Effect of Different Fire Severities on Coppicing of Caatinga Vegetation in Serra Talhada, PE, Brazil

Abstract

The sprouting response of the vegetation in three areas that were slashed and burned under different fire severities was determined in a 12 year second growth tropical dry forest (caatinga) near Serra Talhada, PE, Brazil. Plots were slashed at the onset of the dry season (July) and burned on 19 September (B), 26 September (C) or 4 October (D). Sprouting responses were also examined in unburned areas. Longer drying periods resulted in increasing fire severity and increasing consumption of the original biomass (; 74 Mg/ha): 72, 87, and 93 percent biomass consumption, respectively. Prior to burning, plant density with a stem diameter - 1 cm at the soil surface was 5815 plants/ha. Greater than 94 percent coppiced after slashing, usually with epicormic sprouts, indicating their adaptation to periodical disturbance. Burning dramatically decreased the number of plants that coppiced. Two months following each burning 43, 21, and 10 percent of the plants had coppiced in the three burns, respectively. The majority of sprouts following fire arose from underground tissues. Coppicing crown area decreased from 1451 m2/ha in the slashed/unburn treatment to 350, 248, and 165 m2/ha in the three fires. The six species with highest plant densities, Croton sonderianus Muell. Arg. (2631/ha); Cordia leucocephala Moric. (1264/ha); Bauhinia cheilanta Stand. (819/ ha); Mimosa sp. (474/ha); Caesalpinia pyramidalis Tul. (308/ha) and Astroneum urundeuva Engl (140/ha) displayed a variable response to increasing fire severity. Mimosa sp. coppicing was little affected (49-43% survival) and its relative abundance increased with increasing fire severity, from 8 percent to dominance with 36 percent. C. sonderianus density decreased with increasing fire severity (946 to 174/ha) but it maintained a high relative abundance in all treatments (31-45%). B. cheilanta had the highest survival rate at low fire severity (78%) but it decreased sharply with increasing severity (down to 9%). Survival of the other species decreased from 30-50 percent to approximately 10 percent. Coppicing of Mimosa sp. was much more vigorous than that of any other species, with the highest number of sprouts per stump, crown area, and sprout height. The level of fire severity of the slash burning will influence future species composition of caatinga vegetation.