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Problems Related to Soil Damage or Loss

Soil is the foundation of the forest.

Fungi feed forests

In healthy soil there is a type of fungi called mycorrhizal fungi. Mycorrhizal fungi spread like a web through the forest soils. If you dig in forest soil you will often see the white fibers of mycorrhizal fungi. They attach themselves to the roots of trees and help these roots collect nutrients and water. In order to remain healthy, trees depend on these nutrients and this extra water.

Mycorrhizal fungi reproduce by growing mushrooms on top of the soil. These mushrooms spread their spores in various ways. They can burst and shoot spores into the wind or sometimes they are eaten and get spread in the dung of various animals.

Soil compaction kills mycorrhizal fungi

Mycorrhizal fungi need air to breathe. They get their air through the pores of healthy soil. If soil gets compacted by cattle or heavy equipment the mycorrhizal fungi can no longer breathe.

Heavy equipment compacts soil in a couple of ways. First the sheer weight of the equipment bearing down on the soil will compact the soil. This means that the soil will be compacted directly under the equipment. But soil is also compacted by the vibration of the equipment. This vibration can be felt quite a ways away from where the equipment is running. Vibration causes the soil to sift down and fill the pores of the soil. When these pores are filled they can no longer supply air to the mycorrhizal fungi and the fungi will die.

When the fungi die they no longer can help to provide nutrients and water to the trees. The trees become unhealthy and are more likely to be attacked by insects and disease.

Soil compaction also causes erosion

Porous soil acts like a sponge; soaking up rain and snow water. When soil is compacted the soil can no longer soak up water and the water runs along the surface of the ground carrying soil into streams. When this soil is washed into streams it is called silt. Too much silt kills the fish and other creatures that live in the streams.

This top soil has most of the nutrients that the trees and other plants depend on. If it is washed down stream it is no longer available to feed the trees and plants.

Dead wood feeds forests

Dead wood rotting on the forest floor eventually gets incorporated into the soil. This underground wood feeds many insects and bacteria which provide nitrogen to feed the trees and other plants in the forest. Underground wood is the major source of nitrogen for dry forests.

This underground wood also acts like a sponge, soaking up water during wet times and releasing it during the dry months of late summer and early fall. In dry forests east of the Cascades, most of the late season water that plants depend on comes from underground wood.

The Forest Service and the Bureau of Land Management claim that in order to save our forests from fire they must thin out the many small trees that have grown up as the result of fire suppression. They claim that these small trees use up too much of the nutrients and water that the bigger trees need to remain healthy.

These small trees are not very valuable. In order to pay for logging them these agencies must sweeten-the-pot with larger more valuable trees. They must also use the cheapest logging systems that they have. This means that they must use ground-based, heavy equipment to log these small trees.

In order to protect the soil these agencies specify that no more than 20% of the logging area will be compacted. They will often specify that logging trails must be spaced a hundred feet apart. Sometimes they will specify that logging only take place over snow or frozen ground since this reduces the direct compaction. (Vibration induced compaction can still occur.)

Despite these measures we are finding that soil compaction standards are regularly violated.  Logging trails, on the ground, are often closer than specified in the logging plan and logging which was specified to be only over snow or frozen ground continues during thaw conditions.
 

Summary

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