Effect magnitudes of operational-scale partial harvesting on residual tree growth and mortality of ten major tree species in Maine USA

Abstract

Silvicultural systems based on partial harvesting (PH) have become increasingly common in areas historically dominated by clearcut-based systems in response to ecological and social concerns. Current knowledge about the effects of PH is based primarily on stand responses from controlled experiments from limited number of sites. A broader scope of inference is needed to fully understand the effects of PH when applied operationally at a landscape scale. We used 835 permanent monitoring plots from the US Forest Service Forest Inventory and Analysis network to quantify the effect magnitude (EM) of low- (5–40% basal area removal) and high-intensity (41–80% basal area removal) PH on the periodic diameter growth and mortality of residual trees of ten major tree species in Maine, USA. Our results showed that the EM and timing of statistically significant effect (p < 0.05) of the two intensities of PH varies across species. Tree diameter growth responses to high-intensity PH was rapid and prolonged for sugar maple (Acer saccharum) and American beech (Fagus grandifolia), while other species did not show significant responses for at least five years. High-intensity PH increased mortality of American beech, balsam fir (Abies balsamea), red spruce (Picea rubens), northern white cedar (Thuja occidentalis), and red maple (Acer rubrum), but not for other tree species. No relationship was found between species shade tolerance and species-specific response magnitude to PH in terms of diameter growth and tree- or stand-level (absolute or relative) mortality. This result suggests that species shade tolerance does not always determine the type or magnitude of response that a given species has to increased resource availability following PH and that other functional traits may be more important. Overall, the findings provide strong evidence that subsequent tree responses to PH are not consistent among contrasting species for at least 15 years following harvest and longer-term regional assessments are needed.