Mosses and liverworts are bryophytes, non-vascular green plants. Having no vascular, or circulatory, system, these small plants must absorb their moisture from the atmosphere through osmotic pressure. That means they also absorb whatever toxins might be present in the atmosphere, but have no way to rid themselves of the toxins. Since the toxins will eventually kill them, bryophytes make excellent monitors of air pollution.

There are large areas in Europe in which the once abundant mosses have completely died off due to pollution. Many European cities have bags of mosses dangling over the sides of bridges to measure air pollutants. Americans tend to want to use expensive, complicated machines for monitoring air pollution, when bryophytes are just as effective and far more reliable.

Mosses and liverworts are resources in other ways than as indicators of air pollution. For example, they capture nutrients from raindrops, which pass over the leaves of trees and then onto the mosses growing on the branches and trunks. When the mosses decay, they transfer these nutrients to the soil beneath. This is one way that bryophytes are vital to genuine forest health.

Another major cause of loss of the moss flora in northern forests is unregulated collecting. Tree trunks are stripped of their moss coverings by day laborers who are dropped off in the remote woods and picked up in the evening with their sacks of moss. The mosses are used for various decorative purposes. All the trees are stripped of moss for the bottom eight feet, an odd sight indeed. Sphagnum mosses are also threatened by harvesting, though not to as great a degree as some of the forest mosses.

Sphagnum mosses are an especially interesting group of bryophytes, not closely related to other types. They are plants of northern wetlands, and are able to greatly acidify their surroundings. This happens when hydrogen ions leach out of the moss into the surrounding wetlands. Some sphagnum bogs are found to be more acidic than lemon juice.

Sphagnum has been used for dressing wounds, since it absorbs 30 to 40 times its dry weight in liquid-including blood! It also disinfects, since most infectious microbes cannot survive in the acid environment created by sphagnum. One exception, oddly enough, is the organism that causes leprosy. So, if you ever need to bandage leprous sores, you cannot count on sphagnum to be of much use.

Sphagnum bogs are important habitats, with all sorts of interesting properties. In some places within a bog the mosses are dead, and in other places they are still living, giving rise to dramatic differences in water temperature in the same bog. An excellent sphagnum bog is near Fort Bragg, owned by the College of the Redwoods. Mendocino County is just far enough north for these bogs to form – most are found further north.