Historical Open Forest Ecosystems in the Missouri Ozarks: Reconstruction and Restoration Targets

Abstract

Current forests no longer resemble historical open forest ecosystems in the eastern United States. In the absence of representative forest ecosystems under a continuous surface fire regime at a large scale, reconstruction of historical landscapes can provide a reference for restoration efforts. For initial expert-assigned vegetation phases ranging from prairie to forest across the Missouri Ozarks landscape, we reconstructed historical (1815 to 1850) forest densities, basal area, percent stocking or growing space, and canopy cover. After examination of structural means and ranges by initial expected vegetation phases, we classified vegetation phases based on percent stocking boundaries of 30–55% for open woodlands and 55–75% for closed woodlands (diameters ≥ 12.7 cm). We suggest that a percent stocking boundary of 10% may separate prairie and savannas, but we did not identify any large scale prairies in Missouri. We provided structure of each vegetation phase for restoration targets; mean historical densities of vegetation phases ranged from 81 trees/ha in savannas to 285 trees/ha in non-oak/non-pine forests (diameters ≥ 12.7 cm). Due to greater densities than expected and larger diameter trees than current forests, historical forests may have been primarily (about 65%) woodlands with nearly closed canopies, unlike the open canopies presumed during settlement in the Missouri Ozarks. However, a closed yet single canopy layer can transmit enough light to sustain an herbaceous ground cover, given an open midstory due to frequent surface fires. Restoration of open woodlands across all public lands is not practical, but restoration of lower density forests composed of drought-tolerant tree species should translate to management for changing climate.