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Pennsylvania forest wildlife gets break from caterpillar collapse

From the Pennsylvania Game Commission

-- By Joe Kosack, Wildlife Conservation Education Specialist -- Heading into this past spring, it appeared stands of oaks on many Pennsylvania Game Commission State Game Lands were going to be hit hard by gypsy moth caterpillars. Limited funding for spraying from state agencies and municipalities had Pennsylvania in a bad way. But that’s changed now.

As the  state braced for what was forecasted to be another nasty gypsy moth caterpillar raid on oaks, conifers, hickories and other species in 25 mid-state and northeastern counties, emerging caterpillars were hit by a fungus – Entomophaga maimaiga – a natural enemy. Although not native to Pennsylvania, the virus – Lymantria dispar Multienveloped Nuclear Polyhedrosis Virus (NPV) appeared in America about the same time the gypsy moth did.

It was assisted by a biological insecticide – Bacillus thuringiensis (Bt) – sprayed on forestlands by the state Department of Conservation and Natural Resources. The caterpillars, thankfully, didn’t have a chance when this triple-threat hit them. That doesn’t mean they’re gone for good; just that they had to return to the starting block in population building.

Dave Henry, Southeast Region forester, considers the gypsy moth collapse a great break for the agency, but he notes that this latest outbreak and others that have occurred since the 1970s have had a serious consequences on State Game Lands and the state’s forest system.

“Although the oak resource on State Game Lands will be spared from a great deal of additional tree mortality, and past locations with moderate to severe damage will have a reasonable chance to recover from the stress of losing most of their leaves, oak resource losses from numerous rounds of gypsy moth caterpillar defoliation have been substantial,” Henry said. “I really wonder about how many more times our oaks and other desirable hardwoods can endure the next rise of gypsy moths or oak-leaf rollers, emerald ash borers or other devastating forest pests.”

The state’s forests have had more than they can handle when it comes to forest pests, tree diseases and invasive plants over the past century. At one time, the Commonwealth’s forests were dominated by thriving stands of American chestnut trees. The blight – also not native to North America – that would claim them struck in the early 1900s. But before it would smother our native chestnuts, gypsy moths would surface in Pennsylvania. So oaks, the mighty mast-producing chestnut’s successor, were already in trouble – at least in the Poconos – when the state’s blighted chestnuts died, the canopy cleared and they got their big moment in the sun.

Of course, a point could be made that deer, wild turkeys, cottontails and other wildlife benefit from the canopy consumption of gypsy moth caterpillars. It allows sunlight to reach the forest floor and spurs the growth of many plants that will provide food and cover. However, such analysis should factor in the reduction/loss of fall mast crops and important shade-loving understory plant species, and the immediate competition for open space that will erupt between native plants and incredibly aggressive, invasive non-native species, such as mile-a-minute weed and ailanthus. It most cases, native species don’t have a chance unless the landscape is sprayed with special herbicides.

In 2008, more than 400,000 forested acres were sprayed with Bt in Pennsylvania and New Jersey. And still, the gypsy moth expansion was expected to steamroll in 2009. It had momentum, and Pennsylvania’s attention, even if the state didn’t have the resources it needed to respond more aggressively. Then Entomophaga maimaiga, NPV and 300,000-plus gallons of Bt hit the emerging caterpillars. Now at the height of the gypsy moth’s egg-laying period – July and early August – many of Pennsylvania’s once imperiled oaks are pushing acorns, not daisies.  

Most kept their leaves. That’s good news for oaks, wildlife and Pennsylvania hunters.

Deer hunters who find the acorns in coming months should have a good chance of finding deer, because deer and many other wildlife species seek out acorns – loaded with carbs, fats and protein – in the fall to store energy in preparation for winter. Last fall, deer hunting was different for many Pennsylvanians, because the oak stands they usually hunted were defoliated earlier by caterpillars and consequently devoid of acorns and deer. Hunters found out at the last minute deer weren’t in their usual places and had to work hard to find where they went. Some never did.

