Large deer population a more immediate threat to Rhode Island's forests than climate change

            While climate change gets most of the media attention these days for the dramatic effects it is predicted to have – and, in some cases, is already having – on coastal communities, it has yet to have serious effects on eastern forests.

Eventually, say local experts, climate change will likely cause a shift in the composition of tree species in the region, due in part to southern species moving into the area and the arrival of new pests and pathogens, which may reduce the abundance of currently common species. The predicted drier weather conditions will also likely play a role in altering woodlands.

But Rhode Island’s forests are already facing what some say is an even greater threat than climate change – an overabundance of deer. That’s the warning from foresters, biologists and ecologists from throughout the Northeast, who say that even without climate change, Rhode Island’s forests are in trouble unless the state’s deer herd can be reduced and managed more effectively.

According to forester Marc Tremblay, outreach coordinator for the Rhode Island Forest Conservators Organization, deer have had a dramatic effect on the forest understory by feeding on the young trees, shrubs and plants.

“They’ve browsed all of the favorable species like oaks and maples, they’ve destroyed our wildflowers, and a lot of the understory plants they like to eat are the ones we rely on for the future stocking of the forest,” Tremblay said. “What’s worse, they don’t like invasive species, so barberry and buckthorn and other invasives are growing like crazy. The end result is a complete alteration of the forest where the invasives have a leg up.”

The Rhode Island chapter of the Society of American Foresters has issued a position statement noting that the long-term health of Rhode Island’s forest is dependent on sufficient tree regeneration to re-occupy openings in the forest canopy created by timber harvesting and natural disturbances. But “deer herbivory at high population levels limits the amount of regeneration and is a serious problem in many parts of the state that, if not addressed, will continue to impact the forest ecosystem and the ability of the forest to regenerate itself.”

It’s not just the trees that are suffering, though. The Nature Conservancy has reported that populations of songbirds and other species that live in the forest understory are declining because deer have consumed their habitat.

“Think about all the species you know that utilize the understory – rabbits and other small mammals, hermit thrushes and other birds, lots of things,” said biologist Numi Mitchell. “They’re very vulnerable if you take away that understory. Think what it’s doing to our biodiversity.”

The Rhode Island Natural History Survey conducted a two-year study of deer herbivory at the University of Rhode Island’s W. Alton Jones Campus that illustrated the dramatic effect of too many deer. Fencing out deer from two half-acre, forested parcels clearly showed how deer had reduced the density and diversity of native plants and exacerbated the expansion of invasive species.

Inside the fence, where deer couldn’t gain access, seedlings of oak, sugar maple, hickory and tuliptrees were abundant, while outside the fence few could be found. Jack-in-the-pulpit plants inside the fence were knee high while those outside were browsed to stubble by deer. Native trillium planted decades ago were blooming inside the fence, while none had been seen elsewhere in a decade.

“Deer look for every plant they can eat and they eat it,” said Natural History Survey botanist Hope Leeson at the conclusion of the project. “We have continuous still images showing them looking for the proverbial needle in a haystack – heads down searching for any little tidbit of a native plant they can find. Due to taste or texture, they tend not to eat invasive plants.

“Deer promote the growth of invasive species, which decreases the biodiversity of native vegetation and sets into motion a cascade of effects on the health of the ecosystem,” she added.

Deer overpopulation isn’t just a problem in Rhode Island, however. The scientific community says that forests throughout the Northeast are in a seriously degraded ecological condition as a result of high deer densities. But deer management is the responsibility of each state, so it cannot be addressed by uniform federal regulations.

Brian Tefft, the state wildlife biologist responsible for tracking deer statistics for the Rhode Island Department of Environmental Management, said that the state is home to about 16,000 deer or 15 per square mile, far more than the habitat can support. About 1,000 deer are killed each year in collisions with vehicles, and another 2,000 or so are harvested by hunters.

Using hunting as the primary means of managing the herd isn’t particularly effective when most hunters want to shoot a buck rather than a doe that is likely to give birth to twins the following spring. For the sake of Rhode Island’s forests, most foresters and biologists suggest altering hunting regulations to encourage the harvesting of more does.

Mitchell said the first step is for sport hunters “to not be so sportsmanlike any more. We need to kill as many does as possible. We’ve gotten rid of our predators, so we need to bring the population down with an increased emphasis by humans.

She also thinks coyotes might be able to help the situation. Mitchell has studied the Aquidneck Island coyote population for more than a decade, and she said that eastern coyotes have about 20 percent wolf genes, which has helped to make them excellent cooperative hunters.

“Coyotes are a piece of the puzzle,” she said. “They can get deer in the suburbs where people aren’t legally able to shoot. I get calls all the time from people saying they have a dead deer in their yard, and I tell them to wait a day or two and the coyotes will eat them.”

The next phase of her research will be to see how coyotes can be used to help manage the state’s deer population.

David Gregg, executive director of the Rhode Island Natural History Survey, admits that deer is the greater immediate threat to Rhode Island’s forests than climate change, but he also notes that climate change could be even more damaging if the deer problem isn’t addressed first.

“I don’t want to downplay climate change, but certainly one plus one equals three, that’s for sure,” he said.

He points to a project his organization is currently undertaking to build resilience into the habitat at Norman Bird Sanctuary and Sachuest Point National Wildlife Refuge in Middletown.  The plan was to install a wide variety of native plants, thinking that a diverse ecosystem will be one that can better withstand the coming climatic changes.

“But what we’re finding is that there is so much deer browse there that we'll be hard pressed to do anything unless it is inside a fence,” Gregg said. “We’re going to need to adapt our strategy a bit.”

Mitchell agrees that the cumulative effect of deer and climate could be catastrophic for Rhode Island’s forests.

“I think climate change is a bigger long-term crisis,” she said, “but deer are our immediate crisis.” 

This article first appeared on EcoRI.org on December 1, 2016.