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Baccharis halimifolia: Seed germination response after exposure to heat, smoke, and charred wood extract.
Billock, Arlene1, Grace, James2, 1 Johnson Controls World Service, Lafayette, Louisiana, USA2 USGS, Lafayette, Louisiana, USA
ABSTRACT- Currently, much effort is being made to reduce the abundance of Baccharis halimifolia using prescribed fire. While exposure to fire often top kills the shrub, the effects of fire on B. halimifolia seed germination have not been determined. The objective of this study was to determine the individual and combined effects of heat shock, smoke, and charred wood extract on seed germination by this species in order to evaluate the potential effects that fire may have. Seeds were tested for germination after exposure to heat shock and smoke with different duration times, and two different concentrations of charred wood extract. Germination was evaluated for a period of 48 days in a greenhouse. We found that germination of presoaked seeds (soaked in DI water for 24hours before treatments) was significantly reduced by exposure to 105oC or 120oC for all durations and by exposure to smoke for all durations, whereas dry seed (i.e., seed not presoaked) was only reduced by exposure to 120oC and 20% charred wood extract. In a combination treatment, dry seeds were exposed to 105oC, 10% charred wood extract and exposure to smoke for 5, 10, and 15 minutes. In these combined treatments, germination was reduced to less than 1%, a dramatically greater reduction than caused by the individual components in isolation. Overall, the main findings of this study were (1) none of the treatments caused a stimulation of germination, (2) presoaked seeds were impacted more negatively by heat, smoke, and wood extract than dry seeds, and (3) the combination of treatments had a much greater effect on germination than the individual components. These findings suggest that fire can be expected to reduce postburn germination by B. halimifolia and that preburn soil moisture conditions may influence the degree of this effect.
Key words: prescribed fire, heat shock, Baccharis halimifolia, germination