Growing deer populations are fundamentally changing the environment of the Gulf Islands off the coast of B.C. and Washington, leaving the region susceptible to invasion by foreign species, says a study by researchers in the Faculty of Forestry at the University of British Columbia.
Researchers looked at the density of black-tailed deer on 18 Southern Gulf and San Juan Islands with forest ecosystems. The study, published today in the journal Biological Conservation, found that the number of birds and vegetation decreased on islands with higher deer densities. Islands with more than one deer per hectare had half as many birds as those with low deer density.
Deer graze on shrubby vegetation for food, and song birds, such as hummingbirds, sparrows and warblers, depend on this vegetation for nesting and feeding. The researchers found that islands with moderate or high deer density had less shrubby vegetation and half as many birds as those with low deer density, or one deer per square kilometer.
“These changes are not the result of natural processes,” says Tara Martin, adjunct professor in the Faculty of Forestry at UBC, senior scientist with Australia’s Commonwealth Scientific and Industrial Research Organisation and lead author of the study. “The environmental changes are an indirect effect of humans. We’ve removed the large animals that preyed on deer and changed hunting policies.”
The researchers suggest that changing regulations and sentiments towards deer hunting have allowed populations to thrive, and may lead to greater numbers of local plant and bird species on threatened species lists in the future.
“As plant species decline, it is inevitable that birds, insect pollinators and other species will also decline,” says Peter Arcese, professor in the Faculty of Forestry and co-author of the study. “I work with several small island communities that have seen dramatic change first hand but are prevented from hunting by local bans.”
The researchers suggest that by reducing or eliminating native plants, deer facilitate the invasion of non-native species, eroding the natural beauty of the coastal Douglas fir forests on the Southern Gulf and San Juan Islands, and reducing the biological integrity and aesthetic appeal of the region.
“We’re hoping to convince government that they need to consider new management initiatives, such as limited entry hunting under community supervision, because failing to act is a decision to favor the black-tailed deer over many other species native to our region and valued by humans,” said Arcese.
This study was funded by the Natural Sciences and Engineering Research Council of Canada.