Microclimate Modification of Tall Moist Grasslands of Natal by Spring Burning

Abstract

The purpose of this study was to investigate modifying microclimatic effects of spring burning in tall grassland, long-term burning trials at Ukulinga, Pietermaritzburg, South Africa. Soil temperature (at 50 mm), soil heat, net radiation and surface reflection coefficient were monitored on various cloudless days before and after burning. Four days after burning there was no significant increase in soil temperature but soil heat and net radiation increases and surface reflection coefficient decreases (from 15% to nearly 3% at local noon) were evident. Between burning date and first day of measurements, a rainfall of less than 2 mm occurred causing greater evaporation at the burnt site (due to greater net radiation) and hence lower soil temperatures, compared to the control site. Burning also resulted in an increase in sensible plus latent plus photosynthetic heat densities (from a daily total density of 9.0 MJ m-2 before to 9.9 MJ m-2 after burning) with soil heat density increasing by 50%. Four weeks after, soil temperature and soil heat were greater for the burnt site compared to the control, but net radiation and surface reflection coefficient were not significantly different between the two sites. The appearance of green material some short time after burning is therefore probably a result of more favourable soil-plant water and surface energy relations.