The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA.
Ecol Appl. 2011 Apr;21(3):750-63. doi: 10.1890/09-1957.1.
Tropical ecosystems play a large and complex role in the global carbon cycle. Clearing of natural ecosystems for agriculture leads to large pulses of CO2 to the atmosphere from terrestrial biomass. Concurrently, the remaining intact ecosystems, especially tropical forests, may be sequestering a large amount of carbon from the atmosphere in response to global environmental changes including climate changes and an increase in atmospheric CO2. Here we use an approach that integrates census-based historical land use reconstructions, remote-sensing-based contemporary land use change analyses, and simulation modeling of terrestrial biogeochemistry to estimate the net carbon balance over the period 1901-2006 for the state of Mato Grosso, Brazil, which is one of the most rapidly changing agricultural frontiers in the world. By the end of this period, we estimate that of the state's 925 225 km2, 221 092 km2 have been converted to pastures and 89 533 km2 have been converted to croplands, with forest-to-pasture conversions being the dominant land use trajectory but with recent transitions to croplands increasing rapidly in the last decade. These conversions have led to a cumulative release of 4.8 Pg C to the atmosphere, with 80% from forest clearing and 20% from the clearing of cerrado. Over the same period, we estimate that the residual undisturbed ecosystems accumulated 0.3 Pg C in response to CO2 fertilization. Therefore, the net emissions of carbon from Mato Grosso over this period were 4.5 Pg C. Net carbon emissions from Mato Grosso since 2000 averaged 146 Tg C/yr, on the order of Brazil's fossil fuel emissions during this period. These emissions were associated with the expansion of croplands to grow soybeans. While alternative management regimes in croplands, including tillage, fertilization, and cropping patterns promote carbon storage in ecosystems, they remain a small portion of the net carbon balance for the region. This detailed accounting of a region's carbon balance is the type of foundation analysis needed by the new United Nations Collaborative Programmme for Reducing Emissions from Deforestation and Forest Degradation (REDD).
热带生态系统在全球碳循环中发挥着重要而复杂的作用。为了发展农业而清除自然生态系统会导致大量二氧化碳释放到大气中，这些二氧化碳来自陆地生物量。与此同时，剩余的完整生态系统，特别是热带森林，可能会从大气中吸收大量的碳，以应对包括气候变化和大气中二氧化碳增加在内的全球环境变化。在这里，我们采用了一种方法，该方法整合了基于普查的历史土地利用重建、基于遥感的当代土地利用变化分析以及陆地生物地球化学模拟模型，以估计巴西马托格罗索州 1901 年至 2006 年期间的净碳平衡。在此期间，我们估计该州 925225 平方公里中有 221092 平方公里已转变为牧场，89533 平方公里已转变为耕地，森林向牧场的转变是主要的土地利用轨迹，但在过去十年中，向耕地的转变迅速增加。这些转变导致了 48 亿公吨碳向大气的累积释放，其中 80%来自森林砍伐，20%来自塞拉多的砍伐。同期，我们估计残余的未受干扰的生态系统因 CO2 施肥而积累了 0.3 亿公吨碳。因此，马托格罗索州在此期间的净碳排放为 45 亿公吨。自 2000 年以来，马托格罗索州的净碳排放平均为 1460 万吨碳/年，与同期巴西的化石燃料排放相当。这些排放与种植大豆的耕地扩张有关。尽管包括耕作、施肥和种植模式在内的耕地替代管理方案促进了生态系统的碳储存，但它们在该地区的净碳平衡中所占比例仍然很小。对一个地区碳平衡的这种详细核算，是新的联合国减少森林砍伐和森林退化所致排放(REDD)合作方案所需的基础分析类型。
