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On islands that inspired theory of evolution, deforestation cuts uneven path

  • The Wallacea region spans Indonesia’s central islands where the biota of Asia and Australasia meet, making it one of the world’s most valuable centers of endemism, home to scores of species found nowhere else on Earth.
  • With development pressure expected to escalate over the coming decades, identifying which of the region’s tracts of forest are most at risk is key to preserving its unique biodiversity.
  • A new study that models future deforestation risk across the region has found that coastal, small and unprotected biodiversity sites are most at risk, with North Maluku and Central Sulawesi projected to lose significant tracts of forest by 2053.
  • The researchers say their results can be used to target programs, such as social forestry, to sites where they will have optimal impact for biodiversity and communities.

Biologists often refer to the Wallacea region of Indonesia as a “living laboratory” for the study of evolution. Spanning 1,680 of Indonesia’s central islands, including the Malukus, Nusa Tenggara and the expansive arms of Sulawesi, it is the transition zone where the biota of Asia and Australasia collide. Isolated for tens of millions of years from neighboring landmasses, a unique assemblage of weird and wonderful species have evolved; and it was here that its namesake, Alfred Russel Wallace, developed his theory of natural selection during the 19th century, around the same time that Charles Darwin was having his own eureka moment in the Galápagos.

Today, Wallacea is recognized as one of the world’s most valuable centers of endemism, supporting scores of species that occur nowhere else on the planet: from the babirusa (Babyrousa babyrussa), a forest pig with enormous recurving tusks; to the anoa (Bubalus depressicornis), an enigmatic dwarf buffalo; and the famous Komodo dragon (Varanus komodoensis).

A babirusa (Babyrousa babyrussa), a forest pig in Nantu forest, Gorontalo. Male babirusa have large recurving tusks. Image by Simon Mitchell

Although the forests of Wallacea have experienced lower levels of deforestation than neighboring Borneo, Sumatra and Java, development pressure is expected to escalate over the coming decades. According to a new study in Environmental Research Letters, the region could lose up to 49,570 square kilometers (19,140 square miles) of forest by 2053.

The research team, comprising scientists from the University of Kent, U.K., and their Indonesia-based colleagues, used dynamic models based on local patterns and drivers of forest loss to reach their findings. It’s the first time deforestation risk in Wallacea has been investigated on such a scale and level of detail.

The researchers say their findings provide a valuable baseline against which to measure future change, especially given recent policy shifts, such as a controversial slate of deregulation, that present both challenges and opportunities for environmental governance and conservation in Indonesia.

“The results that we provide are a baseline to what could happen if things continue as in the past,” Maria Voigt, lead author of the study and conservation biologist at the University of Kent, told Mongabay in an interview. “Now it is on Indonesia to decide on the options and how to develop.”

Map of the Wallacea region in central Indonesia. The researchers divided it into 9 sub-regions to look at geographic variation in deforestation risk. Image from Voigt et al. (2021). Environmental Research Letters, 16(9). doi:10.1088/1748-9326/ac15cd via Creative Commons (CC BY 4.0)

Regional variation

To train their models to predict future deforestation risk, Voigt and her colleagues used satellite data on forest cover and spatial information on deforestation risk factors, including proximity to previously deforested areas, history of fires, and land-use designations that permit logging or resource extraction.

They found that between 2000 and 2018, the rate of deforestation in Wallacea was half that of Borneo. According to Matthew Struebig, conservation scientist at the University of Kent and study co-author, this can be accounted for by the region’s approach to agriculture: Wallacea has largely escaped the pressures of large-scale agribusiness because communities favor small-scale plantings of coconut, cocoa and coffee over expansive monocultures of oil palm and rubber.

Nonetheless, deforestation and forest fragmentation are set to increase. The research team’s models project forest loss across Wallacea at an average rate of 1.23% per year — higher than current levels in Borneo and more than twice the current global average for tropical forests (0.49%).

