"Nature Guide Journal"

14 June 2001

I'm occasionally asked why more dead snags and downed trees aren't taken out of the forest and "made use of."

In fact, such large woody material is of critical use in the forest.

Although we may take more notice of the leaves, flowers, and fruits of a tree, the tree's twigs, branches, trunk, and large roots make up much more of the mass of the plant. That wood represents a large investment by plants: most of the solar energy captured by the forest eventually becomes fallen woody material on the forest floor. At any given time, about 20% of the total biomass (total weight of all the living organisms) of a well-established forest is downed woody debris.

Logs on the forest floor are a vital source of nutrients for fungi, green plants, and many species of animals–though few organisms can use the log in it's original form. The organisms that target downed woody debris tend to do so in a predictable manner. Each wave of different kinds of fungi, plants, and animals alters the log environment while feeding on or using it; the alterations make way for the next generation of log-users.

Tree bark protects tree wood very well–as long as it is intact. Even on dead trees, the bark usually needs to be pierced before many organisms can make use of the wood beneath. Insects, notably wood borer beetles, then carpenter ants, and somewhat later, termites, chew through the bark and tunnel into the wood. The insect borings give an avenue for fungi and other animals, such as nematodes and springtails, to enter deep into the downed tree.

The fungi aids the growth of green plants above. Further, with the termites and some of the fungi come certain bacteria that play a vital role in fixing nitrogen from the air and making it available to plants.

The advancing decomposition, aided by the fungi and the building insect frass (waste material), loosens the tree's bark, giving plant roots easier opportunity. Nutrients seep into the soil from the loose and falling bark. Sheets and chunks of bark offer prime shelter for larger species of animals, and many of them feed on the earlier arrivals.

Large insects, salamanders, frogs, shrews, even small birds, find shelter between the bark and wood and among the torn up roots of the fallen tree. As the wood continues to soften and decompose, more fungi, plants, insects, and small animals find better entry to the nutrients stored there.

Softened and made available by the burrowing animals, the nutrients in the dead tree and in the waste of the wood-eaters now feed young trees–oftentimes the same species as the fallen forest member. While walking in the woods, look for these "nurse logs;" which are eventually reduced to long, mossy lumps, often sporting a line of similarly aged trees and shrubs.

Finally, the decomposed wood adds to the soil, improving its water-holding ability and lightening its bulk to allow better insulation and aeration. The young trees that sprouted many years earlier on the fallen parent may now stand bow-legged over the space opened up by the rotted log.

Stumps, too, host this parade of life as the wood decays, forming pillars of lush growth standing up from the forest floor.

The silvery snags have a similar life-history, although drier and more exposed to the sun and wind. Softened by the same process of introductory beetles and pioneering fungi, tall-rising snags give habitat to bats, nest sites for osprey and eagles, and roosting space for other large birds. Woodpeckers, especially the chiseling pileated woodpecker, excavate large nesting cavities that are used later by other birds and mammals, such as owls and flying squirrels.

Water is stored in the downed woody debris, as well. And the moisture-soaked log protects it's store of water and nutrients–as well as many of its inhabitants–from fire.

Wet, rotting logs and gray, shiny snags are two of the finest examples of natural recycling in action.

Wavecrest Discoveries can craft your personal discovery of this delightful part of our world by customizing one of our distinctive guided excursions.   Our walks, tours, and special activities are wonderful ways to explore this fascinating region—and are the perfect entertainment for guests.