Factors determining hurricane disturbance and forest recovery in ELM-FATES

The linear regression coefficient of biomass recovery (R_recovery) for experiments with varied hurricane mortality rates. (a) and (b) show the R_recovery based on a relatively equal and a realistic pre-hurricane biomass partition between plant types.

The Science
Hurricanes are affecting the tropical forests. This study uses the Functionally Assembled Terrestrial Ecosystem Simulator of the Energy Exascale Earth System Model Land Model (ELM-FATES). The model simulations in the Luquillo Experimental Forest (LEF) of Puerto Rico and the random forest feature importance imply that hurricane mortality and background mortality are the two major factors regulating post-hurricane forest recovery. Increased hurricane mortality leads to the transformation of the LEF into an ecosystem dominated by light-demanding plant functional types. ELM-FATES provides a reasonable representation of the seasonality of carbon and water fluxes at the LEF, when compared to various data products.

The Impact
This research improves understanding of the Functionally Assembled Terrestrial Ecosystem Simulator of the Energy Exascale Earth System Model (E3SM) Land Model (ELM-FATES) behavior associated with hurricane disturbance and post-hurricane forest recovery. This accomplishment involved conducting model simulations that incorporated hurricane disturbances of varying intensity at the Luquillo Experimental Forest of Northeast Puerto Rico. Additionally, random forest feature importance estimates were used in the process. This research provides guidance for ELM-FATES parameterization and dynamic vegetation model development in representing hurricane-induced forest damage with various intensities.

Summary
To enhance the understanding of forest recovery after hurricanes, we implemented hurricane-induced forest damage into the Functionally Assembled Terrestrial Ecosystem Simulator, coupled with the Energy Exascale Earth System Model Land Model (ELM-FATES). We performed ensemble ELM-FATES simulations with varied forest damage intensities in the Luquillo Experimental Forest, Puerto Rico, and used the output to identify factors controlling the post-hurricane forest recovery, which was further evaluated with random forest feature importance (RFFI) that quantifies the sensitivity of the key model parameters to the post-hurricane forest recovery. The results imply that hurricane mortality and background mortality are the major factors regulating post-hurricane forest recovery. Changes to the intensity of simulated hurricanes could alter forest composition and structure during recovery, which modifies forest ecological processes and potentially shift the wet forests in Puerto Rico to states with increased vulnerability to tropical cyclones. This research enhances our understanding of the ELM-FATES model behavior associated with hurricane disturbance and broadens the application of RFFI in quantifying the parameter sensitivity of a dynamic global vegetation model (DGVM). This research addresses the essential role of representing hurricane induced forest damage in DGVMs, an advanced tool for the future studies of tropical forest dynamics.

Contact
Mingjie Shi
Pacific Northwest National Laboratory
mingjie.shi@pnnl.gov

Funding
This research was conducted at Pacific Northwest National Laboratory, operated for the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC05-76RL01830. This study was supported by the Department of Energy’s (DOE) Office of Biological and Environmental Research as part of the Terrestrial Ecosystem Science program through the Next-Generation Ecosystem Experiments (NGEE)-Tropics project.

Publications
Shi, M., Keller, M., Bomfim, B., Li, L.,et al. “Functionally assembled terrestrial ecosystem simulator (FATES) for hurricane disturbance and recovery.” Journal of Advances in Modeling Earth Systems, 16, e2023MS003679 (2024). https://doi.org/10.1029/2023MS003679

The distribution and abundance of ectomycorrhizal trees in lowland tropical forests are independent of soil fertility.

The association between the probability of observing EcM trees and their relative abundance in relation to soil fertility across and within 16 lowland tropical forests. a,b, The black lines indicate the mean quadrat-level (20 × 20 m) predictions for the probability (prob.) of observing EcM trees (a) and their conditional relative abundance (cd. rel. abun.) in basal area across sites (b). Coloured dots indicate observations, varying by site, whereas the coloured lines show site-level mean predictions. Shaded areas around the mean lines show the 95% credible intervals of these predictions. Colours represent 16 sites from the lowland tropical regions of Africa (Ituri and Rabi), the neotropics (Amacayacu, BCI, Luquillo, Manaus and Yasuni), Oceania (Wanang), and Asia. Dashed lines indicate that the predicted slopes are not different from zero. PC1 is positively correlated with soil nutrient availability. Note that while panel a shows an association between soil fertility and the probability of observing EcM trees, predictions indicate that the probability of observing EcM trees consistently exceeds 0.75. Image courtesy of the authors.

