Advanced search
1 file | 10.81 MB Add to list

The role of lianas for the structure and function of tropical rainforests of the Congo basin

(2021)
Author
Promoter
Hans Verbeeck, Marijn Bauters and Constantin Lubini Ayingweu
Organization
Project
  • TREECLIMBERS (Modelling lianas as key drivers of tropical forest responses to climate change)
Abstract
Tropical forests constitute an important terrestrial biome, playing a vital role for the global carbon cycle and providing human population with valuable goods and services. Within this biome, many plant life forms coexist, including trees, shrubs, herbs, epiphytes, and lianas. Compared to trees, lianas have traditionally received less attention in ecological research. In recent years, however, there has been an increasing interest on the probable role of lianas in forest functioning. The general focus of these studies is to understand the mechanisms of liana diversity, distribution and coexistence with other life forms, but also to elucidate the effects of lianas on ecosystem processes and biodiversity. However, most of these studies on lianas have been conducted in the Neotropics. In Africa, which encompasses the second largest block of tropical forest, baseline field data on the ecology of lianas are cruelly lacking for many regions. Consequently, a comprehensive comparative analyses of liana research between tropical regions is hampered by the limited number and geographic range of the studies. In this thesis, I describe liana communities and analyzed a number of structural/functional characteristics of lianas, in most cases comparative to trees, along different environmental gradients in the tropical forest in central Congo basin. I mainly focus on structural and functional shifts in lianas along different forest gradients, including productivity (forest types), successional, and elevational gradients. As far as species diversity and distribution are concerned, I found that liana diversity was higher in old-growth edge forests, but lower in secondary forests than in mixed old-growth forests. This suggests that a moderate level of disturbance in tropical forests of the central Congo basin can increase and facilitate liana diversity, particularly in forests edges. However, the expansion of forest fragmentation due to agriculture activities may hinder the recovery pathways of tropical forest in the central Congo basin with a potential loss of liana diversity. I further demonstrated a progressive colonization of tropical forests by lianas after agricultural abandonment with a peak density at the intermediate successional stage. I also found low liana diversity, but high liana density in the monodominant old-growth forest, suggesting that closed canopy forests in the central Congo basin can also harbor a high number of lianas, and this high density of lianas might be driven by other abiotic and biotic factors than disturbance. In terms of functional strategies, I demonstrated the flexibility of liana functional strategies along a secondary succession, allowing liana species to coexist with tree species. The responses of lianas and trees to changes with succession converged in terms of specific leaf area (SLA) and leaf nitrogen content (LNC), but diverged in terms of leaf phosphorus content (LPC). These patterns in functional composition most probably resulted from environmental filtering, induced by a change from nitrogen to phosphorus limitation as the succession progressed to a mature forest. I further showed that lianas operate at relatively constant intrinsic water- and nitrogen- use efficiencies along an elevational gradient as opposed to trees, suggesting the existence of a functional divergence of water and nutrient use strategies between lianas and trees along elevation. This finding shows that lianas appear to be less impacted than trees by the increasing level of drought stress, and nutrient limitation with increasing elevation. On the effect of lianas on trees, I found a negative association between the presence of lianas on trees and the tree diameter increment in the old-mixed forest, suggesting a potential negative effect of lianas on tree growth. I further showed that larger tree individuals and slow-growing tree species harbored relatively more lianas in both the old-growth mixed forest and the monodominant old-growth forest in the central Congo Basin. This finding suggests that the exposure time could be an important driver of liana infestation, and that slow-growing tree species are more prone to liana infestation. However, I also found that the colonization and level of infestation of trees by lianas were not associated with tree leaf functional traits. This may imply that the negative effect of lianas on trees in the central Congo basin might not vary with tree functional identities, but mainly with tree structural attributes. Altogether, these findings provide new insights that can advance our understanding of mechanisms that control the abundance and distribution of lianas as well as liana and tree coexistence in the central Congo basin, an area of the tropics that has been understudied. Furthermore, the collected data on liana structural attributes and functional traits that can serve as basis to parametrize vegetation models capable of predicting the impact of lianas on the future of the Congo Basin carbon balance.
Keywords
Congo basin, ecosystem functioning, Functional traits, liana community assemblage, Nyungwe, Structural attributes, Tropical rain forest, Yangambi, Yoko

Downloads

  • Mumbanza Mundondo PhD Thesis Final Biblio.pdf
    • full text
    • |
    • open access
    • |
    • PDF
    • |
    • 10.81 MB

Citation

Please use this url to cite or link to this publication:

