Effects of Soil Temperature during Fire on Seed Survival in Florida Sand Pine Scrub

Soil temperatures recorded with thermocouples and temperature-sensitive paints were quantified during Florida sand pine scrub prescribed fires at Ocala National Forest and Archbold Biological Station in May 1993. Thermocouples and glass petri dishes painted with temperature-sensitive paints and containing seeds of Eriogonum floridanum were placed at 0 cm and 2 cm depth, and in vegetated and open micro sites. Maximum temperatures were higher and peak temperature durations shorter at 0 cm than at 2 cm depth. Temperatures did not differ between micro sites during the Ocala fire, but were higher in open micro sites during the Archbold fire, probably due to combustion of well-aerated litter. Maximum temperatures of petri dishes were lower than those of adjacent thermocouples due to time required to melt paints. All Eriogonum seeds recovered from petri dishes after the Archbold fire failed to germinate. Germination was quantified for Eriogonum floridanum and Garberia heterophylla seeds heated to 100 degree C and 6 C under laboratory conditions. Seeds failed to germinate at 100 degree C, while germination was similar to controls for seeds exposed to 60 degree C. Results from this study suggest that small-scale spatial variation temperatures at the soil surface during fires is essential for seed survival and subsequent post-fire recruitment.