Historical trajectories and restoration strategies for the Mississippi River Alluvial Valley

Abstract

Unlike upland forests in the eastern United States, little research is available about the composition and structure of bottomland forests before Euro-American settlement. To provide a historical reference encompassing spatial variation for the Lower Mississippi River Alluvial Valley, we quantified forest types, species distributions, densities, and stocking of historical forests using General Land Office (GLO) records from Missouri. For modeling historical species distributions, we applied random forests classification and predictor variables included terrain and soil characteristics. Historical forest types predominantly were sweetgum, black and white oak, and elm. Contemporary forests increased in maples and hickories, which are replacing sweetgum and oaks. Forest densities increased from 215 to 350trees/ha to 350 to 400 trees/ha for trees ⩾12.7DBH. Basal area historically was greater by a factor of 1.6–2.6 and percent stocking historically was full, except in an open oak-dominated ecosystem, whereas forests today have lower stocking comprised of young, small diameter trees. Land types, elevation, and soil texture determined historical species distributions, and we expect that with loss of fire and flooding, ecological separation by site factors has become less influential for current species distribution. Selection of sweetgum and oaks for planting would restore historical composition better than planting of ash and other shade-tolerant species, which promotes conversion to forest types under undisturbed conditions rather than restoration of forests under historical disturbance regimes. We also recommend managing for large diameter trees by thinning to promote more rapid growth of residual trees. Although there is uncertainty in historical reconstruction, these results provide new information about the presence and spatial variability of sweetgum and oak in historical forests of the Lower Mississippi River Alluvial Valley and post-settlement transformation of alluvial landscapes.