New Study Challenges Previous Assumptions about Southeast Asian Forests’ Response to Climate Change

Bingkai Karya – A recent paleoecological study has revealed that the forest environment in Southeast Asia has demonstrated a higher resilience to climate change since 119,000 years ago than initially thought by researchers, as long as its ecosystem diversity remains intact.

This contrasts with the earlier theory suggesting that the lowland forests of Southeast Asia abruptly transformed into extensive savanna corridors in response to cold and seasonal climates during the peak of the last ice age around 20,000 years ago.

Instead of a sudden shift from forest to grassland savanna, researchers documented a smooth transition between lowland rainforests, seasonal dry forests, open canopies with grassy understories, to tropical montane forests.

This mosaic of forest types suggests that the ecosystems of Southeast Asia have the capacity to “resist and recover” from climate pressures, the study asserts.

These findings further support conservation efforts by conservationists to preserve various forest types within interconnected networks throughout Southeast Asia.

Rebecca Hamilton, a paleoecology expert at the University of Sydney and the lead author of the new study, stated, “Conserving forest types that support resilience [to climate change] should be a priority.”

She added, “Seasonal dry forests, for example, are often overlooked. Although these forests may not appear as important in terms of biodiversity compared to tropical rainforests, they harbor beta diversity reserves at the landscape level.”

The forests of Southeast Asia have faced significant pressures due to human activities over the past few decades. Widespread deforestation of lowland rainforests has paved the way for urban expansion, agriculture, and the cultivation of palm oil and rubber in alarming rates of forest encroachment.

In investigating the ancient landscapes of Southeast Asian forests, Hamilton and her colleagues employed detective-like methods. They examined fossilized pollen grains’ biochemical data from 59 paleoecological sites across the region to determine which tree species thrived at a given time.

The late glacial period chosen for this study was selected to understand extreme seasonal periods, where the data was used to determine whether the natural landscape at the time was dominated by forests or savannas.

These climate changes during that period would unveil the seasonal patterns during the rainy and dry seasons in Southeast Asia, triggering extreme rainfall and droughts, and revealing how ecosystems responded to these conditions.

Hamilton noted that the study’s results indicate indications that forests in the Southeast Asian region may respond to large-scale disturbances differently than what has been observed in other parts of the world.

For instance, forest biologists in South America have documented ecosystem “tipping points” triggered by major disturbances such as forest fires by El Niño and large-scale land clearing for agriculture.

However, such tipping points are not as apparent in Southeast Asia. The forests in this region tend to act as “stepping stones” in the form of seasonal dry forests, bridging between rainforest ecosystems and grasslands.

“In Southeast Asia, we do not see sudden transitions to savannas. We only see gradual shifts towards more open forest types,” Hamilton explained.

However, this does not mean that forests in Asia are immune to adverse regime changes. Human activities continue to undermine forest resilience in this region.

“[This] potentially poses a major disaster for the sustainability of rainforests across the tropics,” Hamilton said.

“We often see forest fragmentation due to human-induced fires that are quite damaging and can lead to sudden transitions from forest to savanna as seen in many regions of America.”

However, another interesting fact is that humans have shaped the world’s forests for thousands of years.

Previous studies have shown, for example, that shifting cultivation systems have maintained structural diversity in forests in some mainland Southeast Asian regions. This may help explain theories about how humans and animals migrated through Southeast Asia during the last glacial period.

“Some schools of thought argue that the savanna environment facilitated human migration; in this view, tropical forests are considered entirely unfriendly to humans,” Hamilton said.

“Now we know that communities utilize and manage tropical forests and have migrated through at least some forest systems to reach Australia [from Asia]. This shows that we as a species historically utilize resources from various ecosystems.”

“The savanna corridor hypothesis has long been questioned in Southeast Asia, and [it has] long-term implications for our understanding of regional biogeography,” explained Alice Hughes, a professor at the University of Hong Kong, who was not involved in this study, said to Mongabay via email.

The sea level during the last glacial period was much lower, known as Sundaland, a vast lowland connecting what are now the Southeast Asian mainland with the islands of Borneo, Sumatra, Bali, and many other islands.

Hughes stated there is new evidence that Sundaland was a forested area, which is crucial for genetic diversity.

“With rising sea levels, the remaining forests are the last bastion of genetic diversity. Undoubtedly, [these forests] are key areas that must be protected to preserve biodiversity (and genetic diversity) across the region,” Hughes wrote.

Current global warming exposes the fact that many species in this region are becoming geographically confined. They are increasingly vulnerable to the impacts of climate change, Hughes added.

“Increasing connectivity in this region is crucial to reconnect forest patches that allow species to survive in the future.”

Source: Mongabay


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