Rhode Island's forests are dying

PROVIDENCE — About 13 percent of Rhode Island’s forest trees are dead, state environmental officials have concluded, the result of an unprecedented combination of heat, drought and insect infestations from 2015 to last year.

The area of dead trees is concentrated across the western half of the state, from Hopkinton to Burrillville, with pockets on Prudence Island and the Sakonnet Peninsula, according to the just-completed assessment by the Rhode Island Department of Environmental Management.

While there are some large contiguous swatches of mortality — in places like Richmond, West Greenwich and Foster — the tree death is, for the most part, diffuse, with pockets spread throughout rural and suburban communities.

All told, the area of death totals about 45,000 to 50,000 acres, short of initial estimates that put the number at nearly twice as much, but still a large portion of Rhode Island’s 369,000 acres of forest.

The assessment by Paul Ricard, forest health program coordinator for the DEM, was based on an aerial survey he conducted in September.

The tree mortality may be a sign of things to come. Recent research summarized in the scientific journal Forestry found that climate change can facilitate the spread of both native and invasive forest pests and weaken the resistance of trees to these pests. The new update to the National Climate Assessment, released last month, makes a similar warning.

“Higher damage from native insects on trees with reduced vigor is expected to be one of the biggest effects of a warmer climate,” says the report authored by 13 federal agencies.

Much of the attention on insect outbreaks in the United States has focused on bark beetles that have decimated forests in the western part of the country, but forest pests are a growing concern in the Northeast. Southern pine beetles have marched north as winters have become milder, reaching Rhode Island in 2015. The emerald ash borer, a species inadvertently imported from China, has moved across the northern half of the country, and was found in Rhode Island for the first time this year.

The majority of trees in the recent spate of deaths are species of oak, the leaves of which are the preferred source of food for gypsy moth caterpillars, an invasive insect that exploded in numbers three years ago and defoliated hundreds of thousands of acres in Rhode Island before finally succumbing to a deadly fungus and virus.

Gypsy moth outbreaks have occurred previously over the past 150 years since the first insects escaped from an experiment in Massachusetts. Some of the worst infestations in Rhode Island and the rest of the Northeast happened between the late 1970s and the mid-1980s, but the damage left in the wake of the recent one was compounded by other factors.

An unusual series of spring droughts impeded the spread of the fungus Entomophaga maimaiga that usually controls gypsy moth caterpillar numbers. The droughts also starved trees of sustenance, making them more susceptible to the caterpillars’ onslaught and depriving them of the fuel necessary to bud new leaves.

High numbers of forest tent and eastern tent caterpillars, both native species, also hit the trees harder than normal. And finally, the two-lined chestnut borer, a native beetle whose larvae feed on the inner cambium wood of trees, colonized weakened oaks and, in many cases, delivered the death blow.

“That’s due to stress,” Ricard said. “They don’t normally kill oak trees.”

The trees killed by chestnut borers stood out in Ricard's aerial survey. Unlike the trees killed by caterpillars and drought that lost their leaves over time, the trees infested by the beetles leafed out but died fast, their foliage remaining but turning brown.

While the caterpillar infestations ended for the most part last year, it took time for the majority of trees to die. So even though there were large numbers of dead trees last year, the problem has become more pronounced this year.

The dead trees represent an economic loss to timber harvesters. Because the wood in dead trees deteriorates quickly, instead of being cut down for lumber, it is being sold off as firewood at a fraction of the price.

The trees pose a safety hazard along roads and near power lines as branches start falling. Communities and National Grid, the state's main electric utility, are facing costs totaling hundreds of thousands of dollars to take down hazard trees.

“These trees are going to start falling on blue-sky days,” Chris Rooney, lead forestry supervisor for National Grid in Rhode Island, said at a meeting last month with the DEM and public works departments from around the state. “ Everyone’s talking about storm preparation. This is everyday preparation.”

The trees are also a fire risk, especially in towns like Richmond and Coventry, where more homes have been built in what’s known as the “wildland-urban interface,” areas in which human development is moving into natural terrain. The DEM is taking down dead trees on state lands to reduce the fuel load, but budget constraints are limiting the surveys needed to identify trees to be felled.

The loss of trees comes at a time when pressure to redevelop forests is growing, with solar companies, aided by state renewable energy incentives, paying a premium to lease large tracts of land. Ricard expressed concern that landowners who have lost hardwood trees that could have provided valuable lumber will consider converting their properties to solar or other uses. John Campanini, technical adviser to the Rhode Island Tree Council, has also raised the issue.

The tree council has documented changes in weather conditions that have likely played a role in the wave of death. Based on data from weather stations around Rhode Island maintained by the council, there has been a 1 to 2 degree increase in temperature in each month of the April-to-October growing season in a comparison of averages for the past 30 years versus averages for the past 100 years.

This past summer, the average temperatures in some of the summer months were 3 to 4 degrees higher than the 100-year benchmark, according to the council. Data collected by the DEM found a similar difference. It added up to the warmest summer on record for Rhode Island, according to the National Oceanic and Atmospheric Administration.

Even though rainfall in Rhode Island is increasing on an annual basis, there is less in the summer months when trees need it most. Last summer, the state had below average rainfall in May, June and July, according to NOAA. So even as the spring rains returned and triggered new growth, for some trees, it couldn’t be sustained because the rainfall didn’t continue.

As temperatures increase, the evaporation rate is also rising. What rain does fall evaporates faster, leaving less behind to soak into the ground where tree roots can absorb it.

“We have to start paying attention to the weather conditions, because they are having an impact,” Campanini said at the November meeting.

The good news is that gypsy moth numbers are expected to continue to be low next year. Ricard is surveying parts of the state for egg masses that will hatch in the spring and has found low numbers so far.

The bad news is that unless the dead trees are cut down, bigger limbs will begin to drop and the trunks will eventually follow.

“It’s going to get worse, sadly,” Rooney said.