Lianas affect forest carbon uptake differently by region, study shows

Lianas affect forest carbon uptake differently by region, study shows

  • A new study has revealed that vine-like lianas typically infest smaller trees in Southeast Asia, in sharp contrast to prior findings in the Neotropics.
  • Scientists have long known that lianas can impede tree growth, alter forest composition and structure, and reduce the amount of carbon stored in aboveground tree biomass.
  • The study suggests that lianas play different ecological roles in forests in different parts of the world, and therefore affect forest carbon sequestration in variable ways.
  • The study authors say that despite their negative effects on forest carbon, lianas are still essential components of natural ecosystems, and managers should apply a targeted, precautionary approach to cutting.

Viewed from above, tropical rainforests look like a blanket of trees, branches extending skyward and leaves fanning out in all directions. But in addition to the trees, up to 40% of the visible foliage can come from a separate group of plants: woody vines called lianas. Rooted in the soil, lianas use the architecture of trees as an energy-efficient way to wind their way up into the canopy, fiercely competing with trees for essential resources like water, nutrients and sunlight.

Scientists have long known that the presence of lianas can impede tree growth and diminish the carbon uptake and storage of tropical rainforests. Recent studies have also revealed that lianas thrive under the warmer, drier conditions wrought by climate change and within increasingly ubiquitous forest patches disturbed by human fragmentation and logging. As a result, the impact of lianas on the global carbon cycle is set to intensify as they grow in abundance around the world.

“Lianas store less carbon than trees, mainly because they have a more extensive leaf canopy and less woody tissue because they use the trees for support [rather] than putting a lot of carbon into their own supportive stems,” Catherine Waite, a research associate at the University of the Sunshine Coast, Australia, told Mongabay.

Lianas twisting through the forest canopy in Danum Valley, Malaysian Borneo. Photo courtesy of Catherine Waite

Waite is the lead author of a new study that indicates lianas might influence forest structure in fundamentally distinct ways in different parts of the world. The study, published in the Journal of Ecology, found that lianas typically infest smaller trees in Southeast Asia, in sharp contrast to prior findings in the Neotropics — Central America, the Caribbean and South America — that found that larger trees there tend to carry more lianas.

“This is important to the understanding of liana ecology in a global approach, as it shows that lianas may behave differently in forests with different vegetation structure,” said Nara Vogado, a researcher at James Cook University in Australia, who was not involved in the study. “The findings suggest that lianas [in the forests studied in Malaysia] do not limit carbon storage as much as they were found to do in the Neotropics. This is because bigger trees that will sequester the most carbon are the least affected.”

Waite, who carried out the research while she was a doctoral candidate at the University of Nottingham in the U.K., said it’s vital to study the effects of lianas on Southeast Asia’s forests because they are home to some of the world’s largest tree species that act as globally significant stores of aboveground biomass. The presence in Malaysia of very tall Dipterocarp trees, named for their two-winged seeds and which can grow taller than 90 meters (295 feet), could explain why lianas are more often found clinging to shorter trees, she said.

“As they grow, Dipterocarps tend to shed branches,” Waite told Mongabay, “so lianas might not be able to reach their canopy as there are [fewer] branches to hook over. We found that emergent Dipterocarps tended to have very [few] lianas in their crown.”

Researchers with drones
The research team used drones to create three-dimensional models of the forest canopy. Photo courtesy of Catherine Waite

Waite and her colleagues used drones fitted with airborne laser scanners to investigate the inaccessible forest canopy and also made observations from the ground in a 50-hectare (124-acre) patch of forest in the Danum Valley in Malaysian Borneo. The three-dimensional models they created are a new way of studying lianas in Southeast Asia’s forests, which could prove an effective method for forest managers to monitor changes in liana abundance.

The team’s models showed that lianas tend to be found more often on smaller trees and closer to canopy gaps where trees have been cleared or fallen naturally. The researchers note that if lianas prevent smaller trees from growing to their full potential at a landscape scale, it could have ramifications for global climate change mitigation.

With forest managers looking to maximize carbon storage in forests around the world, monitoring liana abundance and cutting them back is an increasingly common practice. To find out more about suitable liana management strategies, Waite is now following up on how lianas impact forest recovery by constructing models of “tipping points” to investigate the point at which lianas switch from being beneficial components of the forest ecosystem to being a hindrance to healthy tree regeneration.

Orangutan
Lianas provide important habitat for forest fauna and flora, including aerial walkways for primates like this orangutan and other mammals. Photo by Rhett A. Butler for Mongabay

Mason Campbell, a research fellow at James Cook University, who was not involved in the study, said it’s important to remember that lianas are not all bad. They’re a natural component of tropical rainforests that contribute to biodiversity and play an important role by providing resources and habitat for other forest organisms.

A study in 2017, for instance, found that the complexity of bird communities increases in line with the number of lianas found in forest canopies. Besides providing habitat for birds, lianas also provide arboreal corridors for other animals, and fruiting lianas like rattans are vitally important food sources for primates.

“The main problem [contributing to increasing dominance of lianas] is the alteration of tropical forests [by humans,] resulting in smaller patches of often highly disturbed forest and a loss of the natural balance that existed,” Campbell said, “which is a long way of saying the best thing we can do is to stop the destruction of tropical rainforests.”

Waite echoed Campbell’s sentiment, noting that despite their negative effects on forest carbon, lianas are still essential components of natural ecosystems, and managers should apply a targeted, precautionary approach to cutting. In some cases, they can actually enhance conditions for tree growth, she said, by boosting forest humidity and protecting young trees from being damaged in fires, or eaten or trampled by animals.

“Lianas are both good and bad,” Waite said, “but I’m not sure that we know enough yet to really be able to speak clearly on how many is too many, especially in all the different types of forest around the world.”

Danum Valley sunrise
Sunrise over the Danum Valley, Malaysian Borneo. Photo courtesy of Catherine Waite

Banner image: A liana winding up through the forest canopy in Sabah, Malaysian Borneo. Photo by Rhett A. Butler for Mongabay

Citations:

Waite, C. E., van der Heijden, G. M. F., Field, R., Burslem, D. F. R. P., Dalling, J. W., Nilus, R., … Boyd, D. S. (2022). Landscape-scale drivers of liana load across a Southeast Asian forest canopy differ to the Neotropics. Journal of Ecology. doi:10.1111/1365-2745.14015

Vogado, N. O., Engert, J. E., Linde, T. L., Campbell, M. J., Laurance, W. F., & Liddell, M. J. (2022). Climate change affects reproductive phenology in lianas of Australia’s wet tropics. Frontiers in Forests and Global Change, 5. doi:10.3389/ffgc.2022.787950

Campbell, M. J., Edwards, W., Magrach, A., Alamgir, M., Porolak, G., Mohandass, D., & Laurance, W. F. (2018). Edge disturbance drives liana abundance increase and alteration of liana-host tree interactions in tropical forest fragments. Ecology and Evolution, 8(8), 4237-4251. doi:10.1002/ece3.3959

Hilje, B., Stack, S., & Sánchez-Azofeifa, A. (2017). Lianas abundance is positively related with the avian acoustic community in tropical dry forests. Forests, 8(9), 311. doi:10.3390/f8090311

Carolyn Cowan is a staff writer for Mongabay. Follow her on Twitter @CarolynCowan11

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