A history of recurrent, low-severity fire without fire exclusion in southeastern pine savannas, USA

The reintroduction and maintenance of historical surface fire regimes are primary goals of ecological restoration across many open, pine-dominated ecosystems in North America. In the United States, most of these ecosystems experienced long periods of fire exclusion in the 20th century, leaving few locations to serve as reference sites for ecological conditions associated with a continuous history of recurrent, low-severity fire. Here, we present a tree-ring perspective of uninterrupted surface fire activity from three pine savanna sites in the Red Hills Region of northern Florida and southwestern Georgia, USA. Our sites include two old-growth stands of longleaf pine (Pinus palustris): the Wade Tract on Arcadia Plantation and the Larkin Tract on Millpond Plantation. We also sampled the largely second-growth mixed pine savannas of Tall Timbers Research Station. Documentary records for burning at these sites are limited to recent decades and are often incomplete, although regional land-use traditions and scattered historical records indicate frequent fire may have persisted through the 20th century to present day. Fire-scarred cross sections from externally-scarred stumps, dead trees, and live trees provided tree-ring evidence of frequent fires occurring from the beginning of our fire-scar record in the late 19th century onward. Both fire frequency and seasonality were relatively consistent throughout time and among sites. Biennial and annual fire intervals were the most common. Most fire scars occurred in the dormant and early-earlywood portions of the rings, indicating that these fires were human-set fires during the months of January to mid-April, before the main lightning-fire season. Our findings regarding post-settlement fire frequency are consistent with previous estimates of fire frequency during earlier centuries, resulting from lightning and Native American ignitions. We recommend that our sites be used as reference sites for restoration as they are among the relatively few areas in the United States with a continuous history of frequent low-severity fire without 20th century fire exclusion.