The ecological importance of three topographical habitat types for the restoration of abandoned rubber plantation at Bukit Gasing, Petaling Jaya, Peninsular Malaysia

A study was conducted in an abandoned (ca. 50 years ago) rubber plantation to obtain basic information on species composition and structure, distribution, richness and diversity of tree populations in different topographical positions (ridge, slope and valley), each with a survey plot area measuring 20 m x 20 m, for restoration of abandoned rubber sites into natural rainforest at Bukit Gasing (3 05' N and 101 39' E, some 57 - 103 m a.s.I.), Petaling Jaya, Selangor, Peninsular Malaysia. Each survey plot was subdivided into 5 m x 5 m sub-quadrats to assess spatial variations in composition and structure. Floristic composition, population census of trees with DBH > 1.5 cm, ground vegetation survey and environmental parameters such as soil moisture, soil hardness, and canopy openness were recorded in each sub-quadrat. A total of 990 individuals in tree layer (excluding tree seedlings in ground vegetation) from 66 families were noted from the three topographical positions. Ridges (composed of 32 spp.) were dominated by the planted Hevea brasiliensis, while the slopes (36 spp.) was dominated by Ixonanthes reticulata, and the valleys (39 spp.) were dominated by both H. brasiliensis and I. reticulata and other species such as, Gynotroches axillaris. Species diversity with Shannon-Wiener diversity index value was high (2.85) in slope topographical positions with the parallel highest value of basal area of 24, 210.6 cm2/400 m2. However, the maximum DBH (82.8 em) and height (29.3 m) of trees were found in the survey plots located in the valley. Valley topographical positions also had the highest soil moisture content (24.6%). High species diversity and richness were recorded in the slope plots but high biomass accumulations (DBH, H) were also found in the valley. The restoration of abandoned rubber sites might have been facilitated through rich species pool at slope position and high potential of biomass accumulations in the valley habitat. Hence, the continuation of topographical habitat conditions from the ridge, slope and valley is important for the future restoration practices.