity Hotspot (WGBH), land‐cover maps for two dates (1977, 1999) were built from various data sources including remote sensing images and ecological forest maps. SOC stocks were calculated from climatic parameters, altitude, physiography, rock type, soil type and land‐cover, with a modelling approach used in predictive learning and based on Multiple Additive Regression Tree. The model was trained on 361 soil profiles data, and applied to estimate SOC stocks from predictor variables using a Geographical Information System (GIS). Comparison of 1977 and 1999 land‐cover maps showed 628 km² of dense forests habitat loss (6%), corresponding to an annual deforestation rate of 0.44%. This was found consistent with other studies carried out in other parts of the WGBH, but not with FAO figures showing an increase in forest area. This could be explained by the different forest definitions used, based on ecological classification in the former, and on percentage tree cover in the latter. Unexpectedly, our results showed that despite ongoing deforestation, overall SOC stock was maintained (～0.43 Pg). But a closer examination of spatial differences showed that soil carbon losses in deforested areas were compensated by sequestration elsewhere, mainly in recent plantations and newly irrigated croplands. This suggests that more carbon sequestration in soils could be achieved in the future through appropriate wasteland management. It is also expected that increasing concerns about biodiversity loss will favour more conservation and reinforce the already prevailing protective measures, thus further maintaining C stocks.     

中国西南地区热带森林演替序列碳动态

热带森林的破坏是全球性问题,我国西双版纳森林覆盖率受砍伐、火烧和短期耕种丢荒后,面积不断减少,取而代之的是大面积的不同演替状态的次生林。次生林演替过程中的碳储量和碳平衡的变化目前还鲜有研究,为了进一步揭示我国西南地区热带森林演替对于碳蓄积的影响,并制定更科学的热带森林经营管理措施,以结构复杂、生物多样和生物量巨大的热带森林为研究对象,并利用3个热带次生林的样地的实测数据,探讨了不同演替状态的热带次生林的碳储量变化,以及森林的净碳蓄积,死亡碳损失和更新碳增长等碳动态规律,分析表明:(1)在森林的演替过程中,森林的胸径分布频度从近正态分布逐渐向小径级的偏态分布发展,也就是随着演替的进展,小径级林木所占的比例越来越高。(2)热带次生林在森林固碳方面发挥着不可忽略的作用。(3)小的干扰,会波及森林的碳动态;大的干扰,如火灾和砍伐,将导致森林的次生演替,对森林的碳动态产生不可逆转的改变。(4)干旱事件是影响凋落物的季节和年间动态的原因,也是短时间尺度上影响碳平衡的一个重要因子。(5)不论原生林还是次生林,大树在生态系统碳动态方面皆扮演着重要的角色,因此本研究推荐注重大树的研究。     

Forest biomass carbon sinks in East Asia,with special reference to the relative contributions of forest expansion and forest growth

Forests play an important role in regional and global carbon (C) cycles. With extensive afforestation and reforestation efforts over the last several decades, forests in East Asia have largely expanded, but the dynamics of their C stocks have not been fully assessed. We estimated biomass C stocks of the forests in all five East Asian countries (China, Japan, North Korea, South Korea, and Mongolia) between the 1970s and the 2000s, using the biomass expansion factor method and forest inventory data. Forest area and biomass C density in the whole region increased from 179.78 × 10⁶ ha and 38.6 Mg C ha^?1 in the 1970s to 196.65 × 10⁶ ha and 45.5 Mg C ha^?1 in the 2000s, respectively. The C stock increased from 6.9 Pg C to 8.9 Pg C, with an averaged sequestration rate of 66.9 Tg C yr^?1. Among the five countries, China and Japan were two major contributors to the total region's forest C sink, with respective contributions of 71.1% and 32.9%. In China, the areal expansion of forest land was a larger contributor to C sinks than increased biomass density for all forests (60.0% vs. 40.0%) and for planted forests (58.1% vs. 41.9%), while the latter contributed more than the former for natural forests (87.0% vs. 13.0%). In Japan, increased biomass density dominated the C sink for all (101.5%), planted (91.1%), and natural (123.8%) forests. Forests in South Korea also acted as a C sink, contributing 9.4% of the total region's sink because of increased forest growth (98.6%). Compared to these countries, the reduction in forest land in both North Korea and Mongolia caused a C loss at an average rate of 9.0 Tg C yr^?1, equal to 13.4% of the total region's C sink. Over the last four decades, the biomass C sequestration by East Asia's forests offset 5.8% of its contemporary fossil‐fuel CO₂ emissions.     

