The Effects of Rainfall Exclusion on Water Use, Flammability and Carbon Storage in Forests and Grass-Dominated Ecosystems of Amazonia and the Cerrado

建议#：DEB-9707556研究员(S)：海普斯塔德和戴维森研究所：伍兹霍尔研究中心近年来与厄尔尼诺-南方涛动现象有关的严重干旱在热带地区很常见，许多气候模式预测热带地区的降雨量将长期减少。多达200万平方公里的亚马逊森林，占世界潮湿热带森林的五分之一，依赖于每年深层(2米)土壤水分的补给，因此容易受到降雨减少的影响。结果，通常像防火林带一样穿过森林-牧场景观的森林变得易燃。易受干旱影响的林下树和阔叶树的死亡导致地上生物量的减少。土壤水分的枯竭还会导致地下生产的减少，从而导致土壤呼吸和土壤碳储存的减少。在这项研究中，将比较两种雨型和土壤相似的热带森林对干旱的反应：亚马逊东部的高常绿森林和巴西中部塞拉多地区的低常绿森林。这些森林对降雨量减少的反应将与两个地区普遍存在的以草为主的生态系统的反应进行比较。降雨量将通过试验减少，使用一个透明的便携式面板网络，在最多雨的月份拦截即将到来的雨水，并将这些水输送到地块之外。对照样地和排除降雨样地的冠层物候和树干液流、精细燃料特性、土壤呼吸和水分、根系分布和树木死亡率将进行比较。

ABSTRACT PROPOSAL # : DEB-9707556 INVESTIGATOR(S) : NEPSTAD AND DAVIDSON INSTITUTION: WOODS HOLE RESEARCH CENTER Severe droughts associated with the El Nino-Southern Oscillation phenomenon (ENSO) have been common in tropical regions in recent years, and long-term reductions in rainfall in the tropics are predicted from many climate models. Up to two million km2 of Amazonian forest, representing one-fifth of the world's moist tropical forest, depends on annual recharge of deep (2 m) soil moisture, and is therefore susceptible to rainfall reduction. As a result, forests that normally extend like firebreaks through the forest-pasture landscape become flammable. The mortality of drought-vulnerable understory and hardwood trees leads to a reduction in above-ground biomass. Soil water depletion also leads to a reduction in below-ground production and, hence, in soil respiration and soil carbon storage. In this research, responses to drought of two tropical forests with similar rainfall patterns and soils will be compared: a high evergreen forest of eastern Amazonia and a low evergreen forest of the Cerrado Region of central Brazil. The response of these forests to rainfall reduction will be compared to the response of the grass-dominated ecosystems that are common in both regions. Rainfall will be reduced experimentally using a network of clear, portable panels that intercept incoming rain during the rainiest months and transport this water outside of the plots. Canopy phenology and stem sapflow, fine fuel characteristics, soil respiration and water content, root distribution and tree mortality will be compared for control and rainfall-excluded plots.