Tropical lowland forests are among the world’s richest and most diverse ecosystems, but everywhere they are under threat from man’s activities. In Bali, the southern slopes of the central mountain range have long been given over to terraced rice fields, and since the late 19th century, rice crops for export have been planted on the drier northern slopes. In this century, the principal cause of depredations to Bali’s forest resources have been the commercial cultivation of coffee, clove and coco- nut via plantations. An increased demand for firewood to fuel brick, tile and quicklime kilns has also had a significant impact, while the volcanic eruptions of GunungAgung and Batur have destroyed substantial areas of forest around their cones. Today, very little remains of the Balinese rainforest below 500 metres.
Rainforests are extremely complex habitats where the struggle for light plays a crucial role in determining the size and shape of the tree and plant species that grow there. In terms of its structure, or morphology, the Balinese rainforest is stratified into four or five distinct layers of vegetation, The upper storey, or forest canopy, consists of a continuous swathe of vegetation formed by the tops of mature tree species. Occasionally, where a tree has died and come crashing down, dragging some of its neighbours with it, natural clearings are formed, allowing light to reach the normally crepuscular forest floor. Here an entirely different range of species will flourish in the period it takes for the mature forest to regenerate. These include giant herbs like the banana and big-leafed tree species belonging to the genus Macaranga. Above the canopy one sees, at intervals, trees of truly gigantic proportions, standing up to 80 metres tall, which erupt from the main forest canopy to stand head and shoulders above their competitors for light. Often there is a lower storey just beneath the canopy comprising species which do well in the reduced light conditions. The forest floor, however, is relatively ‘open’, the dominant feature being slender seedlings vigorously sprouting from the leaf litter and decomposing organic matter which forms a thick carpet between the massive trunks of mature trees. The need to reach the canopy as quickly and efficiently as possible means that the majority of rainforest tree species have very tall, straight trunks, which soar vertically for 50 to 60 metres, sometimes more, before branching into a crown of foliage, This distinctive tree profile is a characteristic feature of the rainforest and is directly attributable to the competition for light. Unlike the lowland forests of Sumatra and Kalimantan, the surviving rainforests of Bali are not characterised by the presence of adominant family or species of tree. Now is there a consistent ‘mix’ of forest composition in terms of typical species found within a given area.
The Forest Floor
Death and decay are the means by which organic materials and nutrients are recycled back into the sys-tem. A lot of this goes on at ground level where beetles and fungi are engaged around the clock breaking down dead leaves, fallen tree trunks and other plant matter into a nutrient-rich humus. The Basidiomycetes, which include the genus Amanita, are the most prominent class of fungi found in the rainforest, being easily recognised by their large, sporeproducing fruiting bodies which come in a wide range of colours, shapes and sizes. Basidiomycetes fungi play an integral part in the decomposition of wood and typically occur in clusters on fallen branches and dead tree trunks.
Bali is home to quite a wide range of forest animals, though this may not always be immediately apparent to the casual observer, given the nocturnal habits of many forest species and the ample cover provided by dense tropical vegetation. In the past, the most celebrated of these was the famous subspecies of tiger, Pantheratigrisbalica, but unfortunately this magnificent creature, like its javanese cousin Pantheratigrissondaica, has become extinct. Diminishing areas of natural habitat mean that a number of other forest species are similarly under threat, particularly in the case of larger creatures which generally need more area to survive as self-sustaining breeding populations. The biggest animal on the island is the banteng (Bosjavanicus), which is a species of wild cattle found in several parts of Southeast Asia. Other notable mammals include the javanlutung (Semnopithecusauratus), a type of monkey endemic to java and Bali, and the javan ferret—badger (Melogaleorientalis), which is also endemic to the two islands. Of the three species of deer, the most remarkable is the minuscule mouse deer (Tragulusjavanicus) which weighs less than two and a half kilograms and seldom measures more than half a metre from its nose to the tip of its tail. Bali boasts a large number of snake species, of which about 30 percent are potentially dangerous to man. These include the venomous triangular-headed pit vipers, variousspecies of cobra, krait and coral snakes, a number of sea serpents, and the non-venomous but constricting, reticulated python (Python reticulatus). The latter is one ofthe largest snakes in the world. Lacking venom, pythons kill their victims by wrap— ping their coils around the unwary and then crushing the breath out of them. It seems that it is brain death through oxygen deprivation, rather than actual suffocation, which causes death. Pythons are mainly nocturnal and can be found in most habitats, including gardens, but only the larger specimens pose a threat to humans.