“In the place where the tree falleth, there it shall be.” Ecclesiastes 11:3
A dead tree is never entirely dead even though it may seem that way at first glance. Observe a dead tree for a while and you’ll see that it is teeming with life. The healthiest, most biologically diverse forests have a good share of dead trees, broken tops and downed logs along with living trees. They aren’t the tidiest looking forests, but they are the most ecologically healthy.
Dead trees in forests and home landscapes provide habitat for more than 1,200 wildlife species in the United States. According to the U.S. Forest Service, this includes about 85 species of birds, at least 50 mammal species, and about a dozen reptiles and amphibians that rely on dead trees for survival. Then there are the dozens of invertebrates like millipedes, beetles, spiders, worms, ants and more who call dead trees home or snack bar. Some estimates indicate that removal of dead trees from wooded areas can cause loss of habitat for one out of five of the animals in the forest’s ecosystem.
Dead trees, also called “snags,” can stand for many decades and are useful in every stage of their decay. When standing, they are used by wildlife as shelter, food sources, lookouts and hiding places.
At least 30 kinds of birds use snags as foraging perches, whether they are flycatchers scooping up flying insects; kingfishers, eagles and ospreys diving for fish; or owls and hawks searching for field mice. In addition, many bird species perch atop dead trees to sing their little heats out. Dead trees are necessary at some point in the life cycles of up to 45% of all North American bird species.
The most well-known and observable use of dead trees is the cavities that birds use for nests. Only 30 species of birds are able to make their own nest cavities in trees but another 80 animal species, called secondary nesters, depend on those pre-made cavities for their homes. Some of the secondary nesters are larger birds, squirrels, bats, raccoons, porcupines and opossums. It’s not uncommon for a series of ever-larger birds and animals to call the same cavity home.
Dead trees attract insects and in the past that was one of the reasons that snags were removed from forests. However, those very insects draw predator insects and birds that actually help control insect pests that can harm the overall forest.
Both standing dead trees and downed logs are home to hundreds of species of pollinating insects like bees and wasps, the primary pollinators of a forest’s flowers and berry-producing shrubs.
AFTER THE FALL
One day, after years of providing for birds, animals and insects, the tree will finally topple. Even then it continues to perform useful ecological services. If it is propped up by its branches, animals like bears, foxes and porcupines may make a den in the protection of the branches. Generations of grouse may use it for drumming stands.
Eventually even those branches will give way and the trunk will lie flat on the ground where fungi and soil microbes will soften the wood, and insects and worms will arrive and thrive. Now the rotting log is performing ecological benefits such as soil fertilizer, erosion control, soil moisture stabilization and carbon storage.
At this point, salamanders arrive and search the downed log for food. Salamanders don’t get much press, but did you know that Wisconsin has seven species of salamanders? And that in eastern forests salamanders make up more biomass than do deer? Salamanders eat insects like beetle larvae, ground beetles, spiders, sow bugs and round worms that would like to consume all the leaf litter on the forest floor. When salamanders prey on these species, a deeper layer of leaf little remains in the forest which holds in moisture important for other forest plants and reduces erosion. Below that leaf litter is a whole other layer of life dependent upon dead wood. A complex food web made up of bacteria, fungi, protozoa, springtails, mites and more tiny organisms work to improve the soil for forest regeneration.
Back to salamanders for a minute. Do you know what eats them? Wild turkeys for one, so you can see how allowing downed logs to remain in the forest can directly affect the results of your spring turkey hunt.
Deer also benefit from dead trees. They eat the lichens that often grow on the bark of dead or dying trees. They’ll also eat mushrooms that grow in the damp rotting wood and leaves, as do insects, turtles, birds, mice and squirrels. Mushrooms can make all the difference in a deer’s survival of a difficult winter.
Over the years, as a log slowly decomposes, it releases its nutrients into the soil and becomes what is known as a nurse log. Bright green mosses and colorful mushrooms may grow on it and tiny plants and even tree seedlings will find purchase on the rich decomposing wood.
When a tree ends up falling into a stream instead of the forest floor, it slows the movement of the water and traps sediment behind it. This provides habitat for fish and amphibians. Most trout fishermen know that streams edged with downed trees produce more fish. Scientists have not pinpointed a maximum density of logs in streams that is too much. Basically, the more wood, the more fish.
HOW MANY DEAD TREES ARE ENOUGH?
If you have wooded acreage, three snags per acre is the minimum that is recommended to be left standing. A single dead tree in a small yard is also vital, sometimes even more so than on acreage. There is no upper limit for number of dead trees, just as there is no size limit. Even a tree with a 6” diameter at breast height can host smaller birds. In general though, the larger the snag the better and the more snags the better!
WHEN A TREE SHOULD GO
When a dead tree is leaning against your house or may fall or drop branches on your house or your neighbor’s house, or your children or your neighbor’s children, it should go. Consider that it may be possible to remove part of the tree and let the remainder stand, or to move the dead tree or its branches to another part of your property.