SOIL AND VEGETATION DYNAMICS AFTER BURNING AT DOI ANGKHANG IN CHIENGMAI PROVINCE

Abstract

Soil and vegetation dynamics after burning were investigated at Doi Angkhang, Amphoe Fang, Changwat Chiengmai during March 1983 to March 1984, Two permanent 20 X 20 m² plots surrounded by 20 – meter wide fireline were laid out along slope gradient. Before burning, fuel loading, species diversity together with physical and chemical properties of soil were determined. During burning, rate of fire spread, fire intensity and flame length were studied. After burning, soil properties were reinvestigated every three months and six plots of 1 x 2 m² in size of each were set in the original plots to recheck the plant species and their number and to record height growth rate every month as well, Average monthly dry weight of plant biomass was taken from four sample plots of 1 X 1 m² In size of each. The results revealed that rate of fire spread and fire line intensity were 667 m/sec and 38,627.83 kw/m, respectively. The type of fire was subjected to a running surface fire with flame length approximately 10 m. After burning soil moisture decreased more than 60 percent. The infiltration rate was decreased as well while the soil bulk density, soil particle density, soil porosity, soil pH, soil organic matter, and the amount of phosphorus were relatively constant.  CEC and calcium slightly decreased, while potassium, magnesium and sulfur decreased almost 50 percent. Regarding to plant succession, the height growth rate was constantly increased and reached maximum at 11 months old. While eight plant species mostly as grasses, perennials and small shrubs appeared after burning, the dominant species was Imperata cylindrica Beauv. The average height of these plants recorded one year after burning was 164 cm. Plant density increased after burning. Plant community in the area was classified as fire stable community due to it can survive with the fire. Biomass varied with plant age, the mean value was approximately 453 g/m² at the age of one year. The maximum and minimum fuel moisture were 256.74 percent in September and 72.07 percent in April, respectively. High possibility of fire appeared in the study are identified as severe fire since the fireline intensity was more than 3458.6 kw/m and the flame length was over 3.35 m. The effective fire suppression should be indirect method of rapid removal materials infront fire. However, the future study should be aimed at determining a longterm fire effects on plant succession and soil properties.