Understory plant community resilience to partial harvesting in riparian buffers of central Canadian boreal forests

Abstract

Partial harvesting in riparian buffers has been suggested as a forest management option to emulate natural disturbance patterns in riparian buffers. However, little is known about the effects of canopy gap creation by partial harvesting in riparian buffers on understory plant communities of boreal forests. We investigated the responses of understory species to gaps created by partial harvesting at up to 50% basal area removal in stream-side riparian buffers of boreal forests in northcentral Ontario, and compared them to nearby un-harvested buffers and riparian reference areas of undisturbed forests. Gap sizes ranged from 10 to 400m2, but most were between 25 and 125m2. Gaps created by partial harvesting measurably increased canopy openness, ground-level solar radiation, and shallow soil temperatures proportional to gap sizes, but the changes were small and only consistently higher than the range of these conditions in un-harvested riparian areas when gaps were >50m2. Understory plant abundance in gaps tended to be higher than in un-harvested sites but significant differences could not be detected. Richness and diversity were higher among medium and large gaps (>20m2) than in small gaps, but they were not higher than in un-harvested buffers or reference riparian areas. Multivariate community composition analyses could not detect significant differences between harvested and un-harvested areas. However, gaps created by partial harvesting affected foliar morphology of selected common understory plants. Leaf dry matter content was higher and specific leaf area was lower in harvested gaps than in un-harvested buffers or reference riparian areas, and both were related to gap size. Based on the unaltered understory community composition coupled with leaf morphological adaptations of selected understory plants to gaps, we conclude that the plant community is resilient to partial harvesting. Implications for riparian forest management under the emulation of natural disturbance paradigm are discussed.