JOHNSTON et al. DEB-9615326 Ponds and meadows created by beaver are key components of the regulation of overall water and nutrient fluxes over large areas in North America. These beaver ponds and meadows occur in landscape positions ideally suited to receive surface runoff, stream flow, and groundwater discharge from upstream sources, giving beaver ponds and meadows a hydrologic control function disproportionately greater than would be inferred by their area alone. Moist graminoid meadows are a key stage through which beaver ponds pass during changes in hydrologic regimes which may govern the dynamics of these landscapes. Building on previous research that has shown N limitation of plant growth in these meadows, this new research will attempt to quantify the relative importance of different N sources in beaver meadows, and the effect of N supply to vegetation on its composition, structure, and productivity. To test these relationships, a spatially explicit model of hydrology and nutrient budgets within beaver ponds and meadows will be coupled to a model of plant growth, canopy allocation, and the vertical light gradient under different nutrient and water regimes. The model will be parameterized using hydrologic data collected in Voyageurs National Park and using greenhouse and mesocosm experiments on species responses to water, light, and nutrients. The model will then be tested against spatial patterns of vegetation along gradients of water depth and nutrient availability in several meadows of different hydrology. This research will provide significant advances in understanding of landscape controls on plant species segregation and productivity via water and nutrient delivery. It will also advance understanding of how species segregation and productivity of graminoid species are controlled in moist ecosystems, in which transient canopy dynamics, rather than total response to nutrients, may be determining community dynamics.
