Ecological Study of Forests in the Resunga Hillalong An Altitudinal Gradient In Nepal

Abstract

The objective of the research was to carry out the ecological study of forests in the Resunga hill along an altitudinal gradient in Central Nepal. An assessment of floristiccomposition, stand structure and use of forests was done on Northern slope ofResunga Hill (690-2339 m asl), during October-Novemember 2005 and March-April2006.The study area was divided into four elevation ranges: Upper TropicalZone(690-1000m), Lower Sub-tropical Zone(1000-1500m),Upper Sub-tropical Zone(1500-2000m) and Lower Temperate Zone (2000-2339m).Twenty eight squarequadrates (20 m × 20 m) for tree, fifty six square quadrats (10 × 10 m) for saplingand fifty six square quadrates(5m × 5 m) for seedling were sampled. In 20 m x 20 mquadrats, all trees were measured for diameter at breast height. In 10m x 10mquadrats, saplings were measured for diameter at breast height. The data wasanalyzed for the stand structure (diameter distribution, basal area, and biodiversityindex) and floristic composition (number of species, species relative frequency, and density, dominance and average importance value). The forest soils of the sampleplots chosen from different bioclimatic zones were analyzed for texture and soilreaction (pH). The questionnaire survey was adopted to analyze the forest resourcesuse of study area. There were altogether 43 species of trees and shrubs, representing 23 plant families.There were totally 13, 19, 16 and 12 tree species with 1643,1173,3700 and 3020 pl/hacontributing to a basal area of 40.15, 32.29, 24.69,and 12.71 m 2 /ha in the Lower Temperate Zone, Upper Subtropical Zone, Lower Subtropical Zone and UpperTropical Zone respectively. As regard the composition of forest by altitude,Shorearobusta(Average Importance Value = 48.01),Pinus roxburghii (Average ImportanceValue = 22.44),Lyonia ovalifolia(Average Importance Value = 21.09) and Quercussemecarpifolia (Average Importance Value = 35.18) were the most ecologically important species in the Upper Tropical Zone (UTZ), Lower Sub-tropical Zone(LSZ), Upper Sub-tropical Zone (USZ) and Lower Temperate Zone (LTZ)respectively. Structure described by size (DBH) class distribution showed that the stems frequencies decreased with an increase in diameter at breast height in the Lower Temperate Zone, Upper Sub-tropical Zone and Upper Tropical Zone. This showed better regeneration and brighter future of forest stands in these zones.However, in the Lower Sub-tropical Zone (LSZ) the stem frequencies increased within crease in diameter upto diameter class 10-19.9cm and then decreased with theincrease in diameter at breast height. The structure of forest stands in the Lower Temperate Zone, Upper Sub-tropical Zone and Upper Tropical Zone indicated over exploitation of higher girth individuals for firewood and other purposes by the local people. Species diversity (Shannon Weiner’s index, H') was higher in Upper Sub-tropical Zone (2.4) than at the other elevational ranges. Similarly, the Evenness(j) was greatest in the Upper Sub-tropical Zone (0.81).This indicated that the Uppersub-tropical Zone had stable vegetation than other zones. Total tree basal area (BA)per hector showed positive relation with elevation. Diversity index did not show any relation with altitude. Average importance value indicated that forest was dominatedby one or two species and the value of evenness showed more or less homogeneousdistribution of plants in all the forest stands. Soil texture in the forest ranged from loams, sand loams, and silt loams.Loam soil(51.1 % sand, 40.1 % silt and 8.8 % clay) was predominant in the Upper Tropicalzone and sandy loam (57.1 % sand, 35.1 % silt and 7.8 % clay) in the Lower Sub-tropical Zone. In both the Upper sub-tropical zone and Lower Temperate zone, soil was silt loam (49.1 % and 47.1 % sand, 45.1 % and 47.1 % silt and 5.8 % and 5.8 %clay).he soil pH ranged from very strongly acidic in the Upper sub-tropical zone(4.7), strongly acidic in both the Upper tropical zone (5.5) and the Lower Sub-tropicalZone (5.3) and slightly basic in the Lower temperate zone (7.3). The dependency of local people on forest was for fuel wood, fodder, water source,recreation and religious importance. The preferred species for fuel wood from this forest were Quercus semecarpifolia, Schima wallichii, Castanopsis indica,Rhododendron arboreumandPinus roxburghii.Similarly, the preferred species for fodder from were Schima walichiiandCastanopsis indica.In comparision to situation10 years ago, dependency on government managed forests for fuelwood, fodder and grazing had increased in 50% of households due to increase in family size, restrictionin use from community forest and decreased supply from farmland. The trend showedthat with increasing population, dependence on government managed forests forfuelwood, fodder and grazing will increase in future unless efficient ways offuelwood and fodder use, alternative energy sources (biogas, solar cell) and moretrees in farmland are developed.The study revealed that both the stands structure andfloristic composition of Resunga Forest were sensitive to anthropogenic stress(pressure) in all the bio climatic zones. Due to over exploitation and illicit felling as well as ruthless exploitation, floristic composition and structure of forest stand shadbeen changed. The reduction in average importance value of Schima wallichii and Castanopsis indica from its natural range i.e. Lower Sub-tropical Zone, absence oftree-sized species from Upper Tropical Zone and much lesser number of highergirth(DBH) class individuals in the Lower Temperate Zone and in the Upper Sub-tropical Zone showed the greater stress in forest stands of these zones.Similarly, the lesser number of small sized trees in the Lower Sub-tropical Zone indicates the stresson forest regeneration Therefore, local control over the management is essential for reducing the stress in plant community structure and ensuring the sustainability of forests products use in the Resunga hill.