Last updated: May 17. 2014 9:14PM - 3422 Views
By - tvenesky@civitasmedia.com

An ash seed cluster which will be dried and preserved by the U.S. Forest Service in Colorado.
An ash seed cluster which will be dried and preserved by the U.S. Forest Service in Colorado.
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One of the more proactive approaches to defending against emerald ash borer is the use of biological controls. The state Department of Conservation and Natural Resources has employed a predator — three species of wasp, that prey on the emerald ash borer, which is an invasive beetle from Asia.

“One reason why invasive species are so disastrous is they are imported to an area that doesn’t have the checks and balances that are in their native habitat,” said Rachel Waggoner, natural resources manager of the Bureau of State Parks. “Our species of ash don’t have the same defenses to withstand the ash borer as the ash trees in Asia do. Nor do those predators occur here.”

But they are starting to.

After years of meticulous research to determine that it is indeed safe to release the wasps in Pennsylvania, DCNR in partnership with the U.S. Department of Agriculture, has released several species of wasps in select locations to see if they will at least limit the impact of the emerald ash borer.

Before being released, the agencies first determined that the wasps, which do not sting, prey only on the emerald ash borer. One species preys on the larva, Waggoner said, and another consumes the eggs.

So far releases have focused on the northcentral part of the state where ash tree populations are greatest.

“That region has not been infested for as long, so when the infestation moves into that high density area we hope the predator is able to move along with it,” Waggoner said. “Our goal is to release them along the leading edge of the infestation.”

Since the wasps were first released in 2012, follow-up visits to release sites have produced recaptures of the wasps, indicating the populations are surviving.

“It doesn’t eradicate a (emerald ash borer) population, but slows the spread and severity,” she said. “We’re not quite there yet.”

Inside the envelopes that are delivered to the Penn Nursery every fall is a future forest.

The envelopes contain the seeds of ash trees, which are collected by staff from the state Department of Conservation and Natural Resources and sent to the agency’s Penn Nursery during a brief two-week period each fall. The effort may be the last chance for ash trees in the state, which are being infested with the emerald ash borer.

Once the insect burrows into a tree and lays its eggs, death is imminent.

But at Penn Nursery in Centre County, there is hope. That’s where the seeds are processed and eventually shipped to a U.S. Forest Service lab in Colorado, where they are placed in cryogenic storage.

“A lot of the seed can be stored for 100 years,” said Tina Alban, forest nursery operations manager for DCNR’s Bureau of Forestry. “Someday, we’ll pull it back out and use it to re-establish the ash tree in Pennsylvania’s forest.”

The emerald ash borer, which is actually a beetle, has killed tens of million of ash trees since it was first identified in Michigan in 2002. It surfaced in Pennsylvania in 2007 and has been found throughout the state, including Luzerne and Wyoming counties.

While there may not be much hope for the species of native ash trees that inhabit Pennsylvania’s forests, preserving their seeds means that the trees’ specific genetic makeup is also saved and can one day be re-introduced as seedlings back into those areas where it disappeared.

To protect the genetic diversity of ash trees, seeds are collected throughout the state. Alban said the work has been underway for the last six years and several hundred envelopes of seeds have been preserved.

The seed collection program presents hope for the ash tree that another tree species, the American chestnut, didn’t have when a blight wiped it out across the state a century ago.

“Should the ash tree go the way of the American chestnut, we would have the ability to bring it back,” said Rachel Waggoner, natural resources manager with DCNR’s Bureau of State Parks.

There is a small window in which to collect ash tree seed. The seeds have to be ripe to a specific degree and placed in cold storage before they germinate. Alban said field staff across the state survey ash trees in July to determine the viability of the seed crop. Where the seed crop is suitable, crews have a two-week window in September or October to collect seeds. Trees that yield seeds for collection are photographed with an identifying number that stays with that particular seed crop all the way to storage in Colorado.

A twig and leaf sample is also collected with the seeds, which are shipped to Penn Nursery where they are dried before being sent to the Forest Service facility.

“They x-ray the seeds and separate out any empty seeds, and then they’re placed in cryogenic storage,” Alban said. “So far, all the seeds we’ve collected have been preserved.”

The nursery also maintains an ash tree orchard that will hopefully be used to collect seeds 20 years from now when the trees are old enough. Alban said those trees are injected with an insecticide to protect them from the emerald ash borer.

Ash trees aren’t the only species that Penn Nursery is working to save. They recently started collecting Eastern hemlock seeds as that particular tree continues to perish from the woolly adelgid.

“We collect hemlock seeds in the first or second week of October right after the cone opens,” Alban said. “You have a few days and then it’s gone.”

Seed collecting isn’t the only tactic the nursery employees to save trees at risk. They also work to develop disease-resistant varieties of species such as black walnut and butternut.

A fungus called thousand cankers disease has turned up in black walnut trees in the southeast part of the state, Alban said, while butternut has also been impacted with a fungal disease.

The nursery raises butternut trees that are “pure” in their genetic makeup and the seedlings are sent to the Forest Service, where the root stock is grafted with a diseased tree. The trees are then planted back at the nursery and the ones that remain disease-resistant are kept.

“It’s a long process that takes 20 years,” Alban said.

It’s a similar process that is being used in attempts to bring back the American chestnut. Surviving species are crossed with Chinese chestnut — which is resistant to the blight, and after several generations there are trees that are 99 percent American chestnut and are blight-resistant, Waggoner said.

That success gives Waggoner hope that the ash tree will persevere through the threat posed by the emerald ash borer.

“We’re doing everything that is prudent to save this tree,” Waggoner said. “I’d like to think that we’ll always have ash trees in Pennsylvania.”

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