Landscape Assessment of a Stable Aspen Community in Southern Utah, USA
Forest Ecology and Management
Recent reports of rapid die-off of aspen (Populus tremuloides), coupled with vigorous debate over long-term reduction of aspen cover in western North America, has prompted considerable research given the importance of this forest type for economic and non-economic interests. Despite this interest, indicators of aspen conditions are poorly understood, and there is a lack of systematic monitoring of stable aspen landscapes. Stable aspen are defined here as being predominantly aspen overstorey (>80% basal area) with little or no conifer regeneration. We examined a putative stable aspen landscape in southern Utah and addressed (1) stand structure and (2) indicators of decline. We sampled 83 aspen-dominated stands within a 275 km2 landscape using established forest health monitoring protocols. Eighty-four percent of sample stands on Cedar Mountain exhibited stable aspen characteristics. Principal findings include: (1) a relatively uniform age of adults within the study area; (2) approximately 10% crown dieback on half of the plots sampled; (3) roughly 50% of the study plots had greater than 50% of the trees with damage to the bole; (4) about 25% of the adult basal area was dead; and (5) over half the plots had few sub-canopy individuals and/or limited regeneration. Physiographic variables including elevation, slope, and aspect were generally not strong indicators of aspen condition, typically explaining less than 15% of the variation in basal area, mortality, dieback, or damage. Healthy stands were rarely observed in the most drought prone locations, though the inverse was not necessarily true; healthy and unhealthy stands were found in more mesic settings. Principal components analysis identified two clusters of plots that differed considerably in regeneration; however, no other variables differed between these groupings. We suggest exogenous factors such as land-use history or altered disturbance regimes and endogenous factors such as soils and geology influence aspen condition on this landscape. Further research is necessary to test these hypotheses.
Rogers, P.C.; Leffler, A.J.; Ryel, R.J. 2010. Landscape assessment of a stable aspen community in southern Utah, USA. Forest Ecology and Management, 259(3): 487-495.