Category: Ecological Research
Title: Plant Community Variability in Ponderosa Pine Forest Has Implications for Reference Conditions
Author: * Gildar, C.N. , * Fule, P.Z. , * Covington, W.W.
Subject: Grand Canyon, Fire ecology, Kaibab Plateau, Ecological Restoration, Ponderosa pine (Pinus ponderosa)
Abstract: Ponderosa pine plant community and forest structure were compared among three stands in Grand Canyon National Park, Arizona: one stand had 120 years of artificial fire exclusion (NOBURN) and the other two nearby stands had been frequently burned (BURN-E and BURN-W). These forests are valuable places to gauge anthropogenic changes associated with European settlement, due to their land history of limited livestock grazing and no logging. Precipitation varied greatly between sampling years (260 mm in 2000, 505 mm in 2001). Tree density was significantly higher at NOBURN (1424 trees ha-1) with significantly higher rotten coarse woody debris (23.2 Mg ha-1) and duff depth (4.3 cm) than at the burned sites, as expected in the absence of fire. Although species richness was not significantly different among sites (48-89 species), richness differed significantly by year. Shannons index of diversity increased by approximately 10(percent) from the dry year to the wet year on all sites. Community composition and plant cover at NOBURN differed significantly from the two burned sites in both years in non-metric multidimensional scaling ordinations. Increasing duff depth was related to decreased plant cover. Two of the three dominant species were different at the fire-excluded site compared to the burned sites. We conclude that although plant community structure was related to fire history, environmental stress and within-stand variability were also important drivers. We suggest selecting reference sites in close proximity to the site to be restored and using a multi-scale, multi-year, multi-site approach to measure reference conditions in ponderosa pine.
Source: Natural Areas Journal
Publisher: Natural Areas Association, http://www.naturalarea.org