- A new study shows that Southeast Asian forests were more resilient to climate change in the late glaciation than previously thought.
- This differs from the theory that savanna corridors extended across Southeast Asia during the peak of the late glaciation.
- Sundaland, a vast lowland land connecting what is now mainland Southeast Asia with the islands of Kalimantan, Sumatra, Bali, during the last glacial period was an important forest area for biodiversity and genetics.
- In addition to ecological implications, these findings provide theoretical insight into how the history of human migration shaped the region's ecosystem
A new paleoecological study notes that forest environments in Southeast Asia dating back 119,000 years were more resilient to climate change than researchers initially predicted, as long as ecosystem diversity remained intact.
This differs from the original theory that Southeast Asia's lowland forests suddenly turned into vast savanna corridors in response to a cold and seasonal climate during the peak of the last ice age, a period about 20,000 years ago.
Instead of a sudden change from forest to grassy savanna, researchers documented a smooth transition between lowland rainforest, seasonally dry forest and open canopy grassy low vegetation, with tropical montane forest.
This mosaic of forest types shows that Southeast Asian ecosystems have the capacity to “resist and recover” from climate stress, the study explains.
These findings also support conservation efforts by conservation activists to preserve various types of forests in connected networks throughout Southeast Asia.
“Preserving forest types that support resilience [to climate change] should be a priority,” Rebecca Hamilton, a paleoecologist at the University of Sydney and lead author of the new study, told Mongabay.
“Seasonally dry forests, for example, are often overlooked. Although these forests do not appear to be as important in terms of biodiversity compared to tropical rainforests, they do have reserves of [beta] diversity at the landscape level.”
Southeast Asian forests have come under heavy pressure due to human activities in recent decades. The felling of large areas of lowland rainforest is paving the way for urban expansion, agriculture, palm oil and rubber plantations at an alarming rate of forest encroachment .
In investigating the ancient landscape of Southeast Asian forests, Hamilton and his colleagues used detective-like methods. They looked at biochemical data on pollen grain fossils from 59 paleoecological sites across the region, to find out which tree species grew at which time.
The late glaciation period investigated in this study was chosen to determine extreme seasonality, where the data is used to determine whether the natural landscape at that time was dominated by forests or savanna grasslands.
Climate changes in this period will also reveal seasonal patterns in the rainy season and dry season in Southeast Asia, which trigger extreme rainfall and drought, as well as to find out how the ecosystem responds to these conditions.
Hamilton said the results of this research indicate that forests in Southeast Asia may respond to large-scale disturbances in a different way compared to what is observed in other regions of the world.
Forest biologists in South America, for example, document ecosystem “tipping points” triggered by major disturbances, such as El Niño forest fires and massive land clearing for agriculture.
But such tipping points are less clear in Southeast Asia. Forests in this area tend to be "stepping stones" in the form of seasonal dry forests, which are located between rainforest and grassland ecosystems.
“In Southeast Asia, we don't see a sudden shift to savanna. "We're just seeing a gradual shift towards more open forest types," Hamilton explained.
However, this does not mean that forests in Asia are immune to detrimental regime changes. Human activities continue to damage the resilience of forests in this area.
“[This] has the potential to be catastrophic for the survival of rainforests throughout the tropical zone,” Hamilton said.
“We often see forest fragmentation due to human fires that are quite destructive and can cause sudden transitions from forest to savanna like many areas of the Americas.”
However, another interesting fact is that humans have been shaping the world's forests for thousands of years.
Previous studies have shown, for example, that shifting cultivation systems have maintained the structural diversity of forests in several regions of mainland Southeast Asia. This could help explain theories about how humans and animals moved in Southeast Asia during the last glacial period.
“Some schools of thought argue that savanna environments facilitate human migration, in this view tropical forests are considered completely inhospitable to humans,” Hamilton said.
“We now know that people utilized and managed tropical forests and had migrated through at least some forest systems to reach Australia [from Asia]. This shows that we as a species have historically used resources from a variety of ecosystems.”
Hamilton said the results of this research indicate that forests in Southeast Asia may respond to large-scale disturbances in a different way compared to what is observed in other regions of the world.
Forest biologists in South America, for example, document ecosystem “tipping points” triggered by major disturbances, such as El Niño forest fires and massive land clearing for agriculture.
But such tipping points are less clear in Southeast Asia. Forests in this area tend to be "stepping stones" in the form of seasonal dry forests, which are located between rainforest and grassland ecosystems.
“In Southeast Asia, we don't see a sudden shift to savanna. "We're just seeing a gradual shift towards more open forest types," Hamilton explained.
However, this does not mean that forests in Asia are immune to detrimental regime changes. Human activities continue to damage the resilience of forests in this area.
“[This] has the potential to be catastrophic for the survival of rainforests throughout the tropical zone,” Hamilton said.
“We often see forest fragmentation due to human fires that are quite destructive and can cause sudden transitions from forest to savanna like many areas of the Americas.”
However, another interesting fact is that humans have been shaping the world's forests for thousands of years.
Previous studies have shown, for example, that shifting cultivation systems have maintained the structural diversity of forests in several regions of mainland Southeast Asia. This could help explain theories about how humans and animals moved in Southeast Asia during the last glacial period.
“Some schools of thought argue that savanna environments facilitate human migration, in this view tropical forests are considered completely inhospitable to humans,” Hamilton said.
“We now know that people utilized and managed tropical forests and had migrated through at least some forest systems to reach Australia [from Asia]. This shows that we as a species have historically used resources from a variety of ecosystems.”