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Borneo and the Peninsula, and their environment
Transformation of the land before the recent
period
Change since World War II
The region
The geological region of which Borneo and the Malay Peninsula (hereafter usually just "the Peninsula") form the north-eastern section is a partly submerged continental spur of the Eurasian plate extending south-eastward from Asia to the Wallace line, known as "Sundaland."' With associated mountain chains, it also includes Sumatra and Java, together with Bali. The eastern side of Sumatra is part of the geological core (fig. 1.1). All of this former large peninsula was dry land during the several low-sealevel periods of the Pleistocene, and the present shorelines date from only a few thousand years ago. The Peninsula has an area of 131,600 km2, and Borneo 642,000 km2, of which two-thirds form Indonesian Kalimantan and one-third the Malaysian Borneo states of Sarawak and Sabah, together with Brunei. Borneo alone is 1.7 times the size of all Japan, and slightly larger than the combined area of France, Belgium, and the Netherlands (fig. 1.2). The region has long been famous for its forests; Indonesian Borneo is estimated to have 51 per cent of Indonesia's standing stock in forests of all types, and 75 per cent of the commercially valuable dipterocarps (FAO/GOI, 1990). Together with the rest of Sundaland, Borneo and the Peninsula constitute the important forest belt of "West Malesia," with a uniquely rich and varied flora and fauna (Whitmore, 1984). The reduction of this forest forms a major focus of discussion in this book.
Fig. 1.1 Regional location Nap
Population and economy
Based on the censuses of 1990 (Indonesia) and 1991 (Malaysia), the combined population of the region was 27.4 million, with 14.7 million in the Peninsula and 12.7 million in Borneo. Within Borneo, 3.3 million lived in Malaysian Borneo, 0.3 million in Brunei, and 9.1 million in the four Indonesian provinces comprising Kalimantan. In addition, there are almost certainly more than 1 million who are unrecorded in census data, most of whom are illegal immigrants or sojourners in the Peninsula and Malaysian Borneo. Population densities for Borneo are shown in figure 1.3.
Borneo and the Peninsula are, however, surrounded by more densely populated territories. The island of Sumatra, to the west, has 33 million people. Over 107 million now live on Java, with a land area about the size of the formerly united Czechoslovakia, which had only some 15 million people. There are almost 3 million in Singapore, while Thailand and the Philippines, to the north, have populations of 56 and 65 million, respectively. Indonesia, Malaysia, Singapore, Thailand, and the Philippines together have 326 million people. Only 8 per cent of these live in Borneo and the Peninsula, but they occupy 26 per cent of the total area.
Fig. 1.2 Location map of Borneo, showing places mentioned in the text
More than half of the 27-28 million people now resident in this region, including all of the Peninsula, are indigenous speakers of the several dialects of Malay, and most Sumatrans are also Malay. The principal minorities form two groups. Many of the Dayak people of Borneo, and the much smaller number of Orang Asli (aboriginal people) in the Peninsula, are ethnically distinct from the Malay majority, though a significant proportion of their languages are related to Malaya.² Numerically larger in Malaysia are immigrant people from China, southern and eastern Indonesia, and India. Chinese traders, miners, and settlers have been in the region for centuries, but the main modern wave of migration began only in the nineteenth century. Today, Chinese still form the majority in most towns of both parts of Malaysia, and are also numerous in the towns of Kalimantan, especially West Kalimantan. Whereas the Chinese are distinctive everywhere, there is a sharp contrast between Kalimantan and Malaysia in the pattern of ethnic identification among the Muslim Malays (Melayu in West Kalimantan) and Banjarese, Javanese, Madurese, Bugis, and others. All retain identity as distinct groups in Kalimantan, as elsewhere in the poly-ethnic Indonesian state. In Malaysia the national ethos is different, and Muslim settlers from different parts of Indonesia, even from only a few decades ago, have mostly sought to submerge their group identity and become indistinguishable from the "Malay" majority.³
Sellato (1995) has studied the problem of ethnic identity among the Dayaks of Kalimantan. He concludes that only in Central Kalimantan do Dayaks form a sufficiently powerful and cohesive group to be able to stand up against central government (basically Javanese) policies seen to be against their interests. In both East and West Kalimantan the Dayaks are under the dominance of coastal Malays, are fragmented, and are culturally fragile. In Sarawak and Sabah the indigenous groups have rather more autonomy and, although their freedom is limited by the central government, are at least prominent in local administration. Interior people everywhere are under pressure from logging and other outside interests, where small but real struggles take place frequently about control over, or access to, customary resources.
