Climate change is expected to alter the geographic distributions of understory plant species and associated ecosystem services. However, effects may depend strongly on silvicultural forest management. Reductions in overstory density and canopy openings associated with variable density thinning increase resource availability above- and below-ground, and increase temperatures in the understory. Therefore, effects of climate change on understory plant communities are expected to depend greatly on forest management. We developed trait-based models to project the responses of understory plant communities to climate change for different management scenarios and effects on ecosystem services. Trait-based models of ecological communities are used increasingly because they promise greater generality, predictive power, and ability to scale between levels of organization. We collected data on 12 continuous leaf, stem and root traits for ~57 understory plant species in Douglas-fir forests of western Oregon. We paired this trait data with community data from a variable density thinning experiment replicated across a gradient in climatic moisture deficit (CMD). We used linear mixed models to examine effects of management-climate interactions on community aggregated traits including: rooting depth and plant height, specific leaf area (SLA) and seed mass. Then we examined the relationships between response and effect traits using multivariate analyses.
Results/Conclusions
Our preliminary results highlight interactions between climatic conditions and forest management that structure understory plant communities. For example, community aggregated SLA increased with (CMD) at high overstory densities but decreased with CMD at low overstory density. Similarly, community aggregated rooting depth decreased with CMD at low overstory density, and increased with CMD at high overstory density. Plant height increased with CMD and decreased with overstory density. Seed mass increased with CMD and overstory density. Ecosystem service traits, including early-seral habitat and cultural values, did not scale directly to community aggregated traits. Our results point to methods of managing forests to manipulate understory community responses to climate change. Furthermore, they suggest that understanding effects on ecosystem services will require more sophisticated models such as the Community Assembly by Trait Selection maximum entropy model.