A collaborative research project will be conducted by the University of Washington, Yale University, and Oregon State University for an experimental study of ecosystem responses to tree-fall gaps and spatial and temporal relationship between above- and belowground gaps. It is hypothesized that mechanisms of community and ecosystem responses to gaps can only be understood if both above- and belowground structures and resources are considered. An experiment to determine the size of aboveground gap needed to form a belowground gap in mature and old-growth coniferous forests will be imposed. The investigators will also measure how above-and belowground structural changes are reflected in resource availability and loss and in vegetative response. To examine the hypotheses, the team will create tree- fall gaps of ranging from small to large in five sizes (0, 2, 8 and 16 and 32 trees removed) in reach of two stand developmental stages: mature (understory reinitiation), and old growth. Above and belowground sampling will be conducted to provide an estimate of the mean of the gap and will consist of root biomass (separated into tree, shrub and herb components), N leaching below the rooting zone, and soil temperature and moisture, light level determinations, shrub and herb biomass, seed germination and monitoring of advanced regeneration. In the old-growth stands, above-and belowground resources (plus net N mineralization) and vegetative biomass will be sampled more intensively to provide not only an estimate of the gap mean but of the within-gap spatial patterns. In addition, trenching experiments will be established in the old-growth stands to test the relative importance of above- and belowground resources on tree establishment and growth and develop predictive models of plant response to resources. The three-institution project team is excellent. Research sites and facilities are first rate. Results should be important to both the fundamental understanding of forest ecology and to forest resource management.