The researchers identified substantial regional variation in deforestation risk forecasts. For instance, the southern island groups in Nusa Tenggara had a relatively low projected deforestation rate, at around 0.1% per year, with very low levels of forest fragmentation. On the other hand, North Maluku is set to lose more than half of its forest by 2053 at a rate of 2.17% per year, and undergo a nine-fold increase in the number of forest fragments. Other highly impacted areas include Central Sulawesi, projected to lose around 21,600 km2 (8,340 mi2) — an area more than three times the size of the island of Bali.

smallscale deforestation
Encroachment into Indonesian rainforest for small-scale agriculture. Image by Rhett A. Butler/Mongabay

Alleviating poverty while avoiding deforestation

The new study “adds solid data to corroborate what many of us have long feared: that deforestation in the Wallacean region is increasing rapidly, and that the region must brace itself for upcoming waves of extinction,” Frank Rheindt, an evolutionary biologist at the National University of Singapore who was not involved in the new study, told Mongabay in an email. “[L]arge-scale habitat loss in Wallacea would translate into losing extremely unique and irreplaceable species.”

In addition to pressures from human-caused deforestation, Rheindt said climate change is already exerting a massive toll on the endemic fauna of Wallacea. In 2020, he led a team that described 10 new bird species and subspecies. One of those species, found on Taliabu Island to the east of Sulawesi, is already gravely endangered because there are only a few hectares of its mountaintop vegetation left.

“A couple of decades further into the future, climate change will also affect lowland habitats,” Rheindt said. “Increasing drought and floods will impact the regrowth capabilities of logged areas, affecting forest regeneration on these islands, which is already much more difficult here than in many continental areas … All we can do at this point is try to make the extinction wave less severe.”

Protected forest in Bogani Nani Wartabone National Park, Gorontalo. Image by Matthew Struebig

To find out how threatened species are likely to fare, the new study authors also looked at a suite of more than 200 “key biodiversity areas” (KBAs) across Wallacea. According to their models, average forest cover in KBAs will decrease by 12% by 2033 and by 26% by 2053, with some sites losing nearly three-quarters of their forest. Sites that are small, coastal and unprotected are particularly vulnerable.

With so much unique biodiversity at stake, identifying the tracts of forest that are most at risk can help target limited conservation resources to the places where they will make the most impact. “If the primary interest is on safeguarding patterns of endemism … targeting those small coastal areas that have already been recognized as important for endemism would be a start,” Struebig said.

For those KBAs that are unprotected, alternative conservation options include community-based initiatives like social forestry. Nonetheless, uptake of social forestry has been somewhat slower in central Indonesia than in Borneo and Sumatra. Voigt said the deforestation risk models can now be used to work out how to prioritize social forestry activities to achieve the dual aims of alleviating poverty and avoiding deforestation.

“By studying where social forestry has worked elsewhere in Indonesia, it should be possible to find out where those conditions exist in the Wallacea region using the models,” Voigt said. “It’s about finding out where the risks lie and what sorts of things could be promoted to minimize the risks.”

“That’s why having a focus on KBAs is interesting, because it enables us to think more about not just protecting and closing off areas, but actually about having mixed-use areas that benefit people as well,” Struebig said. “Ultimately, the future of biodiversity and forests and all the ecosystem functions that they provide is down to people. If people don’t benefit from the system then we can’t expect the system to be sustainable in the long term.”

Banner image: Overlooking Manusela National Park, Seram Island, Maluku. Image by Simon Mitchell


Voigt, M., Supriatna, J., Deere, N. J., Kastanya, A., Mitchell, S. L., Rosa, I. M., … Struebig, M. J. (2021). Emerging threats from deforestation and forest fragmentation in the Wallacea centre of endemism. Environmental Research Letters, 16(9), 094048. doi:10.1088/1748-9326/ac15cd

 Rheindt, F. E., Prawiradilaga, D. M., Ashari, H., Suparno, Gwee, C. Y., Lee, G. W., … Ng, N. S. (2020). A lost world in Wallacea: Description of a montane archipelagic avifauna. Science, 367(6474), 167-170. doi:10.1126/science.aax2146


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