Nutrient and regeneration responses to biomass harvesting and prescribed fire in a northern mixedwood forest

Biomass harvesting is common across the northeastern United States, yet plant and soil responses in the years-to-decades after harvest are poorly understood. We assessed regenerating species composition and foliar and soil element concentrations after clearcutting with whole-tree harvesting, stem-only harvesting, and stem-only harvesting with prescribed burning in spruce-fir-hardwoods in Maine, U.S.A. We made measurements 50 years after the first treatment (applied 1964–65) and within 10 years after the second treatment (applied 2018), providing one of the longest evaluations of biomass harvesting in naturally regenerated temperate forests. In 2014, 50 years after the first treatment, there were few detectable differences in the composition of advance regeneration, or foliar and soil element concentrations among treatments; parent material was the primary driver of soil element variation. However, after the second repeated treatment, advance regeneration shifted toward early-successional species for at least seven years, and soil element concentrations of ammonium, phosphorus, potassium, and sulfur were elevated when prescribed burning was recently applied and the water table was shallow. These findings suggest that biomass harvesting with or without prescribed fire in spruce-fir-hardwoods has limited, transient effects on nutrients, though persistent shifts in overstory species as a result of intensive forest management may result in stand type conversions with ecological and economic implications.