Indians are the smallest of the modern immigrant groups and almost all are in the Peninsula. The population history of Borneo and the Peninsula is dominated by migrations, into and within the region, from earliest times to the present day (Andaya and Andaya, 1982). A majority among the immigrants, even among the recruited Chinese and Indian workers of the colonial period, have remained in the region. Emigration - except, as we shall see below, from the distinctive Banjarese heartland in south-east Kalimantan - has been of minor significance.4
This fact underlies another: for most of the past two centuries this has been a region of economic growth. Although there have been many failures among enterprises and some settlement forays, and these continue, there has almost consistently been more work available than people to perform it. Barriers against immigrants are now erected in all parts of South-East Asia, but they remain selective in their administration. Few of the many attempts to enforce repatriation of immigrant workers and their families and descendants have been pursued with sustained vigour.5
The context of economic growth is of central importance in understanding the environmental history. Equatorial South-East Asia is both the most populous and the most rapidly developing part of the lowlatitude tropics. Singapore and Malaysia, but not yet Indonesia, have attained levels of per capita national income above or comparable with those of southern Europe. The annual GDP growth rates of all three countries over the period 1965-1989 were consistently high, though more spectacular in the 1970s than in the 1980s (World Bank, 1992: 220-221). As in all of East Asia, high growth rates have resumed in the 1990s, and until 1994 stood out against a global slow-down as among the highest in the world. People of both Indonesia and Malaysia, and of all ethnic groups within them, are proud of their national achievements since independence and impatient for further development. It would be folly to disregard this essential part of the total context of environmental change.
The geological base and its history
The Sundaland spur, or small plate forming an extension of the Eurasian plate, has remained relatively stable since late Tertiary time, encircled by the volcano-pierced island and mountain arcs formed, and still being formed, by the collision between the whole Eurasian plate and the Indo-Australian and Philippine plates to the south and northeast. Before this time, however, there were major changes along the northward and eastward sides of Borneo, as the Malay Peninsula and western and southern Borneo rotated counter-clockwise during the late Mesozoic and early Tertiary (Taylor and Hayes, 1983). The core of the Peninsula and the western part of Borneo are composed of Palaeozoic granitic, volcanic, and metamorphic rocks, which constitute the heart of the Sundaland plate. Mesozoic limestone formations occur widely and, though not large in area, are characterized by very distinctive karst landforms, which are particularly well marked in western and central parts of the Peninsula. Additions to the plate, containing mudstones, shales, and limestones of marine origin, were created by mountain systems formed during the rotation, especially in eastern Borneo.
Faulting of the Sunda shelf, in the early Tertiary, created the present set of basins and montane blocks frol Malaysia north to Thailand. However, the last major accretions to the core landmass took place before the end of the Mesozoic (Burton, 1972; Katili, 1974; Taylor and Hayes, 1983; Tjia, 1988; Pieters and Supriatna, 1990). They may have included attachment to eastern Borneo of a southward extension of the eastern Philippines arc toward Java, a remaining fragment forming the Meratus mountains in the south-east of the island (Holloway, 1981). The Mesozoic eastward rotation of Borneo brought the large island into the west Pacific mobile belt so that the northern and eastern sides have been an area of active tectonic movement right through the Tertiary and into more recent times, and thus geologically distinct from Sundaland. A complex geological history, now in part unravelled, includes the formation and destruction of island arcs and basins, collision of plates, substantial faulting and thrusting accompanied by volcanism, and in northern Borneo the creation of a sharply defined mobile zone uplifted on its inland side and depressed on the seaward side (Taylor and Hayes, 1980, 1983; Holloway, 1981; Mitchell, Hernandez, and Dela Cruz, 1986).
During the Tertiary era, therefore, there were major changes in northern Borneo, associated first with the closing of an oceanic gap separating the Asian mainland from an island arc extending from north-west Borneo to Luzon, attaching micro-plate sections of this mainland to the arc, then splitting the whole from Asia to form the present South China Sea. This sea first opened then narrowed as subduction began along the Manila trench in the late Tertiary; this subduction did not extend southward, where a trench off Palawan and Sabah became inactive. In the process, major uplift took place along the persistent line extending north-east from western Sarawak through Sabah. This uplift, extending from the late Tertiary into the Quaternary, changed the course of rivers and elevated the Gunung Mulu massif to 2,600 m (Haile, 1967). It also contributed substantial bodies of sedimentary mudstones to the eastern side of the island. The seaward side of this uplifted belt is still actively subsiding toward a continuing downwarping in the South China Sea. The floor of the South China Sea north of Borneo is itself composed in part of oceanic plate materials, and in part of a series of shallowly submerged continental outliers from the Asian mainland.
