Deer Exclosures

Margaret Shea

Margaret Shea’s studies at Highstead Arboretum’s deer exclosures

Since its formation in 1982, Highstead Arboretum in Redding, CT has developed as a sanctuary for the study and appreciation of woodland plants and habitats. The past two decades have witnessed remarkable activity at Highstead that has yielded a range of effective programs, including: one hundred acres of diverse woodland, meadow, pond, and swamp habitat; the national Kalmia collection; a growing base of ecological and conservation studies based on permanent plots, large experiments, GIS, and historical research conducted in collaboration with local, regional and national groups including local land trusts, The Nature Conservancy, and the Harvard Forest at Harvard University.
On a walk through the 50 acre site with Director Margaret Shea last year she pointed out some of the evidence of the impact of the overpopulation of deer in the area. 
The azalea collection is fenced to protect it from the deer and as a result of this fencing (which has openings large enough for all other animals to pass through) they are seeing the return of native orchids within the protected area. 
These are absent outside the fencing.
As a result of casual observations such as these, an experimental enclosure was created to study the effects of excluding deer from an area of 30 year old forest and an area of 80 year old forest. Adjacent to the fenced area is an identically sized unfenced area of the two forests. All areas are subdivided into managed and unmanaged areas. In the managed plots all exotic plants are removed to leave only natives. The areas have been studied now for 8 years to see the effects of the exclusion of deer and to see if invasive shrubs such as barberry can protect the native wildflowers from the deer (as has been suggested they might).   Her conclusions after 8 years are that the fenced area contains twice the number of understory species in both the managed and unmanaged plots compared to the unfenced areas. She found no evidence of survival of wildflowers under the invasive exotic shrubs such as barberry. 
The species that were found inside the 8 year deer exclosure (protected from the deer) included the following: Trout lilies, red trillium, ramp, clethra and spice bush-lindera.
The ground under the trees was found to be 20% covered by native plants in the unfenced, unmanaged area whereas it was 40% covered in the fenced unmanaged area. There was 80% coverage by native plants in the fenced managed area where competition from exotic plants had been removed.

These results are good evidence of the effects of deer overbrowsing on native woodlands, and of the harmful effects of invasive plants on Connecticut’s native wildflowers.

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