Lianas Significantly Reduce Aboveground and Belowground Carbon Storage: A Virtual Removal Experiment

Abstract

Lianas are structural parasites of trees that cause a reduction in tree growth and an increase in tree mortality. Thereby, lianas negatively impact forest carbon storage as evidenced by liana removal experiments. In this proof-of-concept study, we calibrated the Ecosystem Demography model (ED2) using 3 years of observations of net aboveground biomass (AGB) changes in control and removal plots of a liana removal experiment on Gigante Peninsula, Panama. After calibration, the model could accurately reproduce the observations of net biomass changes, the discrepancies between treatments, as well as the observed components of those changes (mortality, productivity, and growth). Simulations revealed that the long-term total (i.e., above- and belowground) carbon storage was enhanced in liana removal plots (+1.2 kgC m–2 after 3 years, +1.8 kgC m–2 after 10 years, as compared to the control plots). This difference was driven by a sharp increase in biomass of early successional trees and the slow decomposition of liana woody tissues in the removal plots. Moreover, liana removal significantly reduced the simulated heterotrophic respiration (−24%), which resulted in an average increase in net ecosystem productivity (NEP) from 0.009 to 0.075 kgC m–2 yr–1 for 10 years after liana removal. Based on the ED2 model outputs, lianas reduced gross and net primary productivity of trees by 40% and 53%, respectively, mainly through competition for light. Finally, model simulations suggested a profound impact of the liana removal on the soil carbon dynamics: the simulated metabolic litter carbon pool was systematically larger in control plots (+51% on average) as a result of higher mortality rates and faster leaf and root turnover rates. By overcoming the challenge of including lianas and depicting their effect on forest ecosystems, the calibrated version of the liana plant functional type (PFT) as incorporated in ED2 can predict the impact of liana removal at large-scale and its potential effect on long-term ecosystem carbon storage.

Removing climbers more than doubles tree growth and biomass in degraded tropical forests

“…Climbing plants tend to proliferate extensively after disturbance and compete strongly with trees for light, water, and other resources, limiting tree growth, survival, recruitment, and aboveground biomass sequestration (Meunier, van der Heijden, et al, 2021;Schnitzer & Bongers, 2002).…”

“…Climbing plants tend to proliferate extensively after disturbance and compete strongly with trees for light, water, and other resources, limiting tree growth, survival, recruitment, and aboveground biomass sequestration (Meunier, van der Heijden, et al, 2021 ; Meunier, Verbeeck, et al, 2021 ; Schnitzer & Bongers, 2002 ). Estrada‐Villegas and Schnitzer ( 2018 ) conclude that lianas have a negative impact on all metrics of tree performance, and it has been estimated that removing climbers in tropical forests enhances tree growth up to 372%, timber yield by 1.51 m 3 per tree over 40 years, and aboveground biomass by ~76% per year compared to untreated forest (Estrada‐Villegas & Schnitzer, 2018 ; Mills et al, 2019 ; van der Heijden et al, 2015 ).…”

Effects of lianas on forest biogeochemistry during their lives and afterlives

“…Current earth system models (ESM) rely on dynamic global vegetation models (DGVMs) that represent forests by a small number of plant functional types (PFT). Some models already incorporate a liana PFT (Meunier, van der Heijden, et al., 2021), and they have been used to investigate the potential impacts of future climate change on liana‐tree competition (Willson et al., 2022). This study highlights the role of the differences in hydraulic traits between the life forms and showed the importance of including a liana PFT in vegetation components of future ESMs, and thus the need for improved parametrization of living liana traits.…”

Reducing uncertainty of high-latitude ecosystem models through identification of key parameters

“…Through motifs, we can identify processes that become reinforced or act reinforcing and are thus more likely to cause substantial Table 1. Overview of the elements modeled in the three terrestrial biosphere models [56,57]. While TEM has two main carbon pools (soil and vegetation), they are further subdivided into leaf, wood, and root vegetation carbon, and chemically resistant soil carbon, physically resistant soil carbon, active soil carbon and coarse plant material for each soil layer, and a coarse woody debris carbon pool [58].…”