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acrylic on illustration board 30" x 20"
|Of all of Borneo's varied ecosystems, perhaps none is more surprising than the biologically impoverished (by equatorial standards) dwarf forests that occur throughout the island, but more commonly in the west. The ecologist P. W. Richards called them "heath forests" after the similarly infertile lands of his native England, but they're better known by the Iban term kerangas, which means "land which will not support rice cultivation." Kerangas soil is typically acidic, sandy and podzolized, or heavily leached. Essential elements enter the soil from decaying leaf litter, but most of these, magnesium, carbon, nitrogen and calcium in particular, leach away very quickly, and are only available in the top few inches. Phosphorus seems to leach away more slowly. Continual deposition of leaf litter is critical to the system, and disease, fire and logging or clearing for agriculture will convert kerangas to a barren habitat dominated by grasses and sedges known as padang ("field" in Malay). Despite the poor soil, healthy kerangas forests are dense with trees, most of them under 30 feet tall and three inches in diameter. In contrast to most equatorial forests, only a few species are represented. (Continues below.)|
Dominant tree species usually belong to the mangosteen family, Clusiaceae, and to one or more of the genera Cratoxylum, Calophyllum and Ploiarium. Orchids show the greatest species diversity among kerangas plants, and terrestrial as well as epiphytic species are usually in evidence. Species of melastomes, laurels, myrtles and gingers are also commonly represented. Many kerangas plant species bear nitrogen-fixing bacterial nodules on their roots, and carnivorous plants also thrive. Borneo's kerangas forests are a center of diversity for the pitcher plant genus Nepenthes, which trap insects in leaves which are modified into water-bearing pitchers. At least one Bornean species, N. rajah, secretes a nectar that attracts tree shrews whose droppings are captured in the pitcher to nourish the plant. In perennially wet padang habitat, Bladderworts (Utricularia spp.) and Sundews (Drosera spp.) also trap small arthropods. Another famous kerangas denizen is the epiphytic ant plant (Hydnophytum spp.), which forms a symbiotic relationship with ants, providing them shelter, while receiving protection from the colony and nutrients from its wastes. This painting depicts a small patch of kerangas forest floor. Included in the leaf litter are shed leaves of the dominant tree Cratoxylum glaucum and shed needles of the podocarp (primitive conifer) Dacrydium becarii. Various mosses of the family Calymperaceae and the showy terrestrial slipper orchid Paphiopedilum javanicum grow from the soil and a single dried Nepenthes ampullaria pitcher sits on the floor while pitchers of N. stenophylla hang from epiphytic vines. Duméril's Monitor (Varanus dumerilii) occurs near rivers in various types of forest throughout the island. The hatchlings, like the one shown, are well-known for their striking coloration. It has been suggested that the colors, which begin to fade at the age of six weeks, mimic the dangerously venomous Red-headed Krait (Bungarus flaviceps), which shares its Southeast Asian range. Among Borneo's diverse and beautiful dragonflies, probably none is more conspicuous than the Red Swampdragon (Agrionoptera insignis), a member of the skimmer family, Libellulidae. Other subjects include the left-handed land snail Dyakia kintana and a Giant Forest Ant (Camponotus gigas), whose dimorphic workers forage for honeydew and other organic matter on the ground and in the canopy. At over an inch in length, the major workers of this species are among the world's biggest ants. Finally, a procession of Longipeditermes longipes termites returns to the nest with balls of lichen in tow. Both the workers and soldiers of this monotypic genus come in two sizes. Like other members of their subfamily, Nasutitermes, the heads of the soldiers are distorted into nozzles, through which they can spray noxious chemicals at enemies, chiefly ants.