Variable-retention harvesting is widely recognized as an alternative to clearcutting, but its impact on indigenous biodiversity intolerant of canopy removal remains unclear due to inadequate long-term monitoring. We examined patterns in bryophyte abundance, diversity, and composition in response to a broad range of dispersed green-tree retention harvesting (2, 10, 20, 50, 75, 100% retention) in conifer-, mixedwood, and deciduous-dominated stands in boreal forests of north-western Alberta, Canada. Bryophytes were sampled in permanent plots before harvest and at two, five, and ten years following harvest in a replicated large-scale experiment designed to test the assumptions of natural disturbance-based forest management (Ecosystem Management by Emulating Natural Disturbance – the EMEND project).
Results/Conclusions
Bryophyte abundance and diversity in control (unharvested) stands changed with time and varied among forest types with higher cover and richness in conifer-dominated forest than in mixedwood or deciduous-dominated forests. Following harvesting, clear-cut and lower retention harvest intensities (< 50% retention) resulted in reduced bryophyte cover and richness in comparison with uncut controls. Harvesting treatment effects were more pronounced in conifer and mixedwood forests compared with deciduous forests which were rather dominated by a few frequent species. Each forest type supported different bryophyte species composition, while bryophyte composition in each forest type varied between clear-cut and the retention harvest levels.
Our results emphasize the sensitivity of bryophytes to intensive forest harvesting, and suggest that high levels of green-tree retention may be required to preserve and maintain bryophyte abundance, diversity, and composition in managed forests.