Epidemic attacks of native beetle populations on western coniferous forests have become increasingly prevalent. In the mid to late 2000s spruce beetles caused widespread mortality in subalpine spruce-fir forests throughout much of the southern Rocky Mountains. The proclivity of spruce beetles to kill large diameter spruce and leave an otherwise intact legacy community present unique conditions for plant community assembly, yet surprisingly little is known about the influence of widespread spruce mortality on understory plant communities in the subalpine. We asked the following research questions: How have understory plant community composition and cover changed since the disturbance? Do the trajectories of understory plant communities differ along a gradient of spruce mortality? Do community-level leaf traits vary along a gradient of spruce mortality? What leaf traits are associated with the species that have increased in abundance over time? We will conduct our study in the Snowy Range of southeastern Wyoming. Understory vegetation sampling was conducted in 1989 and 2010, providing ample pre-disturbance data. We will sample post-disturbance communities in the summer of 2020 following the same methodology to ensure consistency across sampling periods. Additionally, we will measure leaf osmotic potential, leaf mass per area, and specific leaf area on 60 species.
Results/Conclusions
Spruce beetle induced mortality led to an approximately 66% loss of forest basal area, 77% of which were spruce. Most killed spruce were >46 cm diameter at breast height. Repeat photography in the understory shows noticeable changes in understory plant community cover between 2010 and 2019. This is supported by a 20% average increase in understory plant cover throughout the forest. We observed a strong positive correlation between an increase in cover (r = 0.9924) as well as an increase in species richness (r = 0.7643) in relation to the reduction of basal area within plots, suggesting that the degree of understory plant community response varied along a spruce tree mortality gradient. The changes in understory plan communities that we observed have important ecological implications for carbon storage, wildlife habitat, and hydrologic function. Further analysis will determine how functional leaf traits influence how a species responds to the gradient of spruce mortality.