甘肃省森林碳储量现状与固碳速率

针对森林碳平衡再评估的重要性和区域尺度森林生态系统碳库量化分配的不确定性, 该研究依据全国森林资源连续清查结果中甘肃省各森林类型分布的面积与蓄积比重以及林龄和起源等要素, 在甘肃省布设212个样地, 经野外调查与采样、室内分析, 并对典型样地信息按照面积权重进行尺度扩展, 估算了甘肃省森林生态系统碳储量及其分布特征。结果表明: 甘肃省森林生态系统总碳储量为612.43 Tg C, 其中植被生物量碳为179.04 Tg C, 土壤碳为433.39 Tg C。天然林是甘肃省碳储量的主要贡献者, 其值为501.42 Tg C, 是人工林的4.52倍。天然林和人工林的植被碳密度均表现为随林龄的增加而增加的趋势, 同一龄组天然林植被碳密度高于人工林。天然林土壤碳密度从幼龄林到过熟林逐渐增加, 但人工林土壤碳密度最大值主要为近熟林。全省森林植被碳密度均值为72.43 Mg C·hm^-2, 天然林和人工林分别为90.52和33.79 Mg C·hm^-2。基于森林清查资料和标准样地实测数据, 估算出全省天然林和人工林在1996年的植被碳储量为132.47和12.81 Tg C, 2011年分别为152.41和26.63 Tg C, 平均固碳速率分别为1.33和0.92 Tg C·a^-1。甘肃省幼、中龄林面积比重较大, 占全省的62.28%, 根据碳密度随林龄的动态变化特征, 预测这些低龄林将发挥巨大的碳汇潜力。     

Current stocks and rate of sequestration of forest carbon in Gansu Province,China

Aims
Carbon sequestration is the basic function and most primary service of forest ecosystems, and plays a vital role in mitigating the global climate change. However, carbon storage and allocation in forest ecosystems have been less studied at regional scales than at forest stand levels, and the results are subject to uncertainty due to inconsistent methodologies. In this study we aim to obtain relatively accurate estimates of forest carbon stocks and sequestration rate at a provincial scale (regional) based on plot surveys of plants and soils.
Methods
In consideration of the areas and distributions of major forest types, 212 sampling plots, covering different age classes and origins (natural forests vs. planted forests), were surveyed in Gansu Province in northern China. Field investigations were conducted for vegetation layers (trees, shrubs, herbs and litter), soil profiles, and sampling of both plant materials and soils for laboratory analyses. Regional carbon stocks were calculated by up-scaling the carbon densities of all forest types with their corresponding areas. Carbon sequestration rate was estimated by referencing the reports of national forest inventory data for different periods.
Important findings Forest carbon stocks at the provincial scale were estimated at 612.43 Tg C, including 179.04 Tg C in biomass and 433.39 Tg C in soil organic materials. Specifically, natural forests stored 501.42 Tg C, approximately 4.52 times than that of the plantations. Biomass carbon density in both natural forests and plantations showed an increasing trend with stand age classes, and was greater in natural forests than in plantations within the same age classes. Soil carbon density also increased with stand age classes in natural forests, but the highest value occurred at the pre-mature stage in plantations. The weighted average of regional biomass carbon density was at 72.43 Mg C·hm^-2, with the average value of 90.52 Mg C·hm^-2 in natural forests and 33.79 Mg C·hm^-2 in plantations, respectively. In 1996, vegetation stored 132.47 Tg C in natural forests and 12.81 Tg C in plantations, respectively, and the values increased to 152.41 and 26.63 Tg C in 2011, with the mean carbon sequestration rates of 1.33 and 0.92 Tg C·a^-1. Given that young and middle-aged forests account for a large proportion (62.28%) of the total forest areas, the region is expected to have substantial potential of carbon sequestration.     

中国森林植被碳库的动态变化及其意义

利用1949年至1998年间7次森林资源清查资料,结合使用森林生物量实测资料,采用改良的生物量换算因子法,推算了中国50年来森林碳库和平均碳密度的变化,分析了中国森林植被的CO2源汇功能,结果表明,70年代中期以前,主要由于森林砍伐等人为作用,中国森林碳库和碳密度都是减少的,碳储量减少了0．62PgC（Pg＝10^15g),年均减少约0．024PgC。之后,呈增加趋势。在最近的20多年中,森林碳库由70年代末期的4．38PgC增加到1998年的4．75PgC,共增加0．37PgC,年平均增加0．022PgC。这种增加主要由人工造林增加所致。20多年来,由于人工林增加导致碳汇增加0．45PgC,年平均增加吸收0．021PgC／a。人工林的平均碳密度也显增加,共增加了约一倍。这除了人工成林增多外,气温上升和CO2浓度施肥也可能是促进森林生长的重要因子。     

