By JOE RANKIN
Forests for Maine’s Future Writer
In 1962 Rachel Carson’s classic enviro-expose Silent Spring was published, laying out how indiscriminate pesticide use was decimating nature, particularly bird populations.
The book helped shape the environmental movement and led to the creation of the Environmental Protection Agency and some of the United States’ most enduring environmental legislation. DDT, one of the main chemical culprits, was banned. In the decades since, top-of-the-food chain species most affected by DDT, including the American Bald Eagle and the Osprey, have rebounded.
But North America’s birds are by no means out of the woods.
Some old threats remain, and new ones have emerged -- loss of breeding habitat, loss of wintering habitat to deforestation in the tropics, industrial agriculture that eliminates brushy field borders, light pollution that steers migrants off course and into fatal impacts with skyscrapers. Then there is climate change, which could cause some species to miss their connections with food sources at key times, or eliminate their habitat.
Today, northeastern North America, with its verdant and extensive woodlands, is a vital habitat for many songbird species that live there year round and the migratory species that come in the spring to court, nest, and raise young.
“Maine forests provide nesting and breeding habitat, which is critical to their larger population dynamics and population cycles,” said Amanda Mahaffey, a forester and the northeast region director of The Forest Guild. She calls them a “baby bird factory.’”
Maine Audubon Society Wildlife Biologist Susan Gallo said, “The northeast and Maine is a hotspot for breeding forest birds compared to the rest of the country. There’s more species diversity here in terms of forest songbirds than in other places in the country.”
Why? When lots of species are in the same place, Gallo explains, each needs its own niche. Maine’s large tracts of forest, with different species of trees and trees of differing sizes and ages, provides lots of different niches for birds to nest in. “There’s also abundant food and lots of insects,” something that Mainers who venture into the woods in June know well, she added.
Maine is the most forested state in the U.S., with almost all of that forest privately owned, by landowners large and small, and much of it is managed for timber production. And when logging occurs it affects birds.
The Forest Guild and Maine Audubon, supported by the Maine Forest Service, have been developing a Forestry for Maine Birds program to educate foresters, loggers and landowners about how various forest management techniques can be used to enhance habitat for birds. It is, they say, “forestry with birds in mind.”
The program is based on a highly successful Foresters for the Birds Program in Vermont. A guidebook for foresters -- Forestry for Maine Birds -- is expected to be printed this spring. A landowner version will follow. Workshops for foresters began last year and more are scheduled this year. Workshops for loggers and landowners are also planned.
Foresters are used to looking at trees -- assessing size, condition and potential use and value. But surveys show that most small woodlot owners are less interested in the economics of a timber harvest than they are in enjoying their woodland by walking there and watching wildlife. Forestry for Maine Birds aims to help educate landowners and the foresters who serve them about how they can help birdlife while still meeting the other goals of a timber harvest, including making money, said Gallo and Mahaffey.
The guidebook, Forestry for Maine Birds, uses 20 bird species and four forest types to show how forestry affects birds. It divides the woods into northern hardwood forest (maples, birches, beech and so on); northern softwoods (spruce and fir), oak-pine (important along the southern Maine coast), and northern mixed woods (various blends of the others.)
The birds focused on in the book are a diverse lot, ranging from the American Woodcock to the Bay-breasted Warbler, the Boreal Chickadee to the Scarlet Tanager, the Northern Flicker to the Ovenbird, the Veery to the Yellow-bellied Sapsucker. There are three woodpeckers on the list and 10 warbler species.
The focus species represent various habitat requirements and were selected because part of their “core” habitat is in Maine, because they are declining in numbers, or because they need key elements of a forest to survive. “We also considered how often you see them, and how easy they are to identify,” said Gallo. “They need to be birds that landowners can see and identify with” to learn their habits and recognize their song.
The Ovenbird, a largish ground-nesting warbler, for instance, likes an open understory and deep leaf litter for its domed nest. The Black-backed Woodpecker needs larger spruce and fir trees. The Blackburnian warbler likes large blocks of softwood or mixed wood forest with dense mid-story and good canopy cover. The Eastern Wood Pewee likes small gaps where it can hunt insects. The Northern Flicker prefers open areas with large snags where it can hammer out nest cavities. The Scarlet Tanager likes larger areas of closed canopy forest, with a preference for oak.
It is these needs and preferences that make it impossible to manage a small woodlot for all species of birds. But Gallo notes that all the species highlighted in Forestry for Maine Birds “represent broader habitat needs. The idea is that if you manage for one or more of the species on the list then you’re also going to benefit a whole other suite of birds and other wildlife” that use the same type of habitat.
The silvicultural treatments recommended by the soon-to-be-printed foresters’ guide are well known, said Mahaffey. “We are not reinventing the silvicultural wheel. This guide simply pairs silviculture with habitat needs so that forests can be managed effectively ‘with birds in mind.’ ”
The workshops and guidebook emphasize seeing the forest in terms of vertical and horizontal layers, from the duff that makes up the forest floor to downed deadwood, the understory, the middle levels, to the canopy. It’s all used by some type of bird.
