Assessing the single-tree and small group selection cutting system as intermediate disturbance to promote regeneration and diversity in temperate mixedwood stands

Published in Forest Ecology and Management 430: 21-32 https://doi.org/10.1016/j.foreco.2018.07.054

Traditional silvicultural systems such as clearcutting and single-tree selection cutting are critiqued for their tendency to simplify forest complexity. By more closely emulating natural disturbance regimes and increasing the availability and heterogeneity in understory light levels, we pose that systems causing intermediate disturbances such as the single-tree and small group selection cutting system can promote tree regeneration, retain stand structural attributes, and maintain high understory plant diversity in temperate mixedwood stands. To assess this, we implemented a harvest intensity gradient experiment (residual basal area [BA], % removal) consisting of uncut control (26 m²/ha, 0%), light (21 m²/ha, 20%), moderate (18 m²/ha, 31%) and heavy (15 m²/ha, 42%) cutting with retention of legacy trees in uneven-aged yellow birch (Betula alleghaniensis Britton) – conifer stands. We evaluated the effects on gap size, light transmittance, abundance of living and dead trees, plant diversity, and regeneration of target species (i.e. yellow birch, red spruce [Picea rubens Sarg.] and balsam fir [Abies balsamea L.]), during the 8 years postcut. Moderate and heavy single-tree and small group selection cutting treatments triggered changes in microenvironments and in understory plant community. Moderate and heavy selection had greater yellow birch seedling density > 30 cm in height compared to the control. Cutting treatments did not significantly improve red spruce and balsam fir regeneration, despite favorable micro-environmental conditions (e.g. gaps averaging 200–350 m² and 15–40% transmitted light). The vascular plant community rebounded quickly after disturbance and harvesting did not depress any diversity metric or alter community composition beyond control levels. Tree species richness increased in moderate and heavy selection cuts, while vascular species diversity (H′) was greatest in the heavy selection cut. Observed richness and diversity gains were driven by augmented yellow birch and mountain maple (Acer spicatum Lam.) recruitment into larger classes as well as greater forb, tree, and shrub cover in response to greater cutting intensities. Species richness and diversity were positively correlated with increased light availability, but not with light heterogeneity. Our results show that this hybrid selection cutting system benefits yellow birch recruitment without negatively impacting plant diversity. However, because increasing harvest intensity simultaneously enhanced interfering non-commercial species abundance (e.g. mountain maple), failed to improve red spruce regeneration, and decreased the abundance of large trees (diameter at breast height > 29 cm), we caution to opt for moderate cutting intensity in this forest type. Additional treatments such as enrichment planting in harvest gaps might be necessary to maintain red spruce over time.

Forests

Scientific Article

Forestry Research, Forests, Silviculture

Dumais, Daniel, Prévost, Marcel, Raymond, Patricia

RAYMOND, Patricia, Alejandro A. ROYO, Marcel PRÉVOST and Daniel DUMAIS

2018

PDF available upon request

Available at the Direction de la recherche forestière

0378-1127

aménagement écosystémique, aménagement inéquienne, peuplements mixtes, coupe de jardinage, diversité végétale, diversité structurale, bouleau jaune, épinette rouge, article scientifique de recherche forestière, Betula alleghaniensis, Picea rubens, sylviculture et rendement des forêts naturelles - peuplements mélangés, silviculture and yield of natural forests - mixed stands, ecological forestry, uneven-aged management, multi-aged silviculture, mixed-species, plant species diversity, structural diversity, yellow birch, red spruce