People Deforested the Central African Tropical Rain Forest 2,600 Years ago

The forested expanses of Central Africa host the second largest block of tropical rainforest on Earth (after Amazonia), stretching over around 2 × 106 km2. They are the great green heart of Africa, and changes in vegetation cover are likely to have important but poorly understood influences on the climate of much of the continent (1). A remarkable feature is that this blanket of forest appears quite tenuous—under the arid climates of the ice ages, the forest appears to have retreated into isolated pockets surrounded by savanna grasslands. Even in the climatically stable Holocene, there appears to have been periods of substantial forest retreat. In particular, there is evidence for a period of major forest loss between 3,000 and 2,000 y ago [termed the Late Holocene rainforest crisis (LHRC) (2)]. Attributing the cause of this decline is complicated by the fact that this period coincided with major expansion of Neolithic and early Iron Age farmers southward from the Nigeria/Cameroon border regions into western Central Africa. Did the farmers take advantage of a forest retreat driven by climate drying, or were they the primary cause of the forest loss? In recent years, there has been a vigorous debate on the cause of the LHRC. Now, Garcin et al. (3) provide new data and an unexpected new insight, presenting strong evidence that there was no strong drying event, and therefore suggesting that it was direct deforestation that caused this retreat of the Central African rainforests.

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Better start rethinking the anthropocene, folks.

The Myth of the Virgin Rain Forest

The little village of Pa Lungan sits in a grassy clearing, high in the hills of Malaysian Borneo, in a region called the Kelabit Highlands. The people here—a few dozen—belong to the Kelabit tribe, one of more than 50 Indigenous groups living on Asia’s largest island. They have sturdy wooden homes with slat glass windows, metal roofs, kitchen sinks, and TVs. Generators and solar panels power a few lightbulbs, laptops, and mobile phones (typically used to play music and games). Most households have a kitchen garden, an outdoor toilet, a cold-water shower, and a laundry line. A patchwork of coops and fences keeps chickens and buffalo in check. Just beyond these homes and yards lie rice fields fed by mountain waters and hemmed in by trees. It’s a tidy, orderly life in Pa Lungan—and it’s an easy walk to some of the most biologically diverse rainforests on Earth.

The Kelabit, like their ancestors, move fluidly between the village and the forest in a culture where notions of domestic and wild intrinsically overlap. Villagers plant fruit trees in the forest; they move wild herbs from the jungle to their kitchen gardens. “Daily living” and “the bounty of the forest” are deeply intertwined, as the Kelabit anthropologist Poline Bala, based at Universiti Malaysia Sarawak, explained to me. In the past few years, new research has begun to shift scientific perspectives—and my own—of the Borneo landscape. It is not the wild, untamed place many people have long assumed it is. Rather, the rainforest we see today bears the marks of long-term human intervention.

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The Forests of SE Asia Have Been Undergoing Anthropic Modification Since at Least the Beginning of the Holocene

New research from Queen's University Belfast shows that the tropical forests of South East Asia have been shaped by humans for the last 11,000 years.

The rain forests of Borneo, Sumatra, Java, Thailand and Vietnam were previously thought to have been largely unaffected by humans, but the latest research from Queen's Palaeoecologist Dr Chris Hunt suggests otherwise.

A major analysis of vegetation histories across the three islands and the SE Asian mainland has revealed a pattern of repeated disturbance of vegetation since the end of the last ice age approximately 11,000 years ago.

The research, which was funded by the Arts and Humanities Research Council and the British Academy, is being published in the Journal of Archaeological Science. It is the culmination of almost 15 years of field work by Dr Hunt, involving the collection of pollen samples across the region, and a major review of existing palaeoecology research, which was completed in partnership with Dr Ryan Rabett from Cambridge University.

Evidence of human activity in rainforests is extremely difficult to find and traditional archaeological methods of locating and excavating sites are extremely difficult in the dense forests. Pollen samples, however, are now unlocking some of the region's historical secrets.

Dr Hunt, who is Director of Research on Environmental Change at Queen's School of Geography, Archaeology and Palaeoecology, said: "It has long been believed that the rainforests of the Far East were virgin wildernesses, where human impact has been minimal. Our findings, however, indicate a history of disturbances to vegetation. While it could be tempting to blame these disturbances on climate change, that is not the case as they do not coincide with any known periods of climate change. Rather, these vegetation changes have been brought about by the actions of people.

"There is evidence that humans in the Kelabit Highlands of Borneo burned fires to clear the land for planting food-bearing plants. Pollen samples from around 6,500 years ago contain abundant charcoal, indicating the occurrence of fire. However, while naturally occurring or accidental fires would usually be followed by specific weeds and trees that flourish in charred ground, we found evidence that this particular fire was followed by the growth of fruit trees. This indicates that the people who inhabited the land intentionally cleared it of forest vegetation and planted sources of food in its place.

"One of the major indicators of human action in the rainforest is the sheer prevalence of fast-growing 'weed' trees such as Macaranga, Celtis and Trema. Modern ecological studies show that they quickly follow burning and disturbance of forests in the region.

"Nearer to the Borneo coastline, the New Guinea Sago Palm first appeared over 10,000 years ago. This would have involved a voyage of more than 2,200km from its native New Guinea, and its arrival on the island is consistent with other known maritime voyages in the region at that time – evidence that people imported the Sago seeds and planted them."

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ReGrowing Tropical Rain Forests Recover Carbon Storage Quickly, but not Diversity

A new study of re-growing tropical forests has concluded that plant biodiversity takes longer to recover than carbon storage following major disturbances such as clearance for farming.

The findings, published in the scientific journal Proceedings of the Royal Society B, have important implications for conservation since there are now many re-growing forests in South and Central America. The new study is the first large-scale analysis of the recovery of both plant biodiversity and carbon pools in re-growing forests.

Over half of all tropical forests have already been converted for agriculture, logged or burnt in the recent past. Re-growing forests could help both to soak up carbon emissions produced by human activities and to reduce species' extinctions.

The scientists, from the Centre for Ecology & Hydrology and Bournemouth University, concluded that although carbon recovered most quickly, even after 80 years re-growing forests tended to have less carbon than old-growth forests. This is probably because these forests are often dominated by small, fast growing trees. It may take centuries for larger trees which hold more carbon to become established.

In contrast, although the number of tree species recovered relatively rapidly, many species characteristic of old-growth forests were rare in re-growing forests. This is worrying because these species are probably those most vulnerable to extinction.

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