Previous work shows that a large fraction of water in seasonally moist tropical forests is withdrawn from below 3.5 meters (often the deepest layer that many ecosystem models represent) during the dry season to support evergreen canopies. While it has been known for nearly two decades that a large fraction of the Amazon is comprised of deeply rooted trees, much remains unknown as to how such a small fraction of a tree's total root biomass can play such a big role in ameliorating dry season drought stress. Further, belowground ecological processes in comparison to their aboveground counterparts remain poorly understood in general. While monitoring root growth and decay is notoriously difficult, we are employing the current best approach for observing fine root phenology by using minirhizotrons (clear plastic tubes inserted into the soil) to conduct regular imaging and digitization of thousands of individual fine roots. We are seeking to understand what the seasonal course of fine root growth and death (and hence, turnover), looks like for a moist tropical forest, and relate it to observed aboveground patterns of dry season leaf flush and vertical gradients in water availability.
Given the importance of deep soil water reserves for seasonally moist tropical forests, we are also seeing to better understand the interaction between moisture availability and vegetation dynamics. Moisture measurements are limited by their very small spatial scale (point measure), and hence provide little information as to the variation of this limiting resource across the landscape. We are employing Electrical Resistance Tomography in conjunction with collaborators at Michigan State University to study how the belowground moisture environment changes in the transition from intact forest into large treefall gaps, which are a predominant feature of tropical forests. Our goal is to better understand how plant phenological patterns and rooting habit influence the evolution of the belowground moisture environment in wet to dry season transitions, in time giving us a better picture of how the rooting zone moisture environment (and hence overall water stress) of the forest changes during gap phase regeneration.
Students and Technicians: Brad Christoffersen, PhD Candidate, Ecology and Evolutionary Biology, University of Arizona; Kleber Silva Campos, Field Technician and Bolsista, Universidade Federal do Oeste do Pará (UFOPA), Brazil; Cleuton Pereira, Field Technician, Empresa Brasileira de Pesquisa Agropecuaria (Embrapa), Brazil.
Project Collaborators: Raimundo Cosme de Oliveira, Empresa Brasileira de Pesquisa Agropecuaria (Embrapa), Brazil; Rafael Oliveira, Assistant Professor, Universidade Estadual de Campinas (UNICAMP), Brazil; Javier Espeleta, Director, Central Científico Tropical, Costa Rica; Remke van Dam, Assistant Professor, Geological Sciences, Michigan State University.