Stand dynamics and disturbance history of five oak -dominated old -growth stands in the unglaciated Appalachian Plateau

Stand Dynamics and Disturbance History of Five Oak-dominated Old-growth Stands in the Unglaciated Appalachian Plateau James S. Rentch Stand dynamics and canopy disturbance histories of five oak-dominated old-growth stands in eastern Ohio, southwestern Pennsylvania, and north central West Virginia were investigated using a combination of ecological field sampling techniques, dendrochronologogical methods, and a review of historical resources of original forest composition and patterns of human and natural disturbance. This study has three objectives: 1) determine the current composition, structure and successional status of these stands, 2) develop stand histories, identifying changes in composition and structure over time, and 3) relate these chronologies to the canopy disturbance regimes under which these forests have originated and persisted. Witness tree tallies from 18 century land surveys show that presettlement forests in the study areas were oak-dominated forests. Quercus alba was dominant by a large margin, at minimum twice as abundant as Q. velutina, the second ranked species. Acer saccharum and Fagus grandifolia were among the top ten ranked species at each site; however their importance value was consistently less than one-third the value for Q. alba. Quercus rubra, Q. prinus, Castanea dentata, and Acer rubrum were relatively minor components of presettlement forests, rarely ranked among the ten most abundant tree species. At all five sites, the oldest trees were oaks and virtually no non-oak species were found in the older cohorts. At three sites, the oldest oaks date to well-defined time periods, suggesting that these stands initiated in the aftermath of major, stand-initiating disturbances. Following initiation, there was an extended pause in tree recruitment consistent with the stem exclusion and understory reinitiation stages of stand development. At the remaining two sites, the absence of clearly defined cohorts among the oldest trees, and continuous tree recruitment events preclude a reliable estimate of stand origin; however, these characteristics are consistent with the age structure of stands that have been uneven-aged for centuries. On average, at least one canopy disturbance occurred on these study sites every three years; larger multiple-tree disturbances occurred every 17 years. Although there was some variation by site and by historical period, there has been little significant change in canopy disturbance rates for the 300-year period reviewed. A review of tree-ring chronologies yielded three growth strategies. For these oaks, the likelihood of originating in a large opening and achieving overstory status before canopy closure is about the same as the probability of requiring a major release, either from the understory or from a smaller gap that closed. Half of the cored trees established as seedlings or spouts individually, and 30% attained overstory status individually, members of no identifiable cohort. The majority of multiple-tree events occurred in gaps < 200 m in area. For trees that required a major canopy release, understory residence times averaged 89, 54, and 50 years for Quercus alba, Q. rubra, and Q. velutina, respectively. Although there is some historical precedence for these values, few contemporary second-growth forests contain understory oaks of this age, particularly Q.