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No tree stands forever. There are many ways for a tree to die: drought or disease, a bolt of lightning or the slow onset of old age. The deteriorating stage is when a tree is most valuable for wildlife. Ah, the irony, having to remove trees just when they have taken over a century to become such a precious resource for Red List organisms. What can be done? Consider preserving these ecological gold mines as wildlife trees. A wildlife tree (or snag as it is sometimes called) is simply a standing dead tree retained for habitat.
In some forests, up to 45 percent of bird species rely on snags for nesting, roosting, foraging, or perching. Crevices formed between the trunk of a dead tree and the peeling bark provide protection from the sun for bats and amphibians. Decaying wood is home to fungi, slugs, snails, and millipedes which need to stay busy, pulling trees apart. They in turn are food for birds, mammals, amphibians, and reptiles. In addition, dead wood stores carbon which is sustainable in the era of climate change.
How long the decaying tree remains standing depends on factors like its species, size and the local climate. Aspen and birch might stay upright for a decade, a large conifer for more than a century. At every stage of decomposition, the snag provides a bounty of benefits to the ecosystem around it. But for maximum biodiversity purposes, you want a snag to be standing for many years. Why do we need that time? Well, because it takes time for the wood to break down, and to be palatable to key invertebrates. As the larvae of those invertebrates develop, that is when it gets interesting for woodpeckers and other insectivores. This can take 3 years to decay, 3 years of insect impregnation and result in only 3-4 years of woodpecker feeding, if the snag lasts for ten years (typical of beech and maple snags).
What can be done to create longer-lasting snags? Select larger diameter stems for snag creation. Limit the height, as taller snags fail earlier (due to leverage/wind drag). A snag of 16-20 feet in height is fine, no need for anything higher, unless there is a particular existing feature to be preserved (e.g., an upper stem cavity or crack). Create snags in low-use areas or move and re-erect them in quiet spots. Do not limit selection to durable wood species (e.g., oak, walnut), as low density woods are highly used (e.g., birch, willow).
We are so conditioned to manicured and highly managed landscapes that we sometimes overlook the importance of dead wood in a functioning forest ecosystem. Trees are great 'giving' organisms. There is a whole lot of life in a dead tree.
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