Prescribed fire is a widely used management tool, yet there are few studies investigating the short- and long-term effects of prescribed fire on soils within region to assess the effectiveness and compatibility of forest management objectives. Therefore, we leveraged a historical fire study (conducted 1959--70) with measurements in 2015 to evaluate the effects of prescribed fire season (dormant, summer), frequency (annual, biennial, periodic), and time (>45 years post-fire) since fire on soil properties in a red pine (Pinus resinosa Ait) forest in northern Minnesota, USA. We used a combination of statistical approaches including meta-analysis, non-metric multidimensional scaling (NMDS), analysis of variance (ANOVA), and linear regression to evaluate treatment effects and relationships of soil properties.

Prescribed fire treatments had legacy effects (>45 years post-fire) on many soil properties including N, P, K, Ca, pH, and forest floor depths but few persistent effects on C and PyC stocks and PyC concentrations. Short- and long-term soil properties appeared to differ by season of burning, and increased fire frequency within season magnified seasonal responses. In general, summer burns decreased nutrient stocks, whereas dormant season burns increased nutrient stocks. Our results suggest that summer burns may be a valuable approach to increase the variability in burn schedules more representative of historical regional fire regimes in red pine forests, and may help promote soil characteristics that maintain overall ecosystem health while supporting carbon sequestration objectives.