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Deer, Disturbance, & Understory Dynamics

Karl Didier

Introduction

In January 1998, a severe ice storm struck northern New York, causing varying degrees of canopy disturbance. It is uncertain whether disturbed stands will successfully regenerate valuable hardwoods, including maple, yellow birch, and black cherry. Browsing by deer on regeneration could shift composition from highly to less valuable species, such as beech or herbaceous species. Information provided by this project will help managers ensure adequate regeneration after this and future disturbances. Heavy canopy disturbance occurred in many hardwood stands In disturbed stands, deer can cause dramatic shifts in community composition, in this case to hayscented fern.

Objective #1
Assess the impact of deer on regeneration relative to the extent of canopy disturbance. We constructed 25 exclosures over a gradient of canopy disturbance (below), and paired each exclosed area with an unexclosed area. Disturbance was indexed by canopy openness, which was measured using fish-eye photographs taken at a height of 3 ft. As expected, exclosed areas did not differ from unexclosed areas for any vegetation class 1 growing season after the storm (alpha =0.05). High disturbance areas differed from low disturbance areas only for trees 1-6 ft. in height. More time is necessary for understory development before deer impacts will be detectable.

Objective #2

Assess the spatial patterns in regeneration and deer impact across the ice-storm area. We are determining spatial patterns in regeneration data from the ice-storm and U.S. Forest Service (above) using a 3-step process.

The first step uses spatial autocorrelation statistics to identify how data are grouped in space. Points closer to one another have similar densities, but as the distance between points decreases, points are less correlated.

The second step uses the autocorrelation model to estimate densities between known points and produce a grid or contour map.

Finally, we can relate spatial patterns in regeneration to other ecological variables, such as deer densities, soil type, or competing vegetation.

Conclusion
In general, not enough time has passed for the understory to develop or for deer to impact regeneration in the ice storm area. Vegetation surveys scheduled for this summer may reveal deer impact, especially in heavily disturbed areas. We are uncertain whether deer will impact relative abundance of valuable trees. Understory densities of sugar maple across broad-scales exhibit note-worthy patterns, but fine-scale variability limits the strength of these patterns. Multivariate analysis using explanatory variables which exhibit broad-scale patterns holds promise for describing regeneration patterns.

Funding provided by the New York State Department of Environmental Conservation, the Roosevelt Wild Life Station at SUNY-ESF, and Hancock Timber Resources Group.

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For More Information Contact Karl Didier kadidier@syr.edu

About the author: Karl A. Didier : B.A. University of Southern California, M.S. SUNY-ESF, currently Ph.D. student at SUNY-ESF. Research interests include the indirect and direct effects of ungulate herbivory on ecosystem dynamics specifically looking at white-tailed deer in northern hardwood forests; broad-scale approaches to evaluating ecological patterns and relationships; and and elk restoration. I also dabble a bit in global environmental and economic issues, plant ecology, forestry, and biogeochemistry. After finishing my Ph.D., I'm thinking "short-order cook" sounds good, low stress.