Fire behaviour, fuel dynamics and the responses of trees and grasses to fire in Carranglan, Nueva Ecija, Philippines

摘要

Fuel dynamics and the response of trees and grasses to experimental fire were studied and quantified to develop a prescribed fire protocol for reforestation of degraded grasslands in Carranglan, Nueva Ecija, Philippines. Stands of Gmelina arborea Roxb.,Tectona grandis L. f., Acacia auriculiformis A. Cunn. ex Benth., Piliostigma malabaricum (Roxb.) Benth. var. acidum (Korth.(de Wit., and Antidesma ghaesembilla Gaerth. were subjected to three levels of fire intensity (low, 56-183 kW m$sp{-1}$; intermediate, 191-262 kW m$sp{-1}$; and high, 701-3730 kW m$sp{-1}$). Fire behaviour was characterized and predictive equations were developed for fire rate of spread based on wind speed, and for fire intensity based on rate of spread, flame height, and flame depth. Tree responses and fire effects in terms of crown scorching, resprouting and tree mortality were related to fire intensity. Acacia auriculiformis had the highest mortality rate at all intensities, while the four other species survived all levels of fire intensities. The sensitivity of A. auriculiformis to fire was ascribed to low bark moisture content, thin bark, and poor coppicing ability.;The response of the grasses Imperata cylindrica (L.) Beauv. and Themeda triandra Forsk. to fire applied at two seasons was quantified in terms of biomass development. The early rainy-season burn reduced significantly the above-ground biomass development because of the damage to newly grown shoots, while the early dry-season burn stimulated shoot growth but reduced overall fuel loading during the critical dry period. Fuel dynamics of tree litter was examined using litterfall trap and litterbag techniques. Litterfall rate was variable among basal area classes, species and time. Acacia auriculiformis produced the highest litterfall rates in all size classes followed by T. grandis, G. arborea, A. ghaesembilla, and P. malabaricum. Litterfall rate increased with increasing tree size. Gmelina arborea leaves had the fastest rate of decomposition requiring less than 1 year. Leaves of the four other species required from 1.2 to 3.2 years to decompose completely. Nitrogen and lignin content of leaves were important predictors of leaf decomposition. Understorey species composition did not differ significantly among stands, but above-ground biomass of the grass component was reduced from 86% in open grassland to 44, 72, 73, 74% under G. arborea, T. grandis, A. auriculiformis, and natural clumps of P. malabaricum and A. ghaesembilla, respectively.;Survival responses and damage to tree seedlings and saplings by fire were influenced by fire intensity, tree species and diameter size. It was concluded that success of reforestation on fire-prone grasslands can be facilitated by the use of prescribed fire and the selection of appropriate tree species.