Prescribed under-canopy burning in Pinus patula plantations of the Mpumalanga highveld: The effects of fire on tree growth

Abstract

The effect of controlled undercanopy burning on tree growth has been studied under 16-year-old Pinus patula trees in Mpumalanga. Three fire intensity treatments and a control “no-burn” treatment, were applied to 1 ha plots. Average fuel depth was 42cm with a mean fuel load of 14.3 tons/ha. Fuel load was reduced by 15%, 30% and 60% in the three intensity burns. Fire intensity parameters were calculated using the BEHAVE fire behaviour prediction and fuel modeling system. Fireline intensity was predicted to be 134, 277 and 761kW/m for low, medium and high intensity experimental burns, respectively. Bark scorch height was found to be significantly greater in the plots under the high intensity burn treatment than in the low and medium intensity treatments. Most trees experienced scorch damage to between 0 and 40% of the crown volume. There was a significant negative effect on tree growth after a period of 36 months in the high intensity burn treatment. A low level (3 dead trees in sample of 360) of mortality occurred. This study showed clearly that undercanopy burning, at a low intensity, could significantly reduce fuel loads without resulting in decreased tree growth. It is recommended that this approach should be explored at an operational scale.

Keywords: Pinus patula, prescribed burning, growth, fire intensity

Southern African Forestry Journal No. 204 2005: 3-13