The Spatial Pattern of Dry Season Fires in the Savanna Forests of Thailand

Abstract

This paper reports the first stage of a research project to investigate the vertical and horizontal spatial pattern of temperatures in the fires which are common throughout the dry deciduous dipterocarp forests of north and northeast Thailand from December to March every year. The work was carried out by using 'Thermocolor' mica pyrometers in experimental burns at three localities. The construction, calibration, field deployment and limitations of the pyrometers are fully described. It is shown that there are two basic types of vertical temperature profile, for which characteristic curves are provided. These occur in different forms in four main types of burn, namely: (1) typical litter burns; (2) extreme litter burns; (3) typical groundcover burns; (4) extreme groundcover burns. The fire characteristics of each are described in detail. Extreme groundcover burns may attain temperatures of between 700 and 900?C at 0.5-1 m above the ground and spread at rates exceeding 3.0 cm/s even in near windless conditions. Unfortunately, a policy of fire exclusion leads to the groundcover associations that give rise to this dangerous type of wildfire and a policy of prescribed burning is preferable. The insulating properties of both the sandy loam soils and the bark of savanna forest tree species are demonstrated and it is concluded that the dry deciduous dipterocarp forest ecosystem is well adapted to fire. Suggestions for further