Fuel Bed Properties and Fire Behavior in Pine Forest, Nam Nao National Park, Phetchabun Province

Abstract

Fuel bed properties and fire behavior in a degraded pine forest and pine-oak subcommunity were carried out in the Nam Nao National Park, Phetchabun province.  The investigation aimed to study and compare the fuel properties and fire behavior between subcommunities in 3 plots each 50x50 m in size.  Fuel bed properties (fuel load, fuel moisture content, fuel height, fuel coverage, post-burn residue and fuel consumption) were recorded before and after burning.  Fire behavior parameters (rate of fire spread, flame height, and flame temperature) and weather conditions (wind velocity, air temperature and relative humidity) were recorded during burning.  The fire line intensity and flame length were determined by Byram’s formula.  Fire danger ratings were determined using the method of Andrew (1980).

The results revealed that all fuel bed properties of the degraded pine forest except the post-burn residue were more than those of pine-oak forest.  Average values of fuel load, fuel consumption, fuel moisture content and fuel height in the degraded pine forest were 13.32 t/ha, 9.65 t/ha, 87.05% and 0.40 m, respectively. The average values of those in the pine-oak subcommunity were 8.30 t/ha, 2.33 t/ha, 83.28% and 0.31 m, respectively.  The average value of the post-burn residue in the degraded pine forest was 3.67 t/ha, while in the pine-oak subcommunity was 5.97 t/ha.  The major and minor fuel types in the degraded pine forest were grass and litter.  The fuel coverage of grass was 74.85%.  The major and minor fuel types in the pine-oak subcommunity were litter and grass and the fuel coverage of litter was 60.82%.  All fire behavior parameters and weather conditions except relative humidity in the degraded pine forest were more than those in the pine-oak forest.  The average values of wind velocity, air temperature, rate of fire spread, flame height, fire line intensity, flame length, flame temperature at 20 and 50 cm above ground in the degraded pine forest were 3.37 km/hr, 28.70 °C, 1.89 m/min, 1.29 m, 362.62 kW/m, 1.20 m, 449.95 °C, 604.93 °C, respectively,  while the same values in the pine-oak subcommunity were 1.26 km/hr, 27.17 °C, 0.55 m/min, 0.39 m, 26.28 kW/m, 0.34 m, 301.22 °C, 471.65 °C, respectively.  The average value of the relative humidity in the degraded pine forest was 47.39% and in the pine-oak subcommunity was 53.72%. The fire danger ratings using the Andrew (1980) method in the degraded pine forest and the pine-oak subcommunity were moderate and low intensities, respectively.

Keywords:  forest fire, fire behavior, fuel properties, degraded pine forest, pine-oak subcommunity