The highest mountains, located in northern Borneo, are therefore Miocene or younger. The Crocker range of Sabah, rising to 4,100 m in Mt Kinabalu, is a mass of geologically recent igneous intrusives. Moreover, there were some Miocene and even Quaternary basaltic lava flows in both parts of the region, sometimes forming volcanic plateaux that cap older formations. These are particularly distinctive in eastern Sarawak and western East Kalimantan, where they rise to between 2,000 and 3,000 m. Other basalts, in Sabah, are associated with Miocene movements against the emerging Sulu basin to the north. Westward of the zone of uplift, Brunei and most of Sarawak are composed of sandstones, mudstones, and shales interbedded with limestones. There are cave systems of great size in these limestones, and they hold important evidence of human prehistory.
There is another Tertiary and Quaternary basin on the eastern edge of the plate, in East Kalimantan, where north-south trending foldlines have also been active into the Recent period. This basin is more closely linked to the tectonic evolution in the Philippines arc. The seaward sides of both eastern and northern basins, and especially their offshore extensions, contain large oil and gas pools, and on land there are extensive deposits of mainly soft coal at shallow depth or in recent geological structures. Most of the late Quaternary formations in the region are, however, coastal or occupy the lower valleys of large rivers; they are related to sealevel change during the Pleistocene and Holocene rather than to tectonics.
The legacy of the Pleistocene
Events in the Pleistocene period had major consequences for the pattern of modern economic development. The western part of the Sundaland core, and its northern extension into Thailand and Yunnan, is quite highly mineralized with gold and other metals, including, most importantly, some of the world's largest sources of tin. Outcrops became deeply weathered during the long period of emergence after the end of Mesozoic orogeny. At times of enhanced erosion, arising from what may probably have been periods of climatic continentality during low-sealevel stands in the Pleistocene, which we discuss further below, these ores became concentrated among a great mass of alluvial gravels laid down in large valleys. When sealevel was lowest during the times of glacial maximum - these valleys reached more than 180 m below the present low-water mark for thousands of years in the major lowlands that are now the Melaka Strait, the Java Sea, and the south-western part of the South China Sea (Tjia, 1970,1988). Subsequent flooding of these valleys covered the gravels and their tin ores with alluvium, and also covered karst extensively formed in limestone during low-sealevel periods.6
The most recent Holocene marine transgression, completed only between 6,000 and 5,000 years ago, left the region with an intricate shoreline, rapidly smoothed by marine erosion and deposition, together with the formation of alluvial plains and large peat swamps behind coastal barriers. The depth and nature of the Pleistocene alluvials are known in some detail from drilling in those areas where there is thought to be tin or oil, especially in the Melaka Strait and on the west side of Makassar Strait. The tin ores, and some gold, mostly concentrated in gravels beneath Holocene alluvium of shallow depth, became a major resource in the nineteenth century. The coastline continues to adapt to sedimentation from inland rivers and in estuaries, together with minor sealevel variations, of which three within the last 4,000 years have been recognized (Tjia, 1988). Several quasihistorical accounts, from both the Peninsula and Borneo, indicate that there may have been considerable local changes in coastal detail even within the past few hundred years.
In the context of this book it needs to be stressed that no more than a tiny proportion of the large amount of alluvium and peat swamp now existing - and mainly formed over the past few thousand years - owes anything to human activity. The massive Pleistocene erosion in the uplands, which created great quantities of readily reworkable material in the valleys and coastal lowlands, was entirely a natural process. However, not all the products of millennia of deep weathering were removed down to sealevel, and simple observation of the shape of valley sides suggests that great masses of colluvium still exist along many lower slopes. A great deal of highly erodible and transportable material remains on the hills and in the valleys throughout the region.
Soil formation
Though climates are not uniform in this region, all are essentially a-seasonal, or only weakly seasonal, and humid. The more strongly seasonal of SouthEast Asia's climates lie beyond this area of interest. Modern literature, which is based largely on zonal soil classification, therefore provides limited information on the considerable variation that is encountered, even in a region much of which has been tectonically inactive since the end of the Mesozoic era. The dominant soils of the deeply weathered uplands are commonly acidic, with coarsetextured topsoils overlying more clayey subsoils. These are the well-known Red-yellow Podzolic Soils, Leached Ferrallitic Soils, or, more recently, Ultisols (Young, 1976; Burnham, 1984), and are so described across a range of parent materials. In the Ultisols, most of the clay fraction is characteristically in the B horizon. These soils are said to erode readily when cleared, but this is not always so (Andriesse, 1972); slope failure in the deeply weathered regolith is a more universal occurrence. The soils are deficient in nutrients such as phosphorus and potassium, and sometimes have high levels of aluminium; aluminium toxicity is very common. In areas of low relief subjected to a longer period of evolution undisturbed by wasting, soils are described as Latosols and Oxisols, and are even poorer in quality.
