Human-induced changes in habitat quantity, disturbance regimes, and propagule pressure have markedly altered Wisconsin upland forest community diversity and structure. Changes we see at the community level are the combined result of individual species responding due to their traits. We investigated how whole-understory traits and metrics of functional diversity have changed over fifty years across Wisconsin. Mesification and plant invasion is likely to shift community-averaged traits towards values typified by weedy, shade-tolerant species. To test this hypothesis, we assembled a database of 30 traits for 230+ Wisconsin understory plant species. Categorical traits were evaluated from the literature or field. For quantitative traits, a minimum of ten individuals across three locations were sampled and averaged. We calculated abundance-weighted trait values for each site.
Results/Conclusions
We found significant variation in measured traits both within and across species. Quantitative traits were significantly different between northern and southern Wisconsin and between time periods. In particular, specific leaf area (SLA) was larger in southern Wisconsin in both time periods, consistent with more graminoids, ferns, and evergreen-leaved species in the north. SLA increased significantly over time in southern Wisconsin, but not in the north. This supports previous work showing increases in shade-tolerant species in the south. In contrast to SLA, other traits including height moved in similar directions in both areas of the state. Our results confirm that landscape-level changes are having significant impacts on the characteristics of plants in Wisconsin forests. Changes in functional attributes at the community scale will have important consequences for ecosystem functioning.
