Cumulative effects of chronic deer browsing and clear-cutting on regeneration processes in second-growth white spruce stands

Abstract

Interactions between multiple disturbances can alter resilience mechanisms, thereby triggering alternative successional pathways. Regeneration processes are important mechanisms of forest resilience because they drive successional pathways. On Anticosti Island, chronic browsing by introduced white-tailed deer (Odocoileus virginianus) shifted composition of understory regeneration of overmature balsam fir (Abies balsamea) forests toward dominance by white spruce (Picea glauca). Historic clear-cutting of these altered forests generated mature second-growth white spruce stands. However, the cumulative effect of chronic deer browsing and recent clear-cutting on regeneration processes of mature second-growth white spruce stands has not yet been evaluated. Our objective is to evaluate if regeneration processes would enable white spruce stands to recover from the cumulative effects of these two disturbances. We studied regeneration in relation to seed availability, substrate suitability for seedling establishment, and substrate availability in mature second-growth white spruce stands and recent clear-cuts of mature second-growth white spruce stands. Our results indicate regeneration failure in both ecosystems, which can be explained by a lack of suitable rotten logs for sufficient establishment of white spruce seedlings. Hence, the cumulative effects of chronic deer browsing and clear-cutting of mature second-growth white spruce stands have altered regeneration processes and triggered an alternative successional pathway toward parklands, i.e., partial deforestation. We propose shelterwood cuttings that create nurse logs should be investigated to maintain white spruce stands without planting.