Structure, Species Composition, and Carbon Storage of Remnant Late-Successional Forests in the Mid-Atlantic Region

Following 400 years of land use, and approximately 100 years of forest re-growth, the age structure of eastern U.S. forests has shifted from the late-successional dominance of pre-settlement, to a landscape of young secondary forests ranging in age from 50 – 100 years. Scattered within this matrix of young forests are a few productive, remnant old growth stands, preserved from harvest due to historical significance or inaccessibility. These mature and old growth remnant forests are a window through which we can understand and predict the future structure, species composition and carbon (C) storage of surrounding secondary forests. However, due to their rarity, surveys of this forest type are rare, particularly in the Mid-Atlantic. Here I begin to fill in this knowledge gap by surveying the majority of remaining mature and old growth forests of the Mid-Atlantic region. In Chapter 2, I describe the forest structure and species composition of this unique ecosystem. In Chapter 3, I discuss C storage in terms of structure and species composition in live aboveground woody material (AGC), dead wood, soil organic horizon (SOC), and leaf litter pools within this forest type. I used the U.S. Forest Service regional inventory to contextualize the structural and C storage characteristics of the matrix forests in comparison to the remnant old growth stands. While I had hypothesized that stand age was the primary driver of species composition and structure among mature and old growth forests, I found environmental conditions were most highly correlated with species composition, and species composition in turn determined structure. The one exception to this trend was dead wood volume, which increased monotonically with stand age. Old growth had lower small stem and snag densities than the younger forests, and large stems and snags contributed more to overall basal area. Species-specific effects were evident in the AGC pool. Dead wood C increased with stand age, reaching levels previously unreported in eastern U.S. hardwood forests. My results suggest that as secondary forest age increased, dead wood volume will be a major contribution to overall C stores.