Overstory species composition of naturally regenerated clearcuts in an ecological classification framework

Abstract

Multifactor ecological classification systems are being developed for many regions. An element of these systems not yet well understood is how disturbances, clearcutting in this instance, may alter the vegetative component of the classification units at the stand and landscape levels. We sampled 1,096 plots in 21–35 year old naturally regenerated clearcuts on the Hoosier National Forest (HNF) in south-central Indiana, USA. We examined overstory species composition of clearcut plots in comparison to reference plots (80+ years old), both within and among six Ecological Landtype Phases (ELTPs) of two ecological sections using non-metric multidimensional scaling and non-metric multi-response permutation procedures. Clearcutting drastically changed species composition in comparison to reference plots within ELTPs ranging from mixed oak-dominated ridges and slopes to bottomland, cove hardwood communities; Quercus species on ridges and slopes were replaced by Liriodendron tulipifera L. and, to a lesser degree, Prunus serotina Ehrh. and Acer rubrum L., in ELTPs of both sections. Contrasts of overstory species composition of reference plots exhibited differences among ELTPs, but clearcut plots showed mixed results and indicated very similar species composition across all ELTPs. Autogenic factors are likely the main drivers of overstory composition of clearcut sites. Species composition of ELTPs will continue to develop in response to autogenic and allogenic factors over time, and differences among ELTPs may emerge in later stages of stand development as the effects of allogenic factors accumulate. It is expected that L. tulipifera, a long-lived species, will be a dominant species in terms of basal area and density of all ELTPs in mature stands. Classification systems not designed to deal with changes related to disturbance and a failure to predict successional pathways after disturbance may limit their usefulness as a management tool in terms of overstory vegetation. For ecological classification systems to be fully effective, we must better understand the role of disturbance in ecosystem function at many different scales and integrate that knowledge into our decision-making and planning regimes to establish realistic and attainable objectives at multiple scales.