There is, however, a major contrast in natural erodibility between the older areas of the Peninsula and western Borneo, built mainly of Palaeozoic rocks, and the newer mudstones, especially those in the east of Borneo that have been laid down only since the mid-Tertiary. A recent comparison shows that natural suspended sediment yields are half an order of magnitude greater in streams draining the mudstones in eastern Sabah than in the main range of the Peninsula (Douglas, 1994). Sensitivity to degradation is, clearly, much greater in these areas of weakly consolidated younger formations.
The zonal literature recognizes that parent material can sometimes outweigh the climatic influence and, in terms of understanding actual complexity on the ground, an approach using parent material, as advocated by Humphreys (1991), is likely to be more informative.' Common parent materials in the uplands include granite, ancient volcanics and various metamorphics, shales, and sandstones; there are small areas of limestone and recent volcanics. Soils derived from granite are commonly very deep, with rounded slopes prone to landslides, whereas soils derived from shales, especially where metamorphosed, are much shallower and more finely textured, in a waterworn landscape of precipitous knife-edged crests (Whitmore, 1984: 226). Soils developed on granites and quartzites are generally inferior to those on andesites and shales (Ho, 1964). Those developed on shales of marine origin have good resilience under cultivation, greater than that of soils on metamorphics. So closely spaced are lithological changes in the sedimentary series that some formations are described as "melange" units, one such in Sabah being formed of interbedded siltstones, sandstones, cherts, spillites, and tufts (Douglas et al., 1992b). Large upland areas of the region have clayey redyellow soils, even brown on slopes (Burnham, 1984). Good structure, a moderate level of inherent fertility, and the constant release of new subsoil minerals for weathering by slope processes make some of these soils "surprisingly good" for agriculture (Ho, 1964: 42).
Among the most distinctive of the region's soils are those based on coarse sandstones and sandy colluvium and alluvium, which, under weathering, yield large quantities of quartz sand. Sometimes these are described as tanah tua (aged land), and in a number of areas sand comprises almost all the topsoil once the thin humic layer is removed from the surface after clearance.8 These soils occupy as much as 7 per cent of the total area of Sarawak, and throughout Borneo are found both at low altitudes and in upland areas, developed on hill and plateau areas of Tertiary sandstones, on Quaternary fluvial terraces with sand and clay in alternating succession, and on Holocene beach-ridge systems (Stein, 1988). They are also present in the Peninsula, mainly on Holocene sands of the east coast. They are true Podsols of the humic variety, and they support a distinctive vegetation, the heath forest or kerangas, which we discuss below. Shifting cultivators use kerangas soils only if no others are available, and plots soon have to be abandoned (Andriesse, 1972; Padoch, 1982a). Unwise attempts to establish permanent agriculture on such land have encountered grave difficulties. At one transmigrant site in West Kalimantan, where 20,000 unfortunate people were settled:
The working areas and gardens consist of quartz sand. The plants are stunted. Vegetation growth is not good and has no production. Topsoil is eroding. A large portion of the land slope exceeds 8 per cent so it is easily eroded. (IIED/GOI, 1985, Annex D).
In all parts of the region there is great variety over quite small areas. Slope, local morphology, and parent material are at least as important as wider pedogenic history. Immature soils on steep slopes are sometimes described as shallow brown earths; some nowadays would be classed as Inceptisols (Burnham, 1984). Panton (1964) classed up to 40 per cent of Peninsular soils as slope soils. On late Tertiary and Pleistocene basalts deep inland in Sarawak and East Kalimantan, in the central Peninsula, and more usefully at low altitude in eastern Sabah are areas of deep clay-loam soils said by some to be of high quality, though those in central Sarawak are also described as Podzolic (Burnham, 1984). The good, deep, and friable soils that certainly exist on some basalts in eastern Sabah and a few other areas are unfortunately of relatively small extent, though important at subregional scale (Thomas, Low, and Hepburn, 1976).
Those indigenous cultivators who seek sites for long-term cultivation, rather than simply swiddens of short duration, have a complex soil taxonomy of their own, based primarily on colour and texture. In an area of interbedded shales and sandstones in East Kalimantan, near the Sarawak border, Lun Dayeh farmers recognize four colours and four textures, and have additional terms to describe specific properties; they clearly recognize the quartz-sand, kerangas soils as unsuitable for any agricultural enterprise. They also recognize a number of plants as indicators of agricultural potential, with ranking precisely the same as that independently offered by a forest botanist (Padoch, 1986). This example is unusual since the Lun Dayeh permanent-field farmers are not typical in the regional context, but it clearly indicates the variation that exists within zonal "uniformity."