The Science
This study investigates the distribution of mycorrhizae, plant-fungal partnerships that influence ecosystem function. Traditionally, it was believed that climate and decomposition rates determined mycorrhizal distribution, with arbuscular mycorrhizal plants being more prevalent in fertile areas and ectomycorrhizal plants in less fertile ones. However, using fine-scale data from lowland tropical forests, the study challenges this notion, revealing that soil fertility is not associated with the distribution of ectomycorrhizal-associated trees. The research underscores the importance of understanding mycorrhizal symbiosis in lowland tropics, refuting assumptions based on temperate and boreal regions, and highlighting historical biogeographies that influence mycorrhizal patterns in tropical forests worldwide.

The Impact
This study challenges our understanding of how plants and fungi collaborate in lowland tropical forests. It reveals that these relationships are more intricate than previously believed, and conventional ideas about nutrient levels and plant partnerships may not always hold true. The study stresses the importance of gaining a deeper understanding of the symbiotic relationships between plants and fungi in tropical regions, cautioning against assuming they operate similarly to other areas, like temperate and boreal regions. Overall, the research makes us rethink how plants and fungi interact in diverse tropical forests, highlighting the need for more studies to understand these complex partnerships.

Summary
Mycorrhizae, a form of plant-fungal symbioses, mediate vegetation impacts on ecosystem functioning. Climatic effects on decomposition and soil quality are suggested to drive mycorrhizal distributions, with arbuscular mycorrhizal plants prevailing in low-latitude/high-soil-quality areas and ectomycorrhizal (EcM) plants in high-latitude/low-soil-quality areas. However, these generalizations, based on coarse-resolution data, obscure finer-scale variations and result in high uncertainties in the predicted distributions of mycorrhizal types and their drivers. Using data from 31 lowland tropical forests, both at a coarse-scale (mean-plot-level data) and fine-scale (20 × 20 metres from a subset of 16 sites), we demonstrate that the distribution and abundance of EcM-associated trees are independent of soil quality. Resource exchange differences among mycorrhizal partners, stemming from diverse evolutionary origins of mycorrhizal fungi, may decouple soil fertility from the advantage provided by mycorrhizal associations. Additionally, distinct historical biogeographies and diversification patterns have led to differences in forest composition and nutrient-acquisition strategies across three major tropical regions. Notably, Africa and Asia’s lowland tropical forests have abundant EcM trees, whereas they are relatively scarce in lowland neotropical forests. A greater understanding of the functional biology of mycorrhizal symbiosis is required, especially in the lowland tropics, to overcome biases from assuming similarity to temperate and boreal regions.

Contact
José A. Medina-Vega
Forest Global Earth Observatory, Smithsonian Tropical Research Institute, Washington, DC, USA
jamedinavega@gmail.com

Funding
This research and J.A.M.-V. were supported as part of the Next Generation Ecosystem Experiments-Tropics, funded by the US Department of Energy, Office of Science, Office of Biological and Environmental Research. Funding for data management, quality control, travel, and consumables was provided by various funding agencies to the principal investigators of the plots used in this study. For detailed information on site-specific funding, please refer to the supporting documents of the manuscript.

Publications
Medina-Vega, JA., Zuleta, D., Aguilar, S. et al. “Tropical tree ectomycorrhiza are distributed independently of soil nutrients”. Nat Ecol Evol (2024). https://doi.org/10.1038/s41559-023-02298-0

Tropical forest responses vary with cyclone intensity, frequency, soil phosphorus and elevation

Image courtesy of Richard J. Norby. Tree and forest canopy damage near the El Verde Field Station in Puerto Rico shown from the ground about one year following Hurricane Maria. 

 The Science
Hurricanes damage forests across tropical regions. With some difficulty, damage to tree canopies is measured on the ground, but satellites can also detect this damage. Researchers evaluated how well tree canopy damage assessed from space matched with leaf and branch damage assessed on the ground. They found that these two types of measurements were related, and that wind speed, site history with hurricanes, elevation and soil fertility influence the amount of damage. Regrowth of leaves and branches occurred in just a few months. Ultimately, ground-and space-based measurements provide complementary views of hurricane effects.

The Impact
Analysis of damage from the same storms using both ground and satellite data reveals strengths and limitations of satellite data for understanding damage. In particular, soil fertility can potentially influence the amount of canopy damage. It would be ideal to evaluate this across a much wider set of storms than have been observed from the ground, but this study indicates that care must be taken in interpreting results because the influence of soil fertility on ground and satellite measurements may differ.

