Forest Structure Drives Avian Diversity in Boreal Peatland Forests

Abstract Peatland forest ecosystems play a critical ecological, economic, and cultural role by sequestering carbon, supporting biodiversity, the provisioning of conventional and non-conventional wood products, and providing habitat for specialists. Historically, forest management in these systems has used clearcut harvests to maximize pulp production, often resulting in structurally simplified stands vulnerable to climate change. As climate change reshapes boreal systems through warming, altered hydrology, and increased disturbance, identifying structural features that promote resilience is increasingly important. Ecological forestry, which aims to emulate natural disturbance and subsequent forest development, is an alternative approach to support a broader suite of ecosystem processes. To inform this approach, we examined how forest structure, quantified through lidar-derived metrics, varies across peatland forest types and stand ages, and how these structural attributes influence avian communities, with emphasis on peatland associate species. We used field measurements, bird point count surveys, and lidar data across productive black spruce, stagnant black spruce, and tamarack stands in lowland conifer peatlands of northern Minnesota. Results showed that canopy height, canopy cover, heterogeneity, vertical canopy complexity, and overall complexity did not differ among cover types but increased significantly with stand age, reflecting the gradual development of structural complexity over time. Total bird species richness and diversity showed limited associations with forest type, stand age, or structural metrics, likely reflecting the broad distribution of generalist species across stands. In contrast, peatland-associated species exhibited clear positive responses: their richness and diversity increased significantly with stand age and were positively correlated with lidar-derived measures of canopy cover and the overall complexity index. These results underscore the ecological value of older, structurally complex peatland stands in sustaining specialist bird assemblages and highlight the importance of incorporating fine-scale structural metrics into biodiversity assessments and climate-adaptive management planning aimed at sustaining habitat function under increasing climatic variability. Further, our results have application to the development of silvicultural approaches that better reflect the natural, complex structural dynamics of these ecosystems. Silvicultural approaches that emulate natural structural development, such as irregular shelterwood with reserves or variable density thinning, may enhance canopy complexity while maintaining forest productivity and habitat for peatland specialist birds.