Trees Just Keep on Giving
Dead trees are one of the most important parts of a forest ecosystem.
Almost everyone knows that living trees provide nesting sites for birds; produce nuts, seeds and berries; give us shade; furnish wood products; and make a percentage of the oxygen that we breathe. Many, however, don’t stop to realize that trees continue to be a critical part of the forest long after they are dead.
Larger dead trees, often called snags, are so important that what seems to be ideal habitat will be devoid of some species if no den trees exist in the area. Raccoons, for example, can occupy excellent habitat at the density of more than one per acre. If the same habitat has no den sites, few to no raccoons will be found.
According to Rance Harmon, extension forest resources specialist at Penn State, 35 species of birds and 20 species of mammals use tree cavities in Pennsylvania. These include many that have been featured in Nature’s Corner; such as the pileated woodpecker, bluebird, gray squirrel, brown creeper, porcupine, downy woodpecker and others.
Although the larger cavity trees provide the most value, even the smaller dead trees are important. To hold the maximum wildlife diversity, forest managers recommend 10-20 smaller dead trees and at least two large snags per acre.
Trees die because of insect infestations, drought, diseases, injury, leaf litter fires, or just because neighboring trees overshadow them. Often it is a combination of factors. In a 25-acre plot, a few trees die each year. Sometimes an insect such as the gypsy moth, oak leaf roller, or fungus such as Dutch elm blight will kill many trees in a small area in a short time. If left alone, these dead trees will prove a multitude of values until they are gone, but they are not as valuable as snags scattered throughout a healthy forest.
Even trees that measure four to five inches in diameter attract a multitude of insects and other invertebrates after they die. The bark loosens and it, as well as the smaller branches, drop off. Fungi and insects, such as carpenter ants, invade the wood — further speeding its decomposition. Birds alight and prospect for invertebrates along the dead branches. Woodpeckers drill into the trunk looking for ants and termites. Titmice, chickadees and other smaller birds enlarge the woodpecker holes to make nesting cavities.
Other values abound. Hollow trees provide thermal cover for many species during the winter. Dead trees are favored singing posts for songbirds. Kingfishers, owls and hawks use them as hunting perches. The soil around dead elm trees often grows the tasty morel mushrooms.
Depending on the species, dead trees can stand for a long time. A few American chestnuts that died 50 years ago are still standing. Aspen, cucumber, hemlock and tulip drop rather quickly, but they are particularly valuable to cavity nesters while standing because their soft wood is easy to excavate. Oaks and locust can last a long time. The gypsy moth infestations of the late 70s killed three large oak trees on our wooded property. One, a red oak, is on the ground, the scarlet oak snapped off during a storm and most of the large white oak is still standing.
Decaying trees are still valuable even after they topple or are cut. Forest ecologists now consider these decomposing logs to be biological “hot-spots.” Insects and fungi continue their action. Woodland salamanders are attracted to the crumbling wood, for it acts as a natural sponge. According to Harmon, in the northeast, “Twenty-three species of amphibians and reptiles take refuge in decaying wood.” Animals from skunks to black bears rip apart rotting logs in search of insects and amphibians.
Decaying logs and stumps provide ideal substrate for tree seedlings such as hemlock and birch. Downed logs stop erosion and eventually all of their once-towering majesty is returned to the soil as molecules that become a part of the next generation of trees.
Safety concerns sometimes outweigh ecological values. Dead trees near houses, trails, or highways must be cut to ensure the safety of people. A good compromise is to trim or have an experienced woodsmen trim all branches from a dead snag and top the tree at 10-15 feet above the ground, or whatever height can safely be allowed to stand. About ten years ago, the power company asked to remove a dead oak that was threatening their lines near our property border. I asked if they could top the tree instead. The crew evaluated the situation and then topped the tree at 15 feet, protecting their power lines while still providing wildlife value.
If you own a woodlot or know someone who does, consider the value of dead trees to forest critters and allow these trees to complete their natural cycle. Let the chain saw pass them by. If you must cut a den tree, consider doing it during the late summer or fall when you are less likely to interrupt reproduction or disturb animals during the cold of winter. As a part of a larger forest, these snags or even their downed decomposing trunks remain an integral part of the ecosystem. Trees are organisms that keep on giving long after they die..
Mark Nale can be reached at MarkAngler@aol.com
