Our grandparent’s generation removed trees from property and logs from streams. But, as Andy MacKinnon RPBio RPF, Research Ecologist with the Coast Forest Region of B.C. Ministry of Forests and Range points out, that was not the best ecological choice. “It’s been recognized over the last three to four decades that logs are critical components of streams and also of lakeshores. They have a very important function. There is huge literature on dead trees in forests where they provide moisture and nutrients and soil structure and environment for a wide variety of habitat. These logs are critical components. It’s almost always better ecologically to leave them.”
Length of Time for a Tree to Decompose
If you opt to leave a dead tree where it falls, how long does it take to decompose? MacKinnon says it depends on a number of factors and there are four main ones. “The primary determinant is climate. Dead trees and logs decompose more quickly in warmer and moister climates. They take a much longer time to decompose in drier, colder climates simply because of the things that decompose them (the fungi, the bacteria, the bugs) are much more active in moist, warmer climates. All things being equal, things will decompose more quickly on the West Coast than they would in the Northwest Territories.”
MacKinnon continues, “Another factor is tree species. As a general principal, the softwoods and the conifers will decompose more slowly than the hardwoods or the broad leafs. So your poplar will, all other things being equal, decompose more quickly than your pine. The third factor is the log length and the fourth is the log diameter. Trees decompose as organisms get into it so that longer pieces and pieces that are bigger around last a lot longer than mature pieces or pieces that are smaller around. Smaller deciduous trees will be gone in one to two decades whereas longer, larger pieces of western red cedar could last six to ten centuries.”
Dead Trees and Nutrients
When you remove dead logs from the ground, you are missing out on returning valuable nutrients to the ground. David Bostock, an arborist with Bartlett Tree Experts, explains, “As a tree breaks down over many years, carbon, nitrogen, and other nutrients are returned to the soil through the activities of earthworms, wood-boring insects, and other organisms. The nutrients are recycled and biological activity is increased. There are organisms that survive only in standing or fallen logs and when those are absent from a forest or from a property, those organisms are obviously unable to survive there.”
A number of creatures thrive on dead and dying trees. According to Bostock, “There is a suite of organisms that are called the detritivores which feed on dead and decayed organic matter. There are also organisms that consume those detritivores so on up the food chain. So there’s a whole ecosystem whose base is in that log. It includes things like woodpeckers, raccoons, and skunks. Those would be the main ones but things like salamanders often live underneath logs as logs provide a moist, damp, organic environment for them to live in.” Bostock mentioned that you may see fungi growing on dead trees as they assist with the process of breaking down a large, solid chunk of wood into smaller softer, more digestible pieces.
When to Remove Dead Trees
All that said, there are times it is better to remove a dead tree. MacKinnon points out, “In general, if it is posing some kind of safety hazard or navigation hazard then obviously it should be removed.”
Leaving Dead Trees Alone
If you plan to leave dead trees alone, Bostock has a few suggestions. “Leave them standing if they don’t pose any risk to persons or property. If they have to be cut down, we generally recommend leaving them in the largest possible manageable pieces in contact with the forest floor. The process of organisms assisting with breaking trees down works much faster if the log is on the ground as opposed to something that is suspended in the air. Lying at an angle up against a tree would take much longer to break down.”
MacKinnon shares some final thoughts, “The death of trees is part of the life cycle. When a tree dies and falls to the forest floor, it provides a lot of benefits. A lot of these trees and logs are invaded by bugs and fungi and insects. Many times we find there’s a lot more biomass or living material in that tree trunk after it’s dead than there ever was when it was alive. It’s just the way that these trees work in the forests and streams.”
Toby Welch - Toby is a full-time freelance writer who specializes in magazine articles, online writing, e-books, and manuscript editing.
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