Forest Ecosystems (Jan 2023)
Forest composition and red oak (Quercus sp.) response to elevation gradients across greentree reservoirs
Abstract
Elevation gradients within forested wetlands have long been recognized for their role in defining species composition through factors such as hydrology and soil characteristics. Greentree reservoirs (GTRs) are levee-impounded tracts of bottomland hardwood forest flooded throughout the winter months to provide habitat for overwintering waterfowl. Artificial flooding of GTRs alters the forest composition due to flood frequency, depth, and duration in combination with slight changes in topography. To evaluate the effect of elevation gradients, soil properties, and management techniques in the overstory species composition and red oak (Quercus spp.) species abundance, we inventoried 662 plots across 12 independent GTRs in eastern Arkansas. In the lower elevations ranging from 50.98 to 54.99 m above sea level, the importance value index (IVI) was highest for nuttall oak (Quercus texana) and overcup oak (Quercus lyrata), whereas IVI shifted to cherrybark oak (Quercus pagoda) in the higher elevations ranging from 54.99 to 58.00 m. Alpha diversity did not differ by elevation gradient, soil property, or management technique within GTRs. Beta diversity, using non-metric multi-dimensional scaling (NMDS) analysis, indicated site-specific variability significantly correlated with the environmental predictors, including elevation (R2 = 0.57), easting (R2 = 0.47), soil texture (R2 = 0.21), and pH (R2 = 0.12). Red oak species-specific mixed-effects modeling of abundance response using Poisson distribution suggested an inverse correlation of nuttall oak and a direct correlation of cherrybark oak abundance with elevation. However, willow oak (Quercus phellos) abundance was not significantly affected by elevation but was by silt loam soil texture and restoration management techniques. These findings will aid management efforts to reduce the dominance of less desirable species that are prominent under specific environmental conditions and promote the dominance of more desirable species. Ultimately GTR sustainability is increasingly important amid the unpredictable impacts of climate change on the preferred red oak species that are economically, ecologically, and environmentally valuable to the sustaining economy of the local community and managing habitats for wildlife.