Net biome production of the Amazon Basin in the 21st century

Global change includes multiple stressors to natural ecosystems ranging from direct climate and land‐use impacts to indirect degradation processes resulting from fire. Humid tropical forests are vulnerable to projected climate change and possible synergistic interactions with deforestation and fire, which may initiate a positive feedback to rising atmospheric CO₂. Here, we present results from a multifactorial impact analysis that combined an ensemble of climate change models with feedbacks from deforestation and accidental fires to quantify changes in Amazon Basin carbon cycling. Using the LPJmL Dynamic Global Vegetation Model, we modelled spatio‐temporal changes in net biome production (NBP); the difference between carbon fluxes from fire, deforestation, soil respiration and net primary production. By 2050, deforestation and fire (with no CO₂ increase or climate change) resulted in carbon losses of 7.4–20.3 Pg C with the range of uncertainty depending on socio‐economic storyline. During the same time period, interactions between climate and land use either compensated for carbon losses due to wetter climate and CO₂ fertilization or exacerbated carbon losses from drought‐induced forest mortality (?20.1 to +4.3 Pg C). By the end of the 21st century, depending on climate projection and the rate of deforestation (including its interaction with fire), carbon stocks either increased (+12.6 Pg C) or decreased (?40.6 Pg C). The synergistic effect of deforestation and fire with climate change contributed up to 26–36 Pg C of the overall decrease in carbon stocks. Agreement between climate projections (n=9), not accounting for deforestation and fire, in 2050 and 2098 was relatively low for the directional change in basin‐wide NBP (19–37%) and aboveground live biomass (13–24%). The largest uncertainty resulted from climate projections, followed by implementation of ecosystem dynamics and deforestation. Our analysis partitions the drivers of tropical ecosystem change and is relevant for guiding mitigation and adaptation policy related to global change.     

20th Century Carbon Budget of Forest Soils in the Alps

Dendrochronological studies and forest inventory surveys have reported increased growth and biospheric carbon (C) sequestration for European forests in the recent past. The potential of concomitant changes in forest soil C stocks are not accounted for in the IPCC guidelines for national greenhouse gas inventories. We developed a model-based approach to address this problem and assess the role of soils in forest C balance in the European Alps. The decomposition model FORCLIM-D was driven by long-term (that is, 1900–1985 AD) litter input scenarios constructed from forest inventory data, region-specific dendrochronological basal area indices, and time series of anthropogenic litter removal. The effect of spatial climate variability on organic matter decomposition across the case study region (Switzerland) was explicitly accounted for by constant long-term annual means of actual evapotranspiration and temperature. Uncertainties in forest development, litter removal, fine root litter input, and dynamics of forest soil C were studied by an explorative factorial sensitivity analysis. We found that forest soils contribute substantially to the biospheric C sequestration for Switzerland: Our “best estimate” yielded an increase of 0.35 Mt C/y or 0.33 t C/(ha y) in forest soils for 1985, that is, 27% of the C sequestered by forest trees (BUWAL 1994). Uncertainties regarding C accumulation in forest soils were substantial (0.11–0.58 Mt C/y) but could be reduced by estimating forest soil C stocks in the future. Whereas soils can be important for the C balance in naturally regrowing forests, their C sequestration is negligible (less than 5%) relative to anthropogenic CO₂ emissions in Western Europe at present. Received 25 August 1998; accepted 17 March 1999.     

Declining Amazon biomass due to deforestation and subsequent degradation losses exceeding gains

In the Amazon, deforestation and climate change lead to increased vulnerability to forest degradation, threatening its existing carbon stocks and its capacity as a carbon sink. We use satellite L-Band Vegetation Optical Depth (L-VOD) data that provide an integrated (top-down) estimate of biomass carbon to track changes over 2011–2019. Because the spatial resolution of L-VOD is coarse (0.25°), it allows limited attribution of the observed changes. We therefore combined high-resolution annual maps of forest cover and disturbances with biomass maps to model carbon losses (bottom-up) from deforestation and degradation, and gains from regrowing secondary forests. We show an increase of deforestation and associated degradation losses since 2012 which greatly outweigh secondary forest gains. Degradation accounted for 40% of gross losses. After an increase in 2011, old-growth forests show a net loss of above-ground carbon between 2012 and 2019. The sum of component carbon fluxes in our model is consistent with the total biomass change from L-VOD of 1.3 Pg C over 2012-2019. Across nine Amazon countries, we found that while Brazil contains the majority of biomass stocks (64%), its losses from disturbances were disproportionately high (79% of gross losses). Our multi-source analysis provides a pessimistic assessment of the Amazon carbon balance and highlights the urgent need to stop the recent rise of deforestation and degradation, particularly in the Brazilian Amazon.     