The alluvial soils, likewise, vary substantially according to the source of the alluvium. Those derived from highly acidic uplands are themselves acid. Those derived largely from marine sources on coasts and in tidal estuaries occupied by mangroves, which trap silt, have a high clay content, and the shells contribute calcium. They may, however, become extremely acid on drainage. Alluvial soils in the region range from areas of high fertility to others that are almost sterile. Moreover, away from salt water and on the margins of the low natural levees formed by the rivers, they graduate into organic peat soils. Large parts of the recently formed coastal lowlands are occupied by peat swamps over marine alluvium, especially in Central and West Kalimantan and in Sarawak, but smaller areas of peat swamp have developed behind beach barriers around all coasts of the region. J. A. R. Anderson (1964) suggests that peat formation originated as coasts aggraded seaward, causing the back-zones of mangrove swamps to become less saline. The high sulphide and salt content of the days then proved toxic to the micro-organisms that decompose plant matter.
With - by definition - more than 65 per cent of organic material and with water tables at the surface, the deep peats of the coastal and subcoastal swamps contain large quantities of woody material and, because of the presence of sulphur compounds, are of very high acidity; pH values below 4.0 are not uncommon. In periods of drought, moreover, dried-out surface layers readily catch fire, which persists until extinguished by rising water. In several parts of the re gion farmers have evolved methods by which to drain the shallower peats in areas on the margins of these swamps and wash the acid from them. These systems cover quite large areas, some of them developed more than a century ago, and in recent years more intensive settlement has been attempted for new land development, with mixed success. In a later chapter we shall further discuss these efforts, for the reclaimed areas are highly vulnerable to both drought and flood, and to even small changes in sealevel. There are also some inland freshwater swamps of considerable extent in Kalimantan; they, by contrast, have high pH.
Notwithstanding the importance of parent material and location, one element of geomorphic and climatic history is of possibly greater significance than has been recognized. The Pleistocene periods of heavy erosion and transportation, discussed above, gave rise to extensive systems of terraces as well as deep alleviation in the valleys. The wide Holocene beach-ridge systems are formed of sand that can hardly have been produced in such quantity from the land, and probably originated from arenaceous sediments in areas now covered by the sea. Moreover, there are iron nodules and a number of laterite caps on low hills and terraces, and extensive areas of bauxite formation on a range of substrates on low hills. Ashton (1972) was among the first to argue that these could not have been formed under present climatic conditions, as is commonly suggested for many duricrusts. It should be noted that the association of particular duricrusts with a distinct climatic type owes much to the theory of zonation, and should not be taken as a fact. Nevertheless, the large changes in land area during the Pleistocene support the possibility that climates were periodically more continental, with - in at least parts of the region lower and more seasonal precipitation than at present. Such changes might have been conducive to the massive erosion that has been recognized. This also has implications for vegetation history, as Ashton (1972) and the discussants of his paper argued at length. Adaptation to moisture stress is better achieved by the heath forest or kerangas than by the floristically rich rain forest (Stein, 1988), and the possibility exists that the large extent of this formation also represents a legacy from drier conditions during the Pleistocene.
The forests
The richness of the flora of the Malesian region as a whole has been described by many writers, most comprehensively by Whitmore
(1984). Conservatively, there are estimated to be 25,000 species of flowering plants (Van Steenis, 1971). On the dry land above the swamps a complex, multi-storeyed association is dominated by canopyemergent dipterocarp species, sometimes in large groups rising to between 45 and 60 m. There are over 350 species of dipterocarp. Species intermingling is common, but is notably greater in the hill forests than on lowland tracts; this difference has been of significance in the history of modern exploitation. Ashton (1972: 47) concludes his review of the Quaternary evidence by arguing that dipterocarps, and most other genera now present, spread through the hills in the late Tertiary under continental climatic conditions; diversification followed during moist phases of the Pleistocene. In northern Borneo, continuing tectonic activity also created new habitats, facilitating diversification.
The dispersal of dipterocarps must have been extremely slow, because studies cited by Whitmore (1984, 1991), Woods (1989), and other writers show that seedlings seldom grow far from the parent tree and that large gaps are recolonized only after considerable time. Some light-demanding species, including many of the 72 Shorea spp. known in Malay as meranti, certainly grow rapidly in gaps, whether natural or anthropogenic, so that after felling a new stand becomes available in only a few decades. Wind-dispersed species establish themselves more widely than those without winged seeds. Some slow-growing species, which include dipterocarps growing only in the shade created by lightdemanding trees, are very rigorous in the conditions required for regrowth and re-establishment (Woods, 1989).
