PARENT SESSION
Poster Session #17: Restoration using Fire.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Fire frequency and tree canopy influences on plant species diversity in oak savannas and woodlands.

PETERSON, DAVID^*,1, REICH, PETER², ¹ USDA Forest Service, Wenatchee, WA² University of Minnesota

ABSTRACT- Creating and maintaining high plant community diversity is a priority in restoration ecology and ecosystem management. We studied prescribed fire frequency and overstory tree canopy effects on plant species diversity in oak savannas and woodlands in east-central Minnesota. We surveyed plant communities on 29 permanent plots representing management units treated with 0-26 fires over a 34-yr period. We calculated species richness for major plant functional groups (grasses, forbs, and woody species) and all species combined. Grass and forb species richness increased with fire frequency, up to 4-5 fires per decade. Woody species richness declined with increasing fire frequency. Grass and forb richness declined with increasing stand basal area, while understory woody species richness increased with stand basal area, peaking at basal area levels near 20 m²/ha. Community heterogeneity within plots increased with spatial variability in overstory canopy cover; it was highest on savanna sites featuring intermediate stand basal area and aggregated tree spatial patterns. Total plot-scale species diversity (24 quadrats) was lowest in densely shaded forests, apparently due to a reduced pool of species that tolerate low-light conditions, and was highest on savanna sites with variable overstory canopy cover. Plot-scale species richness was also maximized at fire frequencies of 3-5 fires per decade; such frequencies also help maintain open savanna structure. Our results suggest that frequent fires and structural heterogeneity both contribute to high species richness in midwestern oak savannas.

KEY WORDS: species diversity, fire frequency, oak savanna, restoration ecology