Genetic and spatial structuring of Populus tremuloides in a mixed-species forest of southwest Utah, USA

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This study examined the genetic composition and habitat associations of aspen in a mixed-species forest in Cedar Breaks National Monument on the Markagunt Plateau, southwestern Utah. Genetic analysis of 94 stems ≥1 cm diameter at breast height (dbh) selected from a population census of 2742 stems within a contiguous 13.64-ha plot revealed 2 spatially cohesive triploid genets and 2 diploid genets (all differing in 8 to 15 alleles). Aspen abundance within the 13.64 ha varied between 0 and 634 stems/ha across 8 distinct habitat types. Regenerating aspen stems (1 cm ≤ dbh < 5 cm) varied between 0 and 112 stems/ha, with higher levels of regeneration in habitats with greater aspen dominance relative to other tree species. Recent regeneration may have been stimulated by a Dendroctonous rufipennis outbreak in the 1990s, which killed a high proportion of Picea engelmannii. Even though the visual impression is of a single aspen clone, the 4 identified genets suggest a higher-than-expected level of genetic diversity in this mixed-species stand which may confer resilience to increasing climate variability and drought. Furthermore, aspen regeneration in areas of both low and high adult aspen densities show that these mixed stands can support vigorous aspen populations.