Modeling the impact of liana infestation on the demography and carbon cycle of tropical forests

Abstract

There is mounting empirical evidence that lianas affect the carbon cycle of tropical forests. However, no single vegetation model takes into account this growth form, although such efforts could greatly improve the predictions of carbon dynamics in tropical forests. In this study, we incorporated a novel mechanistic representation of lianas in a dynamic global vegetation model (the Ecosystem Demography Model). We developed a liana‐specific plant functional type and mechanisms representing liana–tree interactions (such as light competition, liana‐specific allometries, and attachment to host trees) and parameterized them according to a comprehensive literature meta‐analysis. We tested the model for an old‐growth forest (Paracou, French Guiana) and a secondary forest (Gigante Peninsula, Panama). The resulting model simulations captured many features of the two forests characterized by different levels of liana infestation as revealed by a systematic comparison of the model outputs with empirical data, including local census data from forest inventories, eddy flux tower data, and terrestrial laser scanner‐derived forest vertical structure. The inclusion of lianas in the simulations reduced the secondary forest net productivity by up to 0.46 tC ha−1 year−1, which corresponds to a limited relative reduction of 2.6% in comparison with a reference simulation without lianas. However, this resulted in significantly reduced accumulated above‐ground biomass after 70 years of regrowth by up to 20 tC/ha (19% of the reference simulation). Ultimately, the simulated negative impact of lianas on the total biomass was almost completely cancelled out when the forest reached an old‐growth successional stage. Our findings suggest that lianas negatively influence the forest potential carbon sink strength, especially for young, disturbed, liana‐rich sites. In light of the critical role that lianas play in the profound changes currently experienced by tropical forests, this new model provides a robust numerical tool to forecast the impact of lianas on tropical forest carbon sinks.

Pervasive shifts in forest dynamics in a changing world

“…However, shifts in frequency or dampening of disturbance regimes could also emerge (110), leading to some uncertainty in outbreak dynamics under future conditions ( Figure 4M). While insects and associated pathogens are globally widespread, lianas, or vines that use other plants as host structures, are increasing in abundance and are thought to be causing increasing mortality in the tropics (7,111).…”

Conceptualising the Global Forest Response to Liana Proliferation

“…Potential for parameterising DVMs to include lianas is improving with emerging inventory data and model accuracy, the two principal challenges for modelling resilience (Purves and Pacala, 2008;Andersen et al, 2009;Scheffer et al, 2009), alongside growing knowledge regarding drivers and liana water use (McDowell et al, 2018). Recent data advances led to reparameterization of a global DVM for two neotropical forests, showing that lianas significantly affect carbon sink strength in secondary forest, while accounting for physiology, biochemistry, structure and functional diversity (di Porcia e Brugnera et al, 2019). With data from more sites in secondary forests, subsequent dynamic model extensions could then identify variation in forest recovery potential (and response classes) vs. drivers, liana dominance, management and climate change scenarios, and hence also vs. parasitoid or bandage effects of different liana species, growth forms, or communities.…”

The biophysics, ecology, and biogeochemistry of functionally diverse, vertically and horizontally heterogeneous ecosystems: the Ecosystem Demography model, version 2.2 – Part 1: Model description

“…These models, however, did not account for the active role of vegetation. The second generation of LSMs considered the active role of vegetation and represented the spectral properties of the canopy, the changes in roughness of vegetated surfaces, and the biophysical controls on evaporation and transpiration (Sellers et al, 1997); examples of these models include National Center for Atmospheric Research Biosphere-Atmosphere Transfer Scheme (NCAR/BATS) (Dickinson et al, 1986) and Simple Biosphere model (SiB) (Sellers et al, 1986). The increasing recognition of the role of vegetation in mediating the exchanges of carbon, water, and energy between the land and the atmosphere led to the third generation of LSMs, which incorporated explicit representations of plant photosynthesis and resulting dynamics of terrestrial carbon uptake, turnover, and release within terrestrial ecosystems (Sellers et al, 1997); examples of such models included LSM (Bonan, 1995) and SiB2 (Sellers et al, 1996).…”