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Matrix to mosaic: habitat fragmentation from 1982-1999 in Sabah, Malaysian Borneo.

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Introduction

As the footprint of human society expands on the earth, habitat loss and fragmentation are global problems of increasing significance. Habitat loss and fragmentation cause the natural matrix of a landscape to become a mosaic of patches. Each patch is a relatively homogenous unit such as an agricultural field, a logged forest, or an urban center of human settlement and industry. In this mosaic, patches are connected by networks of roads. These landscape changes have strong effects on the composition of biodiversity (Saunders et al. 1991; Chung et al. 2000; MEA 2005). Scattered among homogenous, anthropogenic patches are remnants of native vegetation, habitat islands in a mosaic of developed land. Patch edges in this mosaic offer a variably permeable boundary that is especially constraining for animals with large home ranges and/or those requiring a suite of different habitats within a landscape (Bach et al. :2004). Boundaries become barriers for sensitive interior species and species such as arboreal animals that require a matrix of connected, natural habitat for movement (Forman 1998; van der Ree 2006). Ecosystem effects of habitat loss and fragmentation include loss of biomass, modified and increased habitat edges, reduced core areas, divided and isolated animal populations, changed species composition, altered population sizes, reduced genetic exchange due to isolated populations, reduced likelihood of recolonization following local extinction events, altered species interactions, and increased probability that humans will access and further modify habitat (Andrews 1990; Forman & Alexander 1998; Trombulak & Frissell 2000; Bickel et al. 2006).

In the tropics, the rate of land-cover change, especially conversion through deforestation, is unprecedente loss tropical land-cover conversion is a primary driver of global environmental change (Geist & Lambin 2002). The inextricably linked processes of habitat loss and fragmentation are reducing biodiversity, increasing risk of extinction for many organisms (Laurance 1999; Myers et al. 2000) and weakening the ability of global ecosystems to resist climate changes. The tropical forests of the world support high tares of endemism, serving as repositories of genetic in formation. Forty-four percent of all plant species and 35% of all vertebrate species are found in just 1.4% of the land area on Earth. These "hotspots" of biodiversity are concentrated in tropical forests and include almost all tropical islands (Myers et al. 2000). Right now, species are being lost that will never be identified.

Nowhere in the world is the crisis of tropical forest loss more immediate than in Southeast Asia (WRI 1996; Laurance 1999; Sodhi et al. 2004). The 1980s were a decade of rapid forest conversion and loss. During this decade, Asia lost 11% of its tropical forest cover, more than any other region (WRI 1996). The current rate of forest loss is higher in Southeast Asia than anywhere else in the world at 0.91% [yr.sup.- 1], nearly twice the global rate of 0.52% [yr.sup.-1] (Langner et al. 2007). If the current rate of deforestation continues, by 2100 Southeast Asia will have lost 75% of its forest cover and 42% of its biodiversity (Sodhi et al. 2004). Lowland tropical forests are among the ecosystems undergoing most rapid change because they are easily harvested, and cleared lands are readily converted to agriculture. These lowland, high diversity forests are becoming increasingly tare and highly fragmented. In Southeast Asia, the area of land remaining in lowland forest is surpassed by the area in both secondary forest and agriculture (Slik 2005). Malaysia, including Malaysian Borneo, typifies those patterns. Malaysia is one of the top 14 deforesting countries in the world, with 250,000 ha being deforested annually (McMorrow & Talip 2001).

Sabah occupies 76,115 [km.sup.2], approximately 10% of the island of Borneo (Marsh & Greer 1992). Sabah's long history of land-cover conversion started in the late 1800s. In the 1890s, colonial governments initiated large-scale timber harvesting, which was quickly followed by introduction of agricultural crops such as tobacco and rubber (McMorrow & Talip 2001). Forest conversion and associated fragmentation accelerated greatly with the timber boom of the 1960s (Bickel et al. 2006). Oil palm (Elaeis guineensis) agriculture, introduced to Sabah in the 1980s is the most dramatic driver of landscape conversion yet seen in the area (Rajaratnam et al. 2007). The period from 1981 to 2000 was characterized...

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