The Kentucky Bluegrass Savanna-Woodland is a globally imperiled ecosystem that was formerly a major vegetation component of the Inner Bluegrass Region of Central Kentucky. Climatic conditions of the region do not limit the regeneration of closed forest systems; therefore periodic disturbances would have been necessary to maintain savanna-woodland historically. Evidence from adjacent physiographic provinces (Cumberland Plateau mixed mesophytic forests, Big Barrens Region of Kentucky/Tennessee) suggest that fires burned on both local and regional scales, however tree ring analysis failed to find fire scars in Bluegrass Savanna-Woodland legacy trees from the time period c1600-1850.
To understand the role of fire impacts on seedling regeneration, burn responses were measured after a dormant season prescribed fire on the largest and best preserved remnant Kentucky Bluegrass Savanna-Woodland. A series of 14 transects (10m wide by 25-100m long) were established to measure fire responses on naturally regenerating Bluegrass hardwood tree seedlings. Species identification, height, diameter, and post-burn responses (topkill, resprouting, mortality) were measured three months after fire exposure. Data was analyzed to determine the species specific responses of diameter/height thresholds for avoiding topkill and diameter/height re-acquisition on topkilled seedlings.
Results/Conclusions
A total of 1911 individuals across 17 species were documented, with the seedling pool dominated by Shellbark Hickory, Black Walnut, Common Hackberry and White Ash. The majority of seedlings, regardless of species, experienced topkill due to the fire, and only about 20% avoided topkill. In those species that experienced topkill, only about half of their diameter was re-acquired in the newly sprouted stems, however, height was generally equal to, or surpassed, the pre-burn height. A minor portion of seedlings experienced outright mortality due to fire.
This research shows that the remnant savanna-woodland seedling pool is dominated by a new cohort of species, that these species are able to tolerate prescribed fire by resprouting, and resprouting stems are reduced in diameter but able to re-acquire pre-burn heights. This height strategy may benefit seedlings by allowing them to better compete for light when herbaceous vegetation has been cleared by fire. Low-intensity fire would not eliminate these species and in fact may help facilitate their recruitment into subsequent age classes due to competition reduction. Prescribed fire may be a useful tool for encouraging seedling regeneration in remnant Kentucky Bluegrass Savanna-Woodlands, though the seedling pool indicates a potential shift in future canopy composition. Consequently, anthropogenically ignited fires may have been part of the disturbance regime that maintained Kentucky Bluegrass Savanna-Woodlands.