A comparison of thinning methods in red pine: consequences for stand-level growth and tree diameter

Long-term replicated experiments that contrast thinning method (dominant thinning, thinning from below) while controlling stocking level are rare. Stand growth and tree size responses to thinning method can be useful for making decisions to achieve desired objectives, whether these are timber or wildlife habitat related. We examined data from two long-term (>50 year old) silvicultural experiments in red pine to understand how alternative thinning prescriptions influence stand-level basal area, volume, and biomass growth, as well as quadratic mean tree diameter. We found that gross growth in stands treated with dominant thinning was often, although not always, greater than growth in stands treated with thinning from below. However, the differences in growth between thinning methods are smallest at stocking levels and stand ages typical for red pine management. We found that biomass growth increases with dominant thinning were generally less than basal area or volume growth increase. Furthermore, greater gross growth associated with dominant thinning versus thinning from below must be weighed against the significantly smaller average tree sizes that result from repeated dominant thinning.