Document: HOW-3-93-9

Simulating tundra vegetation at varying levels of aggregation: An analysis of functional groupings.

EPSTEIN, H.E.* ¹, F.S.CHAPIN III ², M.D.WALKER ² and A.M.STARFIELD ³

University of Virginia, Charlottesville, VA 22903 USA ¹
University of Alaska, Fairbanks, AK 99775 USA ²
University of Minnesota, St. Paul, MN 55108 USA ³

Abstract:
Grouping organisms into categories based on common traits has been a tool of ecological scientists for some time now. Defining groups of species, examples being life forms and functional types, is an operational procedure, conducted to answer a particular question. This becomes rather practical when performing analyses at coarse spatial scales, given data limitations and the potential for species redundancy. However, the implications of aggregating organisms for modeling purposes are still unclear. Does averaging the traits of several species into a functional group sufficiently represent the dynamics of the individual components? How much variability in the system is lost when we aggregate species into groups? In an attempt to address these questions, we examined how the level of vegetation aggregation affected a variety of ecosystem properties using a regional-scale model of arctic tundra ecosystems (ArcVeg). We used four levels of aggregation: species (15 dominant ones), functional groups (7), life forms (4) and vegetation type (1). All model parameters were averaged across species to determine the parameters of the aggregate vegetation. We found that the level of aggregation consistently affected community composition, total community biomass and ecosystem net primary production (NPP). In particular, aggregation of vegetation (i.e. reduced parameter variability) led to decreases in simulated community biomass. Aggregation of certain parameters led to either no change or an increase in ecosystem NPP.

Keywords: aggregating vegetation, arctic tundra, dynamic vegetation modeling, net primary production, plant community biomass, plant functional groups, regional scale

This abstract is being presented at: 10:45 AM in session:
Oral Session #59: Plant Communities: Vegetative Analysis.