Decay Following Fire in Young Mississippi Delta Hardwoods

During the summer and fall of 1932, 602 fire-scarred trees of 9 species of Delta hardwoods were dissected and analyzed for decay and insect activity. The trees were between 3 and 11 inches in diameter, and were taken from 4 parishes in Louisiana and 3 counties in Mississippi. Forest fires have been of frequent occurrence in the Mississippi Delta area at least for the past 30 years, with the fire seasons 1917-18 and 1924-25 outstanding in severity of damage done during those seasons. Fire scars healed most rapidly in the oaks and red gum, followed by ash, hackberry, and persimmon. The greater the num ber of years since scarring, the greater the proportion of scarred trees decayed. Of the species studied, hackberry was found to be the most susceptible to initial infection, followed by the oaks, ash, red gum, and persimmon. Following scarring, in red gum and persimmon, wound gum is produced just under the scarred surface, which protects the trees against infection. Much of this protective effect is lost, if subsequent fires kill the exposed sapwood. Decay spread upward from the fire scar most rapidly in the oaks (2.3 inches per year), followed in order by ash, red gum, hackberry. And persimmon. A definite relation was found between the rate of decay and each of the following factors: Age of tree, percentage of tree circ~mference scarred, diameter at the time of scarring. Present diameter, and fungus causing the decay. The breaking-over of young trees at the base, because of decay following firescarring, was found to be of infrequent occurrence and chiefly confined to overtopped trees and trees otherwise in poor vigour. A large number of fungi, from several families of the Hymenomycetes, were found to cause decay behind fire scars in the Delta area. Many of these fungi, including Lentinus tigrinus and Polyporus lucidus, can rot dead sapwood, old sapwood of living trees, and the heartwood of living trees. But one fungus in anyone tree was responsible for the major decay. A large variety of insects, chief among which are ants and termites, invade the decayed wood behind fire scars in this area. Only one insect, Parandra brunnea, was found to invade the sound wood beyond the decay column for any distance. Insects appeared to play a minor role in the uitimate damage.