When a tree falls in the forest, it may or may not make a sound. One thing for sure is that when it does fall, or even just dies, the whole ecological community rejoices for all the benefits it will bring. It may seem that the health of the forest would be defined solely by the abundance of living trees and plants, when in reality the number of dead and dying trees is just as important. In fact, many studies suggest that the volume of deadwood in a forest can be used as an indicator for biodiversity (the variety of life found in a single area) (Lassauce 2011). This makes sense given the number of species that benefit from this resource during their lifetime. The presence of dead wood such as standing snags, downed logs and rotting stumps is not, as it would seem, an indication of death and disease, but rather, a telltale sign of life. It would take many blog posts to go into all of the reasons why deadwood is important, so I’ll just discuss a couple of them here.
Food, shelter and a safe passage through the woods
If you notice a theme here from my last post, that’s because there is a common thread that unites the animal kingdom, and that is the need for food and habitat. Deadwood plays a key role in providing these necessities to a wide variety of living things, from birds, to insects, to squirrels, and even to fungi, lichens and mosses. Some estimates say that up to 40% of organisms in forest ecosystems rely on deadwood for their survival at some point in their lifetime!
The Townsend’s chipmunk (Tamias townsendii) is one species that was shown by a group of researchers to rely heavily on downed dead trees for their survival. Scientists observed the travel paths of the chipmunks through conifer forests in Oregon. The results of their study revealed that Townsend’s chipmunks will disproportionately choose travel paths on top of downed dead trees, possibly because they provide quick and silent passage through the forest (Waldien et al 2006).
Aside from these interesting findings, deadwood also provides important habitat for many insects and edible plants, lichens and fungi, all of which are on the menu for small mammals, birds and other forest residents.
Deadwood and fungi, the dynamic duo
It’s no secret that fungi play a key role in forest ecosystems in the way that they break down and decompose trees after they die. Not only do they obtain nutrients from the wood, but throughout the process they create a cascading effect of benefits for the forest and its inhabitants. Shelf fungi, like the polypores pictured above, will break down the protective lignin layer of the wood, making it available as a food source for many insects like beetles and ants. Predators like woodpeckers, song birds and even small mammals will then move in to feed on the insects. The presence of these species is sure to also attract larger predators like sharp-shinned hawks, spotted owls, and even mesocarnivores like weasels and skunks. Further down the road, wood-decaying fungi influence the formation of soil, the recycling of nutrients and the sequestration of carbon in the soil (Lonsdale 2007). All of these important ecological processes begin with the relationship between fungi and dead trees. To bring some of these ideas full circle and show you how connected things can be in the forest, the aforementioned Townsend’s chipmunks are also known to distribute the spores of fungus as they run through the forest on downed logs!
Sources
Bauhus, Jürgen; Baber, Kristin; Müller, Jörg. Deadwood in Forest Ecosystems. Oxford Bibliographies. February 2018.
Lassauce, A., Paillet, Y., Jactel, H. & Bouget, C. Deadwood as a surrogate for forest biodiversity: Meta-analysis of correlations between deadwood volume and species richness of saproxylic organisms. Ecological Indicators 11, 1027–1039 (2011)
Lonsdale, D., Pautasso, M. & Holdenrieder, O. Wood-decaying fungi in the forest: conservation needs and management options. European Journal of Forest Research 127, 1–22 (2007). Waldien, D. L., Hayes, J. P. & Huso, M. M. P. Use Of Downed Wood By Townsends Chipmunks (Tamias Townsendii) In Western Oregon. Journal of Mammalogy 87, 454–460 (2006).
