COS 275-6 - Effects of prescribed fire over 20 years on the ground flora and stand structure of three Missouri Ozark community types in the Current River Watershed

Background/Question/Methods

Fire is a major driver of many plant communities, but decades of suppression have caused drastic changes to community structure and composition across ecosystems, including in Ozark woodlands in the central Midwest. Reintroducing fire can restore ground flora by reducing midstory tree density, increasing light for the ground layer, and reducing leaf litter accumulation, but we lack a clear understanding of how these effects vary across time and space. To address this gap, we investigated the effects of repeated prescribed fire on ground flora species richness and abundance, stand structure, and species composition over 20 years in a landscape matrix of glades, dry woodlands, and dry-mesic woodlands using data collected from the Ozark National Scenic Riverways Fire Effects Monitoring program. Plots of 1000m² in dry (n=21) and dry-mesic woodlands (n=14) and 250m² in glades (n=27) were established in the Current River Watershed in the Missouri Ozarks. Burns were conducted at the landscape level, and plots received 2-5 burns with a mean fire return interval of 4.0 years. In the first growing season after each burn, crews surveyed ground flora and stand structure using 1m² quadrats, 50m transects (woodlands) or 30m transects (glades), and measured tree species, counts, and size (DBH).

Results/Conclusions

We found that fire plays a key role in driving community structure and dynamics across community types, although with varying levels of intensity. Preliminary results from linear mixed-effects models indicate that herbaceous species richness increased across all community types (p< 0.01), while the density of midstory trees (trees per hectare, TPH) declined across community types with repeated fire (p< 0.01). These effects varied across community types: the number of burns significantly affected overstory TPH overall (p< 0.01), but overstory TPH only declined in dry woodlands and glades and not in dry-mesic woodlands. Our results suggest that landscape fire, as typically implemented by management agencies, can shape plant community structure and dynamics. Specifically, these findings show that fire effects vary among community types. Understanding repeated fire effects over several years across multiple community types is critical to informing fire-driven woodland restoration across landscape scales.