Abstract
This study was designed to examine the structure and tioristic composition a lowland rainforest on the southern slope of Cyclops Mountains, Jayapura. at 300-500 m above sea level. Plants were sampled in 6 plots of 40 m x 40 m each and 1 plot of 20 m x 20 m. The study recorded 130 tree species (DBH equel or bigger than 10 cm at dbh) belonging to 39 families, with density of 743 treeslha and total basal area 1993.62 mz. Anisoptera thurffera dan Mallolus echinatus are the leading species. The bigest diameter reoorded was 95 cm (Anisoptera thunifera) and the tallest tree reach 50 m (Anisoptera thur.'ra, Hopea iriana and Syzygium leptoraphleboides). Tree species richness is similar to other forests in the north of Papua (Mamberamo) and north of the Cyclops Mountains. Regeneration was very poor. There is an indication that the forest sampled was at one time disturbed.