MLA
Mumbanza Mundondo, Francis. The Role of Lianas for the Structure and Function of Tropical Rainforests of the Congo Basin. 2021.
APA
Mumbanza Mundondo, F. (2021). The role of lianas for the structure and function of tropical rainforests of the Congo basin. Ghent.
Chicago author-date
Mumbanza Mundondo, Francis. 2021. “The Role of Lianas for the Structure and Function of Tropical Rainforests of the Congo Basin.” Ghent.
Chicago author-date (all authors)
Mumbanza Mundondo, Francis. 2021. “The Role of Lianas for the Structure and Function of Tropical Rainforests of the Congo Basin.” Ghent.
Vancouver
1.
Mumbanza Mundondo F. The role of lianas for the structure and function of tropical rainforests of the Congo basin. [Ghent]; 2021.
IEEE
[1]
F. Mumbanza Mundondo, “The role of lianas for the structure and function of tropical rainforests of the Congo basin,” Ghent, 2021.
@phdthesis{8716180,
  abstract     = {{Tropical forests constitute an important terrestrial biome, playing a vital role for the global carbon cycle and providing human population with valuable goods and services. Within this biome, many plant life forms coexist, including trees, shrubs, herbs, epiphytes, and lianas. Compared to trees, lianas have traditionally received less attention in ecological research. In recent years, however, there has been an increasing interest on the probable role of lianas in forest functioning. The general focus of these studies is to understand the mechanisms of liana diversity, distribution and coexistence with other life forms, but also to elucidate the effects of lianas on ecosystem processes and biodiversity. However, most of these studies on lianas have been conducted in the Neotropics.  In Africa, which encompasses the second largest block of tropical forest, baseline field data on the ecology of lianas are cruelly lacking for many regions. Consequently, a comprehensive comparative analyses of liana research between tropical regions is hampered by the limited number and geographic range of the studies. In this thesis, I describe liana communities and analyzed a number of structural/functional characteristics of lianas, in most cases comparative to trees, along different environmental gradients in the tropical forest in central Congo basin. I mainly focus on structural and functional shifts in lianas along different forest gradients, including productivity (forest types), successional, and elevational gradients.   
As far as species diversity and distribution are concerned, I found that liana diversity was higher in old-growth edge forests, but lower in secondary forests than in mixed old-growth forests. This suggests that a moderate level of disturbance in tropical forests of the central Congo basin can increase and facilitate liana diversity, particularly in forests edges. However, the expansion of forest fragmentation due to agriculture activities may hinder the recovery pathways of tropical forest in the central Congo basin with a potential loss of liana diversity. I further demonstrated a progressive colonization of tropical forests by lianas after agricultural abandonment with a peak density at the intermediate successional stage. I also found low liana diversity, but high liana density in the monodominant old-growth forest, suggesting that closed canopy forests in the central Congo basin can also harbor a high number of lianas, and this high density of lianas might be driven by other abiotic and biotic factors than disturbance. 
In terms of functional strategies, I demonstrated the flexibility of liana functional strategies along a secondary succession, allowing liana species to coexist with tree species. The responses of lianas and trees to changes with succession converged in terms of specific leaf area (SLA) and leaf nitrogen content (LNC), but diverged in terms of leaf phosphorus content (LPC). These patterns in functional composition most probably resulted from environmental filtering, induced by a change from nitrogen to phosphorus limitation as the succession progressed to a mature forest. I further showed that lianas operate at relatively constant intrinsic water- and nitrogen- use efficiencies along an elevational gradient as opposed to trees, suggesting the existence of a functional divergence of water and nutrient use strategies between lianas and trees along elevation. This finding shows that lianas appear to be less impacted than trees by the increasing level of drought stress, and nutrient limitation with increasing elevation. 
On the effect of lianas on trees, I found a negative association between the presence of lianas on trees and the tree diameter increment in the old-mixed forest, suggesting a potential negative effect of lianas on tree growth. I further showed that larger tree individuals and slow-growing tree species harbored relatively more lianas in both the old-growth mixed forest and the monodominant old-growth forest in the central Congo Basin. This finding suggests that the exposure time could be an important driver of liana infestation, and that slow-growing tree species are more prone to liana infestation. However, I also found that the colonization and level of infestation of trees by lianas were not associated with tree leaf functional traits. This may imply that the negative effect of lianas on trees in the central Congo basin might not vary with tree functional identities, but mainly with tree structural attributes. 
Altogether, these findings provide new insights that can advance our understanding of mechanisms that control the abundance and distribution of lianas as well as liana and tree coexistence in the central Congo basin, an area of the tropics that has been understudied. Furthermore, the collected data on liana structural attributes and functional traits that can serve as basis to parametrize vegetation models capable of predicting the impact of lianas on the future of the Congo Basin carbon balance.}},
  author       = {{Mumbanza Mundondo, Francis}},
  isbn         = {{978-9-4635742-3-5}},
  keywords     = {{Congo basin,ecosystem functioning,Functional traits,liana community assemblage,Nyungwe,Structural attributes,Tropical rain forest,Yangambi,Yoko}},
  language     = {{eng}},
  pages        = {{301}},
  school       = {{Ghent University}},
  title        = {{The role of lianas for the structure and function of tropical rainforests of the Congo basin}},
  year         = {{2021}},
}