Summary
Researchers obtained satellite images associated with hurricanes that had been studied using ground-based observations of litterfall. The study used two alternate vegetation indices derived from satellite images to assess hurricane damage and recovery affecting tropical forests in Hawaii, Puerto Rico, Mexico, Australia, and Taiwan between 2004 and 2017. Changes in leaf area index (LAI) and enhanced vegetation index (EVI) were found to moderately correlate (r = −0.52 and −0.60) with changes in ground-based litterfall measurements. The largest drops in LAI (−77%) and EVI (−77%) occurred in Mexico (Jalisco) and Puerto Rico, respectively. LAI recovered to pre-hurricane levels in about four months, and EVI in two months, while litterfall took ten months. LAI and EVI reductions were larger in forests with more phosphorus-rich soil, but with low confidence. The historical frequency and intensity of hurricanes also influenced the amount of damage. 

Contacts
Dellena Bloom (former SULI Intern)
University of Florida and Lawrence Berkeley National Laboratory
develyn.bloom@ufl.edu

Dr. Barbara Bomfim
Lawrence Berkeley National Laboratory
bbomfim@lbl.gov or babomfimf@gmail.com

Funding
This research was supported as part of the Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics), funded by the U.S. Department of Energy, Office of Science and by the U.S. Department of Energy, Office of Science, and Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internship (SULI) program. 

Publications
Bloom, D.E., et al. “Combining field and remote sensing data to estimate forest canopy damage and recovery following tropical cyclones across tropical regions” Environmental Research: Ecology 2 035004 (2023). https://doi.org/10.1088/2752-664X/acfaa3

Using data from a 65-m tall flux tower in the Amazon, researchers found that a hot drought in 2015 had lasting impacts on leaf abundance and water cycle.

Instrumented eddy covariance tower (left) at the Tapajós National Forest, Brazil, and the forest as seen from the tower (right). Data from the tower were used to study how water and energy cycles in the Amazon respond to extreme dry and extreme wet years. Photos by Natalia Restrepo-Coupe.

The Science
Droughts and very rainy years are both becoming more common in the Amazon because of climate change. Researchers used a long time series of data collected from a tower in the middle of the Amazon to study how water exchange between plants and the atmosphere (evapotranspiration) varies during droughts and rainy periods. They found that when rain is abundant, evapotranspiration barely changes. In contrast, during the El Niño drought of 2015, evapotranspiration was low, because plants lost leaves or stopped transpiring. They also found that recovery after drought was slow.

The Impact
The Amazon forest is very important for the earth’s water and energy cycles. The team found that the recent drought in 2015 was hotter and drier than previous droughts because of climate change. This result is important because the impacts of this drought on leaf abundance were stronger, lasted longer, and changed how the forest interacted with the atmosphere. If droughts become too frequent, the forest may not have enough time to recover before the next drought hits the forest. This could permanently shift the Amazon water cycle.

Summary
Over the past decades, the Amazon forests experienced multiple extreme droughts and wet years. This research used data collected between 2001 and 2020 at an eddy covariance tower at the Tapajós National Forest (Brazil) to study how evapotranspiration and sensible heat flux varied during periods of drought and excessive rain.  The team also implemented a model that separates the contribution of plants (transpiration) and soil (evaporation) to the water fluxes. The long time series included a strong La Niña wet event (2008-2009) and a strong El Niño drought (2015-2016).

The team found that the La Niña event did not affect evapotranspiration and sensible heat fluxes. The magnitude and the seasonal cycles of all fluxes were similar between the wet and normal years. However, during the El Niño event, many plants closed their stomata or lost leaves. This impact resulted in lower transpiration and higher sensible heat fluxes, indicating water stress. Moreover, the forest did not return to normal conditions until one year after the drought had ended. The slow recovery suggests that the Amazon forest was close to reaching a tipping point during the 2015 drought, which could have resulted in long-lasting changes in the forest.

Contacts
Natalia Restrepo-Coupe
Department of Ecology and Evolutionary Biology, The University of Arizona
nataliacoupe@gmail.com

Marcos Longo
Lawrence Berkeley National Laboratory
mlongo@lbl.gov

Funding
This research was supported by the Next Generation Ecosystem Experiments-Tropics, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. The measurements at the Tapajós National Forest were supported by multiple projects, including the Brazilian-led Large scale Biosphere Atmosphere experiment in Amazonia, the National Aeronautics and Space Administration, the GoAmazon project (jointly funded by the U. S. Department of Energy, Office of Science, and the Brazilian science foundations FAPESP and FAPEAM), and the U. S. National Science Foundation (NSF).

Publications
Restrepo-Coupe, N., B. O. Christoffersen, M. Longo, L. Alves, K. S. Campos, A. C. de Araújo, R. C. de Oliveira Jr., N. Prohaska, R. da Silva, R. Tapajós, K. T. Wiedemann, S. C. Wofsy, S. R. Saleska. “Asymmetric response of Amazon forest water and energy fluxes to wet and dry hydrological extremes reveals onset of a local drought-induced tipping point.” Global Change Biology (2023). https://doi.org/10.1111/gcb.16933