A nurse log in winter, supporting mosses, ferns, and various sapling sprouts
Photo: Kevin McKeon
Nurse Logs Essential to the Health of Our Forests
By Kevin McKeon, Maine Master Naturalist
As algae crawled from the seas to begin plant life on Earth about 400 million years ago, evolutionary processes led to the formation of forests. Scientists’ recent discovery in Southwest England, among the sandstone cliffs abutting Bristol Channel, dates Earth’s earliest forest to 390 million years ago. The findings included 13-foot-tall, palm-like trees that began the process of soil formation along the beaches, as decaying material from fallen leaves, twigs, and downed trees mixed with sediment captured in tree roots. This activity also provided suitable habitat for seashore-based invertebrate populations. Four million years later, this process repeated in New York State, forming a forest with a wider variety of species.
As we enjoy our walks through the glorious trail networks among the properties owned and cared for by the city of Sanford, local land trusts, and generous landowners, this process of living and dying continues. And by slowing our walks a bit, the forest can reveal the wonders of a tree passing itself back to the soil in the form of nurse logs, lying among the forest floor’s coarse woody debris, or CWD. This is the collection of those relatively large pieces of tree limbs, logs, fallen trees, and stumps hugging the forest floor in various stages of decomposition.
As CWD slowly decomposes, many vital soil functions are supported to help ensure forest health. Various soil organisms live and feed among CWD, releasing nutrients back to the soil. During these processes, CWD transforms to a spongy mass, the captured water mitigating the effects of droughts. Increased aeration caused by the various micro- and macro-tunneling actions of small and large soil creatures increases soil health. Micro- and macro-habitats are created to both shelter and feed the forest’s insects, fungi, birds, and animals, adding to the forest food chain. Carbon is sequestered, mitigating climate change. Stream and river health are enhanced and maintained by increased aquatic biological food availabilities, reduced erosion, and water-cleansing filtration. During winter, the snow blanket covers and surrounds CWD, creating a multitude of snow tunnels and caverns — winter homes and foraging habitat for the forest’s many small mammals and birds, which in turn feed the weasels, owls, fox, coyote, and other denizens of the woods. As esteemed natural scientist E.O. Wilson observes, “Every corpse is an ecosystem.”
All this to say: A “messy forest” is a healthy forest, with all its crisscrossed branches and logs, and the dead, standing/leaning snags which together support four times the biological activity in the forest compared to the living trees. So, we have come to realize the value of nurse logs — those rotting remnants gifted to the forest ecosystem and soil by trees. Squirrels and other ground-living critters use them as travel lanes and feeding stations — feeling safe above the ground with a better view to detect predators. Birds nest against them and some perch upon them, “drumming” for mates. Various amphibians live in and under them. Foraging predators travel on them, gaining a better view of their prey.
Moss, lichen, and fern spores settle onto our nurse log, colonizing on this rich habitat, attracting tiny bugs that make holes for fungi to begin their decomposing magic. The squirrels’ pinecone scales begin to cover the log. Birch, hemlock, and maple seeds land on this rich seedbed, where they germinate and sprout into more forest tree members. Larger bugs soon enter the log, creating tunnels for even larger bugs. These pioneer decomposers attract and feed other forest critters, which in turn, feed and attract larger critters. Cavities are formed and grow from successional use by bugs, grubs, woodpeckers, owls, salamanders, frogs, turtles, skunks, rabbits, raccoon, fox, even dens for black bears. Small trees sprout, their roots growing over the log and reaching the rich soil underneath — leaving behind their tell-tale stilted roots to evidence their beginnings on the now decomposed log. All we as humans need to do is nothing — simply let “ecological facilitation” happen naturally by leaving the CWD, nurse logs, and snags where they lie, lean, and stand. We can also consider creating CWD during our forest management practices. Our reward is a more diversified wildlife-rich forest, messy to some, but beautiful to those who realize the biological diversity all this “mess” provides.
Editor’s note: Did you see something unusual last time you were out in the woods? Were you puzzled or surprised by something you saw? Ask our “Out in the Woods” columnist Kevin McKeon. He’ll be happy to investigate and try to answer your questions. Email him directly at: kpm@metrocast.net
Stilted Roots: https://sanfordspringvalenews.com/out-in-the-woods-21/
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