Experimental natural disturbance-based silviculture systems maintain mature forest bird assemblage long-term in Maine (USA)

Natural disturbance-based silvicultural systems are forestry approaches that emulate ecological patterns and processes and are assumed to accommodate native bird assemblages better than conventional alternatives. The Acadian Forest Ecosystem Research Program (AFERP) represents the longest-running experimental application of expanding gap approaches to ecological forestry in the northeastern US. This project assessed long-term ecological effects of two expanding gap silvicultural systems (irregular expanding-group shelterwood with reserves and expanding-group selection with reserves) as indicated by the abundance, diversity, and composition of the bird assemblage associated with mature forest conditions. Birds were surveyed using a territory mapping method during three periods: pre-harvest, immediately after initial gap creation, and twenty-five years later after the third harvest entry. Declines in bird abundance and diversity occurred in all treatments and paralleled declines in abundance observed at regional scales, suggesting that treatments did not cause declines. Species-specific responses varied, but 65% were similar to regional population changes. Assemblage similarity among treatments was stable through time. The natural disturbance-based silvicultural systems studied did not disrupt the mature forest bird assemblage following three harvest entries despite declines in bird abundance and two measures of diversity across all treatments. Minor changes in the structure of the bird assemblages were noted, which corresponded to habitat elements associated with the gap harvests. Natural disturbance-based approaches to forest management have broad potential to meet landowner objectives while minimizing negative ecological impacts on mature forest ecosystems.