Forest stand structure is closely linked to a variety of ecosystem functions. Structure can influence habitat availability, carbon storage, primary productivity, and resilience in forests and associated ecosystems. As one example, riparian forest structure has a direct impact on associated stream system functions. Over time, changes in structure due to stand development and disturbances have implications for how we understand ecosystem services and functions across the landscape. In the northeastern United States, forests are recovering from historic cutting for timber and agriculture, and the recovery of old-forest characteristics is still on-going. As forests continue to develop late-successional structure in coming decades, this will have direct impacts on carbon storage and stream ecosystems within forests. Thus, it is important to understand: how forest structure is developing across the northeastern United States, which elements of structure are most important for ecosystem functioning, and how humans can effectively manage for these characteristics. To advance our understanding of the long-term structural dynamics of northern hardwood forests, this dissertation takes three approaches. The first study quantifies the regional range of variability in stand structure for mature northern hardwood-conifer forests with varied land-use histories. This chapter then assesses whether differences in past land-use have altered forest development at the regional scale. Results suggest that forests recovering from partial harvests or from multiple, light management entries have recovered more old-forest structure than clearcut forests. This provides evidence for novel recovery pathways driving forest structure across the northern forest region. The second study examines how management for old-growth forest structure alters carbon storage over two decades in comparison to conventional management and unmanaged forests. This chapter finds that management designed to create old-forest structure provides carbon benefits over conventional management techniques and may be a viable natural climate solution. The final chapter focuses on the relationship between forest structure and the carbon stored in large wood in headwater streams. This chapter then analyzes how continued stand development towards an old-growth condition may change this carbon pool. Large wood in headwater streams stored more carbon per area than large wood on the forest floor and was linked to the basal area of large trees in the riparian forest. Old-growth forests stored substantially more carbon in in-stream large wood, indicating that this carbon pool will grow as forests continue developing late-successional structures. This dissertation outlines novel stand development pathways in the northeastern United States, suggests that active management for old-forest conditions can benefit ecosystem carbon storage, and indicates that continued development of old-growth structures, particularly large trees, will benefit in-stream wood loads and carbon storage. Taken together, this provides insights into the regional dynamics of forest structure and the implications for ecosystem functions.
Stephen Peters-Collaer (Wed,) studied this question.