Other Soil Organisms

There are many other types of organisms in the forest soil about which little are known. These include groups such as earthworms, potworms, nematodes, rotifers, snails and slugs, algae, bacteria, actinomycetes and cyanobacteria.

Nematodes are perhaps the largest single group by numbers of animals in the soil and act as predators, pathogens, and fungivores. All nematodes appear to feed on living tissue and there are at least 1000 species of soil nematodes.

In many situations, earthworms may be the largest faunal biomass in the soil. Estimates of earthworm mass have been as high as 12,000 kg/ha for sites in the Cariboo Forest Region, but estimates of 3000 kg/ha are not uncommon.

It was believed that earthworms were rare in conifer forests, but in many cases, that now appears to have been incorrect. Earthworms are important for speeding up decomposition of organic matter and improving the structure of mineral soil.

Bacteria have many roles as well, including disease causation, decomposition, and nitrogen fixation. Bacteria may fix nitrogen in association with plants, but there is considerable evidence about the importance of nitrogen fixation by free-living bacteria in forests.

Actinomycetes are filamentous bacteria that are common in soils and are responsible for giving soil its characteristic earthy smell. Actinomycetes are a major source of antibiotics for human use and they are involved in nitrogen fixation in symbiosis with woody plants.

Cyanobacteria are a special group of bacteria that can photosynthesize, and in many cases fix nitrogen. In some forest environments, it has been determined that cyanobacteria make a significant contribution to the nitrogen budget of the forest.

In short, there are many kinds of organisms living in the soil and contributing to the cycling of nutrients through the forest as well as other functions. To really see the complexity of a forest ecosystem, one has to look small.

Managing Forest Soils for Biodiversity

The concerns about biodiversity from a soil's point of view reflect many of the same issues surrounding aboveground diversity.

The relationships and workings of the soil ecosystem, as with other ecosystems, are too complex to fully understand the possible impacts of forest management.

The creation of large-scale, uniform disturbances of only pioneer species will reduce the rich diversity of habitats and hosts that characterize the many communities of soil organisms.

Alternatively, under natural disturbances such as fire, the forest will retain island remnants of living trees, undisturbed forest floor and coarse woody debris, all of which act as biological legacies for the succeeding forest.

At this time all we can do, to reduce the risk of damaging the soil ecosystem is practice management that results in patterns of disturbance more similar to those caused by natural processes.

Island remnants left by mimicking natural disturbance patterns will hopefully act as refuges from which species of mycorrhizae, fauna, and other organisms can spread back into the disturbed forest.

In the case of some organisms, dispersion may be slow, and thus the retention of habitat on the small scale is important. This requires the retention of some coarse woody debris and undisturbed forest floor and mineral soil (e.g., by avoiding intense burning or excessive mechanical site preparation).

Some types of organisms, such as the underground mushrooms, need an intact community of mammals, particularly small mammals, to disperse spores from areas where colonies of the fungi remain to areas where they have been lost. This requires the conservation of larger islands.

Some species of fungi show fairly large differences in strain characteristics with adaptations to specific environmental conditions. These types of strains are sometimes referred to as ecotypes.

The ecological function of ecotype variation is currently not well understood but it may be important for providing very site-specific adoption.

As a measure to retain this genetic variability, as well as the specific complement of fungi and other organisms present in a stand, one approach may be to preserve island remnants of each stand that is harvested.

In other words, island remnants should not consist only of immature or riparian areas within a block but also representatives of the types being harvested.

In some cases, it may be desirable to leave at least one or more widely spaced windfirm dominant trees. Even this will contribute to preserving the soil biological legacy.

A second issue for management of soil biodiversity is the maintenance of soil integrity.

Soil degradation, such as through the compaction of mineral soil, for example, will reduce porosity and alter moisture conditions, often to such an extent that this habitat becomes lost to many species.

Soil displacement exposes new and possibly poorer substrates from deeper in the soil profile, which take some time to be colonized and become stable productive environments.

In addition, soils that are greatly disrupted become biologically pioneering environments that may be susceptible to invasion by a variety of organisms that are alien to the intact ecosystem. These may be thought of as weed species, and in fact, weedy plant invasion may be one consequence of such disturbance.

Other organisms, such as disease organisms, may also use this opportunity to establish. Losses of soil from erosion and mass wasting will also remove soil volume and reduce the biological legacy of the soil.

Managing soils from a conservation point of view will, at the same time, help maintain biological diversity as well as biological integrity.