Abundance of mites, but not of collembolans or nematodes, is reduced by restoration of a Pinus ponderosa forest with thinning, mastication, and prescribed fire

Thinning, mastication, and prescribed fire are restoration treatments frequently employed in unnaturally dense second-growth Pinus ponderosa forests of the Western United States. Although a goal of these treatments is to restore ecosystem structure and function, little information is available regarding treatment effects on soil micro- and mesofauna, which comprise the overwhelming majority of metazoan forest inhabitants and occupy key positions in soil food webs. We quantified nematodes, mites, and collembolans in soil and litter habitats within untreated control, thinned (comprising thinning and masticating wood), and burned (comprising thinning and masticating, followed by broadcast burn) in P. ponderosa forest management units at Valles Caldera National Preserve in New Mexico, USA. We linked patterns in animal abundance to resource and habitat characteristics, hypothesizing that resources and available habitat for many taxa would increase with thinning and decrease with burning. Two years after thinning, densities of collembolans and nematodes in the thinned unit were higher than in the untreated control unit, but one year post-fire, their densities in the burned unit were similar to those of the untreated control unit. Mite abundance, however, was not elevated in the thinned unit and was lower in the burned unit. Although faunal communities were highly heterogeneous, a significant proportion of the variance in faunal abundances was explained by easily and inexpensively measured habitat and resource characteristics: bulk density, soil organic matter (SOM), pH, grass cover, and litter cover and depth. These findings demonstrate the abiotic and biotic factors that structure faunal habitats so that forest managers have a more complete understanding of the impacts of forest restoration treatments.