PARENT SESSION
Oral Session #49: Restoration Ecology. Presiding: J. Callaway.
Wednesday, August 8, 2001. 1:00 PM to 4:30 PM. Madison Ballroom D.
Effects of ecological restoration treatments on legumes, shrubs and C4 grasses.
Springer, Judith1, Fule, Peter1, Moore, Margaret1, Covington, W. Wallace1, 1
ABSTRACT- Recovery of understory plant communities is essential following ecological restoration treatments in southwestern ponderosa pine forests. Historical evidence suggests that a century of active fire suppression, along with heavy domestic and wild ungulate grazing and browsing has led to canopy closure and declines in abundance of shrubs, legumes, and C4 grasses, and increases in non-native species. Restoration of these ecosystems involves thinning small diameter trees and reintroducing low intensity fire. We hypothesize that frequencies of these functional groups should increase following thinning and prescribed burning treatments. To test these hypotheses, post-treatment surveys were conducted for 2 or 4 years at two sites in northern Arizona where cattle were excluded. Populations of C4 grasses had not recovered to pre-treatment levels by post-treatment year 2 or 4, and one site had no naturally regenerating populations of C4 grasses. However, prescribed fire substantially enhanced legume abundance (500% or more in some cases) one year after burning, but species richness remained low, ranging from 0 to 4 species per plot post-treatment. Shrub abundance also increased following restoration treatments. This study demonstrates the need for long-term monitoring in these forests, and suggests that areas undergoing restoration are highly variable between and within landscapes. Decisions to seed or conduct repeated burnings should be dependent on pre-treatment conditions (such as the abundance of species in the soil seed bank) and should be evaluated on a case-by-case basis.
KEY WORDS: ponderosa pine, legumes, C4 grasses, shrubs