Forests of South East Asia are more resilient than previously thought

A new study led by geoscientist Rebecca Hamilton at the University of Sydney is challenging long-held views on the ecological history of South East Asia. 

Contrary to the previous belief that dry savannahs dominated the region during the Last Glacial Maximum more than 19,000 years ago, the team discovered a varied landscape of closed and open forest types. 

Resilience of tropical forests

The research, published in the journal Proceedings of the National Academy of Sciences, has significant implications for understanding the resilience of tropical forests to climate change.

Dr. Hamilton emphasizes the importance of this discovery in the context of accelerating climate change. She notes that maintaining a diversity of forest types is key to conserving the region’s ecosystems. 

Transformation of forested areas 

“Our work suggests that prioritizing protection of forests above 1,000 meters (‘montane forest’) alongside seasonally dry forest types could be important for preventing future ‘savannization’ of Asia’s rainforests,” she said.

Savannization refers to the transformation of forested areas into savannah ecosystems, characterized by open wooded plains. This process can be triggered by climate changes, human activities, or natural ecological shifts.

Focus of the study

“The dominant paradigm is that large tracts of Southeast Asia’s lowland rainforests were replaced with a ‘savanna corridor’ during the cooler, more seasonal climates of the Last Glacial Maximum,” wrote the study authors. 

“This interpretation has implications for understanding the resilience of Asia’s tropical forests to projected climate change, implying a vulnerability to savannization.” 

“A savanna corridor is also an important foundation for archaeological interpretations of how humans moved through and settled insular Southeast Asia and Australia. Yet an up-to-date, multiproxy, and empirical examination of the palaeoecological evidence for this corridor is lacking.”

Paleoenvironmental sites 

To investigate, the researchers analyzed records from 59 paleoenvironmental sites across tropical South East Asia. The team challenged the savannah model, which postulated a vast, uniform grassland expansion during the Last Glacial Maximum. 

Instead, their analysis of pollen grains from lakes and other biochemical indicators revealed a coexistence of forests and expanding grasslands during this period.

Study implications 

“We put forward the idea that these seeming discrepancies can be reconciled if, during the cool and seasonal climate of the Last Glacial Maximum, montane forests (above 1,000m) persisted and expanded in high-elevation regions, while lowlands experienced a shift to seasonally dry forests, which have a naturally grassy understory,” Hamilton explained.

The research not only offers a revised perspective on the ecological past of South East Asia but also provides valuable insights into the potential resilience of the region’s tropical forests in the face of ongoing climate change. It highlights the critical need for preserving a diversity of forest landscapes to safeguard these ecosystems for the future.

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