Above about 900-1,200 m, the lowland and hill forests give way to montane forests in which a range of non-dipterocarp species, particularly Fagaceae and Lauraceae (oaks and laurels), dominate. Among dipterocarps, only Shorea curtisii is locally a dominant, especially on ridge crests where, in the Peninsula, this wind-resistant tree sometimes forms pure stands (Whitmore, 1984: 226-230). Structural changes are significant, with a lower canopy height, few emergents, an absence of buttressing, and the disappearance of flowers borne on the trunks of the trees (cauliflory). Higher still, the forest becomes stunted, with large numbers of mosses and epiphytes. Altitudinal zonation, of both associations and individual species, varies considerably from place to place according to exposure and the frequency of mountain-hugging cloud. Only the summit area of Mt Kinabalu in
Sabah rises altogether above the tree line, but there are patches of very stunted forest on several other high mountains in both Borneo and the Peninsula. From the analogy of studies of the higher mountains on the island of New Guinea, it may be that the whole upper montane vegetation is still in course of adaptation to post-Pleistocene warming and increased cloudiness. Zonation is, however, compressed by comparison with that in New Guinea.
There is less diversity in the swamp forests, where only a few species dominate over large areas. One dipterocarp, Shorea albida, is sometimes dominant or co-dominant, but other species form the greater part of the stands. There is commonly a concentric pattern of tree communities, outward from the centre of the swamp, seeming to represent a succession in time (J. A. R. Anderson, 1964, 1976; Whitmore, 1984: 180-195). Despite the difficulties of access, certain swamp-forest trees, particularly Gonostylus bancanus (ramin in Malay), were among the earliest Borneo timbers other than ironwood (Eusideroxylon zwageri) - exported since at least the nineteenth century - to be exploited for international trade. On the seaward fringe are the mangroves, also floristically richer than elsewhere in the tropics (Whitmore, 1984: 178). They are extensive along the west coast of the Peninsula and around the eastern, southern, and western coasts of Borneo; most coasts facing the South China Sea are fringed with sand. These were the earliest forests to be used commercially, with silvicultural management, as important sources of both timber and charcoal. In recent years they have suffered most heavily from human impact, both for their wood and, by reclamation, for fish ponds and, on the inland sides, rice fields. Their value as breeding grounds for marine life has been greatly reduced by these incursions.9
As with soils, there is considerable local variation in the dry-land forests. In detail, this is related to location, with different communities growing along rivers, in other moist locations, on drier slopes, and on ridge crests. Some species of importance to forest dwellers are rather specific in their location; an example is the upland sago-palm Eugeissona utilis, important to Penan huntergatherers in Borneo, which is associated particularly with springs (Brosius, 1986). In the peat swamp forests, Shorea albida is commonly sited halfway along the catena from most favourable to most unfavourable conditions (J. A. R. Anderson, 1964).
Greater variation is associated with soil type. Agathis spp., valuable softwoods that have the most tropical distribution of all the conifers, occur as large stands only on so-called "a-zonal" soils, especially sandy soils, though they also occur in peat swamp forest in southern Kalimantan, where they were exploited in the 1950s.
The heath forest (kerangas) has already been discussed in the context of its soil associations. This type is structurally and floristically quite different from the dipterocarp rain forest. Kerangas is of uniform canopy, with small trees, but ranges all the way from degraded dipterocarp formations to low, bushy scrub and sometimes, as at higher altitude in the rift valley behind the Crocker range in Sabah, is dominated by pines. Also mainly associated with quartz sands, kerangas is sometimes encountered on waterlogged, infertile soils with a hard pan (Richards, 1952: 243-246; Whitmore, 1984: 161-165). Kerangas land is a fragile ecosystem, and is so described by Whitmore (1990: 145). When cleared, recovery of a forest cover is extremely slow; the fast-growing Macaranga shrub, characteristic of early regrowth in gaps made in the dipterocarp forest, will not thrive.10 Quite large areas, especially on beach sands along the east coast of the Peninsula, have been cleared by burning and are now open, sandy savannas.
Climatic shocks and the forest
No part of this region is close to active volcanoes and, although there are traces of ashfalls in some soils, there is no evidence of catastrophic destruction of forest from this cause as has happened in Sumatra (Ashton, 1972). On the other hand, there is growing evidence that important areas have been subjected to climatic shocks. Though cyclones are almost unknown in the southern part of the South China Sea, there is clear evidence that hurricane-force winds smote Kelantan, in the north-east of the Peninsula, in 1880 and felled large areas of lowland dipterocarp forest. When studied in the 1950s, the commonest species were still of secondary, light-demanding character, and there was a much reduced number of dipterocarps by comparison with other areas (Wyatt-Smith, 1954). This forest has since been felled more thoroughly by human hands, bringing an interesting natural "experiment" to an untimely end.
