PARENT SESSION
Poster Session #32: Plant Ecology I.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Multivariate effects on species richness in floodplain oak savannas.

Meisel, Jennifer¹, Trushenski, Nicole¹, Weiher, Evan¹, ¹

ABSTRACT- In order to address the classic species richness - biomass relationship, we investigated how a suite of environmental factors affect species richness in 168 quadrats (0.25 m²) from 10 floodplain oak savannas located along the Chippewa River in western Wisconsin. There is a strong unimodal (humped) relationship between species richness and biomass, and for species richness and many environmental factors. These relationships appear to be triangular envelopes constraining richness below some upper limit. We used the EcoSim program (Gotelli and Entsminger) to test for triangular patterns. The upper limit of species richness significantly declined with increasing biomass, biomass heterogeneity (coefficient of variation), light reaching the soil surface, tree canopy cover, fire frequency, years since burning, and several measures of soil quality. The upper limit of species richness significantly increased with soil moisture. The next step is to use Structural Equation Modeling to untangle these multiple dependencies and to test Grace and Pugesek's general model, which suggested that light reaching the soil surface is the main driver affecting species richness. We expect that our data will not conform to their model because of the complex effects of canopy trees on light reaching the ground (due to open-grown oaks within the savanna and adjacent forest patches).

KEY WORDS: richness, diversity, savanna, prairie