Effects of forest fire on the nitrogen cycle in a dry dipterocarp forest, Thailand

Abstract

The losses of carbon and nitrogen by the forest fire were measured in a dry dipterocarp forest (DDF), northeast Thailand. Seasonal changes in the aboveground biomass of understorey grass and their nitrogen concentrations were measured. The aboveground biomass of grass was increased from March to July during the rainy season and reached the peak of 5.8 Mg ha-1 in July. Then, the biomass gradually decreased to 2.5-2.6 Mg ha-1 at the end of rainy season. The nitrogen concentration in grass biomass decreased gradually from 1.7 % at the beginning of rainy season to about 1 % at the end of rainy season, and dropped markedly to 0.4 % at the burning time in January. So about 60 % of the peak nitrogen mass (45 Kg ha-1) were lost or retranslocated from the aboveground biomass to belowground. Carbon and nitrogen lost by the forest fire were 2.3 Mg ha-1 and 28 kg ha-1, respectively. The occurrence of forest fire synchronized with the senescent period of grasses, resulting in the minor loss of nitrogen in the forest ecosystem.