Moisture stress, however, occurs in most years at the north-western and south-eastern extremities of the region, in the north-west of the Peninsula and in the east and south-east of Borneo. In the latter, it has been realized since the drought and fires of 1982/83 that, periodically, severe droughts and also floods are characteristic of the climate. Moreover, they affect areas far beyond the range of quasiannual moisture stress. We discuss the drought/fire problem, and its consequences and implications, in detail in chapter 8 below, but at this stage note that tree death from drought and fire has clearly been a persistent element in the forest ecology of the whole eastern side of Borneo, and periodically also of other areas (Woods, 1989; Whitmore, 1991; Wirawan, 1993). If large parts of the region were significantly more continental in climate during the Pleistocene, we might expect both drought and fire to have been much more widespread than this in the past. Even now, as we shall see in chapter 8 below, fire has been important in the modern ecology of regions in centralwestern Borneo as recently as 1965 and probably later. The full implications of these new findings for interpretation of the natural history of the forests, their differentiation from place to place and their localized replacement by grassland, have not yet been analysed in the literature, although there was early discussion by Brünig (1971) and more recently by Stein (1988).
The historical record
Although new to each generation of nineteenth-century colonial reporters, the prolonged periods of drought and flood that are recorded in the documentary history of South-East Asia from the 1840s onward have probably been a stable characteristic of Holocene climate. These are the El niño and La Nina events widely discussed in recent years, the former bringing dry conditions to South-East Asia, and the latter wet conditions, the reverse of what occurs on the western coast of South America where the events were first described. With a mean return interval of around 4.5 years, these phenomena yield either a more pronounced, longer, and geographically more extensive dry season, usually coupled with a poor wet season, or else a long period of abnormally heavy rain. Once established, these spells tend to have a duration of about a year, but some go on for longer (Working Group, 1992; Nicholls, 1993).
The record for this and a much wider west Pacific region has been brought together by Allen, Brookfield, and Byron (1989) and by Brookfield and Allen (1991). It is also discussed by Nicholls (1992), whose detailed record for nearby and climatically related Australia since 1789 offers an important checklist by means of which fuller study of the Indonesian and Malaysian historical and anecdotal record can be calibrated. Little of this work has yet been done, except in chapter 8 of this book, but a project on the environmental history of Indonesia, now in its early stages in the Instituut voor Taal-, Landen Volkenkunde at the University of Leiden, may soon begin to fill a large gap in knowledge (D. Henley, pers. comm.). A much longer list, also using flow records on the river Nile, provides a more distant and less sure means of calibration extending back well beyond the time that any anecdotal or other Indonesian record is likely to cover (Quinn, 1992).
Borneo and the Peninsula, lying astride the equator, have a considerable range of mean rainfall regimes. A two-maximum regime of rainfall, coinciding with the overhead passages of the sun, is characteristic of most areas north of the geographical equator, including the western side of the Peninsula, Sarawak, and Sabah.11 South of this equatorial zone there are generally two seasons: a wet season between November and April and a drier season between May and October. Only in the south-east of Borneo is this drier season normally a truly dry season with little rain. During the mid-year months the climate is dominated by a south-easterly airstream, and the continental shadow of Australia makes this an almost rainless season in the south-eastern islands of Indonesia beyond Sundaland, though including eastern Java. The notable effect of an El Niño event is to intensify the dry season and enlarge its areal extent westward and northward, while the deep convection that normally occurs in the November-April period is greatly reduced. In major events, such as occurred in 1877/78 and 1982/83, the wet season might produce little or no more rain than the normal precipitation of the drier months.
The basis for these quite common events lies in the equatorial "Walker circulation," especially its Pacific segment. "Normally" the South-East Asian region is the principal centre of vertical convection in this system, the air travelling eastward aloft to descend off the west coast of South America. During an El Niño, the vertical convection shifts eastward into the midPacific; during a La Niño, on the other hand, the "normal" pattern is intensified.12 This oscillation has taken place six times since 1965, to major effect in 1982/83, somewhat less seriously but over longer time in 1991-1993, and with lesser but still significant effect in 1987. The last of these, however, was followed by an extremely wet La Nina event in 1988. The spatial pattern of impact is, however, by no means always the same, and this is examined in much greater detail below in chapter 8.
