Overstory tree mortality resulting from reintroducing fire to long-unburned longleaf pine forests: the importance of duff moisture (Varner III et al., 2007)

Full citation: Varner, J. M., et al."Overstory tree mortality resulting from reintroducing fire to long-unburned longleaf pine forests: the importance of duff moisture." Canadian Journal of Forest Research, vol. 37, no. 8, 2007, pp. 1349-1358.

Abstract: In forests historically maintained by frequent tire, reintroducing fire after decades of exclusion often causes widespread overstory mortality. To better understand this phenomenon. we subjected 16 fire-excluded (ca. 40 years since fire) 10 ha longleaf pine (Pinus pulusrris Mill.) stands to one of four replicated burning treatments based on volumetric duff moisture content (VDMC): wet (1 15% VDMC): moist (85% VDMC); dry (55% VDMC); and a no-burn control. During the first 2 years postfire. overstory pines in the dry bums suffered the peatest mortality (mean 205%); pine mortality in the wet and moist treatments did not differ from the control treatment Duff reduction was greatest in the dry burns (mean 46.5%). with minimal reduction in the moist and wet bums (145% and 5%. respectively). Nested logistic regression using trees from all treatments revealed that the best predictors of individual pine mortality were duff consumption and Crown scorch (P < 0.001; R' = 0.34). Cmwn scorch was significant only in dry bums, whem duff consumption was significmt across all treatments. Duff consumption was related to moisture content in lower duff (Oa; R2 = 0.78, P < 0.001). Restoring tire to long-unburned forests will require development of bum prescriptions that include the effects of duff consumption. an often overlooked fire effect.