Scale dependence of oak woodland historical fire intervals: Contrasting the Barrens of Tennessee and Cross Timbers of Oklahoma, USA

Abstract

Characterization of scale dependence of fire intervals could inform interpretations of fire history and improve fire prescriptions that aim to mimic historical fire regime conditions. We quantified the temporal variability in fire regimes and described the spatial dependence of fire intervals through the analysis of multi-century fire scar records (8 study sites, 332 trees, 843 fire scars) derived from two historically post oak (Quercus stellata Wangenh.) woodland landscapes. Despite large differences in fire environment conditions, study sites (~1 km2) burned frequently (mean fire interval [MFI] ≤10 yr) before Euro-American settlement (pre-EAS), with sites in Tennessee showing higher overall fire frequency than sites in Oklahoma, USA. Pre-EAS MFIs decreased exponentially with increasing spatial extent from individual trees (~1 m2) to landscapes (~100 km2). The relationship between MFI and spatial extent may help to explain how historical observations of annual burning could be recorded in woodlands, when experimental studies suggest that this is too frequent for tree recruitment. Further investigations of spatial dependence of fire intervals would improve our ability to relate historical and experimental fire data to present day fire prescriptions, and vice versa.