Recreation impacts on high elevation soils : a comparison of disturbed, undisturbed and restored sites

Abstract

Mountainous regions comprise more than 30% of the world's terrestrial biomes and are valued for livestock forage, mineral and timber assets and recreation opportunities. Disturbance has resulted in major ecological changes in high elevation ecosystems, including vegetation loss, soil compaction, and reduced soil organic matter (SOM). Restoring high elevation disturbed sites has proven challenging for many years, possibly because of our limited knowledge of disturbance effects on belowground biota, and the ecosystem functions they facilitate. This research compares soil physiochemical and biological properties on disturbed, undisturbed and restored subalpine soils in two national forests in Montana and Washington. Soil physiochemical properties measured include soil moisture, bulk density, SOM, soil nitrogen (N; both total and plant available), phosphorous (P) and potassium (K). Biological processes measured include mycorrhizal infectivity potential (MIP), decomposition, enzyme activity, substrate induced respiration (SIR) and N mineralization. Soil moisture and SOM were significantly lower, while bulk density was higher, on disturbed sites. Total nitrogen (N) was lower on disturbed sites, while NO3 - and NH4 + differed only between geographic locations. MIP was low overall and did not differ between disturbance. Decomposition rates did not differ between disturbance after 3, 12 or 24 months. Enzyme activity differed with disturbance and location, with significantly lower activity on disturbed sites for 1 substrate, while nearly significant lower activities for 4 out of 8 substrates measured. SIR differed with disturbance and location, with lower responses on disturbed sites for 6 of 26 substrates. Soil physiochemical and biological characteristics are affected by disturbance and location, however results vary between the parameters measured. This suggests ecosystem components, including soil physiochemical and biological properties are decoupled, responding individualistically to disturbance and restoration.