Methods to Improve Our Understanding of Aspen Regeneration and Aspen Distribution Across the Intermountain West

Quaking aspen (Populus tremuloides) is the dominant broadleaf tree and an ecologically important species at upper elevations in the Intermountain West. Recent large-scale forest mortality events have raised questions about how physiological and climatic factors influence aspen’s distribution across the western U.S. Aspen is particularly well-known for reproducing asexually from its root sprouts, leading to the formation of large clonal stands. In addition, as a wind-dispersed species, aspen sexual reproduction plays an important role in how it is distributed at a landscape scale. My research focuses on questions relating to both sexual and asexual reproduction of aspen. My first research question was to determine how is aspen distributed by sex and climatic variables across the Intermountain West? My results indicated that there were nearly 2:1 male:female aspen across the landscape. These results indicate an overall male bias among established aspen in the Intermountain West, which may suggest male aspen clones are persisting longer or expanding more than female clones. My second research question was to determine how well above- and below-ground measurements predict aspen suckering sized root mass and regeneration potential. Results indicated a few strong correlations between the mass of suckering-sized roots and understory associated species cover, as well as proportion of crown dieback. There were also strong correlations between root phloem diameter proportion and root carbohydrate measurements. These results suggest that the use of stand- or root-level measurements can improve prediction of aspen suckering response