PROVIDENCE, R.I. (AP) — A combination of heat, drought and insect infestations have killed about 13 percent of trees in Rhode Island’s forests since 2015, according to state environmental officials.

The 45,000 to 50,000 acres of dead trees are concentrated across the western half of the state, from Hopkinton to Burrillville, with pockets on Prudence Island and the Sakonnet Peninsula, Department of Environmental Management experts told the Providence Journal Thursday. Rhode Island has about 369,000 acres of forest.

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

The majority of the dead trees 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.

Southern pine beetles have moved north as winters have become milder, reaching Rhode Island in 2015. The emerald ash borer, an invasive species from China, was confirmed in Rhode Island for the first time this year.

Droughts have starved trees of sustenance, making them more susceptible to caterpillars and depriving them of the fuel necessary to bud new leaves.

The dead trees represent an economic loss to timber harvesters. Wood from dead trees, instead of being cut down for lumber, it is being sold as firewood at a fraction of the price.

Falling branches from dead trees are also a safety hazard along roads and near power lines, and towns and National Grid, the state’s main electric utility, may have to spend hundreds of thousands of dollars to take down hazardous trees.

Dead trees are also a fire risk.

The Rhode Island Tree Council has documented changes in weather conditions that have likely played a role in tree mortality. This past summer, the average temperatures in some summer months were 3 to 4 degrees higher than the 100-year benchmark, according to the council.