By Deya Ramsden, Virginia Department of Forestry
In February, the winter forest may not appear to be particularly active. However, below ground, the soil remains dynamic in temperate forests even when outdoor temperatures are chilly. In a mature forest, the soil is made up of a complex mix of tree roots and a community of fungus, microbes and good bacteria.
The soil organisms are vital for breaking down organic matter so nutrients are available for uptake by the tree roots and to sustain the community itself. The soil bed maintains at a fairly comfortable temperature year-round. Even if above grounds temperatures are below freezing, soil temperatures never drop below 30˚F. In addition, the deeper layers of soil maintain even higher temperatures.
t is this deep warmth that contributes to the spring thaw. This buffered temperature protects the soil organisms and roots allowing them to survive through the winter. Some members of the soil community are more active in cold temperatures than others. Soil bacteria will go dormant in cold temperatures, while fungi can continue to function. Although, we in Central Virginia do not experience the deep freeze of the arctic tundra, studies have found that soil microbes in the tundra will produce the equivalent of “antifreeze” to survive. Microbes are in fact aquatic organisms, living on the film of water around tree roots. As temperatures drop, water is drawn out of the microbe, leaving behind high levels of salt, keeping the organism from freezing.
Take heart that a riparian forest buffer’s soil is still working to improve water quality even when the tree’s branches are bare. In winter, more water will enter a stream, because dormant, leafless trees are not transpiring water to the atmosphere. Frozen soils will limit water infiltration, also increasing runoff to waterways. However the tree roots, soil and leaf litter within a buffer still benefit water quality by slowing down flow, allowing sediment, nitrogen, phosphorus and other pollutants, to be captured before they enter the stream. The soil organisms are just waiting in their cozy soil bed to break down those captured pollutants as they become more active in the spring.
Forest fact: Soil scientists call the spongy soil within a mature forest mull.
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