More and more woodlot owners are taking a broader view of their forests. They look for values other than the immediate return on wood harvested. These values include other forest products such as ground hemlock and mushrooms; carbon storage; water purification; leaving a legacy for their children; and healthy wildlife populations.
Wildlife trees (dead or dying trees used for nesting, feeding, denning and roosting) go through several stages that can start with ants tunneling into the rotting centre to flycatchers perching on the bare branches. For cavity-nesting birds they are critical habitat. Some species excavate cavities for their nests, while others take over and enlarge existing holes. Many of these birds in turn help the forest, eating insects which can damage trees. The following birds use cavities for nesting on Prince Edward Island:
The brown creeper, a small bird that is occasionally seen eating insects living on tree bark, makes its nest under a loose piece of bark hanging from a dead tree. That big old white pine with the broken top that is starting to die might just be the perfect nesting platform for a pair of bald eagles or osprey. Looking at the bigger picture, we have too few of these old giants left in suitable locations.
Eastern redback salamanders also make great use of wildlife trees. They thrive in older Island woodlands that have a strong hardwood component. These 7-10cm (2.8-4″) long amphibians make good use of the dark, moist conditions under loose bark. Once the wildlife tree falls to the ground, it continues providing those conditions and can be home to blue spotted and (yellow) spotted salamanders, as well as redbacks. Birds of prey, such as hawks and the smaller falcons, and many of our flycatchers rely on snag trees as perches. The loose bark of dead trees is an ideal roosting spot for little brown bats and spring peepers. Raccoons, red squirrels, northern flying squirrels and deer mice use cavities for nesting or denning.
Snags are not just home to birds and mammals – insects and other invertebrates, as well as fungi, recycle dead tissues of the tree into new life. They also provide habitat for ants and other important food sources for many birds.
Now that we have an idea about how important dead and dying trees are to wildlife populations, how do we ensure that our forestry practices reflect this?
Think of dead and dying trees as the “condominiums” of forests. Due to the large number of species that rely on wildlife trees, it is important that we see dead and dying trees not as “wasted resources” but as critical habitat in healthy forests. The poplars in an old-field white spruce stand are important not only for the leaf litter they produce but because they get large quickly and begin to rot in the centre. This makes them ideal places for chickadees, nuthatches and woodpeckers to make nests. And as so often happens in the complex world of nature, these holes can later be taken over by the owls who, with their hooked beaks, can’t drill holes in solid wood but can easily enlarge a flicker hole in the soft poplar.
Leave plenty of wildlife trees. A review of existing literature finds a wide range of guidelines on both amounts and sizes that should be present in forests. Some guidelines call for leaving 10-12 snags per hectare (4-5 per acre), but are working with much larger trees than we generally have left in Island forests. Since there is much left to learn about the complexities of forests, it makes sense to err on the side of caution and perhaps leave double that amount. And not surprisingly, snags with the largest diameter support the greatest number of species, so we need large snag trees. According to the Forest/Wildlife Guidelines and Standards for Nova Scotia, “Large trees over 50cm (20″) diameter at breast height are better for cavity users because they provide habitat for both large and small wildlife species. Trees smaller than 20cm (8″) dbh are of limited value to cavity nesters and will not provide nesting habitat for woodpeckers larger than the downy woodpecker, our smallest.” In Maryland, wildlife managers suggest that leaving 10-20 small snags, and 2-5 large snags greater than 30cm (12″), per acre, or 25-50 small and 5-12 large snags per hectare.
Plan for a continuous supply of wildlife trees. This means that young and middle-age trees must be left to become future snags, not just the ones you leave for today. Ideally you would find 2-3 larger wildlife trees and leave clumps of other trees around them, including a mix of younger and non-merchantable trees. These clumps should be scattered as evenly as possible throughout the cut.
If a woodland lacks snags but has large living trees, you can speed up the natural process and create snags by girdling a few trees, both coniferous and deciduous. With an axe or chainsaw, remove a complete ring of bark and cambium layer to prevent nutrients from flowing from the roots to the crown of the tree. On larger trees, make two cuts around the tree at least 5-7.5cm (2-3″) into the sapwood.
Allow at least some trees to become quite large. Studies on the pileated woodpecker in Oregon suggest that size of nest and roost trees is an important consideration. Research showed the smallest diameter nest tree to be 61cm (24.5″) while the mean diameter was 80cm (32″). Snags of that size are only possible when we consciously allow trees to get old. If we view them as important to both wildlife and the forest itself, there is no loss, only gain.
Attention to wildlife trees should be part of any sound forest management plan. The time it takes to maintain and enhance this valuable habitat will be worth the effort.
What you can do: