LAUSR

ABSTRACT A Forest ecology research has been done in Batangtoru watershed, North Sumatra to determine the species composition and vegetation structure. The study was conducted by using plots in four locations: Purnama, Gerhana, Kejora, and Teluk Nauli. A total of 387 species in 184 genera and 77 families were found. The species richness of trees (dbh >10 cm) was 192 species in 116 genera and 55 families, the richness of saplings (dbh 2 - 10 cm) was 211 species in 111 genera and 55 families, while the richness of seedlings (dbh <2 cm) was 153 species in 95 genera and 50 families. Tree density ranged from 850–1,700 individuals/ ha, while basal area was around 66.76 to 104.54 m2/ha. The forest canopy at Purnama and Gerhana plots was relatively similar, forming three layers, while the Kejora and Teluk Nauli plots were simpler with only two canopy layers. Based on a principal components analysis of tree species, the forests in the research area tended to form three community types: 1) forest dominated by Pentaphylacaceae, 2) mixed dipterocarp forest, and 3) 'forest garden', or natural forest communities enriched with a variety of economically valuable forest tree species and therefore classified as an agroforestry system. Keywords : Floristic, structure, forest community type, Batangtoru watershed, North Sumatra