A hemlock woolly adelgid infestation can destroy a hemlock tree in just a few years. The insect gets its name from the fuzzy, white masses that the females produce. Photo: Michael Montgomery, USDA Forest Service.
In New York, climate change may make it easier for an invasive species to continue its spread to hemlock forests further to the north.
The threat comes from the hemlock woolly adelgid, an aphid-like insect that feeds on hemlock trees. The species gets its name from the fuzzy, white masses that the females produce. The adelgid uses its long mouth to extract nutrients from hemlock needles. This disrupts the flow of nutrients in the tree. Needles dry out, turn color, and drop off. Larger limbs start dying off within a couple of years. Trees become badly damaged and in many cases die after several years.
Hemlock forests provide unique habitat for wildlife. Their shade helps keep soil and water temperatures cool and provide microclimates in which many plants and animals thrive.
The hemlock woolly adelgid was first discovered in the United States in Virginia in the 1950s. It is native to Asia and was likely introduced to the U.S. by accident. It has thrived along the east coast and has damaged hemlock forests from Maine to Georgia.
In New York State, the hemlock woolly adelgid was discovered in the 1980s. Infestations are now found in 25 counties. The infestations are clustered in two regions: the Hudson Valley, which includes most of the lower portion of the state, and the Finger Lakes. There is great concern over the possibility of the insects eventually spreading to the forests of upstate New York, including Adirondack Park.
Climate change may help accelerate the spread of the hemlock woolly adelgid. According to a report by the New York State Energy Research and Development Authority on the possible impacts of climate change in New York State, “extensive loss of hemlock forests will have cascading, far-reaching effects on a variety of wildlife species and their ecosystems.”
The main barrier to the spread of the hemlock woolly adelgid is cold temperatures.
Hemlock foliage with a moderate infestation of hemlock woolly adelgid. The hemlock woolly adelgid is an invasive species, native to Asia, first discovered in the United States in Virginia in the 1950s. It has damaged hemlock forests from Maine to Georgia. Photo: New York State Department of Environmental Conservation. Download.
“If, as we think, cold is one of the main limiting factors, then climate change has a chance to turn the tables and make the hemlock woolly adelgid problem even worse,” said Jason Denham, Forest Health Specialist with the New York State Department of Environmental Conservation.
Projected increases in overwintering temperatures may allow the insects to expand their range into more northern hemlock forests, according to the New York Invasive Species Information website. The report by the New York State Energy Research and Development Authority states that temperatures across New York State are expected to rise by 1.5 to 3º F by the 2020s, 3 to 5.5º F by the 2050s and 4 to 9º F by the 2080s.
Perhaps the species most at risk from continued loss of hemlock forests is the brook trout, New York’s state fish. Brook trout rely on cold water refuges in streams and lakes for their survival. Hemlock forests provide shade needed to maintain lower water temperatures. Brook trout will become increasingly vulnerable as water and air temperatures rise.
Needle loss on a heavily infested hemlock. The adelgid extracts nutrients from hemlock needles with its long mouth, disrupting the flow of nutrients in the tree. The needles then dry out, turn color, and fall off. Photo: New York State Department of Environmental Conservation. Download.
The loss of hemlock can mean a change in the biodiversity of an ecosystem.
“When you take hemlock out of a hemlock stand, the first thing happens is more sunlight hits the ground,” said Denham. “Because of that you get warmer stream temperatures, warmer soil temperatures and more direct sunlight on the forest floor.” In the lower Hudson Valley, this has led to an increase in the number of invasive plants that normally can’t live in the cooler, shady conditions found under a healthy hemlock overstory.
Currently there is no way to eradicate the hemlock woolly adelgid, but researchers are exploring options to identify infested trees and slow down the rate that the insect spreads. Introducing beetles that feed on adelgid have shown some promise, and researchers are looking into fungi that could be introduced that would be harmful to the species.
Climate Change Focus: Adaptation
Author: Frank Wolff
Contacts: Terri Edwards, USFWS, 413-253-8324, firstname.lastname@example.org