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Conflict in the canopy as human and climate factors drive liana dominance over trees

  • Lianas, woody vines that rely on trees for structural support, are growing more abundant in tropical forests around the world, negatively impacting forest recovery and carbon sequestration.
  • A new study shows that forest disturbance and climate change give lianas a competitive edge over trees.
  • Understanding how climate change and disturbance influence liana growth can help forest managers develop management practices to aid recovering forests.

When a tree falls in the forest, lianas hear an opportunity. Figuratively, at least. These long-stemmed woody vines hitch a ride to the canopy by climbing up trees, rather than investing in their own structural support, i.e. a trunk. Evolving an impressive arsenal of adaptations, lianas compete aggressively with other plants for nutrients, water and sunlight — especially near gaps in the canopy. This botanical battle plays out in forests across the world, but it’s particularly prevalent in tropical forests, where lianas can comprise up to 25% of woody plant species.

Researchers have known for decades that woody vines are becoming more abundant, with negative impacts on tree growth and carbon sequestration. Now, a new study published in the journal Global Change Biology shows that forest disturbance and climate change are driving lianas’ dominance over trees in a way that could intensify harm to forest recovery and carbon drawdown.

“These changes could lead to a shift in the balance of competitive power between lianas and trees, altering forest structure, dynamics, and function, with negative consequences for forest biodiversity and carbon storage,” says study lead author Alain Ngute from the Forest Research Institute at Australia’s University of the Sunshine Coast.

Boosted by climate change and forest disturbance (like the treefall gap pictured above), lianas are becoming increasingly dominant in tropical forests around the world. Image by Logan Rance.

According to a growing body of research, lianas are getting too good at what they do. The new study analyzes data from more than 1,000 previous liana studies conducted all over the world, untangling some interesting trends: forest disturbance and rising heat are powerful predictors of lianas outcompeting trees. When forests lose trees (naturally or due to human activity), it opens up new space in the canopy. Opportunistic woody vines thrive in these disturbed areas, especially at lower elevations. The analysis also confirmed that lianas gain competitive advantages in forests with low precipitation, higher temperatures, and lengthy droughts — conditions already intensifying due to climate change and expected to worsen as the world continues to heat up.

2023 was the hottest year on record so far, and very likely the warmest year in at least 125,000 years. Climate change, coupled with more resource demands from a growing human population — including the deforestation and forest degradation associated with agriculture — are putting enormous pressure on Earth’s forests.

“Lianas can seriously depress forest biomass by limiting tree growth and survival,” says study co-author Bill Laurance of James Cook University in Australia. “They can shift forests toward hyper-disturbed states with reduced carbon storage, stunted structure, and altered ecological dynamics.”

Previous research shows that lianas can significantly reduce the amount of carbon stored in tropical forests by stifling the ability of trees to sequester CO2. This is especially important to consider for tropical forests, some of the most carbon-rich environments on Earth.

With a better understanding of what gives lianas their competitive edge, forest managers and conservation agencies may be able to implement better restoration strategies for recovering forests. However, this isn’t as simple as chopping away at every liana in sight.

According to Robyn Burnham, a professor of ecology and evolutionary biology at the University of Michigan in the U.S., lianas bring a host of benefits to local ecosystems.

“Some whole lineages of lianas (for example, the genus Passifloras) add tasty fruits for animals and have a strong pollination system that provides for insects,” Burnham, who studies lianas in the Amazon Basin but wasn’t involved in the new paper, told Mongabay by email. “So, they increase biodiversity with very little extra space needed.”

Understanding the conditions that allow lianas to dominate can help forest managers protect biodiversity and improve forest recovery. Image by Logan Rance.

Lianas bring plenty of good things to the table. They boost the biodiversity of insectivorous birds, and provide shelter for plants and animals. They even enhance soil fertility through the shedding and decomposition of their leaves.

“We should not aim to eliminate lianas from forests, but rather to maintain a balance between lianas and trees that allows for both forest recovery and biodiversity conservation,” Ngute says.

He adds that effective liana management may look like monitoring vine dominance and keeping them below a certain threshold to allow for faster tree regeneration. Forest managers may even include lianas in restorative plantings when certain species boost ecosystem functioning. Forests in regions vulnerable to liana dominance, like the Amazon, the Congo Basin, and the Borneo-Mekong Forest Basin, should also be prioritized by forest managers, Ngute says.

While there’s still plenty to learn about how to manage these increasingly abundant crafty vines, this new research can help inform conservationists and policymakers about the best ways to restore and protect the world’s forests.

“This work means a lot to me, as it addresses a global challenge that affects millions of people and ecosystems,” Ngute says. “I believe that understanding the role lianas play in forest dynamics is crucial for developing effective and sustainable forest restoration strategies.”

Banner image: : A large liana (Entada sp.) grows in the canopy of the Udzungwa forest in Tanzania. Image courtesy of Alain Ngute.

Correction (03/22/204): The previous banner image depicted epiphytes attached to a tree trunk and not lianas. The image has been replaced. We regret the error.


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