The climatic feedbacks from vegetation, particularly from tropical forests, can alter climate through land‐atmospheric interactions. Expected shifts in species composition can alter these interactions with profound effects on climate and terrestrial ecosystem dynamics. Ecosystem demographic (ED) models can explicitly represent vegetation dynamics and are a key component of next‐generation Earth System Models (ESMs). Although ED models exhibit greater fidelity and allow more direct comparisons with observations, their interacting parameters can be more difficult to calibrate due to the complex interactions among vegetation groups and physical processes. In addition, while representation of forest successional coexistence in ESMs is necessary to accurately capture forest‐climate interactions, few models can simulate forest coexistence and few studies have calibrated coexisted forest species. Furthermore, although both vegetation characteristics and soil properties affect vegetation dynamics, few studies have paid attention to jointly calibrating parameters related to these two processes. In this study, we develop a computationally‐efficient and physical model structure‐based framework that uses a parallel surrogate global optimization algorithm to calibrate ED models. We calibrate two typically coexisted tropical tree species, early and late successional plants, in a state‐of‐the‐art ED model that is capable of simulating successional diversity in forests. We concurrently calibrate vegetation and soil parameters and validate results against carbon, energy, and water cycle measurements collected in Barro Colorado Island, Panama. The framework can find optimal solutions within 4–12 iterations for 19‐dimensional problems. The calibration for tropical forests has important implications for predicting land‐atmospheric interactions and responses of tropical forests to environmental changes.
Tropical forests are a key determinant of the functioning of the Earth system, but remain a major source of uncertainty in carbon cycle models and climate change projections. In this study, we present an updated land model (LM3PPA‐TV) to improve the representation of tropical forest structure and dynamics in Earth system models (ESMs). The development and parameterization of LM3PPA‐TV drew on extensive datasets on tropical tree traits and long‐term field censuses from Barro Colorado Island (BCI), Panama. The model defines a new plant functional type (PFT) based on the characteristics of shade‐tolerant, tropical tree species, implements a new growth allocation scheme based on realistic tree allometries, incorporates hydraulic constraints on biomass accumulation, and features a new compartment for tree branches and branch fall dynamics. Simulation experiments reproduced observed diurnal and seasonal patterns in stand‐level carbon and water fluxes, as well as mean canopy and understory tree growth rates, tree size distributions, and stand‐level biomass on BCI. Simulations at multiple sites captured considerable variation in biomass and size structure across the tropical forest biome, including observed responses to precipitation and temperature. Model experiments suggested a major role of water limitation in controlling geographic variation forest biomass and structure. However, the failure to simulate tropical forests under extreme conditions and the systematic underestimation of forest biomass in Paleotropical locations highlighted the need to incorporate variation in hydraulic traits and multiple PFTs that capture the distinct floristic composition across tropical domains. The continued pressure on tropical forests from global change demands models which are able to simulate alternative successional pathways and their pace to recovery. LM3PPA‐TV provides a tool to investigate geographic variation in tropical forests and a benchmark to continue improving the representation of tropical forests dynamics and their carbon storage potential in ESMs.
more » « less- NSF-PAR ID:
- 10363436
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 26
- Issue:
- 8
- ISSN:
- 1354-1013
- Format(s):
- Medium: X Size: p. 4478-4494
- Size(s):
- p. 4478-4494
- Sponsoring Org:
- National Science Foundation
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Abstract Lightning is a major agent of disturbance, but its ecological effects in the tropics are unquantified. Here we used ground and satellite sensors to quantify the geography of lightning strikes in terrestrial tropical ecosystems, and to evaluate whether spatial variation in lightning frequency is associated with variation in tropical forest structure and dynamics. Between 2013 and 2018, tropical terrestrial ecosystems received an average of 100.4 million lightning strikes per year, and the frequency of strikes was spatially autocorrelated at local‐to‐continental scales. Lightning strikes were more frequent in forests, savannas, and urban areas than in grasslands, shrublands, and croplands. Higher lightning frequency was positively associated with woody biomass turnover and negatively associated with aboveground biomass and the density of large trees (trees/ha) in forests across Africa, Asia, and the Americas. Extrapolating from the only tropical forest study that comprehensively assessed tree damage and mortality from lightning strikes, we estimate that lightning directly damages c. 832 million trees in tropical forests annually, of which c. 194 million die. The similarly high lightning frequency in tropical savannas suggests that lightning also influences savanna tree mortality rates and ecosystem processes. These patterns indicate that lightning‐caused disturbance plays a major and largely unappreciated role in pantropical ecosystem dynamics and global carbon cycling.
