Ecology of Sulawesi. Tony Whitten

      Droughts in Sulawesi seem to occur about every 20-30 years but information on their ecological effects have not been found. The grassy Sook Plain in Sabah, however, was formed when fire burned rainforest and the peaty topsoil on which it grew after an exceptionally dry period in 1915 (Cockburn 1974). In 1972-73 a prolonged dry spell caused changes on Mt. Kinabalu, Sabah, which it has been estimated will take a century to be reversed (Whitmore 1984a). In most areas of the world, but particularly around the Pacific region, 1982-83 was exceptionally warm and dry, and weather patterns were most unusual. For example, Watampone had 5, and Tobea Besar 6, consecutive rainless months at the end of 1982. This was related to the anomalous sea surface temperatures which in parts of the Pacific rose by as much as 8°C above normal. Around Sulawesi, however, the sea was only about 0.2°C warmer than normal. The sea surface temperature anomaly first appeared in the region of the Sulawesi Sea during the middle of 1982 but its major effects were not felt until December 1982-February 1983 (Barber and Chavez 1983; Cane 1983; Gill and Rasmusson 1983; Rasmusson and Wallace 1983; Chavez et al. 1984; Whitmore 1984a). Although 1982 was generally a very dry year on Sulawesi, 1972 seems to have been even drier.

      VEGETATION

      Palaeovegetation

      Impressions of leaves of grassy plants and rattans have been found in rocks in Minahasa (Koorders 1895) but the vast majority of information regarding palaeovegetation is derived from the careful analysis of pollen remains in deep organic sediments from the bottom of swamps or lakes. The oldest-known Sulawesi pollen is of a relative of Sonneratia mangrove trees from Tertiary rocks in north Central Sulawesi (Sohma 1973).

      Attention of palaeobotanists on Sulawesi has been concentrated on two areas: Lake Tempe and in topographic depressions in ultrabasic rocks around Lake Matano. One particularly long core of possibly considerable age has been collected recently from one of the latter sites but results will not be available for some while (Hope 1986).

      In the Lake Tempe region cores were taken from the swampy Lake Rawa Lampulung about 4 km east of Sengkang and the pollen shows that at least part of the surrounding area was covered by mangrove vegetation, that is, it was inundated by the sea, from about 7,100 to 2,600 years ago. The rise in sea-level needed to produce this effect is about 5 m which matches the palaeo-climate information (p. 21). A core from the edge of Lake Tempe, 5 km northwest of Sengkang, reveals that at least from 4,400 years ago the area was dominated by freshwater vegetation and that the sea was probably prevented from reaching the lake by a squat molasse ridge to the east.

      The history of the vegetation during the Quaternary and late Tertiary is very closely linked with the climatic changes. During the drier periods of the Pleistocene the area of seasonal forest would have extended while the area of rain forest became less. Thus the populations of rain forest species would have been reduced but isolated populations of certain species probably maintained some level of contact or gene flow along riverine areas or wetter soils. In the driest parts of Sulawesi it is quite likely that monsoon or even savannah forest predominated.

      Many mountain plants are unable to live successfully in the lowlands, but the lowering of zones on mountains during the cool periods gave opportunities for these plants to spread because the available stepping-stones of suitable habitat increased in area and number.

      Present Vegetation

      Fewer botanical specimens have been collected on Sulawesi than on any other major island/region in Indonesia. To date only about 23 specimens per 100 km² have been placed in herbaria whereas over 200 per 100 km² are known from Java. A density of 100 specimens per 100 km² would represent an adequately-known flora. Allowing for this, the number of higher plant species¹⁰ may be about 5,000. Only seven genera are known to be endemic compared with 17 in Sumatra, 59 in Borneo and 124 in New Guinea (E. de Vogel pers. comm.). In addition, some species are barely known: a forest shrub Thottea celebica (Aris.), for example, has been collected only once, from Lambarese, northeast of Palopo (fig. 1.19) (Ding Hou 1984).

      The natural vegetation¹¹ growing in a particular area is dependent on various factors such as soil chemistry, soil water, climate, altitude, distance from the sea, and distance from areas of similar conditions (table 1.5; fig. 1.20).

      The coasts of Sulawesi are fringed by coral reefs, mudflats, mangrove forests and rocky or sandy beaches (chapters 2 and 3). The freshwater habitats are generally rather nutrient-poor (although there are striking exceptions) and as a result freshwater vegetation is not well developed (chapter 4). The lowland and hill forests of Sulawesi (chapter 5) have the most tree species of all forest types (table 1.5) but have only seven species of dipterocarp trees, the mainstay of forestry operations in Borneo and Sumatra where there are 267 and 106 species respectively (Ashton 1982). The major trees of commerce are the tall Agathis (Arau.)¹² trees with broad, flat leaves; the magnificent yellow-flowered legume Pterocarpus indicus (Legu.) (huge pollarded specimens of which are commonly seen around town squares such as Ujung Pandang) which is deciduous and found most commonly in the more seasonal areas; the gum tree Eucalyptus deglupta (Myrt.), usually found wild in riverine habitats and which is extensively used in reforestation projects; beremban Duabanga mollucana (Sonn.), and gutta percha Palaquium spp. (Sapo.). The hemi-parasitic¹³ sandalwood Santalum album (Sant.), from the heartwood of which sandal wood oil is extracted, used to be found in the dry Palu valley (chapter 6) but even in the Poboya reserve set up to protect one of the last stands of this tree, only 62 small individuals exist (Sidiyasa and Tantra 1984).

      Figure 1.19. Thottea celebica leaves and flower; one of a number of endemic plants known from just one specimen. Scale bars indicate 1 cm.

      After Ding Hou 1984

      Based on van Steenis 1950; Whitmore 1984a

      Figure 1.20. Major natural vegetation types on Sulawesi.

      Based on Anon 1982a

      Sulawesi has both freshwater and peatswamp forests, though neither is particularly extensive, as well as forests growing on volcanic, limestone and ultrabasic soils (chapter 6). The mountain forests have tree species absent from or rarely found in the lowlands, and the vegetation of the mountain summits includes many brightly-coloured shrubs and herbs (chapter 7).

      A large number of areas, particularly in the southwest peninsula, have lost their original vegetation because of the activities of man, and are now made up largely of agricultural landscapes with areas of dry, barren land used to some extent for cattle grazing. The driest areas, in the Palu valley and in the south of the southwest arm, have a generally open appearance with a scrub of prickly pear cactus and other drought-tolerant species. Many grasslands are dominated by alang-alang grass Imperata cylindrica (Gram.) (Steup 1939), but it is not correct to label all grasslands as alang-alang wastelands; some grasslands comprise communities of numerous grasses (not including alang-alang) and small legumes (Steup 1939). Sword grass occurs predominantly along roadsides and around villages. Grassy savannas often have scattered trees of a variety of species such as Morinda tinctoria (Rubi.), Albizia procera (Legu.) and, where burning has been frequent, Fagraea fragrans (Loga.). There are also areas where teak Tectona grandis (Verb.) is common but these are usually the remnants of old plantations (Steup 1939). Teak was introduced

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