IBET Paper 2013-3-7

The Effects of Tree Density on Deer Population Concentrations in the Elizabeth Hartwell Mason Neck Wildlife Refuge
Zeal An, Tarun Punnoose, Danny Wang, Eke Wokocha
The costs of culling and reducing deer populations have historically been very high; the cost of killing deer can be as high as $300 per deer killed (Bishop, Glidden, Lowery & Riehlman, 2007). As the cost of management of the populations of these deer can be too high for some local governments, many deer populations are growing past the carrying capacity of their habitats. As a result, a considerable amount of human property and large expanses of forests are damaged. A possible factor in deer population is tree density; as such a correlation could be found between tree density and white-tailed deer populations in the Elizabeth Hartwell Mason Neck Wildlife Refuge.
The increasing population of white-tailed deer is becoming harder and harder to manage. After reaching a historic low of 100,000 in the early 1900’s, the deer population is now estimated at between 16 and 20 million deer (Rondeau & Conrad, 2003). Many of the habitats in which these deer reside are not able to support the growth in population, and thus deer commonly exceed the carrying capacity of their habitats. Unchecked deer population is causing over-browsing, which in turn often leads to a decrease in forest diversity. This can have drastic effects on the ecosystem and can cause declines in the abundance of forest life (Levy, 2006).
Additionally, white-tailed deer are the cause of much damage to human property. Deer commonly damage landscaping and property in densely populated suburban areas, and they are known to ruin farmland and crops, especially corn and fruit-bearing orchards, causing monetary loss to farmers (“Deer information,” n.d. ). Additionally, an average of 4,000 to 5,000 deer-auto collisions occur per year in Fairfax County (“Deer information,” n.d. ), where this study is located; in the United States of America, approximately 1.5 million collisions killed between 100 and 200 motorists and caused about 2 billion dollars in damages (Rondeau & Conrad, 2003). Controlling these deer is also costly; population management through baiting and shooting costs an average of $300 per deer killed, capturing and relocating can range as high as $800 per deer, and treatment of an orchard with chemical repellents can cost anywhere between $10 and $400 (Bishop, Glidden, Lowery & Riehlman, 2007). Furthermore, deer are contributors to the spread of certain diseases, such as lyme disease or babesiosis (Suszkiw, 2007).
Various factors that can cause the increase in deer population include a lack of natural predators and human hunting, as well as an ideal habitat, plentiful in space and food. A 2004 study by Pollock et al concluded that mature, male white-tailed deer appeared to select more tree-dense areas in southern Texas. Presence of greater canopy cover, more woody species, and more dense screening cover in the most-heavily used areas compared to unused areas support this conclusion (Pollock et al, 2004). We predict that a similar correlation between tree density and deer habitat selection exists in northern Virginia. If a correlation can be found, such a relationship will allow hunters to analyze the tree densities of the hunting region and focus hunting efforts on areas where deer are more likely to be found. The increased hunting efficiency will decrease the cost needed to manage deer populations, reducing monetary strain on local and national governments, and the decreased population will decrease pressure on the environment.
Literary Review
Pollock, Whittaker, Demarais, and Zaiglin (1994) investigated the effect of vegetation characteristics in southern Texas on the site selection by male white-tailed deer. The study was conducted from 1986 to 1988. The researchers monitored thirteen radio-collared animals every
season, and measured structural vegetation attributes using transect-oriented data collection techniques within the most heavily used and unused areas of each animal’s home range. Then, comparisons between these areas determined whether site selection by deer was in response to differing vegetation characteristics. The results of the investigation showed that more heavily used areas of forest possessed higher total canopy cover (alpha = 0.05).
	Weckerly, Kennedy, and Stephenson (2005) studied hunter effort-relationship size relationships relevant to managing and monitoring hunted populations with multiple hunt types. The data used was a 12 year harvest record from a hunt program in western Tennessee from 1988-2000. The researchers used slopes of regression to track relative deer population change with harvest size to hunter effort ratio. Hunter effort was measured through days expended hunting. The study concluded that there was no significant difference between the 6 hunt types and the efficiency of the hunting.
Hypothesis
Previous studies indicated that mature, male white-tailed deer appeared to select more tree-dense areas and that costs between different methods of hunting were irrelevant. The purpose of our study was to determine whether there is a significant correlation between tree density and deer population so that hunting can be made more effective through better modeling. We hypothesize that areas in which tree density is higher will show higher deer pellet counts than areas in which tree density is lower.
Site Description
Elizabeth Hartwell Mason Neck is a wildlife refuge 922 hectares large (US Fish and Wildlife Service, n.d). The refuge is located 29 kilometers south of Washington, D.C. It borders the Potomac River and the Occoquan Bay. The refuge is located in the lower region of the Potomac watershed (Weller, 2011). The park is largely comprised of upland hardwood forest (1,883 acres); four miles of coastline and 364 acres of wetlands are also present (“Management”, 2013).  Within the refuge, 72 plots were selected from areas adjacent to two major roads cutting through the refuge, Anchorage Road and Selway Road. Anchorage (N 38o 37’ 28’’, W 77o 10’ 39’’ ) and Sycamore Road (N 38o 37’ 52’’, W 77o 11’ 39’’).
Procedure
We bisected each plot using a 22-meter length of string. Afterwards, we combed the ground for droppings up to 3 meters away from the bisecting string. Any droppings we found were recorded, photographed, and placed outside of the plot. Additionally, we conducted tree counts. Trees within a plot were defined as being of a width such that we could not wrap our hands around the trunk. We repeated this procedure at each plot.