Assessing the effect of climate change on carbon sequestration in a Mexican dry forest in the Yucatan Peninsula

Assessing the effect of climate change on carbon sequestration in tropical forest ecosystems is important to inform monitoring, reporting, and verification (MRV) for reducing deforestation and forest degradation (REDD), and to effectively assess forest management options under climate change. Two process-based models, Forest-DNDC and Biome-BGC, with different spatial modeling scales were evaluated to estimate the potential effect of climate change on carbon sequestration in a tropical dry semi-deciduous forest in the Yucatan Peninsula of Mexico. The results from the simulations using the two models show that carbon sequestration in this dry forest is highly sensitive to warming. Carbon uptake in this forest may increase or decrease slightly with a corresponding increase or decrease in precipitation; however, with an increase in temperature, carbon uptake may decrease significantly, showing that warming may be the main climate factor that impacts carbon storage in this tropical dry forest. Model performance evaluation indicates that both models may be used to estimate C stocks, but DNDC may be better than BGC for assessing the effect of climate change on C dynamics.     

Soil organic carbon stocks in China and changes from 1980s to 2000s

The estimation of the size and changes of soil organic carbon (SOC) stocks is of great importance for decision makers to adopt proper measures to protect soils and to develop strategies for mitigation of greenhouse gases. In this paper, soil data from the Second State Soil Survey of China (SSSSC) conducted in the early 1980s and data published in the last 5 years were used to estimate the size of SOC stocks over the whole profile and their changes in China in last 20 years. Soils were identified as paddy, upland, forest, grassland or waste‐land soils and an improved soil bulk density estimation method was used to estimate missing bulk density data. In the early 1980s, total SOC stocks were estimated at 89.61 Pg (1 Pg=10³ Tg=10¹⁵ g) in China's 870.94 Mha terrestrial areas covered by 2473 soil series. In the paddy, upland, forest and grassland soils the respective total SOC stocks were 2.91 Pg on 29.87 Mha, 10.07 Pg on 125.89 Mha, 34.23 Pg on 249.32 Mha and 37.71 Pg on 278.51 Mha, respectively. The SOC density of the surface layer ranged from 3.5 Mg ha⁻¹ in Gray Desery grassland soils to 252.6 Mg ha⁻¹ in Mountain Meadow forest soils. The average area‐weighted total SOC density in paddy soils (97.6 Mg ha⁻¹) was higher than that in upland soils (80 Mg ha⁻¹). Soils under forest (137.3 Mg ha⁻¹) had a similar average area‐weighted total SOC density as those under grassland (135.4 Mg ha⁻¹). The annual estimated SOC accumulation rates in farmland and forest soils in the last 20 years were 23.61 and 11.72 Tg, respectively, leading to increases of 0.472 and 0.234 Pg SOC in farmland and forest areas, respectively. In contrast, SOC under grassland declined by 3.56 Pg due to the grassland degradation over this period. The resulting estimated net SOC loss in China's soils over the last 20 years was 2.86 Pg. The documented SOC accumulation in farmland and forest soils could thus not compensate for the loss of SOC in grassland soils in the last 20 years. There were, however, large regional differences: Soils in China's South and Eastern parts acted mainly as C sinks, increasing their average topsoil SOC by 132 and 145 Tg, respectively. In contrast, in the Northwest, Northeast, Inner Mongolia and Tibet significant losses of 1.38, 0.21, 0.49 and 1.01 Pg of SOC, respectively, were estimated over the last 20 years. These results highlight the importance to take measures to protect grassland and to improve management practices to increase C sequestration in farmland and forest soils.     

Carbon sequestration by forests in the National Parks of Italy

Abstract

Recent attempts to mitigate global change have brought forestry-based carbon (C) sequestration into sharp focus due to its potential to absorb CO₂ from the atmosphere. However, the consequences of actual forest management practices on C storage capacity are still controversial to a certain extent. Under such a perspective, a distinctive relevant issue concerns the management of forest ecosystems within areas specifically designated for nature conservation. From the analysis of biomass data from forests in the National Parks of Italy, we found that the average forest C stock and sink per unit area is relatively higher within National Parks (81.21 and 2.18 tons ha^?1, respectively) than on the overall national territory (76.11 and 1.12 tons ha^?1 year^?1, respectively). The analysis confirms the influence of ecological conditions and management approach on C sequestration capacity. Although the results of the proposed assessment approach have to be considered as rough estimates, the trial proves interesting, given the relative lack of specific information, at least on a large scale, about C stocks and sinks within forest areas designated for nature conservation, and the direct comparison with those forest areas not designated to such an end. The C storage capacity can be enhanced by increasing the productivity of forests, minimizing the disturbance to stand structure and composition. Extending conservation strategies adopted in National Parks to other forest areas of the national territory would allow the restoration of C sequestration potential, where unsustainable management practices have degraded relatively large stocks of biomass.     

