The European arrival in British Columbia resulted in an explosive growth of the deer population. This is particularly true in the Gulf Islands, where there natural predators (cougars, bears and wolves) have virtually been eliminated. Deer populations can be as high as 170 animals per square-kilometer. Now there are reports of plant species defending themselves against deer.

Plant Species Defending Themselves Against Deer

Researchers from the University of British Columbia discovered that the seablush has learned to make itself less visible on islands where there are large deer populations. They stay closer to the ground, limiting their growth to 10 or 20 cm until after March or April. A recent experiment on Sidney Island proved this tripled their chances of survival.

“In order to restore this endangered ecosystem, seeds from seablush that have genetically adapted to withstand or resist being eaten need to be collected and replanted on the islands that have deer,” said researcher Cora Skaien, a PhD candidate in the department of forest and conservation sciences, whose work is supervised by professor Peter Arcese.

The Primula Farinosa has undergone a similar adaption. After being exposed to deer populations for about eight years, plants grow much shorter. It takes a similar time, after deer are removed, for Primula Farinosa to start growing tall again.

Large Deer Populations

Songbird populations also decline, as a result of competition for vegetation, when there are large deer populations.

“The lack of top-down control from predators (natural or human) has allowed the deer densities to rise well above the standard carrying capacity of the islands,” said Skaien.

The fallow deer found on many Gulf Islands travel in herds. This increases the density and competition for food. Many “are sickly, or starve, and their offspring are not carried to full-term.”

Skaien said meat from the first deer cull on Sidney Island was inedible. However the decrease in population resulted in a resurgence of plants like camas, Oregon grape and seablush.

The Northern Islands

The problem has not been as great in the northern islands. The population is made up of black tailed deer, which tend to be more solitary. There are also predators to keep the deer populations in check.

“What is interesting is that we still see a distinct difference in plant height between populations with and without deer, even in the north. Thus, although deer densities are lower, seablush still appears to be locally adapted to deer browsing. It was much easier to find seablush populations throughout the drier parts of Desolation Sound and NW of Powell River near Sarah Point. On some of the islands in the south, seablush has been driven extinct due to such high browsing pressures! I do suspect that populations of seablush would fair much better in the north in the presence of deer if the exclosures were planted there, but that survival would still be substantially lower outside of exclosures than inside,” said Skaien.

Photo Credit: Musgrave Island, which has no deer – courtesy Cora Skaien, UBC