Human Impacts on Water Use by Deep-Rooted Amazonian Forests

人类正在改变亚马逊高地的景观，从几乎连续不断的高山森林变成牧场、次生林、砍伐森林和原始森林遗迹的马赛克。伴随地球生物圈剧烈变化而来的大规模生态变化，人们知之甚少，但可能非常重要。例如，对这种转变的区域气候影响的最佳预测表明，亚马逊地区在未来几年将变得更加干燥和温暖，巴西中南部的粮食带可能会发生气候变化。我们预测亚马逊森林砍伐后果的能力很差，可以追溯到原始森林和正在取代它们的人为生态系统的比较信息的惊人缺乏，特别是在从贝伦南到戈亚尼亚和西到阿克的主要森林转换区。例如，目前还没有发表过对这一120万平方公里区域的初级和次级生态系统的水文进行比较的研究。对亚马逊生态系统蒸散和水分平衡的唯一基于经验测量的估计是在亚马逊中部和北部的原始森林进行的，远离不断发展的农业前沿。据推测，深层土壤和明显的季节性干旱是“森林转换弧线”的特征，支持以现有潮湿热带森林生态学文献未预测的方式利用水和矿物质营养的根深蒂固的原始森林。这些森林的深层土壤功能，包括碳储存、旱季吸水、湿季蓄水、细根生产、营养吸收是潮湿热带森林研究最少的方面，但必须了解它才能预测伴随森林转化的生态变化。这项关于根深蒂固的亚马逊森林和正在取代这些森林的生态系统用水的研究将有助于检验上述假设。初步研究结果表明，亚马逊流域的新生态系统相对浅根且功能独特。这项研究将为在深根潮湿的热带森林中建立降雨季节模式与根系和树冠动态的关系模型提供基础。

Humans are transforming the upland landscapes of Amazonia from nearly continuous expanses of high forest to mosaics of pasture, secondary forests, logged forests and primary forest remnants. The large-scale ecological changes that accompany this radical alteration of Earth's biosphere are poorly understood, but probably very important. For example, the best predictions of regional climatic impacts of this transformation suggest that Amazonia will be drier and warmer in the years to come and that climatic shifts may follow in the grain belt of south-central Brazil. Our poor ability to predict the consequences of Amazonian deforestation can be traced to a surprising dearth of comparative information for primary forests and the anthropogenic ecosystems that are replacing them, particularly in the major zone of forest conversion extending from Belem south to Goiania and west to Acre. For example, there are no published studies comparing the hydrology of primary and secondary ecosystems of this 1.2 M km2 region. The only estimates of evapotranspiration and water balance for Amazonian ecosystems based on empirical measurements were conducted on primary forests in central and northern Amazonia, far from the advancing agricultural frontier. It is hypothesized that the deep soils and pronounced seasonal drought that characterize the "arc of forest conversion" support deep-rooted primary forests that use water and mineral nutrients in ways that are not predicted by the existing literature on moist tropical forest ecology. Deep-soil functions of these forests, including carbon storage, dry season water uptake, wet season water storage, fine root production, and nutrient uptake are the least studied aspects of moist tropical forest and yet must be understood to predict the ecological changes that will accompany forest conversion. This research on water use by deep-rooted, Amazon forests and the ecosystems that are replacing these forests will assist in testing the hypothesis above. Results from initial studies suggest that the new ecosystems of Amazonia are relatively shallow-rooted and functionally distinct. This study will provide the basis for development of a model relating seasonal patterns of rainfall to root and canopy dynamics in deep-rooted, moist tropical forests.