January 2, 2013
Study Shows How Dense Deer Populations Damage Plant Diversity
Brett Smith for redOrbit.com - Your Universe Online
The proliferation of roe deer in the U.K. appears to be impacting woodland ecosystems, according to a new study from researchers in at Durham University.
After visiting sites and collecting data over a span of two years, the ecologists found that the area with the largest roe deer population also had the lowest level of vegetation cover and bird population. It is the first study on U.K. deer with this type of precision and scope.
"Much of the recent literature on impacts of deer on their environment has focused on multi-species systems and, there, authors cannot attribute impacts they find on vegetation to one particular species," said Georgina Palmer, a postdoctoral researcher at Durham´s School of Biological and Biomedical Sciences.
"My study is the first in Britain which both looks solely at the roe deer, and within natural environments, i.e. without the use of deer exclosures where deer densities are artificially managed."
According to Palmer, her team set out to investigate roe deer and bird population densities, along with the status of vegetation in U.K. woodlands.
"I collected data on vegetation cover, diversity and abundance at 35 woodland field sites across England during May and June 2011 and 2012," explained Palmer. “Each of these field sites are part of the Breeding Bird Survey scheme, so — along with the vegetation data I collected — I also had access to long-running bird and deer abundance data."
Based on both the site and the survey data, the scientists were able to establish a relationship between increasing roe deer density and a decrease in shrub diversity and cover. However, they were unable to establish a direct cause and effect relationship.
"I am still analyzing this data, so cannot yet say whether roe deer are causing the reduction in shrub layer cover and, consequently, bird abundance or whether roe deer are more strongly associated with woodlands with open shrub layers,” she added.
A non- profit organization called the The Deer Initiative has been one of the bigger U.K. players in finding ways to promote the "sustainable management of wild deer" in England and Wales. The group advocates a two-pronged strategy: understanding the specific impacts that deer have on the environment, and working with landowners to better manage the area they own.
Palmer's research builds on another recent U.K. study which showed that landowners who maintain conservation-oriented partnerships over large areas were best able to deter deer damage. Based on data from 80 Sites of Special Scientific Interest (SSSIs), that study also suggested that overgrazing by deer negatively impacted woodland ecosystems.
Experts warn that deer grazing contributes to a reduction in the growth and density of saplings, bark damage and a shift in the composition of forest floor vegetation.
There are currently six species of deer found within the U.K., two native species, roe and red deer, and four others that have been introduced, fallow, muntjac, sika and Chinese water deer. The British government regulates deer hunting — known colloquially as ℠deer stalking´ — through a law known as the Deer Act, which designates specific seasons for each type of deer.