Impact of fire on bellyache bush (Jatropha gossypiifolia) plant mortality and seedling recruitment

Abstract

A 2-yr trial investigated the efficacy of fire as a control technique for bellyache bush (Jatropha gossypiifolia) in riparian habitats. Spring burns were applied in successive years (September 1999 and October 2000), and their impact on juvenile, mature and old bellyache bush plants was determined. Post-fire seedling recruitment was monitored for 21 months after the initial burn. The first fire significantly (P < 0.05) reduced the original bellyache bush plant density by 76% (from 10 750 plants/ha to 2580 plants/ha). A second fire a year later extended the kill rate (8 months after the second burn) to 92%, with a residual plant population of 860 plants/ha. Monitoring for a longer period would confirm the results obtained with the second burn. The relative sensitivity to fire was juvenile > mature > old. In contrast, seedling emergence was significantly (P < 0.05) increased after burning. Emergence in burnt plots over the wet season following the first fire was 2.7-fold that in unburnt controls. Even with high mortality during the subsequent periods, seedling density in burnt plots at the end of the study averaged 368 000 per ha compared with 40 000 per ha in the unburnt controls. It is expected that the residual population of bellyache bush would produce enough seed to soon reinfest the area. These results stress that fire should be one of a number of tools, which may be used for control of bellyache bush. They also highlight the need for development of integrated control strategies that not only treat the primary infestations but also the many seedlings that emerge from the residual soil seedbank.