Study on the effect of altitude on the forest community structure at Mt. Irau, Cameron highlands, Pahang State of Malaysia

The influence of increasing altitude on the forest community structure on Gunung Irau, Cameron Highlands, Pahang have been carried out in plots set at five different 2100 m (Plot 5). The total sampling area of these five plots is 0.5 hectare. The estimated tree density was 1838/ha. A total of 919 trees ( greater than or equal to 5 cm dbh), representing 33 families, 59 genera, and 67 species, were obtained. Unequal distribution of species, genera and individual trees was found among the families. Lauraceae was the family with the highest number of species and genera (5 genera and 8 species), while Myrtaceae (294 trees; 31.99%) was the family with the highest number of individual trees. The dominant and co-dominant species, having the highest and second highest I sub v values varied among the altitudes of 1500 m, 1650 m, 2100 m, but not between 1800 m and 1950 m. At the altitude of 1500 m, 1650 m and 2100 m, the dominant and co-dominant species were Quercus-sp. (48.23%) and Myrica esculenta (41.02%). Decaspermum fruticosum (36.01%) and Syzygium enasensis (28.66%), Vaccinium laurifolium (55.57%) and Leptospermum sp. (42.89%), respectively, while at the altitudes of 1800 m and 1950 m, they were Decaspermum fruticosum (41.22%, 72.85%) and Rhododendron wrayei (35.48%, 24.98%). The highest values of Margalef Richness Index (R), Pielou Species Evenness Index (E), Shannon-Weiner Diversity Index (H') and mean tree height were recorded at 1500 m, followed by 1650 m, 1800 m and 1950 m. Analysis showed a negative correlation between R, E, H' and mean tree height with increasing altitude. Mean diameter at breast height, mean basal area, mean biomass, and tree density were found to be fluctuated with increasing altitude due to local factors such as fallen and dead trees, presence of large bamboos, trails and narrow ridges. These conditions were limiting the potential growth and spread of the individual trees.