LTREB: Sustainability of Soil Fertility in Reconstructed Tropical Ecosystems

9318403 Ewel在潮湿的热带地区，维持土壤肥力是森林恢复和可持续发展的主要挑战，在那里，有机质分解迅速，矿物质风化迅速，高降雨量浸出植物生长所必需的营养物质。在控制土壤肥力的许多因素中，有两个可能是非常重要的：植物生命形式的数量（树、棕榈、灌木、藤蔓等）和植物群落被收获或干扰的频率。1991年在哥斯达黎加的La Selva生物站建立的由速生热带树种（Hyeronima、Cordia和Cedrela）组成的复制人工林将用于研究这两个因素对土壤肥力的控制。在一些种植园里，树木是单一栽培的；这些将在1年、4年和16年的间隔中收获和重新种植。其他种植园种植树木和其他生命形式的植物，如棕榈树和类似香蕉的草本植物。浸出是通过土壤水的化学特性和水中营养物质浓度乘以其向下移动的速率来确定的。向下运动将通过一个水平衡模型来估计，该模型结合了土壤的蒸发和蒸腾作用，蒸腾作用来源于能量平衡测量（太阳辐射、风速）、植物通过叶子传递水分的能力（气孔导度）和空气的蒸发能力（来自树冠层的温度和湿度测量）。随着轮作间隔时间的增加和植物生命形式多样性的增加，预计淋滤率会降低。植物群落利用土壤资源的有效性对维持土壤肥力也很重要，而且它也可能随着生物复杂性和收获或干扰的频率而变化。为了评估这种有效性，将通过测量植物和土壤中养分储存和周转的变化来获得养分吸收、恢复和消耗的效率。再加上养分淋失数据，比较林分之间的这些效率将为热带森林恢复和热带土壤的可持续利用提供生态上合理的指导。

9318403 Ewel Maintenance of soil fertility is a major challenge to forest restoration and sustainable development in the humid tropics, where organic matter breaks down quickly, weathering of mineral matter is fast, and high rainfall leaches nutrients essential for plant growth. Among the many factors that control soil fertility, two are likely to be of great importance: the number of plant life forms (trees, palms, shrubs, vines, etc.), and the frequency with which the plant community is harvested or disturbed. Replicated plantations consisting of fast-growing tropical tree species (Hyeronima, Cordia,and Cedrela), established in 1991 at La Selva Biological Station in Costa Rica, will be used to study the controls that these two factors exert on soil fertility. In some of the plantations, the trees are grown in monoculture; these will be harvested and replanted at intervals of 1, 4, and 16 years. Other plantations contain the trees plus plants of other life forms, such as palms and banana-like herbs. Leaching is determined by characterizing the chemistry of soil water and by multiplying the concentrations of nutrients in the water by the rate of its downward movement. Downward movement will be estimated from a water-balance model that incorporates evaporation from the soil and transpiration, which is derived from energy balance measurements (solar radiation, wind speed), the ability of the plants to pass water through their leaves (stomatal conductance), and the evaporative power of the air (from temperature and humidity measurements in the tree canopies). Leaching rates are expected to diminish with increasing time intervals between rotations and with increasing diversity of plant life forms. The effectiveness with which plant communities exploit soil resource is also important to sustaining soil fertility, and it, too, is likely to vary with biotic complexity and frequency of harvest or disturbance. To assess this effectiveness, efficiencies of nutrient uptake, recovery, and us e will be obtained from measures of changes in nutrient storage and turnover in both plants and soil. Coupled with the nutrient leaching data, comparison of these efficiencies among stands will provide ecologically sound guides to tropical forest restoration and the sustainable use of tropical soils.