Forest floor and mineral soil respiration rates in a northern Minnesota red pine chronosequence

We measured total soil CO₂ efflux (R_S) and efflux from the forest floor layers (R_FF) in red pine (Pinus resinosaAit.) stands of different ages to examine relationships between stand age and belowground C cycling. Soil temperature and R_S were often lower in a 31-year-old stand (Y31) than in 9-year-old (Y9), 61-year-old (Y61), or 123-year-old (Y123) stands. This pattern was most apparent during warm summer months, but there were no consistent differences in R_FF among different-aged stands. R_FF represented an average of 4–13% of total soil respiration, and forest floor removal increased moisture content in the mineral soil. We found no evidence of an age effect on the temperature sensitivity of R_S, but respiration rates in Y61 and Y123 were less sensitive to low soil moisture than R_S in Y9 and Y31. Our results suggest that soil respiration’s sensitivity to soil moisture may change more over the course of stand development than its sensitivity to soil temperature in red pine, and that management activities that alter landscape-scale age distributions in red pine forests could have significant impacts on rates of soil CO₂ efflux from this forest type.