Dry seasons of varying length are therefore characteristic of most parts of the region, arising even in areas normally per-humid (Sham Sani and Chong, 1991). For the island of Borneo, one may generalize from mean data that eastern and south-eastern districts of Kalimantan tend normally to experience both lower annual rainfall and longer dry seasons, while interior, particularly upland, districts and western areas have more uniformly distributed rainfall and higher annual totals. Droughts might also be experienced periodically in parts of Sabah, especially in the lee of the ranges or on the south-east coast, but should rarely be a problem in Sarawak. In the Peninsula, except for the central mountains and parts of Johor, annual means tend to be lower than in much of Borneo. However, although seasonality is marked along the east and north-west coasts, monthly rainfalls fall frequently below 100 mm in only a few areas (Dale, 1959/60). Nowhere in this region do conditions resemble those in eastern Indonesia, where eight-month dry seasons are regular events.
Notes
1. We are grateful to G. S. Humphreys and Ian Douglas for useful comment, information, and advice on matters concerning geology, soils, and geomorphic history in this chapter.
2. Orang Asli means "aboriginal people" in the Peninsula, and it has now replaced the older and derogatory Malay term, Sakai, meaning "slave" or subject people. Dayak is widely used as a generic term for all the tribal people of Borneo, and is in general use in Kalimantan. In Sarawak, however, it is used only of Iban and some other western people. In Sabah it is not used; Dusun or Kadazan, while also meaning a particular people who are the majority, is sometimes used loosely to describe all. The tribal people of eastern Sarawak are known as Orang Ulu, meaning the "people of the headwaters, or interior."
3. Moreover, recent fieldwork among Banjarese-Malay migrants from Kalimantan living in Krian and Johor on the Peninsula reveals a desire among these long-standing immigrants to forget their origins and become local Malays. The stigma associated with current illegal Indonesian migration may help explain this (Potter, 1993a).
4. Very few of those who, in the period 1945-1958, left the new Indonesian state together with the Dutch, either from preference or from fear, came from Kalimantan. There have been some very modern moves to Saudi Arabia, and other lands of opportunity, which are now becoming numerically significant.
5. Several thousand Chinese detainees were deported from the Peninsula to China early in the communist uprising after 1948. However, following the 1949 communist victory in China, ports refused to accept the returnees, a fact that also halted moves to deport some Chinese from Indonesia. In the Peninsula, suggestions were even made that "the detainees be loaded onto amphibious landing equipment, shipped across the South China Sea, and dumped on China's south coast" (Stubbs, 1989:117). Fortunately, this early enforced creation of "boat people" did not happen. Some Indonesian immigrants, among them Banjarese, were forcibly repatriated from the Peninsula to Kalimantan at this time. After the coup in Indonesia in 1965, many thousands of the Chinese community were killed, whether or not they had been associated with the communists, and a considerable number left the country voluntarily.
6. Concealed karst pinnacles and hollows underlie large parts of the city of Kuala Lumpur, and their exploration has become important in order to establish firm foundations for the large number of highrise buildings erected in the city since 1970.
7. Humphreys (1991: 89) comments additionally on the use of Soil Taxonomy that "the classification stems from the heartland of the US Soil Conservation Service, the corn belt of central USA, and as a result many users outside this region have found the system wanting. In the tropics several great groups are prefixed by 'trop-' meaning a particular soil is the tropical variety of the suborder ... Calling a soil a tropical soil in a tropical country adds very little to further characterization and understanding."
8. After clearance, "the soil very quickly degenerates. The surface humus layer is either eroded, burned, or oxidized. The small amount of clay in the soil washes down the profile to leave almost pure silica sand, which unlike the clay and humus has no electrical charge to which nutrient ions can attach" (Whitmore, 1990: 145). These soils are described as "sandy leached ferrallitic soils" by Young (1976: 139).
9. In both countries, the management of mangroves is legally regulated. However, the allocation of areas for timber extraction and uncontrolled reclamations continues in defiance of legislation.
10. A Japanese project, charged with reforesting the site of a failed transmigration (settlement) scheme on such land, found that even so tolerant a tree as Acacia mangium would make little growth (S. Sasaki, pers. comm).
11. The thermal equator lies 1-3° north of the geographical equator.
12. This is a highly simplified statement. The system is well described in numerous sources, most recently in Glantz, Katz, and Nicholls (1991) and by Nicholls (1992, 1993). Moreover, the South-East Asian pattern does not always correspond closely with events in the eastern Pacific, so that a "minor" El Nino in 1914, as recorded in the eastern Pacific, became a major drought year in South-East Asia; the converse occurred in 1925, a great event in the eastern Pacific but relatively minor in South-East Asia. Allen, Brookfield, and Byron (1989) and Brookfield and Allen (1991) have analysed the record of these anomalies from the west Pacific point of view.
