Effects of deer on the photosynthetic performance of invasive and native forest herbs

The notion that deer can facilitate plant invasions has been increasingly appreciated but the mechanisms remain unclear. In a deciduous forest stressed by overabundant deer and plant invasions, midsummer understory light levels were lower in fenced areas where deer were excluded. Further, invasive garlic mustard (Alliaria petiolata) exhibited 50% higher maximum photosynthetic rates in areas where deer were present. This trend was similar in one native (Maianthemum racemosum) while another native (Trillium grandiflorum) showed the opposite pattern. These results indicate that deer can affect the ecophysiology of invasive species indirectly through modifications to the understory.