Consideration of scale in the restoration of woodland and savanna ecosystems in the Central Hardwoods of North America
Woodland and savanna restoration is a common practice in many former degraded or converted woodland and savanna ecosystems throughout the world. Over the past few decades, forest managers in the Central Hardwoods region of North America have initiated efforts to restore oak woodland and savanna ecosystems across the region. In many instances, these efforts consist of restoring disturbance regimes that include both fire and the removal of canopy trees to reach woodland and savanna structural characteristics. Restoration has proven successful on scales up to approximately 1000 ha, but restoration on landscape scales, greater than 10 000 ha, is rare and the feasibility of restoration at this scale is unknown. We initiated our study to examine the impact and efficacy of woodland and savanna restoration on a landscape scale. We collected vegetation measurements at 70 locations within and around the White Rock Ecosystem Restoration Area (WRERA) on the Ozark-St. Francis National Forest, Arkansas, USA, and used generalized linear models to understand changes in woodland and savanna components under different restoration conditions. We also used LANDFIRE data to assess the efficacy of restoration at producing woodland and savanna conditions, such as canopy closure, on large areas of the landscape.
We found the number of large shrubs decreased and small shrubs increased with prescribed fire severity. We also found that visual concealment from ground level to 1 m in height increased with time since prescribed fire, and woody ground cover decreased with the number of prescribed fire treatments. We observed no increase in herbaceous ground cover components that are indicative of woodlands and savannas ecosystems in the region. Using LANDFIRE datasets, at the landscape scale we found that since the initiation of prescribed fire, canopy cover was lower but not to levels characteristic of woodlands and savannas. We did not find successful restoration of woodlands and savannas over large areas after 10 years at a landscape scale. However, the success of restoration can differ across spatial and temporal scales and could take greater than 50 years to achieve. Based on our findings, restoration managers should make special consideration at the scale they plan to implement restoration efforts and understand the hurdles to implementation on landscape scales.