Shift Assessment of Upper Tree Species Limit and Tree Line Recruitments in Manaslu Area, Nepal

The upper species limit shift of Abies spectabilis and its tree line dynamics under climatic stress was studied in A. spectabilis forest of Lho village in Manaslu Conservation Area, central Nepal. The census of A. spectabilis was carried by belt transect laid covering tree line as well as tree species limit and the sample belt was located by purposive sampling method. Total number of tree individuals, basal diameter, diameter at breast height (DBH), and crown diameter, number of seedlings and saplings of A. spectabilis were recorded. Tree age was estimated by tree-ring counts and the count of branch whorls and bud scars in sapling and seedlings. Two LANDSAT MSS imageries of year 1976 and 2001 were used to delineate the change in vegetation. The area of interest of altitudinal belt of 3,700m to 4,200m was generated and the vegetation change was analyzed. The analysis of the precipitation and temperature data of 30 years (1971-2010) showed that there was an increase of mean temperature by 0.10oC per year and decrease in precipitation by 1.777mm per year. The establishment of the species in the study area was dated back to 1900. Total 76 individuals of tree, 112 saplings and 77 seedlings were recorded. The recruitment of A. spectabilis was positively correlated with mean annual temperature (r = 0.35, P = 0.04) and negatively correlated with mean annual precipitation (r = -0.36, P<0.5). Between the periods of 1900 and 2012 A. spectabilis upper limit has shifted at a rate of 10.8m/year with the upslope shifting of 110m with 1911 tree line reference. Similarly, the NDVI analysis of the Landsat images has shown 9.06sq.km of non-vegetated area in 1976 have turned to vegetated area in 2001.