Vegetation Restoration and Its Effects on Carbon Balance in Guangdong Province, China

The significance of the regional carbon (C) balance of vegetation restoration to global change was studied in Guangdong Province, one of the most populated provinces in China. The percentage of the province in forestland cover increased steadily from 26.23% in 1979 to 50.11% in 1998 owing to restoration of forests. During this period, the area increase in the conifer forest was 424.83 × 10⁴ ha, whereas the area in broad-leaved, mixed, and other forests increased by 68.82 × 10⁴, 18.94 × 10⁴, and 60.46 × 10⁴ ha, respectively. C sequestration by forest soils from 1979 to 1998 was 389.36 Mt, equivalent to 1.43 Pg fixed carbon dioxide (CO₂). The total annual CO₂ sequestration by forests and the soils was 118.05 Mt, which was about half of the annual CO₂ emission in Guangdong. The role of forest management and restoration in improving the carbon balance is discussed.     

Temporal patterns of land-use change and carbon storage in China and tropical Asia

Evaluating the annual sources and sinks of carbon from land-use changehelps constrain other terms in the global carbon cycle and may help countries choose how to comply with commitments for reduced emissions. This paper presents the results of recent analyses of land-use change in China and tropical Asia. The original forest areas are estimated to have covered 546×106 ha in tropical Asia and 425×106 ha in China. By 1850, 44% of China's forests had been cleared, and another 27% was lost between 1850 and 1980, leaving China with 13% forest cover (29% of the initial forest area). Tropical Asia is estimated to have lost 26%of its initial forest cover before 1850 and another 33% after 1850. The annual emissions of carbon from the two regions reflect the different histories over the last 150 years, with China's emissions peaking in the late 1950s (at 0.2-0.5 Pg C@a-1) and tropical Asia's emissions peaking in 1990s (at 1.0 Pg C@a-1). Despite the fact that most deforestation has been for new agricultural land, the majority of the lands cleared from forests in China are no longer croplands, but fallow or degraded shrublands. Unlike croplands, the origins of these other lands are poorly documented, and thus add considerable uncertainty to estimates of flux before the 1980s. Nevertheless, carbon emissions from China seem to have decreased since the 1960s to nearly zero at present. In contrast, emissions of carbon from tropical Asia were higher in the 1990s than that at any time in the past.     

中国森林面积变化及其温室气体储量模拟研究

陆地生态系统承载的温室气体对全球碳循环及气候调节服务意义重大,森林生态系统是陆地生态系统的重要组成部分,量化森林对温室气体的储量有利于从生物地球化学角度研究全球变化问题。针对中国森林生态系统承载的温室气体在大尺度上无法有效量化的问题,基于2000与2010年两期土地利用数据和前人的相关研究,通过一个生态系统温室气体值模型,模拟得到中国森林生态系统承载的三大主要温室气体(CO_2,CH_4,N_2O)的量。结果表明:(1)中国森林生态系统的面积从2000年的224.3×10~6 hm~2略增到2010的224.6×10~6 hm~2;其中落叶阔叶林、常绿阔叶林和针叶林的面积减少,而混交林与灌木林的面积增加;(2)对应地,2000和2010年中国森林的温室气体储量分别为154.03和154.37 Pg CO_2当量,10年间增加了0.34 Pg CO_2当量。其中,常绿针叶林、常绿阔叶林、落叶阔叶林在研究时段内的GHG储量减少,而混交林和灌木林增加。分区来看,温室气体储量增长较多的区域有华北、西北与西南地区,分别增长了0.13 Pg CO_2、0.12 Pg CO_2与0.15 Pg CO_2当量。温室气体储量减少较明显的是东北地区,减少了约0.1 Pg CO_2当量。本研究分别用本地化参数和模型自带参数,首次尝试对中国森林生态系统的GHG储量进行了模拟研究,并与他人的研究做了对比分析。研究同时发现,当前的相关研究存在很多不确定性,未来需要多源数据和方法提升精度,而模型模拟是一个重要的手段。