For example, researchers monitoring the restoration of ponderosa pine (Pinus ponderosa) forests

in Arizona explored the relationship between mycorrhizal and plant functional groups (Korb et

al. 2003). They discovered that arbuscular mycorrhizal (AM) fungi were highly positively

correlated with increases in grasses and forbs, and negatively correlated with tree cover and pine

litter. Ectomycorrhizal (EM) fungi had no response to the restoration treatments, but had a high

positive correlation to stand basal area (Korb et al. 2003). A companion study found that as

plant species richness increased primarily due to an increase in legumes and stress tolerant

plants, there was a corresponding increase in soil fungi and an abundance of fungi relative to

bacteria (Smith et al. 2003).

 A growing number of studies have indicated that soil microbial communities with distinct

functional groups inhabit different forest types (Pennanen et al. 1999). A black pine forest in

northeastern Austria was found to have higher relative amounts of fungi and actinomycetes in the

soil microbial biomass than were found in a neighboring oak-beech hardwood forest (Hackl et al.

2005). Chapman et al. (2003), investigating native woodland expansion in England, found that

soil moisture, pH, and microbial biomass levels decreased along a successional gradient from

moorland to grassland to mature pine forest, but the fungal component increased. In beech

(Fagus sp.) forests of Denmark, researchers found that different fractions of coarse woody debris

supported distinct fungal species. Larger trees parts contained more fungal species, smaller

pieces had higher densities of a few species, and snags were species-poor. They concluded that

coarse woody debris should be left as whole trees compared to smaller or larger pieces to insure

high species richness in the fungal community of the forest floor (Heilmann-Clausen and

Christensen, 2004). These studies illustrate the strong interactions that exist between soil

biogeochemical properties and aboveground cover type.