Soil Scarification and Wildfire Interactions and Effects on Microbial Communities and Carbon

Abstract

Nutrient availability is an important constraint on sustainable forest productivity, and it is crucial to understand the long‐term effects of management practices, including soil scarification, on soil microbial communities because they store and cycle nutrients. In addition, because forests are subject to wildfires, it would be useful to understand potential interactive effects of wildfire and management practice on forest soil ecosystems. We studied the individual and combined effects of soil scarification and a subsequent wildfire on microbial community structure of a ponderosa pine (Pinus ponderosa C. Lawson) forest soil in the central Rocky Mountains. Experimental plots were scarified by rototilling in 1981, and in 2002, some of the plots were burned during a mixed‐severity wildfire. In 2005, mineral soil samples (0–10‐cm depth) were collected and assayed for soil chemical properties, fungal and bacterial biomass, C mineralization potential, and microbial community fatty acid composition. Compared with undisturbed soil, soil from scarified‐only plots was relatively high in pH, low in total C and organic matter (OM) concentrations, low in fungal and bacterial biomass, and enriched with Gram‐positive biomarkers. Regardless of scarification treatment, soil from burned plots was relatively high in pH and extractable P, low in fungal but not bacterial biomass, and enriched with Gram‐negative bacterial biomarkers. Compared with scarified‐only plots, scarified‐plus‐burned plots had greater soil C and OM concentrations. Carbon mineralization rates were not different among the plot soils. While scarification is a positive practice for aiding seedling establishment, we found long‐term effects on soil C reserves and microbial communities.