Changes in the composition and structure of mixed-oak, second-growth forest ecosystems during the understory reinitiation stage of stand development

The composition and structure of the living and dead woody vegetation in seventeen relatively undisturbed, second-growth forests in the understory reinitiation stage of stand development (70 to 149 years old) were examined using a chronosequence on a single south-facing ecological landtype phase in southeastern Ohio. Principal components analysis (PCA), in conjunction with historical information, was used to support the assumption that plots had similar physiography, soils, and disturbance histories. The first axes of canonical correspondence analyses (CCA) based on canopy species importance values, as well as sapling and seedling relative densities, represented a successional continuum of increasing Quercus alba L. Canonical correspondence analysis (CCA) relating canopy composition with the density of dead snags and fallen logs suggested that during understory reinitiation there may be several species-specific waves of density-independent mortality, such as scarlet oak (Q. coccinea Muenchh.) decline 70 to 89 years after stand initiation. Understory shade-tolerant species (e.g., Acer saccharum Marsh.) increased in relative density with the waves of canopy mortality and relegated oak species to the seedling structural layer. Although there are many possible pathways of development in mixed-oak ecosystems, the later-stage development pathways of mixed-oak ecosystems on the south-facing ELTPs in southeastern Ohio are predictable, and should be considered in the development of ecological classification systems