Mid-term response of understory plant communities after different regeneration treatments in temperate hardwood forests of Quebec, Canada.

Context: Increased intensity of soil and canopy disturbances tends to increase species richness due to early-successional species establishment. Competitive pioneer species from early stages of succession can become recalcitrant, which can alter patterns of natural regeneration.

Aims: While short term effects of disturbances intensity on plant communities are well documented, only few studies have examined longer term effects.

Methods: We measured taxonomic and functional diversity indices and soil properties using four levels of disturbance intensity in six temperate hardwood forests of Quebec distributed along a longitudinal gradient. Reference forests, i.e. control forests with no silvicultural treatment known for ≥ 80 years (CON), were compared to 20 years old single-tree selection cuts (SIN); group-selection cuts (GRP); and group-selection cuts with soil scarification (GRPS).

Results: Species richness in both group-selection treatments was higher than that in reference forests. Plant equitability and beta diversity among sites in GRP and GRPS were lower than in SIN and CON forests. More intense treatments (GRP and GRPS) contributed to the mid-term persistence of recalcitrant competitor species (e.g., Rubus idaeus, Prunus pensylvanica) whereas soil scarification appears to have negative sustained effects on species known to be sensitive to regeneration treatments (e.g. Monotropa uniflora, Dryopteris spinulosa).

Conclusion: Of the treatments studied, single-tree selection cutting appears to be the most appropriate silvicultural treatment for maintaining heterogeneous understory plant communities with compositions and structures similar to natural forests, while more intense treatments rather maintain and expand species that are better adapted to a wider range of environmental conditions, including open environments.