Deer Impacts on Vegetation in Ann Arbor Natural Areas: Key Monitoring Metrics for 2018–2019

Vegetation monitoring metrics for 2018 showed a decrease in deer browse damage on experimental red oak seedlingsin manysites, including mostareas where deer were actively managed in or near the site from 2016–2019. However, browse levels on oaks were still high, and deer were linked to significant reductions in blooming of trillium and experiment wildflowersat most sites. Deer browsed 56% of experimental red oak seedlings across all Ann Arbor sites. Wildflower experimental plantings showed high levels of deer browse—higher than red oak seedlings planted in the same plots, suggesting that deer browse levels on red oak seedlings are a conservative estimator of damage to wildflowers. Deer were linked to considerable reductions in flowering of experimental asters and goldenrods. Trillium abundance orflowering(or both) remainedlower in plots where deer were presentthan in plots protected from deer in 2018. Deer browse levels on trillium in 3 of 5 sites are above the 5-15% level that previous studies have shown will allow for persistence of trillium populations over time. Fenced trillium populations protected from deer showed clear increases in trillium number and flowering from 2016-2018. Deer browse levels on trillium in 2018 were similar to those in 2016, suggesting that deer populations are still high enough to exert negative impacts on trillium.

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