Drivers of ɑ-diversity
Overall, our models explained a relatively large amount of variance in
species richness (ɑ-diversity: mean conditional
Rc2 = 0.54, ranging between 0.31 -
0.76). A considerable amount of this variance was explained by site, as
indicated by the difference in model fit between the conditional and
marginal R2 (ɑ-diversity variation explained by site:
mean Rc2–Rm2 = 0.34, range 0.14-0.56). Site
was a particularly strong predictor of ɑ-diversity of springtails,
protists and fungi, where it explained at least twice as much variation
as all other variables combined (Table 2). Explanatory soil variables
differed strongly between groups of soil organisms (Table 2). Species
richness of all microbial groups (bacteria, fungi and protists) was most
strongly and positively related to soil pH and to a lesser extent to
litter biomass, soil bulk density and moisture content. Species richness
of nematodes was also related to pH, albeit less strongly than for soil
microbes. Nematode species richness was also explained by soil carbon
content, and interaction effects between pH*grazing removal and litter
biomass*grazing removal. Conversely, species richness of springtails and
mites was unrelated to soil pH. Species richness of springtails was
negatively related to bulk density and the interaction effect between
grazing removal and cover of grasses and herbs, soil bulk density and
mineral nitrogen concentration, while mite richness was explained by the
interaction effect between soil moisture*grazing removal.
Effects of abandonment on β-diversity .
Cessation of grazing caused a significant decrease in β-diversity for
protists and fungi (both approximately 5%), whereas β-diversity of
plants and bacteria was unaffected (Figure 3B). In contrast, cessation
of grazing caused an increase in β-diversity for mites (5%),
springtails (15%) and nematodes (15%).