Healthy Forests Are Messy Forests: Lessons from Acadia National Park

By Kate Miller, forest ecologist with the National Park Service's Northeast Temperate Network, based at Acadia National Park.

Sargent Mountain Pond and forest, Acadia National Park. Credit: National Park Service.

The author has spent ten years monitoring forest health in national parks across the eastern United States, much of it in Acadia National Park. A decade of monitoring gives the Northeast Temperate Network a good understanding of the health of, and threats to, the region's forests — and helps park managers decide how to manage them.

Acadia's forests are in good shape

• Better than many parks to the south, which are often badly affected by invasive plants, too many white-tailed deer, or both.
• Older than most in Downeast Maine, with significantly more old-forest habitat — regionally important for species that depend on it, such as northern flying squirrels and brown creepers.
• Mostly native. Partly by luck and partly thanks to Acadia's Exotic Plant Management Program, its forests are largely made up of native species.
• Following natural processes, another strong sign of health. Forests burned in the 1947 fire are going through expected succession: pioneer species such as paper birch and big-tooth aspen are dying back and being replaced by shade-tolerant red spruce and red maple. Elsewhere, the forests are mostly even-aged, mature spruce–fir, some now shifting towards late-successional forest.

Untidy on the way to old growth

That shift often means the even-aged canopy breaks up — think of blowdowns after a big storm. It can look untidy and chaotic, but it adds structure (fallen branches and trunks, upturned root mounds) and makes room for other trees to grow larger. The end result, which half or more of Acadia's forests are expected to reach in the next century or two, barring major climate change, is a structurally complex old-growth forest, mostly red spruce often more than 16 inches across, with standing dead trees and fallen logs of all sizes and stages of decay — as in one of Acadia's few remaining old-growth stands, along the Sluice Way Trail on Bernard Mountain.

Threats, and a mostly hands-off approach

Acadia's forests face invasive plants, exotic forest pests, atmospheric deposition such as acid rain, and climate change. How climate change will affect them is uncertain, but that it will — if it is not already — is certain.

• In the short term (years to decades), reducing other stressors, such as invasive plants and forest pests, is one of the best ways to make forests resilient to a changing climate.
• In the long term, climate adaptation will be needed, and Acadia is already planning for it.
• Otherwise, hands off. Let forests develop through natural succession and disturbance, and intervene only when a stressor — such as too many deer — disrupts those processes.

Advice for landowners

The same approach suits private landowners and agencies alike, especially where land is not managed for timber. Well-meaning landowners often harm forests by trying to "clean them up." Healthy forests are messy. The author's guidelines, followed on the author's own land:

1. Let it be. Where timber is not the main goal, doing nothing is a perfectly good way to manage a forest. Nature does not usually need human help to be healthy; let disturbances happen and trees die.
2. Dead wood is good wood. A tree has only partly fulfilled its ecological role when it dies. Standing dead trees (snags) and fallen wood shelter birds, small mammals, amphibians, insects, mosses and fungi; fallen wood is a seedbed for young trees; and the mounds left by uprooted trees give seedlings places to grow and shelter small mammals and ground-nesting birds — the winter wren, with its long, bubbling spring song, specialises in nesting in their root wads.
3. Encourage native species. Do not plant non-native species, and remove invasive ones already present — the author has spent five years fighting a stand of oriental bittersweet on the author's own property.
4. Keep the good bugs happy and the bad bugs out. Pollinators are vital and very vulnerable to pesticides: garden organically and plant a variety of native flowers. Exotic forest pests, a big threat to several common northeastern trees, spread mostly on firewood — out-of-state firewood is banned in Maine.
5. Protect the soil. Earthworms are not native to the Northeast; good for gardens, they are bad for northern forests, quickly eating the leaf litter that feeds plants and keeps soil from drying. Trout lilies, trilliums, and sugar maple and northern red oak seedlings suffer where earthworms arrive. Throw unused bait in the trash, not the woods, and do not dump mulch or compost in the forest.
6. Keep forest buffers along streams, ponds and wetlands. They slow and clean water flowing in, shade streams for cold-water fish such as trout, and give upland homes to amphibians that breed in water.

Sources

• Kate Miller, "Healthy Forests Are Messy Forests," National Park Service, Acadia National Park. https://www.nps.gov/articles/000/messy-forests.htm
• The idea that a dead tree has only partly fulfilled its ecological role is from Franklin and others (1987). The article points readers to the Maine Natural Areas Program, the Xerces Society, the Maine Forest Service and the Great Lakes Worm Watch for more on invasive plants, pollinators, forest pests and earthworms.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.