Ecologists and natural resource managers alike now recognize that landscapes exhibit a high degree of heterogeneity, both spatially and temporally. The spatial heterogeneity of terrestrial landscape is the result of differences in landcover, local and regional climate, past and ongoing geomorphological processes that alter landform and soils, and human disturbance. Gower and colleagues, working in northern Wisconsin, have shown that many important structural and functional characteristics differ among the major upland forest ecosystems and are directly or indirectly related to geologic landform and soils. Nutrient cycling characteristics such as forest floor carbon and nitrogen mean residence time also differ among these forests (Fassnacht and Gower 1996).
Superimposed on the complex mosaic forested landscape of north central Wisconsin is one of the highest density of lakes in the world (Magnuson and Frost 1982). The hydrologic and geochemical characteristics of the North Temperate Lake – Long Term Ecological Research (NTL-LTER) lakes differs substantially, but the cause(s) can not be fully explained by within lake processes. To date, North Temperate Lakes Long Term Ecological Research (NTL-LTER) scientists have focused exclusively on aquatic ecosystems; however, there are a number of terrestrial ecosystem processes that influence the quality and quantity of water entering the groundwater system that connects terrestrial and aquatic ecosystems.
Despite the great need to understand; (1) the influence of landform, topographic position, and their interaction on the structure and function of forest ecosystems and (2) the transfer of energy and water across heterogeneous landscapes and between adjacent land- and water-scapes (Gosz 1986), the direct and indirect effects of spatial pattern on ecological processes are not well studied (Turner 1989). Peterjohn and Correl (1984) demonstrated the beneficial role riparian forests play when juxtaposed between agricultural and aquatic ecosystems, emphasizing the need to understand processes regulating carbon, water and nutrient cycling within a stand and how that stand "interacts" with stands downslope. The objective of this study is to elucidate the influence of natural vegetation, management regime and climate change on the carbon, nitrogen and water budgets of forest ecosystems and their interaction with aquatic systems via the groundwater using empirical data and process-based models.
Objectives
Measure key components of the forest carbon and hydrologic cycle for two catenas on contrasting landform/soil types. We note that the objective is NOT to develop complete carbon and hydrologic budgets, but only to measure key parameters and processes that reflect the cumulative environmental controls on forest growth and are simulated in the process-based models that we propose to use.
Develop a forest growth model using simplified concepts of absorbed photosynthetically active radiation, radiation use efficiency, environmental constraints on stomatal conductance and carbon allocation.
Compare estimates of NPP derived from a simple epsilon and complex canopy photosysthesis models (modified FOREST-BGC) to measured NPP values for a variety of forests to ascertain the appropriate level of complexity needed to adequately characterize two key process: canopy photosynthesis and evapotranspiration.
Comparison of an existing integration of forest ecosystems process models with a hydrologic model (RHESSys-D, Mackey and Band 1996) that moves water based on indices of topographic position, to a similar coupling that incorporates a hydrology model that explicitly routes flow (MODFLOW, Cheng and Anderson 1993).
Couple a dynamic carbon allocation forest ecosystem process model to a hydrologic model that simulates water budgets to examine the influence of geologic landform, environmental factors, land use, and potential climate change on ground water quality and quantity and how this would influence aquatic ecosystems in northern Wisconsin.
