In Mt, Gadut area of Padang, Sumatra Nature Study Project established 6 permanent plots for study of tropical rain forest structure and its dynamics, such as the foot hill plots (Gajabuih, Pinang Pinang, Pinang Pinang Bawah, Pinang Pinang Atas), the hill plot (Airsirah), and the mountain plot (G. Gadut). This region characterized by heavy rainfall, annual precipitation reached 6000 - 8000 mm.
Number of tree species of these plots given the richest flora in tropical region; over 300 species in 1 ha Pinang Pinang plot (DBH > 8 cm), and 276 species in narrow 0.33 ha of Pinang Pinang Atas transect (DBH> 5 cm).
This richness caused by:
(1) Multistratum construction of the foot hill forest resulted vertical complexity of the tree species.
(2) Species distributions depend by topographical gradients and mosaic environmental factors resulted horizontal complexity of forest structure.
(3) Gap regeneration process of the forest resulted to complexity mosaic distribution pattern of tree species.
These things will contribute to the richness of species number of the foot hill plots.
These plots have special tree genera. The genus Eugenia (Myrtaceae) and Diospyros (Ebenaceae) have many species in a narrow area of the plots. Species of these genara closely related and occupied same habitat (under the canopy tree layer). Twenty-five genera belonging to the family Sapotaceae, Fagaceae, Burseraceae, and others characterized by this strange speciation group that represented more than 40% of tree species of the plots.
The tree species that only one tree appears in plots are much too. In Pinang Pinang Atas transect, for example, 112 species, ca. 2/5 of 276 species, found only one tree in the plot.
Studies about speciation of the various tree groups are necessary for understanding of richness in the tropical rain forest.