Assessment of stable aspen communities on the Roan Plateau, Colorado
Date
2017
Authors
Correia, Kelsey M., author
Cheng, Antony S., advisor
Pelz, Kristen, advisor
Sibold, Jason, committee member
Journal Title
Journal ISSN
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Abstract
Since the late 20th century, a growing scientific debate over the prospective future decline or persistence of aspen cover across North America has prompted interest in understanding aspen structure and regeneration dynamics over regional and landscape scales. While research has heavily focused on 'seral' aspen dynamics in response to altered fire regimes and conifer encroachment, less is understood over 'stable' aspen dynamics, as defined by their ability to maintain aspen dominate overstories with little to no conifer presence. This research focused on the stable aspen atop Colorado's Roan Plateau, found in non-contiguous 'island-like' patches among the Plateau's prevalent and narrow ridges. These unique patches of stable aspen are believed to be susceptible to increasing temperatures and drought conditions and yet, there is little known of their regeneration and stand dynamics. This research's main objective was to characterize the aspen on the Roan Plateau to better understand stable aspen stand dynamics by identifying the dominant decades and patterns of aspen establishment, the distribution of aspen mortality and regeneration across the Plateau and land ownerships, and investigate any likely drivers for aspen regeneration with varying browsing pressure and environmental site characteristics. I examined 30 aspen stands, 15 on public lands and 15 on a private ownership, using established forest inventory protocols. All of the aspen stands sampled on the Plateau were characterized as stable, with 70% of the stands showing continuous aspen establishment occurring through the late 19th century through the 21st century. Aspen mortality and regeneration varied across the Plateau and land ownerships, with 83% of sampled stands considered self-replacing based on regeneration and subcanopy tree densities. While annual mean temperature, aspect, percent stand mortality, and percent browsing damage were found to significantly influence aspen regeneration, the most significant predictor variable threshold was percent stand mortality. Browsing damage negatively influenced regeneration densities, but a one-meter3 exclosure cage did not significantly promote aspen suckering from ungulate browsing. Without the threat of conifer encroachment in these stable aspen stands, I identify the largest influence to aspen regeneration, and subsequently aspen persistence on the Roan Plateau, to be browsing damage occurring at levels that exceed regeneration establishment with compounding influences from senescing canopy trees and stress from increased temperatures and drought events into the future. Future monitoring of the stable aspen on the Roan Plateau is necessary to understand their temporal and natural range of variation.