Soil functional responses to ecological restoration treatments in frequent-fire forests of the western United States: a systematic review

We investigated general effects of ecological restoration treatments on soil function in frequent-fire forests of the western United States using a systematic review methodology. We searched numerous publication databases for original research papers and used well-defined criteria developed a priori to select papers for review. We used meta-analysis and qualitative summaries to compare reported responses of macronutrients, nitrogen cycling, and soil respiration among tree thinning (thin), prescribed fire (burn), and thinning plus prescribed fire treatments (composite). Results of meta-analysis showed that mean differences in macronutrients were consistently higher in composite treatments (standardized using controls) when compared to thin-only and burn-only treatments. Mean responses related to nitrogen cycling showed similar patterns, with significant increases detected in composite treatments for all nitrogen cycling variables (mineralization, ammonification, and nitrification) and insignificant responses for the majority of the burn-only and thin-only treatments. Mean difference in response for soil respiration following composite treatments showed increases as compared to the controls, and no significant differences were detected in response to burn- and thin-only treatments. While soil function, nutrient cycling, and soil respiration differed among treatments, the most significant effects were observed for nitrogen and carbon responses, net mineralization and nitrification, ammonium availability, and soil respiration rate, which experienced the greatest increase following treatments that were both thinned and burned.