Background/Question/Methods   Models and simulations indicate that climate change may cause shifts in forest species composition as southern species are able to successfully migrate northward. Forest harvesting currently provides opportunities for forest community composition to change and could play an important role in facilitating climate-related species migration. To investigate how climate change might affect an early successional vegetation community, we established a 2 x 2 factorial experiment in a 2007 clear cut of a mixed deciduous forest in central Pennsylvania. We had four replicates and our experimental factors included increasing the air temperature 2˚C above ambient conditions and a 20% precipitation increase above long-term averages. In 2009, we conducted 22 vegetation inventories in all 16 research plots to assess the impacts of our climate treatments on community composition, percent cover, leaf area index (LAI) and phenology. We used permutation-based multivariate analysis of variance (PerMANOVA) to assess the relationship between community composition and our experimental treatments. LAI and percent cover were analyzed using repeated measures ANOVA. The average observed date of leaf out was assessed using standard ANOVA.

Results/Conclusions   Community PerMANOVA results indicated that the overall and herbaceous community composition was influenced by water (p = 0.05 for both) while the woody community responded to the interaction heat*water (p = 0.03). PerMANOVA of the woody community described by stem density showed a strong reaction to heat alone (p = 0.005). Analysis of potential canopy species suggested that heat*water interaction might affect composition (p = 0.056). LAI and the cover of canopy tree species showed a strong heat*day interaction (LAI p = 0.0002, cover p = 0.0001). These heat effects on LAI and canopy species cover occurred early in the spring when heat caused earlier leaf out of canopy tree species (p = 0.0087). The effects of heat and day in large tree cover and leaf out suggests that heat-based changes in phenology could be the source of increased LAI and a driving mechanism for changes in species composition. Our results indicate that community composition of young post-harvest forests may be altered under climate change scenarios. The effects of heat and heat*water on canopy tree species composition, cover and phenology could imply that climate change may alter succession in a way that has long-lasting impacts on forest communities.