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Tropical forests are well known for their high woody plant diversity. Processes occurring at early life stages are thought to play a critical role in maintaining this high diversity and shaping the composition of tropical tree communities. To evaluate hypothesized mechanisms promoting tropical tree species coexistence and influencing composition, we initiated a census of woody seedlings and small saplings in the permanent 50-ha Forest Dynamics Plot (FDP) on Barro Colorado Island (BCI), Panama. Situated in old-growth, lowland tropical moist forest, the BCI FDP was originally established in 1980 to monitor trees and shrubs ≥1 cm diameter at 1.3 m above ground (dbh) at ca. 5-yr intervals. However, critical data on the dynamics occurring at earlier life stages were initially lacking. Therefore, in 2001 we established a 1-m2 seedling plot in the center of every 5 x 5 m section of the BCI FDP. All freestanding woody individuals ≥20 cm tall and <1 cm dbh (hereafter referred to as seedlings) were tagged, mapped, measured, and identified to species in 19,313 1-m2 seedling plots. Because seedling dynamics are rapid, we censused these seedling plots every 1–2 years. Here we present data from the 14 censuses of these seedling plots conducted between the initial census in 2001 to the most recent census, in 2018. This data set includes nearly 1M observations of ~185,000 individuals of >400 tree, shrub, and liana species. These data will permit spatially-explicit analyses of seedling distributions, recruitment, growth, and survival for hundreds of woody plant species. In addition, the data presented here can be linked to openly-available, long-term data on the dynamics of trees and shrubs ≥1cm dbh in the BCI FDP, as well as existing data sets from the site on climate, canopy structure, phylogenetic relatedness, functional traits, soil nutrients, and topography.more » « less
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Abstract Plant functional traits are thought to drive biomass production and biogeochemical cycling in tropical forests, but it remains unclear how nitrogen (N)‐fixing legumes influence the functional traits of neighbouring trees and forest‐wide biomass dynamics. Further, the degree to which effects of N‐fixers are density‐dependent and may depend on stem size and spatial scale remains largely unknown.
Here, we examine 30 years of stem demography data for ~20,000 trees in a lowland tropical forest in Trinidad that span a wide range of functional traits thought to drive above‐ground biomass (AGB) dynamics.
These forests show positive but decreasing long‐term net AGB accumulation resulting from constant average productivity but increasing mortality of non‐fixing trees over time. We find that high abundance of N‐fixing trees is associated with compositional shifts in non‐fixer functional traits that confer lower competitive performance and biomass accumulation. Across tree size classes, most interactions between N‐fixers and non‐fixers were negative, density‐dependent, and strongest at smaller spatial scales.
Synthesis . Overall, our findings suggest that local trait‐based interactions between N‐fixing and non‐fixing trees can influence long‐term carbon accumulation in tropical forests. -
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Abstract Forest dynamics and tree species composition vary substantially between Paleotropical and Neotropical forests, but these broad biogeographic regions are treated uniformly in many land models. To assess whether these regional differences translate into variation in productivity and carbon (C) storage, we compiled a database of climate, tree stem growth, litterfall, aboveground net primary production (ANPP), and aboveground biomass across tropical rainforest sites spanning 33 countries throughout Central and South America, Asia, and Australasia, but excluding Africa due to a paucity of available data. Though the
sum of litterfall and stem growth (ANPP) did not differ between regions, both stem growth and theratio of stem growth to litterfall were higher in Paleotropical forests compared to Neotropical forests across the full observed range of ANPP. Greater C allocation to woody growth likely explains the much larger aboveground biomass estimates in Paleotropical forests (~29%, or ~80 Mg DW/ha, greater than in the Neotropics). Climate was similar in Paleo‐ and Neotropical forests, thus the observed differences in C likely reflect differences in the evolutionary history of species and forest structure and function between regions. Our analysis suggests that Paleotropical forests, which can be dominated by tall‐statured Dipterocarpaceae species, may be disproportionate hotspots for aboveground C storage. Land models typically treat these distinct tropical forests with differential structures as a single functional unit, but our findings suggest that this may overlook critical biogeographic variation in C storage potential among regions.
