Modeling the long-term dynamics of tropical forests: from leaf traits to whole-tree growth patterns

Abstract

21Tropical forests are the most diverse terrestrial ecosystems and home to numerous tree species 22 with diverse ecological strategies competing for resources in space and time. Functional traits 23 influence the ecophysiological performance of tree species, yet the relationship between traits 24 and emergent long-term growth pattern is poorly understood. Here, we present a novel 3D forest 25 stand model in which growth patterns of individual trees and forest stands are emergent 26 properties of leaf traits. Individual trees are simulated as 3D functional-structural tree models 27 (FSTMs), considering branches up to the second order and leaf dynamics at a resolution of one 28 m 3 . Each species is characterized by a set of leaf traits that corresponds to a specific position on 29 the leaf economic spectrum and determines light-driven carbon assimilation, respiration and 30 mortality rates. Applying principles of the pipe model theory, these leaf scale-processes are 31 coupled with within-tree carbon allocation, i.e., 3D tree growth emerges from low-level 32 processes. By integrating these FSTMs into a dynamic forest stand model, we go beyond modern 33 stand models to integrate structurally-detailed internal physiological processes with interspecific 34 competition, and interactions with the environment in diverse tree communities. For model 35 calibration and validation, we simultaneously compared a large number of emergent patterns at 36 both the tree and forest levels in a pattern-oriented modeling framework. At the tree level, 37 varying specific leaf area and correlated leaf traits determined the maximum height and age of a 38 tree, as well as its size-dependent growth rate and shade tolerance. Trait variations along the leaf 39 economic spectrum led to a continuous transition from fast-growing, short-lived and shade-40 intolerant to slow-growing, long-lived and shade-tolerant trees. These emerging patterns 41 resembled well-known functional tree types, indicating a fundamental impact of leaf traits on 42 long-term growth patterns. At the forest level, a large number of patterns taken from lowland Neotropical forests were reproduced, indicating that our forest model simulates structurally 44 realistic forests over long time spans. Our ecophysiological approach improves the understanding 45 of how leaf level processes scale up to the tree and the stand level, and facilitates the 46 development of next-generation forest models for species-rich forests in which tree performance 47 emerges directly from functional traits. 48 49 Key words: 3D forest stand model, functional-structural tree model, agent-based model, 50 individual-based model, leaf economic spectrum, leaf traits, canopy structure, canopy dynamics, 51 tropical forest, physiological processes, pipe model theory, tree architecture 52 53 54 Tropical forests provide multiple social, ecological and economical services, represent the most 55 diverse terrestrial ecosystem, and play an important role in the global carbon cycle (Heywood 56 an...

Agent‐based modeling of the effects of forest dynamics, selective logging, and fragment size on epiphyte communities

“…Another source of uncertainty is related to the forest input data. Although the forest model has been calibrated extensively (Petter et al., 2020), we expect that ongoing development in terrestrial and airborne laser scanning technologies will further improve the calibration of structural forest models. Repeated LiDAR data of canopy substrate could also be directly used as forest input.…”

“…Such data could be obtained from ground or airborne LiDAR scans or from statistical and process‐based models. Here, we used a previously developed three‐dimensional functional–structural forest model that realistically reproduced the structure and long‐term dynamics of tropical forests as data source (Petter et al., 2020; Appendix ).…”

“…F I G U R E 1 Flowchart of the coupled forest-epiphyte model. Based on dynamic three-dimensional input data from a functional-structural forest model (Petter et al, 2020), a microhabitat matrix characterizing the epiphytic habitat at each time step is generated. To this end, the simulated spatial distribution of leaf area, branches, and trunks for each annual time step (left panel) is used to calculate the light distribution, total substrate area and relative annual change of substrate area for each 1 m 3 -voxel in the microhabitat matrix (middle panel), which ultimately influences the initialization and all three submodels of the epiphyte model (right panel) & , and it has only one parameter which can be derived from three species-specific traits (see Appendix S2 for equations).…”