Growth and mortality response of forest regeneration to partial harvesting varies by species’ shade tolerance

Abstract

Does species’ shade tolerance regulate natural regeneration abundance and composition when partial harvestings (≤80% of basal area removal) are operated on a landscape scale? We examined this question using 835 permanent plots located across forested landscapes of Maine, USA. These plots were surveyed for regeneration growth, mortality, and recruitment before and after treatment application (i.e., partially harvested and unharvested). Our results showed that relative to unharvested stands, high-intensity partial harvesting (41%–80% of basal area removal) increased the number of seedlings (diameter at breast height (DBH) < 2.5 cm) recruited to saplings (DBH of 2.5–12.69 cm) and sapling diameter growth irrespective of species’ shade tolerance over a 15-year period after treatment. However, high-intensity partial harvesting increased sapling mortality during the initial 5 years since harvesting, whereas low-intensity partial harvesting (5%–40% of basal area removal) maintained the natural regeneration dynamics (growth, recruitment, and mortality) of unharvested stands. We found that harvesting intensity, basal area, and seedling density by shade-tolerance group before harvesting are more important attributes than species’ shade tolerance for determining the responses of natural regeneration to partial harvesting. The greater importance of preharvest stand attributes on postharvest regeneration may suggest an integrated overstory and understory manipulation approach for attaining the desired regeneration composition.