Structure and floristics of an old secondary rain forest in Central Kalimantan, Indonesia, and a comparison with adjacent primary forest

Abstract

The study of tropical secondary forests, and of the time taken for them to revert to ‘primary’ forest, is of increasing importance given the current global destruction of tropical rain forests. We describe a 55-year-old secondary rain forest at Barito Ulu, Central Kalimantan, Indonesia, and compare it with the adjacent, undisturbed, primary forest. Three 0.25 ha plots were set up in each forest type and all stems over 10 cm dbh were measured and identified, soil samples were taken and analysed, and the composition of the seed bank was examined. Although the basal area, tree height and biomass of the old secondary forest approached that of the primary forest (82% for basal area, 88% for tree height and 74% for biomass), there were still major differences in the floristics and species diversity. The old secondary forest was dominated by Cratoxylon arborescens (Hypericaceae) and Pternandra caerulescens (Melastomataceae), whereas the primary forest was dominated by dipterocarps. The Shannon–Wiener diversity index was 3.40 for the old secondary forest plots and 4.17 for the primary forest plots; the Jaccard’s coefficient of similarity was 24%. Mortality, recruitment, turnover and tree growth rates were greater in the old secondary forest. The seed bank of the old secondary forest contained more than double the number of seeds of the primary forest seed bank and many more seeds were of shrub species; there were the same number of species in the two forests seed banks. There were no major differences between the two forest types in terms of soil chemistry. Despite the close proximity to potential seed sources, succession in the Barito Ulu area has proceeded more slowly than in some other tropical areas. This may be due to the low concentrations of soil nutrients and/or the poor dispersal of dipterocarp seeds. Fifty-five years of succession is concluded to be insufficient time for the return of most primary forest species. However, the forest structure of the old secondary forest shows a closer resemblance to the primary forest than does the floristic composition.