Twenty-year change in aspen dominance in pure aspen and mixed aspen/conifer stands on the Uncompahgre Plateau, Colorado, USA
Citation
Frederick W Smith, and Amy E Smith, Twenty-year change in aspen dominance in pure aspen and mixed aspen/conifer stands on the Uncompahgre Plateau, Colorado, USA: .
Summary
Reports of decreasing quaking aspen (Populus tremuloides) cover in forests of the western USA have caused concern about the long-term persistence of aspen on landscape scales. We assessed changes in overstory aspen dominance on the Uncompahgre Plateau in western Colorado over a 20 year period. We measured stand density, species composition and regeneration in 53 undisturbed, mature pure aspen, pure conifer, and mixed aspen/conifer stands originally inventoried between 1979 and 1983. Ages of overstory and understory trees were used to evaluate long-term change in regeneration and overstory development. While pure aspen stands occupy 16% of the study area, mixed aspen and conifer stands cover 62% of the forested landscape on the Uncompahgre [...]
Summary
Reports of decreasing quaking aspen (Populus tremuloides) cover in forests of the western USA have caused concern about the long-term persistence of aspen on landscape scales. We assessed changes in overstory aspen dominance on the Uncompahgre Plateau in western Colorado over a 20 year period. We measured stand density, species composition and regeneration in 53 undisturbed, mature pure aspen, pure conifer, and mixed aspen/conifer stands originally inventoried between 1979 and 1983. Ages of overstory and understory trees were used to evaluate long-term change in regeneration and overstory development. While pure aspen stands occupy 16% of the study area, mixed aspen and conifer stands cover 62% of the forested landscape on the Uncompahgre Plateau. Pure aspen stands were self-thinning, but stable over the twenty-year study period, with high amounts of regeneration and without conifer invasion. Mixed stands of aspen and conifer had undergone significant change. In aspen dominated mixed species stands, conifer basal area increased from 10 to 23 m2 ha−1 in the last 20 years, while aspen basal area decreased. In conifer dominated mixed species stands, conifer basal area increased from 18 to 24 m2 ha−1. Most overstory aspen in pure aspen stands were between 80 and 120 years old. Substantial aspen suckering was occurring, but all suckers were <20 years old, indicating lack of current growth into the overstory. Aspen suckering was occurring in mixed species stands, but again, most suckers were <20 years old, and few overstory trees were <100 years old. In contrast, understory and overstory conifers spanned ages from <20 to over 250 years old. Aspen dominance is decreasing in the forested communities of the study area. Pure stands are likely to persist without decline for a considerable time. Mixed stands are likely to continue to experience a decrease in overstory aspen canopy dominance. These changes are probably within the historic range of variability, but restoration of aspen canopy cover consistent with an early- to mid-seral landscape condition would require disturbances such as fire or cutting to create canopy gaps to permit growth of suckers into the overstory of mixed species stands.
Published in Forest Ecology and Management, volume 213, issue 1-3, on pages 338 - 348, in 2005.
