Unraveling the Mechanisms of Below- and Aboveground Liana-Tree Competition in Tropical Forests

Authors

David Medvigy¹ (dmedvigy@nd.edu), Jennifer Powers²*, Peter Tiffin², Jérôme Chave³, Isabelle Maréchaux⁴, Alejandra Perez-Enriquez², Ariadna Mondragon², Laura Jessup²

Institutions

¹University of Notre Dame, Notre Dame, IN; ²University of Minnesota–Twin Cities, Minneapolis/St. Paul, MN; ³Le Centre National de la Recherche Scientifique, Toulouse, France; ⁴Institut National de la Recherche Agronomique, Montpellier, France

Abstract

Trees and lianas dominate the canopy of tropical forests and comprise the majority of tropical aboveground carbon storage. These growth forms respond differently to variation in climate and resource availability, and their responses to future climate change are poorly understood. The overarching objectives of this project are to carry out an observational campaign to advance the understanding of liana traits and strategies, develop a liana-enabled forest dynamics model that leverages the observations, and to engage with the Earth System Modeling (ESM) community to plan for the eventual inclusion of lianas into ESMs. Here, researchers report on four activities, which have brought researchers closer to meeting these objectives. (1) Researchers have measured liana traits and conducted meta-analysis of liana trait data. On average, researchers find marked differences between lianas and trees in terms of their hydraulic traits and xylem anatomical traits. They also identified significant variation in hydraulic traits across liana species. (2) Researchers incorporated these results into a mechanistic but simple model of liana-tree couplet and subjected the model to different tropical hydroclimate scenarios. Due to differences in hydraulic conductivity, the model indicated that lianas are much more susceptible than trees to reaching a hydraulic threshold for viability by 2100. (3) Researchers measured tree growth and liana colonization status of over 1,700 trees at a study site in Guanacaste, Costa Rica. They found that the number of colonized trees is increasing and that heavily infested trees have lower relative growth rates that other trees. Liana colonization also impacted the relationship between tree growth and rainfall. (4) Researchers incorporated lianas into the TROLL forest dynamics model and developed new schemes for leaf production and turnover. TROLL represents the three-dimensional canopies of trees and lianas, discretized into 1 m³ voxels. Thus, for a given host tree canopy, the scheme specifies where it is that lianas prefer to grow new leaves. Researchers have carried out a sensitivity analysis and tested the model’s ability to simulate observed patterns. (5) Researchers have implemented liana-enabled forest dynamics in TROLL. These dynamics include the ability of lianas to colonize an arbitrary number of trees in its neighborhood and the ability of trees to shed lianas.