‘Lianas threaten Earth’s carbon sinks’

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As the world grapples with rising temperatures, a groundbreaking study led by the University of the Sunshine Coast, Australia exposes an unlikely menace: Lianas. These woody vining plants, thriving in disturbed forest areas, harm the very trees they climb upon. 

The study unveiled that as lianas compete for sunlight in the canopy, they suppress trees. Their lower carbon sequestering capacity compared to trees further exacerbates the threat to carbon storage. Lead author Alain Ngute warned that this takeover could worsen global warming by compromising forests’ effectiveness as carbon sinks and altering carbon cycles.

“Liana dominance can indeed have implications for carbon sequestration. Trees are major carbon sinks, absorbing significant amounts of carbon dioxide from the atmosphere. Lianas store less carbon than trees. As lianas out-compete trees worldwide, global forest capacity to sequester carbon diminishes,  potentially exacerbating global warming by reducing the effectiveness of forests as carbon sinks and altering global carbon cycles,” said lead author, Alain Ngute, in an exclusive interview with Down To Earth.

Alain Ngute, originally from Cameroon, is a passionate field ecologist specialising in tropical forest ecosystems, species responses to environmental change and climate change impacts and adaptation of mountain socio-ecological systems. His recent PhD focused on the role lianas play in the recovery of tropical forests from disturbance. 

Alain’s work, so far, has been recognised by several grants and awards, reflecting his passion for integrating traditional knowledge with modern conservation practices to address environmental challenges.

In the following interview, Ngute explains the findings of the study and what it means for the fight against climate change.

Edited excerpts: 

Ngala Killian Chimtom: The major outcome of the study is that lianas tend to win the battle for canopy. What drives this lianas dominance over trees and how?

Alain Ngute: The dominance (competitive success) of lianas over trees is driven by a combination of forest disturbance, climate and topography. Lianas perform better relative to trees when forests are disturbed, under warmer temperatures and lower precipitation, and towards the tropical lowlands. Forests recovering from disturbances like deforestation initially lack the structural support essential for liana growth, which can lead to a positive feedback loop favouring liana proliferation. 

Lianas particularly thrive in disturbed forest areas — such as those affected by logging, natural treefalls, landslides, among others — because they can quickly grow towards the forest canopy using trees as support. In terms of climate, lianas are more resilient to variations in moisture and temperature, which gives them a competitive advantage over trees, especially in climates experiencing more extreme conditions due to global warming. 

Furthermore, the topography of an area can influence sunlight availability and soil moisture levels, both of which can further favour lianas over trees. Essentially, lianas use their climbing ability, resilience to climatic stress, and efficient water and nutrient usage to outcompete trees for sunlight and resources.

NKC: How does this dominance affect the forest ecosystem?

AN: An increase in lianas’s competitive success over trees can significantly affect the forest ecosystem. Lianas, being a disturbance-favouring plant form, can impact trees from the understory to the canopy. Their prolific growth following heavy disturbance can lead to decreased tree regeneration, growth and survival, altering forest structure and ecosystem function, which, in turn, can affect the subsequent recovery of forest. 

Additionally, liana proliferation can alter nutrient cycling within forests and decrease the overall resilience of forests to environmental changes, making ecosystems more susceptible to further disturbances.

NKC: Could there be implications of this dominance for carbon sequestration and if yes, how would this affect the global fight against global warming?

AN: Liana dominance can indeed have implications for carbon sequestration. Trees are major carbon sinks, absorbing significant amounts of carbon dioxide from the atmosphere. Lianas store less carbon than trees. As lianas outcompete trees worldwide, global forest capacity to sequester carbon diminishes, potentially exacerbating global warming by reducing the effectiveness of forests as carbon sinks and altering global carbon cycles. 

Liana competition with trees also threatens the global carbon sink by slowing the recovery of forests following disturbance. This is because forests with abundant lianas have slower rates of tree growth, and, hence, also slower forest recovery following disturbance, compared to those with fewer lianas. This could potentially affect the global fight against global warming, as slower forest recovery could mean less carbon being sequestered by the forest.

NKC: Should lianas be eliminated from forests?

AN: No, not at all. We should not aim to eliminate lianas from forests. We should rather aim to maintain a balance between lianas and trees that allows for both forest recovery and biodiversity conservation. It should entail keeping them below a certain threshold to allow faster tree regeneration.

NKC: What would the results of this study mean for forest managers and people involved in forest conservation?

AN: First of all, these findings are critical for successfully restoring the world’s forests, and gives forest managers and conservation agencies direction on where to concentrate their restoration efforts.

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 prioritised by forest managers.