Variation in species composition, tree and soil carbon stock between burnt and unburnt forest in Chure Range of Butwal, Nepal.

Abstract

Frequent forest fires in dry season are shaping forest vegetation and landscape in different parts of Nepal and cause great loss to the forest ecosystem. The main objective of this study was to to analyze impact of forest fire on species composition and carbon dynamics of Shorea robusta forest of burnt and unburnt forest in Chure region of Butwal area. Identification and selection of burnt areas were done based on historical ground fire data in conjunction with satellite remote sensing data provided by ICIMOD and Department of Forest and Environment, Nepal. The species composition, diversity indices and regeneration status of trees, saplings, seedlings, shrubs, and herbs in two different forests were conducted by systematic random sampling methods. Average vegetation carbon stocks of burnt and unburnt forest were calculated manually. Soil samples were collected by soil core methods from different soil depths (0-2, 2-10, 10-30, 30-60cm) to measure soil parameters like soil pH, bulk density, soil organic carbon and soil charcoal stocks. In burnt forest, Shorea robusta and Lagerstromia parviflora were dominant, with Terminalia alata, Careya arborea, etc. as associates’ species whereas S. robusta and Anogeissus latifolia were dominant with Tectona grandis, Mallotus philippensis etc. as associates in unburnt forest tree layer. The value of Shannon-Wiener diversity index (1.80) and Margalef’s species richness index (2.94) were higher in unburnt forest for tree layer. The average density of S. robusta was 749.71±25.15 (in/ha) and 1031.79±36.284 (in/ha) for unburnt and burnt forest, respectively. The average height of S. robusta was recorded 19.16±0.249m and 16.289±0.211m for unburnt and burnt forest respectively whereas average DBH was 0.412±0.011 m and 0.371±0.163m respectively. The total vegetation carbon stocks were 200.38±22.69 t/ha and 233.72±29.63 t/ha in burnt and unburnt forest respectively. Mean soil pH of burnt forest was (6.02 to 6.13) and unburnt forest range from (5.05 to 5.53). For bulk density, mean minimum value (0.85±0.038 g/cm3 ) was recorded in topsoil of burnt forest and mean maximum value (1.05±0.01g/cm3 ) was recorded in unburnt forest at the depths of 30 cm above. Total soil charcoal stock (SCS) was higher (35%) in the topsoil and lower (2%) in >30cm depth. The SOC was highest (251.90±10.73t/ha) at topsoil followed by (226.52±8.53 t/ha) at 0-2cm depth of burnt forest. Present study suggested that forest fire was essential to maintain the species composition, diversity, as well as soil organic stock in burnt forest of S. robusta.