The Balance between Biodiversity Conservation and Sustainable Use of Tropical Rain Forests TREE DIVERSITY IN THE RAIN FORESTS OF KALIMANTAN Kade Sidiyasa ABSTRACT Kalimantan, which has large areas of forest, encompasses a variety of forest types comprising mangrove forest, coastal forest, swamp forest, evergreen tropical rainforest, forest over limestone and heath forest, and stretching from sea level up to 2556 m altitude. The mixed dipterocarp forests are situated mostly in lowland areas, below 600 m altitude. Very few Dipterocarp species occur at high altitudes, i.e., Hopea mengerawan, Shorea curtisii ssp. curtisii, Shorea sp. and Vatica oblongifolia. The high quality timber species Agathis endertii is found only at an altitude of 1450-1600 m, where it mainly grows together with some species of Lithocarpus, Nageia wallichiana and Podocarpus neriifolius. Eugenia spp., Adinandra and Lithocarpus dominate vegetations on the mountain peaks of Mt. Lunjut and Mt. Mencah (Kayan Mentarang National Park). A typical highland species, Weinmannia borneesis is also found here. Tristaniopsis sp. can be dominant on very steep and rocky slopes. Shorea balangeran and Cratoxylum glaucum usually grow on peat or kerangas forests, whereas Gonystylus bancanus, Alstonia pneumatophora, Alstonia spatulata, Combretocarpus rotundatus, Dactylocladus and Lophopetalum javanicum are adapted to the swampy areas. Detailed information on the vegetation (trees) of Sungai Wain Protected Forest in East Kalimantan is presented. In a plot area of 3.6 ha, divided into 9 subplots, 385 tree species with the dbh of 10 cm or more were recorded. These species belong all to 143 genera and 49 families. The species composition in the different subplots sometimes varies greatly. Ranked by importance of species, Shorea laevis, Madhuca kingiana, Eusideroxylon zwageri, Shorea smithiana, Koompassia malaccensis and Drypetes kikir are the dominant species in the subplots. INTRODUCTION The forests of the Malaysian region are very species-rich in all groups of biological organisms. Of the estimated 42,000 vascular plant species (Roos, 1993) or from the 25,000 species of flowering plants according to Whitmore (1990), the vast majority occur in forest ecosystems, and a very high proportion of these plant species are trees and large shrubs. Kalimantan, which has large area of forest, is believed to be one of the islands that still harbours numerous unknown and endemic species that have not yet been described. This is a reasonable assumption because, in the area of flora, most of the biologists (especially botanists) agree that the Indonesian provinces of Kalimantan area are still under-collected. Relatively few botanical explorations have been made in the past. In the period 1989–1999, collections by the staff of the Wanariset Herbarium added more than 11000 items to the collection of Kalimantan (Sidiyasa et al., 1999). These collections comprise mainly trees from the East Kalimantan area. Borneo, including the Indonesian provinces of Kalimantan and the Malaysian states of Sarawak, Sabah and Brunei, is the largest island in the Sundanic biogeographical subregion. It is a centre for many genera and species of the Malaysian flora. It is said that Borneo is also the home of the South East Asian Dipterocarps. According to Newman et al. (1998), there are 273 species and 69 The Tropenbos Foundation, Wageningen, the Netherlands 20 subspecies of Dipterocarpaceae in this area. Most of the island comprises undulating hilly lowland and swampy plains. The Kalimantan part reaches from sea level up to 2556 m altitude. The highest peak is unnamed and is located above the headwaters of the Bahau River in East Kalimantan. The climate is humid, with a rainfall varying between 2000 and 4000 mm/year. The FAO (1981) described Borneo as an island covered by a continuous carpet of evergreen rain forest dissected by swirling brown rivers. Today, a lot of forest areas have been cleared for timber, agricultural land, industries and resettlement. Forest fires in 1982/1983 and 1997/1998 had a disastrous impact on remaining forest conservation areas. Soon, after the forest cover had been removed, people who live nearby, automatically extended their ladang area into the conserved forest lands. Kartawinata et al. (1981), Bratawinata (1986), Sidiyasa (1987, 1995) and Riswan (1987), among others, have already published information and detailed studies on the structure and the species composition of forests at some places in Kalimantan. However, much more research is still needed. The present paper elaborates on the results of the research on tree species diversity in primary forests carried out by the MOFEC-Tropenbos-Kalimantan Project during its existence in this area (since 1987). Literature study