Description of the primary lowland forest of Berau

The structure and species composition of the primary lowland dipterocarp forest in Berau is presented. This study mainly focuses on the primary forest based on 3 control plots of 4 ha each, totalling 12 ha, where 93% of the trees (dbh (10cm) were identified at the taxa level. Tree identification led to a collection of herbarium samples and to development of a herbarium reference which now contains more than 3 000 samples representing 45 families, 129 genera and 579 species or taxa. In primary forest, the average figures for density, basal area and standing volume are 530.7 trees 31.5 ha-1 , and 402 m3 ha-1, respectively. In the study area dipterocarps represented 25% of the tree population, 50% of the basal area and 60% of the standing volume. In the three control plots of primary forest (12 ha), 538 different taxa were recognised representing a mean of 182 trees per ha. The families Dipterocarpaceae and Euphorbiaceae were the most important taxa in both density and number of species (61 species each). Two dipterocarp species, namely Shorea leptoderma Meijer ex Wood and Shorea symingtonii Wood were recorded for the very first time in Indonesia. The structure of the forest of Berau is very similar to that of Sabah or other parts of northern Borneo. The main characteristic of this forest is its remarkable richness in dipterocarps which is exhibited in a mean of 29 species per ha. The forests of Sabah are mainly dominated by light-demanding dipterocarp species such as Parashorea spp. and Dryobalonops spp. This could result from important canopy disturbance caused by climatic events like cyclones or long periods of drought. The high species richness of the Berau forest may be linked to a longer-term stability and a relative constancy of the climate in the region.