The mesophication hypothesis, which proposes a positive feedback between fire and vegetation, rests on two underlying hypotheses. These hypotheses concern the history of fire and vegetation. First, fires are thought to have occurred frequently—every few years to a decade—before the era of fire-exclusion. Second, these frequent fires thwarted the establishment of fire-intolerant mesophytes, such that xerophytic oak and pine stands were not invaded by mesophytic species until fire was excluded. Here, we evaluate these hypotheses through proxy records (primarily dendroecological data) on fire history and stand structure in the Appalachian Mountains.
Results/Conclusions
Fire-scar data from oak- and pine-dominated landscapes indicate that fires burned frequently, generally at intervals of less than 10 years, before exclusion. At study sites with long fire-scar records that cover multiple land use phases, fires generally burned at high frequencies from before European settlement until the beginning of fire exclusion in the early- to mid-twentieth century, after which fire frequency declined sharply. These findings are supported by radiocarbon-dated soil and sediment charcoal, which indicates that fire has shaped Appalachian vegetation for many centuries to millennia. Dendroecological data on age structure of xerophytic stands show that oak and pine species regenerated under the frequent burning of the past, while other species generally did not. Oaks likely persisted under the historical fire regime by sprouting repeatedly, with occasional fire-free intervals of abnormal length (e.g., > 10 years) permitting some sprouts to grow large enough to survive subsequent fires. The onset of fire-exclusion was marked by an abrupt pulse of tree establishment across many species, including mesophytic species such as maples. These findings support both of the historical hypotheses on which the mesophication hypothesis is founded.