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.
Highlights
Forest management approaches using clear cutting can often simplify vegetation composition and produce structural homogeneity, especially when followed by artificial regeneration practices (Paquette and Mes sier, 2010; Puettmann et al, 2015)
Conspecific overstory basal area (CBA) was similar in unharvested and partial harvesting (PH) stands for balsam fir and yellow birch, but not for other species where CBA was slightly greater in high-intensity PH stands for American beech and red maple yet lower for sugar maple compared to unharvested stands (Table 1)
In low-intensity PH stands, the CBA was slightly higher for American beech, red maple, paper birch, red spruce, and white pine, but lower for sugar maple, eastern hemlock, and northern white cedar compared to unharvested stands (Table 1)
Summary
Forest management approaches using clear cutting can often simplify vegetation composition and produce structural homogeneity, especially when followed by artificial regeneration practices (Paquette and Mes sier, 2010; Puettmann et al, 2015). Our current understanding about the effects of PH has generally been based on limited number of controlled experiments where trees are carefully selected to create theoretical post-harvest stand patterns (Bataineh et al, 2013; Leak, 2005; Prevost and Gauthier, 2013; Raymond and Bedard, 2017). This may create uncertainties for wider application of our current knowledge, especially when PH is applied operationally at a landscape scale. The existing knowledge on growth and mortality responses to PH is limited to just a few tree species even at the experimental level (e. g., Baral et al, 2016; Carter et al, 2017a; Forget et al, 2007; Jones and Thomas, 2004)
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