white-tailed deer

Monitoring Deer Browsing

White-tailed deer (Odocoileus virginianus) are large herbivores that are most active during dawn and dusk. Their daily routines to and from feeding and bedding areas are very predictable, facilitating the monitoring of resident populations.

As ruminants (4-compartment stomach), deer can consume large amounts of food and regurgitate and remasticate when they retreat to cover. When given a choice, deer prefer herbaceous materials like grasses, forbs, herbs, leaves and clovers. They will actively seek out fruits in season (including commercial crops) and will focus on high fat content foods like acorns when they are available.

Deer have adapted to survive the winter by conserving energy and eating the buds of woody shrubs and trees. During this period of limited food availability, overabundant deer populations can have significant negative effects on forested ecosystems. By selectively feeding on seedling and sapling buds below ~2 meters in height, deer thwart the growth of young trees. If 50% or more buds are consistently removed from a sapling or seedling, its survival is unlikely. As the next generation of canopy trees providing essential food and cover for forest animals, the health of the seedling and sapling layer is of great concern to forest ecologists.

Winchcombe has been monitoring the amount of woody browse consumed by deer on Cary Institute grounds since 1983. Presently, this effort consists of surveying 45 sites in our forested habitats each spring. Seven major tree species are used to index browsing levels, they include: red maple, sugar maple, black birch, black cherry and any oaks, hickories and ashes. A random walk around each site is conducted until an index species is observed. All buds below 2 meters in height are counted and examined for browse damage. At each site a minimum of 100 buds are counted, with a total of approximately 6,000 buds examined yearly. Most sites usually include 3 or more index species.

Over-winter browsing rates, as determined by the spring surveys, have remained fairly low (overall range: 3-16%). Browsing rates for individual species, however, can have wide annual variation. Red maple has varied from 1-33%, black cherry from 0-47% and black birch from 0-52% in any given year. Browsing rates are typically driven by deer numbers and winter severity. At Cary, however, annual snowfall (total inches, Nov. 1-Mar. 31) appears to be driving fluctuations in browse consumption. This is reasonable since deer numbers do not fluctuate widely on our grounds, but snowfall amounts do. Annual snowfall (total inches) is a good predictor of how many sites will be browsed at a rate of 20% or greater.

Cary Institute of Ecosystem Studies | Millbrook, New York 12545 | Tel (845) 677-5343

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