PROVIDENCE — Rhode Island’s forests, decimated by pest infestations, heat and drought in recent years, may be on their way to recovery this spring.

Populations are down among several species of insects that were largely responsible for the deaths last year of large swaths of oak trees in the western half of the state, parts of the Sakonnet peninsula and pockets of other rural and suburban areas. That doesn’t mean that weaker trees won’t continue to succumb as temperatures climb in the summer, but the numbers are expected to be lower than last year.

“It seems to me that it’s really leveled off,” said Heather Faubert, research associate at the University of Rhode Island's Plant Protection Clinic. “The wet spring is really bringing everything back to life.”

The rain has also created the perfect, moist conditions for the spread of a fungus that is deadly to gypsy moth caterpillars, the prime culprit in the die-off of trees that may be unprecedented in its scale in Rhode Island.

Numbers of the invasive insect exploded in 2015 and continued to rise for two more years as the caterpillars defoliated hundreds of thousands of acres of forest. Their rise was fostered by an unusual series of spring droughts that impeded the spread of the fungus Entomophaga maimaiga that, in concert with a virus, usually controls the caterpillars' population.

In the same years in which the gypsy moth caterpillar thrived, other types of caterpillars added to the damage. They included the winter moth caterpillar, another invasive insect, and two native species, the Eastern tent caterpillar and the forest tent caterpillar.

The numbers of all three species eventually dropped off, and after the rains returned, in mid-2017, so too did the number of gypsy moth caterpillars fall. But species of oak, whose leaves are the preferred source of food for gypsy moth caterpillars, were so weakened by the damage to their foliage that large areas started to die last year. The two-lined chestnut borer, a native insect that preys on debilitated trees, also contributed to the loss.

The tree mortality totaled about 45,000 to 50,000 acres, about 13 percent of Rhode Island’s 369,000 acres of forest, according to an assessment conducted by Paul Ricard, forest health program coordinator for the state Department of Environmental Management.

While numbers of gypsy moth caterpillar egg masses are still down in Rhode Island, they can still be found in higher concentrations in nearby parts of Massachusetts. Faubert has visited one blueberry farm in the town of Franklin that she described as “loaded with egg masses.”

Through her work with farms in Rhode Island, she is regularly seeing egg masses of winter moth caterpillars this spring, but not in large numbers.

“I can find them wherever I look, but I’m not expecting any defoliation,” she said.

It’s likely that native insects and birds, as well as a parasitic fly and wasp that were introduced to prey on the moth, have been controlling the population. Natural predators are also keeping down the numbers of Eastern tent caterpillars and forest tent caterpillars, Faubert said.

As for other forest pests, such as the southern pine beetle and the emerald ash borer, which are both invasives found recently in Rhode Island for the first time, it’s still too early in the year to predict whether they will have an impact on the state’s trees.

In the meantime, new growth is occurring in the forests.

“White pines are just growing up like crazy,” Faubert said. “It won’t take long to repopulate our forests.”

— akuffner@providencejournal.com

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