Aspects of the temporal pattern of dry season fires in the dry dipterocarp forests of Thailand

ABSTRACT: This thesis reviews the role of fire, and especially its seasonal timing, in the moist savanna forests of mainland Southeast Asia, and, in particular, of Thailand. Based on one year's experimental fieldwork carried out in Uthai-thani Province, West Thailand, the thesis investigates the development of conditions for burning and fire behaviour throughout the dry season. Spatial patterns of fire temperature and the duration of maximum temperature are measured, along with a wide range of other key variables, such as fireline intensity and speed of fire spread. The climatic preparation of fuels for ignition is also examined.

It is argued that fire is endemic in this formation, although its character has changed much over time. Conditions for burning were found to be optimal in March (the late dry season), when fire occurrence and behaviour measurements were at their peak. Two ground cover fuel-fire regimes are recognized: 1) heterogeneous ground cover, with a high proportion of non-grass species, producing patchy, low temperature burns (<650°C), except where conditions are very favourable, as in the late dry season; 2) homogeneous grass cover, notably of Heteropogon triticeus (R.Br.) Stapf.ex Craib, which tends to burn evenly, and extensively, with a high temperature (750-900°C) and speed of spread (0.6-3.0 cm s¹), when the grass stalks have collapsed after the arrival of the Northeast monsoon (early February mid dry season). As in African moist savannas, short-term recovery shows a tendency for low temperature burns on partially dry grass to favour woody species, while discouraging grass growth.

It is suggested that fire timing and placement can be used as an effective tool in ecological management, to: 1) prevent the extensive occurrence of destructive wildfires; 2) meet a range of different planning objectives. It is further argued that, since the fire ecology is local, the management pattern must also be devised locally. A change from central state control of policy is thus proposed.