Fifty years of change in northern upland forest understories: Identity and traits of “winner” and “loser” plant species

Resurveys of plant communities provide valuable information on changes in species composition over time and clues about how species respond to environmental change. We report results from resurveys of 62 upland forest stands in northern Wisconsin and the western Upper Peninsula of Michigan first surveyed around 1950. We identify plant species that have significantly increased or decreased in frequency in 1 m2 quadrats (‘winners’ and ‘losers’) and evaluate the traits that distinguish these groups. Twenty-one winner species increased across sites (by 25–400%), while 21 loser species decreased (by 21–95%). Winners include both common, native species and five invading exotics. Many are grasses or sedges and most are abiotically pollinated or dispersed (e.g., Carex, which increased 286%). Losers are mostly rarer native forbs that rely on animals for pollination and/or dispersal. Losers appear sensitive to desiccation, anthropogenic disturbance, and/or herbivory by white-tailed deer (e.g., Streptopus roseus, which decreased 73%). Declines in loser species are heterogeneous and stochastic across sites whereas increases in winners are more uniform and deterministic. Increases in common widespread native species account for most of the community change we observe across sites. The fact that winners resist or tolerate deer herbivory while many losers are sensitive to deer suggests that deer may be a key driver of the shifts we observe in these forests.