Overstorey leaf production and emergence of sassafras saplings in a southwest Missouri oak woodland: An analysis based upon long-term effects of fire

Missouri Ozark woodlands are a unique, but imperilled ecosystem type due to fragmentation, lack of proper management and a changing climate. The management, restoration, and conservation of Ozark woodlands is a conservation priority. The Ozark woodlands contribute to the sequestration of carbon and nutrients through their robust productivity, effectively removing carbon dioxide from the atmosphere and storing it in the biomass and soil while cycling essential nutrients to support the ecosystem's health and vitality. We have assessed the over- and mid-storey leaf production, collecting leaves in baskets every autumn in a 1 200-ha conservation area in southwest Missouri since 2000. The leaf production data from 2000 to 2021 were compared among sites; control (not burnt for over 80 years), burnt (fire resumed in March of 1999 and repeated in 2001, 2003, 2008, 2010, 2013, and 2021) and reference (fire resumed in 1980 and repeated every 2 years). The average oak leaf production was statistically higher in the burnt site than the reference site, but only marginally higher than the control site. The leaf production varies statistically between the years. We applied a regression analysis among the productivity, temperature, and precipitation to associate the temporal variability in the weather with the productivity. The reference woodland showed statistical significance with the precipitation, but not with the temperature, while the other sites did not show any statistical significance with the precipitation. No statistically significance difference was observed between the productivity and temperature across any of the woodland burn histories. The March-June, March-May, and June-August precipitation statistically predicted the productivity. The results indicate that long-term burning is predictably associated with woodland leaf production and precipitation, but the precipitation is uncoupled with the productivity in woodlands that were more recently burnt or where burning has been suppressed. Sassafras saplings of approximately 1 m in height have emerged as the dominant species in the understorey of burnt woodlands while being completely absent from the control and reference woodlands. However, the productivity is the highest in the woodlands where burning has been suppressed and 20 years of prescribed fire does not significantly reduce the productivity. Oak regeneration over 20 years of burning is being suppressed by competition with sassafras, which may result in a significant shift in the ecosystem variables.