Response of soil microbial and invertebrate communities to tracked vehicle disturbance in tallgrass prairie

Soil biota drive fundamental ecosystem processes such as decomposition, nutrient cycling, and maintenance of soil structure. They are especially active in grassland ecosystems such as the tallgrass prairie, where much of the net primary productivity is allocated belowground and ultimately processed by heterotrophic soil organisms. Because both soil microbes and soil fauna display perturbation responses that integrate the physical, chemical, and biological changes to their environment, the structure of belowground microbial and faunal communities is used widely as an indication of the ecological status of soils. To investigate the effects of military training on tallgrass prairie soil communities, a replicated small-plot study of tracked vehicle disturbance effects was initiated at Fort Riley, Kansas in 2003. This article reports subsequent rates of recovery for soil microbial and invertebrate communities over a range of disturbances encompassing different soil types (silty clay loam and silt loam soils), environmental conditions (wet vs. dry traffic events), traffic intensities (single vs. repeated traffic), and track areas (curve vs. straightaway). Microbial biomass in wet silty clay loam soil treatments and on curve areas in silt loam soil was suppressed for 1-2 years following disturbance but increased to levels greater than undisturbed plots in all treatments by the fourth year. Nematode abundance, family richness, trophic composition, and community structure also displayed maximum disturbance for wet treatments and curve areas. Trophic composition and community structure continued to exhibit disturbance effects throughout the 4-year study period, even after recovery of nematode abundance. Earthworm abundance displayed the most severe reductions (78% across soil types, treatments and areas) immediately following tank traffic but, like microbial biomass, subsequently increased to levels greater than undisturbed plots. Nematode community structure provided a reliable and comprehensive assessment of the status of the soil food web and was an effective bioindicator of ecosystem recovery following traffic disturbance. In addition, given the dominant role of earthworms in ecosystem processes and their extreme sensitivity to tracked vehicle disturbance, it is recommended that this group be included in monitoring protocols for military training land managers.