“This unexpected reprieve from serious forest defoliation will hopefully make it somewhat easier for hunters to find deer activity centers in the state’s heartland and the northeastern counties,” said Robert C. Boyd, agency Bureau of Wildlife Management assistant director. “These were the areas where gypsy moth caterpillars were poised to do the most damage this year. But this reprieve doesn’t mean it’ll be easier to shoot a deer this fall. Hunting deer is almost always a challenging pursuit.”

This spring, the Game Commission’s gypsy moth suppression efforts in south central counties included spraying about 3,000 acres of State Game Lands in Juniata, Perry and Snyder counties. In the Northeast Region, the agency focused on State Game Lands in Luzerne, Monroe and Pike counties. In the Southeast, State Game Lands in Berks, Dauphin, Lebanon, Lancaster and York counties were targeted.

On State Game Lands in the state’s northeastern counties, the previous three years were worse than this spring, according to agency forester Warren Harris.

“The last round of gypsy moth defoliation was not as devastating to State Game Lands in the northeast as some of the previous outbreaks,” Harris explained. “There was a lot of defoliation over the past three years, but many of our State Game Lands were not hit and where caterpillars were found in large numbers we sprayed. Last year, parts of Columbia, Luzerne, Monroe and Pike counties had the largest populations. When the caterpillars emerged this spring, they continued to cause moderate to heavy damage until their population collapse occurred.”

Wherever gypsy moth caterpillars have caused damage on State Game Lands there still is considerable potential for habitat to rebound as it has in some northeastern counties. Many of the defoliated trees can recover. The same applies to understory that suddenly found itself in direct sunlight. But whenever habitat changes, there are always winners and losers among the area’s flora and fauna. Such is life; and death.

“It’s important to remember our State Game Lands have been through this before, and our losses this time weren’t as great as they could have been,” explained Bill Capouillez, agency Wildlife Habitat Management Bureau director. “Where gypsy moths have hit us hard the past couple years, we have salvage cut and started new forested areas. Where caterpillar damage was only moderate, we hope the trees will recover and forest interior species can make do.”

Southeast Regional Forester Henry noted that hard mast trees have a propensity to respond vigorously after gypsy moth population crashes.

“Trees stressed by gypsy moth caterpillars will attempt to produce more mast while attempting to survive,” Henry said. “The response of oak trees will depend on the level of stress the trees experienced. Trees subjected to lower levels of impacts, along with less drought stress, will respond more quickly and potentially produce more acorns.”

If you decide to keep score in afflicted areas, please note that red, black, pin and scarlet oaks produce acorns that mature only every two years. White and chestnut oak acorns mature annually. Consequently it could be one to three years until you see an average or better acorn crop in the area(s) you’re watching.

South central Region Forester Tom Lewis pointed out that salvage operations were conducted Bedford and Fulton counties to harvest stands of trees that were dead or dying from gypsy moth defoliation. Additional oak mortality salvage cuts will be made in Blair, Franklin and Perry counties.

“Some of these areas are already stocked with sufficient levels of regeneration, which will eventually develop into quality sources of food and cover for wildlife,” Lewis said. “However, a few areas either lack sufficient desirable regeneration or contain a high proportion of less-desirable plant species and may require remedial silvicultural treatments to enhance the establishment and development of beneficial trees and shrubs for wildlife. Either way, the forest we want will grow, one just requires a little more of our attention.”

Sometimes, removing trees isn’t an option. But that’s not always such a bad thing either, according to Harris, the Northeast Region forester.

“Dead trees that are left standing provide an abundance of snags that are used by insects and nesting songbirds,” Harris said. “I have worked areas where my ears were ringing at the end of the day after listening to the constant calling of juvenile birds in cavities that had mistaken the sound of my footsteps for their mother returning to their nest with food.”

Trees are important to wildlife. In fact, the overwhelming majority of wild birds and mammals that inhabit or pass through this state on migratory routes depend on or use trees, their fruits or the shady places they create at one point or another in their lifecycle. Trees matter. So does forest composition, which is why gypsy moths can wreak so much havoc in forestland by killing/severely stressing trees, giving sunlight access to the forest floor, and promoting unwanted changes in forest composition.

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