Large-scale ranching and logging operations are converting mature, forested ecosystems of Amazona to frequently-burned, regrowth forest. In a mature forest relict at the heart of an Amazonian ranching and lumbering center, root systems extend to at least 12 m depth and apparently enable this ecosystem to maintain carbon assimilation and transpiration through the 5 month dry season. The project will evaluate the hypothesis that frequently- burned, regrowth forests (1) are shallow-rooted, (2) extract less water from the soil during the dry season and (3) store less rainfall in the soil during the wet season in comparison to the mature forests that they are replacing. These prediction are tested by a comparative study of root distribution, fine root growth, soil water availability, soil water uptake and rainfall storage in mature forest, intact regrowth forest, and recently- burned regrowth forest. This will be accomplished using a network of soil shafts, 7 m deep, in which measurements of root distribution and monitoring spatial and temporal patterns of root growth, soil water potential and soil water content will be observed. The studies proposed here will ask basic questions about an important, but previously neglected aspect of ecosystem structure and function within the context of a rapidly changing tropical landscape. The investigator are well qualified for this type of research and have more than adequate institutional support.
