Thursday, June 30, 2016

When caterpillars eat our trees

The massive defoliation of trees in southern New England by winter
moth and gypsy moth caterpillars this spring and summer has totally changed the
look of the regional landscape. And while scientists say it’s unlikely that
many trees will die as a result of one year of defoliation, it raises the
question of how it will affect other species of wildlife.

University of Rhode Island ornithologist Peter Paton noted that
several varieties of songbirds are likely benefiting from the huge number of
caterpillars swarming the area. Black-billed and yellow-billed cuckoos, two
species that are known to eat large numbers of caterpillars, including the
prickly gypsy moth caterpillars that many other birds avoid, are likely to
thrive this year.

He said birdwatchers in the region have noticed an unusually
large number of very active cuckoos since the birds arrived from their
wintering grounds in South America in May. As a result, these birds will probably
have a very successful nesting season.

“Last week I was watching some robins 40 feet up in a tree
foraging, which is a pretty unusual place to find them eating,” Paton said. “So
I’m guessing they were probably feasting on caterpillars, too.”

Paton also observed blue jays and hairy woodpeckers tearing apart
some of the abundant caterpillar cocoons, another unusual behavior brought
about by the caterpillar infestation.

“And if the defoliation ends up killing trees,” he said, “that
could eventually have a positive impact on woodpeckers,” which consume insects
that live in dead trees and which drill nesting cavities in dead trees.

As for other possible impacts on wildlife, he speculated that the
absence of leaves on many trees will enable sunshine to filter down to the
forest floor and other areas that are typically shady, which may provide
additional sunny areas for turtles and snakes to nest and sun themselves.

On the other hand, fewer shady areas may make it more difficult
for wood frogs and salamanders living in the forest to remain cool and moist,
according to David Gregg, executive director of the Rhode Island Natural
History Survey.

“Ferns and other forest floor plants are also more likely to have
a negative experience of this phenomenon than a positive one,” he said.

Natural History Survey botanist Hope Leeson said there will be
both winners and losers on the forest floor, depending on the needs of the
species living there. “If there is an understory of trees and shrubs, they’ll
be happy to have the sun.”

Photo by Will Collette

Leeson noted greenbrier as one plant that will thrive with the
additional sunlight penetrating to the forest floor, and it will provide
benefits to other species that may be at risk.

“At the moment, any small mammal living in the forest doesn’t have
any cover,” she said. “Deer have eaten all the tree seedlings and shrub
seedlings, so there isn’t anything for the mice and chipmunks to hide under.
Once the canopy was removed by the caterpillars, it made it easy for the hawks
and owls to see the small mammals pretty well.”

The increased growth of greenbrier, she said, will provide the
small mammals with new places to hide.

Both Leeson and Gregg also noted that some unwanted invasive
species may also thrive this year, thanks to the defoliation. Amur cork trees,
for instance, an Asian species, have invaded forests throughout the
Mid-Atlantic states and are now found in small numbers in coastal forests of
Rhode Island as well. They grow very slowly in the shade, with some 25-year-old
trees no more than 8 feet tall with trunks only an inch or two in diameter.

“They just wait it out in a shady situation,” Leeson said. “They
just eek out an existence and wait for the moment when there’s light, and
that’s when they put on a lot of growth.”

This year could be the year they will shoot skyward.

According to Rick Enser, retired biologist for the Rhode Island
Department of Environmental Management, if the region experiences another gypsy
moth infestation next year, tree mortality will likely increase, which could
create gaps in the forest for new species to move into.

Winged Euonymus, a.k.a. Burning Bush.National Parks Service photo

“Unfortunately, invasives are highly adept at dispersal, although
small infestations within forest openings should theoretically be reduced or
eliminated as the canopy returns,” he said.

Enser noted winged euonymus, also known as burning bush, as one
invasive species that can spread quickly to new areas and survive when the
forest canopy returns. It’s a shrub that has become a primary concern at URI’s
W. Alton Jones Campus in West Greenwich.

Since it has been more than 30 years since Rhode Island has
experienced such a severe defoliation, many of the environmental effects are
uncertain and unstudied, leaving some scientists with more questions than
answers.

“I was wondering about the nutrient balance,” Gregg said.
“Normally oak leaves breakdown in a certain way at a certain time, but this
year they've been consumed by caterpillars and turned into manure and sprinkled
all over the forest floor. So is that good for the plants? What’s the nutrient
analysis of gypsy moth poop?”

Thought for the day

“Charlottesville is a great place that’s been very badly hurt over the last couple of days. I own, actually, one of the largest wineries in the United States. It is in Charlottesville.”

Donald Trump, responding to a question whether he would go to Charlottesville to offer support and comfort as so many Presidents have done in the past.

Quick fact check: Donald Trump does not own the winery; his idiot son Eric does under the name Eric Trump Wine Manufacturing LLC. And at 36,000 cases annual production, the winery is not even the largest winery in Virginia, never mind the United States.

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