PARENT SESSION
Oral Session #59: Conservation Ecology: Terrestrial Biodiversity. Presiding: K. Schulz.
Thursday, August 9, 2001. 8:00 AM to 12:15 PM. Madison Ballroom D.
Response of understory herb species richness and cover to Acer saccharum regeneration thickets.
Schulz, Kurt1, Marriage, Tara 1, Nauertz, Elizabeth2, Garske, Steven2, Zasada, John3, Buckley, David4, Crow, Thomas3, 1 2 3 4
ABSTRACT- Sugar maple dominates the canopy and herb layer of mesic stands in northern Wisconsin and Upper Michigan. Seedlings (< 1 m tall) respond vigorously to increases in light availability caused by canopy opening, forming convex thickets. Thickets > 2 m tall cast dense, uniform shade over the forest floor, and continue to do so for several decades until individuals reach pole size. Field observations suggest that natural thickets > 2 m tall exhibit a reduced herbaceous understory. Such thickets are common in selectively managed stands, and could have negative effects on herb species populations and diversity. We sampled summer understory herb species richness and cover, as well as surrounding seedling, sapling, and tree populations in randomly chosen thicket and control plots in the Sylvania Wilderness, Upper MI. As the maple seedling population matures into the sapling size class, herb species richness and cover decline. Herbs in thicket understories appear to be in poorer condition and of smaller size. Assessed on a post hoc basis, there is little relationship between the neighborhood of surrounding trees and the existence of thickets. Because regeneration thickets are a common outcome of most commercial tree harvest systems, risks to understory communities probably exist in most harvested stands.
KEY WORDS: forest herbs, plant diversity, forest management, competition