Data from: Longleaf pine proximity effects on air temperatures and hardwood top-kill from prescribed fire
Bigelow, Seth W.; Whelan, Andrew W. (2019), Data from: Longleaf pine proximity effects on air temperatures and hardwood top-kill from prescribed fire, Dryad, Dataset, https://doi.org/10.5061/dryad.vm692vr
Background Regulation of the dominance of sprouting understory hardwoods is a common objective for prescribed fire in open-canopy longleaf pine woodland of the southeastern USA. Nevertheless, little is known about the influence of individual pines on fire and hardwood mortality. We studied growing-season fires in stem-mapped stands in southwest Georgia USA which displayed large variation in structure due to cutting treatments applied 7 yr earlier. We measured air temperature and heating duration, and measured post-fire sprouting behavior of four guilds of understory hardwoods: mesic oaks, upland oaks, xeric oaks, and fleshy-fruited hardwoods. Mean air temperature (i.e., of flames, buoyant plume and smoldering combustion) and heating duration (time over 60°C) were analyzed with respect to fuel-bed conditions and neighboring tree density. Hardwood top-kill was analyzed with respect to neighboring tree density and hardwood height. Results Size of and distance to longleaf pines strongly affected time over 60°C, which increased linearly from a mean of 87 s to a mean of 234 s across a gradient of pine basal area from 0 to 30 m2 ha-1. Mean air temperature during prescribed fire was unaffected by pine density but increased linearly from a mean of 114°C to a mean of 148°C across a gradient of wiregrass cover from 0 to 100%. Neighborhood models showed that time over 60°C during the burns was longest at the base of pines and decreased by two-thirds at 3.3 m distance. Pines affected hardwood top-kill probability at a similar scale, the effect at 4.4 m decreasing by two-thirds compared to at the base of the pine. The four hardwood guilds were readily top-killed when ≤ 1 m tall, but at 2 m height upland and xeric oaks had become more resistant to top-kill than mesic oaks or fleshy fruited broadleaved trees. Conclusions The influence of individual pine trees on heating duration and top-kill power of prescribed fire drops by ⅔ of maximum within 3 to 4 m of a tree, compared to a maximum at the base of the tree. Neighborhood models provide a method to estimate tree effects on prescribed fire heating duration and top-kill probability, and thus a way of predicting stand structures that provide ecological benefits of openings while remaining below thresholds that trigger vigorous hardwood response.
Southeastern Coastal Plain