It has taken me years as a forester to come to one personal conclusion, dead trees play a beautiful and valuable part in a balanced forest ecosystem. It is true that a dead tree does not make a tree farmer "money" and may be ugly to some. I was educated and pushed early in my career to remove or cut all trees that take up space where potential timber growth could be promoted.
But If you will look at an average forest, there are ALWAYS places were old and decaying trees can productively survive, have many more years of providing invaluable benefits to the ecology and will not effect even the most intensive timber oriented forest management plan.
These places take up very little commercial space even when your main objective is timber growth.
The decaying and death of just one tree will result in a slow process of returning value to the forest inhabitants and understory floor. While briefly providing nesting cavities, wildlife food in the form of insect-laden dead limbs, the "snag" will ultimately play an important role in nutrient cycling and assisting in the ecological processes.
So Why Leave a Dead or Dying Tree
I have a favorite sycamore den tree (see photo) where I can always count on seeing mammals, amphibians, reptiles and birds nesting in natural cavities called dens. The tree is in a shaded wet spot, not particularly important for commercial forestry and is home to raccoons and opossums for nesting, cover and relief from the hot midday Alabama sun. The snag is actually shaded by baldcypress trees in summer and warmed by the sun in Winter.
Studies suggest that mammals do not create a tree cavity but are secondary users and always move into a prebuilt den.
The primary first user of a cavity is most often a woodpecker and will establish a nest in a cavity it has carved out. The bird will nest only once in the same cavity but tends to stick with the same tree for creating more nests. Large pileated woodpeckers excavate the largest nesting cavities while smaller downy woodpeckers prefer dead branches on living trees. Flickers prefer dead trees.
Birds love aging trees. They use snags, limbs, and logs for perching, foraging, and nesting and nearly one third of bird species are cavity nesters. Of all the birds in North America, 55 species nest in cavities, primary excavators choose hardwoods, weak excavators choose conifer deadwood. It is interesting that eastern bluebirds and wood ducks are examples of bird species that must have prebuilt cavities for successful reproduction.
Managing Your Forest for Den Trees
So, how many dead trees should you leave, and where should you leave them? The answer depends on the part of your forest that has wildlife-loving trees that can be left and on your commitment to non-game wildlife management.
Larger den dependent mammals prefer large snags that are over 15 inches dbh with some significant height. Larger climbing mammal species seek cavities that are created by the larger pileated and red head woodpecker. .Remember also that many of these trees have basal or bole cavities from past injury and wildfire. Smaller animals may use snags or dead limbs from 4 inches in diameter.
You should try to keep the greatest number of snags possible while remembering that a larger den tree will also stand longer, decay more slowly and have a greater benefit on the local ecosystem and ecology than smaller counterparts.
You will have choices when considering dead and aging tree speces. All creatures will favor snags of certain tree species and have adapted to a particular ecology. You need to remember that these tree species preferences may vary from region to region. Select from the best choices available to you.
In a region with overwhelming conifer trees, You have the opportunity to leave older trees standing near trees to be harvested. Be sensitive to a fragile nesting site and try to leave a small buffer. You may have a larger unloggable wet area where harvest decisions are less problematic.
Consider the level of snag decay as another important factor to recognize when making management decisions. Hardwood trees that have recently died with intact bark will stand longer than older, softwood trees that have lost their bark. Depending on the existing animal species, you may need to leave a variety of softwood and hardwood snags. One thing to remember is that some animal species need trees that are partially alive. Most den trees are living trees where the heartwood has decayed to create cavities.
Tips for Locating Your Den Tree
The location of aging trees will impact opportunities to provide wildlife habitat. Here are ways to increase wildlife nesting in your forest.
- Research suggests maintaining 2 to 4 large den trees per acre for wildlife benefit if available.
- Leaving more snags will lessen competition for nesting, foraging, and roosting sites.
- Living trees with existing cavities should be given preference.
- Leave average of 10-20 small (<12" diameter) cavity tree candidates per acre.
- Logging debris should not exceed 8 inches depth near wildlife den areas.
- Determine if a snag presents a substantial hazard to forest workers or property.
- Install nest boxes as "cavities" for some species to reproduce.