And changes in that forest will in turn affect the birds that call it home, benefitting some and not others.
One place where forestry research and birds have been studied together is the Holt Research Forest in Arrowsic. They have been monitoring breeding birds there since 1983, said Holt Manager Jack Witham. There was a harvest in 1988 and later timber stand improvement work to eliminate red maple sprouts, both of which help illustrate how birds respond to forest management.
Winter Wrens had not been seen in the Holt Forest before the harvest, Witham said. But in the first year afterward five breeding pairs were observed. The Common Yellowthroat and the White-throated Sparrow were present in open ledge areas before the harvest and afterwards were found in the larger post-harvest gaps, Witham said. The Black-throated Blue Warbler, which prefers taller trees with a dense understory, was present in the 10 years after the harvest, but then disappeared after the maple sprouts were eliminated.
Any timber harvest will affect birds, but it’s the intensity of the harvest that governs which, and how many, species will be affected, said Andrew Whitman, a senior scientist with the Manomet Center for Conservation Sciences, which has done research on how clearcutting and partial cutting affect bird populations. “In most situations it’s a tradeoff,” Whitman said. Landowners can generally increase the number of bird species with a modest harvest. The heavier the cutting, the more chance that some mature forest species will drop out, he said. “But the upshot is that cutting wood does not have to be fundamentally at odds with maintaining songbirds” on your land.
While landowners need to decide what their objectives are for their land and then work with their forester to factor birds into the equation, it’s helpful to look at the situation from a bird’s-eye view, taking in the area around your woodlot rather than just concentrating on your own property. “If you have a stand of mature forest and you’re surrounded by early successional forest, your block is really important, or vice versa,” said Gallo.
Of course, there’s no guarantee that the trees on your neighbor’s property today will be there next week. So, while it’s good to take a landscape-scale look-around, a landowner still has to work with what they have. After all, they have their own objectives, financial and silvicultural.
It’s important not to get too hung up on outcomes, cautions Whitman. “One thing about being in Maine, a state that’s so heavily forested, is you don’t have to think of your relatively small woodlot as being responsible for bird populations. What is happening across the landscape can also help populations of songbirds, especially if there is a lot of mature forest.”
At Hidden Valley Nature Center in Jefferson -- the northeast region Outstanding Tree Farm for 2014 -- wildlife, especially birds, is factored into the timber harvesting equation. At Hidden Valley they’re working to maintain a continuous canopy forest, since much of the surrounding lands have been heavily cut or are recovering farmland, said Director Andy McEvoy. Hidden Valley consulted with birders, biologists and naturalists in developing its strategy. “There seems to be a general agreement that local bird populations don’t need more early successional habitat,” he said.
“For this and other reasons, our timber harvests are generally light and leave behind mostly single tree canopy gaps. The exceptions are our small yards, which are dotted around the harvest area. Even those gaps are quite small, like an eighth of an acre, and there might be four of them on a 10-acre harvest block,” McEvoy said.
While working to maintain a mature forest, Hidden Valley is also trying to create more diversity in the canopy height. They also make sure to leave a lot of coarse woody debris -- downed deadwood -- and snags. “We also are pretty careful to identify large diameter dead and dying cavity trees,” McEvoy said. “There are some spectacular old, gnarly red oaks that are tempting to remove from a strict silvicultural perspective, but they provide some good shelter for everything from Downy Woodpeckers to Fishers.”
Sometimes forestry for the birds isn’t just about cutting -- or not cutting -- trees.
Manomet’s Whitman said that, in central and southern Maine controlling White-tailed Deer populations and invasive species should be priorities as well.
“There are pockets where deer populations are high enough that they are changing the understory vegetation, which can have effects on Black-throated Blue Warblers and Ovenbirds. Also, in the long run, deer in these areas may make it hard to regrow a forest,” he said.
Invasive species -- mainly imported exotics from elsewhere in the world, such as Japanese Barberry and Oriental Bittersweet, can crowd out native vegetation. Often their fruits or seeds aren’t as nutritious or useful to North American birds as those of native species. Some exotics can change the makeup of the forest itself. The Emerald Ash Borer, which has a voracious appetite for ash trees, has already been found in New Hampshire and most experts say it is likely to make it to Maine
Gallo acknowledges that the number of threats birds face in the 21st century are numerous and extend far beyond Maine’s borders. “Improving habitat on the breeding grounds is not the whole answer,” she said. “We need others to work on elements of habitat along the migratory pathway and in the wintering grounds. But that work will be for naught if the birds aren’t finding places to nest and feed and raise young. So the work here in Maine is an important part of the solution.”
Joe Rankin writes on forestry, nature and sustainability from his home and woodlot in central Maine.