USDA Forest Service, Rocky Mountain Research Station
Abstract
To test an approach for restoring historical stand densities and increasing plant species diversity of a pinyon-juniper ecosystem, we implemented a demonstration project at two sites (CR and GP) on the Grand Canyon-Parashant National Monument in northern Arizona. Historical records indicated that livestock grazing was intensive on the sites beginning in the late 1800s and continuing through the mid 1900s. Repeat aerial photographs (1940 and 1992) indicated recent increases in stand density and encroachment of trees into formerly open areas. Age distributions indicated that the majority of pinyon trees at both sites were less than 100 years of age and juniper establishment appeared to peak in the late 1800s to early 1900s, although some junipers had establishment dates as early as 1700-1725. Pretreatment understory communities were sparse (50% pinyon mortality, which was positively related to tree size and age. The demonstration treatment consisted of thinning small trees (< 25 cm diameter at root collar (DRC)), lopping and scattering thinned trees, and seeding native understory species. Thinning and mortality reduced overstory density from 638 and 832 trees per hectare pretreatment (258 and 337 trees per acre) to 280 and 251 trees per hectare (113 and 102 per acre) posttreatment at CR and GP, respectively. Posttreatment densities were similar to those suggested for the late 1800s by dendrochronological stand reconstructions. Thinning small diameter pinyon increased residual quadratic mean diameter (QMD) at CR and the relative importance of juniper at both sites. Live canopy fuels were reduced by treatment at CR and by thinning plus beetle-related mortality at GP. Although thinning slash was lopped and scattered, woody surface fuels were not significantly different between treated and control units at either site, perhaps due to the small size of thinned trees and the large interspace areas into which slash was scattered. Treatment had no immediate effects on herbaceous cover or species richness, both of which may take more time to develop. Further monitoring will help to clearly evaluate the effectiveness of this treatment for satisfying restoration and conservation goals
