Fluctuation of soil temperature after prescribed burning in some semi-natural grasslands in eastern Japan

Abstract

In humid temperate regions such as Japan, prescribed burning has been proposed to conserve semi-natural grassland ecosystems and endangered species.　The effect of prescribed burning on vegetation has been evaluated through comparing the vegetation of “burning site” and “control site”.　Most of these studies focus only on vegetation.　However, this kind of method makes it difficult to clarify what kind of environmental change is caused by burning semi-natural grassland vegetation.　Therefore, in this study, we measured long-term fluctuations of soil temperature, and clarified the effect of fire in four sites with both burning and control treatments （un-burned） across semi-natural grasslands in eastern Japan.　The maximum daily soil temperatures were overall higher in burned sites than in control sites, with some burned sites reaching over 40°C.　By contrast, daily minimum soil temperatures did not differ between burned and control sites.　As a result, the difference between the highest and the lowest soil temperatures （range of daily soil temperature fluctuations） increased at burned sites.　We can conclude that the soil temperature increases after prescribed burnings because the fire removes litter, thus allowing direct sunlight to shine down on the soil surface.　Contrastingly, at the control site, where no burning occurred, soil temperatures did not rise given that litter shielded the soil from sunlight.　The differences in the range of daily soil temperatures between the burned and control sites disappeared in summer. This may be due to vegetation regrowth after the burning, which allowed vegetation to restore to its original state, and afterwards block sunlight from reaching the soils surface.　In conclusion, the present study has demonstrated that the use of burning application methods in semi-natural grassland management in Japan dramatically alters soil temperatures.　This may directly affect plant germination and growth, which are critical for maintenance of plant communities in semi-natural environments.