is also incorporated in order to provide more adequate information. GENERAL FLORISTIC DIVERSITY OF KALIMANTAN Lowland forest The area where lowland forest occurs refers usually to the area below 700 m above sea level, and does not include specific habitats like kerangas forest, swamp forest, coastal forest and mangrove forest. Most of the Kalimantan forests are in this category, where the Dipterocarp species may be dominant. In many cases, the dominance of the Dipterocarpaceae in the area is related to their trunk or bole sizes, which is usually very large. It is different from the family of Euphorbiaceae, which is also very often dominant, but the dominance is related to the higher number of genera and species found. Nine genera of Dipterocarpaceae are found in Kalimantan. They are Shorea, Anisoptera, Parashorea, Dipterocarpus, Cotylelobium, Dryobalanops, Hopea, Vatica and Upuna. From the 10 genera of the Malaysian Dipterocarps, only Neobalanocarpus has not been recorded from Borneo so far. This species occurs in Thailand and in Peninsular Malaysia. As the most suitable habitat, it is well known that the lowland forests consist of the highest diversity of plants, especially trees. The most durable timber species “iron wood” (Eusideroxylon zwageri) is mostly adapted to flat lands along rivers, sometimes dominant, and it is extremely slow growing. Sidiyasa (1995) found this species was also growing well on undulating areas in Sintang, West Kalimantan. Other common and important tree species in lowland primary forests in Kalimantan are Koompassia excelsa, Pometia pinnata, Dracontomelon dao, Durio spp., Artocarpus spp., and Dialium spp., These species, except Koompassia excelsa, are important and well known because of their fruits, which are edible. Sindora spp. and Palaquium spp. are known for their timber quality. Pometia pinnata and Dracontomelon dao are some of the trees which usually grow along the rivers and small tributarys. Pometia pinnata especially is very easy to distinguish in the field because of its young leaves, which are dark red. 70 The Balance between Biodiversity Conservation and Sustainable Use of Tropical Rain Forests Montane forest It is already well known that, in most places at higher altitudes, the diameter of trees tends to be smaller than that of trees growing at lower altitudes. This characteristic is very obvious when the habitats are rocky or are higher than 1600 m altitude. Very few Dipterocarp species occur at this level. During our botanical exploration in the Kayan Mentarang National Park (Mt. Lunjut and Mt. Mencah), four species of Dipterocarpaceae were collected. They are Hopea mengerawan, Shorea curtisii ssp. curtisii, Shorea sp. and Vatica oblongifolia. Shorea curtisii ssp. Curtisii, in particular. is found at the altitude of 1000 - 1600 m. The high quality timber species Agathis endertii is found only at an altitude of 1450-1600 m. It grows mainly together with some species of Lithocarpus, Nageia wallichiana and Podocarpus neriifolius. At the top of Mt. Lunjut (1900 m), Eugenia spp. are very dominant, while on Mt. Mencah (1980 m) the vegetation is dominated by Adinandra spp. and Lithocarpus. A typical highland species, Weinmannia borneesis, is also found here. Tristaniopsis sp. which is easily recognised from its filling and red-orange outer bark can be dominant on very steep and rocky slopes. Heath forest In Kalimantan and the other parts of Borneo, this forest formation is called ‘kerangas’. The forest grows on very acid soils, that usually consist of white sand.Nutrients are therefore very low and rice will not grow. The most common tree species that occur in kerangas forests are Shorea balangeran, Cratoxylum glaucum and Eugenia spp. Some species of Lithocarpus and Buchanania arborescens also occur here. In Sarawak, Casuarina nobilis and Calophyllum incrassatum were also recorded (Whitmore, 1990). Swamp forest Depending on the type of the habitat of its occurrence, this forest is may be called ‘peat swamp forest’, if it occurs in a wet area with waterlogged condition, or ‘freshwater swamp forest’, if it occurs in an area where flooding is periodic, either daily, monthly or seasonally. In peat swamp forest, some tree species such as Gonystylus bancanus, Alstonia pneumatophora, Alstonia spatulata, Cobretocarpus rotundatus (Anisophylleaceae), Dactylocladus and Lophopetalum javanicum grow particularly well. In freshwater swamp forest many more species are usually adapted to the habitat conditions. Calophyllum spp., Eugenia, Vatica venulosa, Horsfieldia spp. are common here. STRUCTURE AND SPECIES COMPOSITION OF SUNGAI WAIN FOREST Introduction The forest of the Sungai Wain Protected Forest (SWPF) is the remaining tract of primary lowland forest nearest to the large cities in East