Using satellite data, researchers assessed water stress in degraded forests and found that structure strongly mediates evapotranspiration in these forests.

Examples of intact forests (left) and forests degraded by selective logging (middle) and fires (right) in the Amazon Forest. Forest degradation changes forest structure and the way the forest exchanges energy and water with the atmosphere. Photos by Ekena Rangel Pinagé.

The Science
Forest degradation through fires and logging is common in the Amazon and changes forest structure. However, little is known on the effects of degradation on the way tropical forests transpire water. Using high-resolution remote sensing of forest structure from spaceborne lidar (GEDI) and evapotranspiration (ET) derived from Landsat, researchers assessed the seasonal water stress and its relationship with forest structure across intact and disturbed forests in the Amazon. They found that forest structure exerts a stronger control on ET in the more disturbed/drier forests than in intact or lightly disturbed forests.

The Impact
New satellite data and products allow us to measure forest structure and evapotranspiration across large areas. With these data, we can better understand how human activities in tropical forests are changing the earth’s water and energy cycles. This study found that forest structure influences evapotranspiration more than climate does. In addition, the team found that forest degradation may make the Amazon forests limited by water. This matters because intact forests in the Amazon are normally limited by energy, not water. These findings have important implications for the global water balance and rainfall patterns.

Summary
Deforestation, timber extraction, and forest fires disturb large areas in the Amazon region. These disturbances alter how forests function. Previous work focused on how deforestation affects the water and energy cycles. To understand how degradation changes the water and energy fluxes, this research used many satellite-based data. The research team analyzed evapotranspiration, land surface temperature, and forest structure (tree cover and forest height) data over a region in the Southern Amazon. This region has a mix of deforested, degraded and intact forests, so researchers could study the effects of forest structure on water and energy cycles.

The research team found that water stress conditions started early into the dry in croplands and pastures. They also found that second-growth and burned forests experience stronger water stress than logged and intact forests. Moreover, they found that forest structure is moderately related to evapotranspiration and temperature, but only in the most disturbed forests. This results of this study show the importance of intact forests in maintaining water balance in the Amazon region. Their findings also suggest that disturbed forests may be less able to cope with the changing climate.

Contact
Ekena Rangel Pinagé
College of Forestry, Oregon State University
ekenapinage@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 Australian Government Research Training Program Scholarship, the USDA Forest Service Pacific Northwest Research Station and International Programs, and the NASA Postdoctoral Program, administered by Universities Space Research Association under contract with NASA. The research carried out at the Jet Propulsion Laboratory, California Institute of Technology, was under a contract with the National Aeronautics and Space Administration.

Publication
Rangel Pinagé, E., D. Bell, M. Longo, C. A. Silva, O. Csillik, A. Huete. “Surface Energy Dynamics and Canopy Structural Properties in Intact and Disturbed Forests in the Southern Amazon.” Journal of Geophysical Research: Biogeosciences, 128(9), e2023JG007465 (2023). http://doi.org.10.1029/2023JG007465

Forest scientists evaluated the influence of crown exposure to light, growth rates, tree size and species wood density in the mortality of canopy trees in the Amazon

Canopy trees at the Amacayacu Forest Dynamics plot seen from a drone image. Location of some canopy trees with their trunk size (diameter at breast height-DBH, cm), species abbreviation and survival status are shown for reference. A standing dead tree of Caryocar glabrum (Caryocaraceae, purple dot) stands out from the canopy. Image courtesy of authors.

The Science
Tree mortality influences forest carbon dynamics and composition. However, despite the ecosystem importance of tree mortality, we still don’t clearly understand the factors that influence it. Forest ecologists evaluated the role of crown exposure to light, trunk size, growth rates and species wood density in the mortality of 984 canopy trees in the Amacayacu Forest Dynamics plot, northwestern Amazon. Researchers found that the probability of tree death decreased for low wood density species as trees have higher proportion of their crowns exposed to light and grew more than their species average. On the contrary, high wood density species were slightly more prone to die when their crowns were more exposed to light.

The Impact
These results underscore the varied tree responses to specific local conditions. The inclusion of life history strategies (e.g., proxied by wood density), when predicting forest demography under vegetation dynamic models can help to reduce the uncertainty of forest outcomes. Future research should focus on better integration between remote and ground-based data to improve the understanding of tree mortality.

Summary
Understanding the factors that influence tree mortality is a research priority to predict forest responses to global change. In this study, researchers evaluated the role of light exposure, trunk size, growth rates and species wood density in the mortality of 984 canopy trees in the Amacayacu Forest Dynamics Plot, northwestern Amazon. Light availability was measured as the proportion of crown exposed to sunlight; a new metric that relates the vertical exposed crown area over the potential crown area, and that was derived from the integration of drone photogrammetry and ground-based data. The research found that the probability of death at changing light conditions varied with species wood density; trees of low wood density were less prone to die when their crowns were more exposed to sunlight, whereas trees of high wood density species were slightly more prone to die at the same light conditions. This result highlights the role of life history strategies, proxied by the species wood density, in shaping tree survival at contrasting light conditions; and demonstrates the importance of the inclusion of plant functional types in vegetation dynamic models aiming to predict forest demography under ongoing global changes.

Contacts:
Luisa F. Gómez-Correa, MSc. – Ecologist (Intern)
Smithsonian Tropical Research Institute – Panamá
luifgomezcor@unal.edu.co

Daniel Zuleta, Ph.D. – Ecologist (Postdoctoral fellow)
Forest Global Earth Observatory
Smithsonian Tropical Research Institute – Washington, DC
dfzuleta@gmail.com

Funding
This project was supported by MinCiencias “Convocatoria 891 2020” and by the Next Generation Ecosystem Experiments–Tropics, funded by the Office of Biological and Environmental Research (BER) within the U.S. Department of Energy’s (DOE) Office of Science. Ground-based data collection was supported by the Forest Global Earth Observatory (ForestGEO) of the Smithsonian Institution. Drone imagery were collected during the 9th Regional SilvaCarbon/GFOI Workshop on Forest Monitoring.

Publication
Gómez-Correa, L, F., et al. “Canopy tree mortality depends on the proportion of crown exposed to sunlight, but this effect varies with species wood density.” Biotropica, 00, 1–12. https://doi.org/10.1111/btp.13258

Interplay of Turbulence Regimes, Deep Convection, and Tree Mortality in the Amazon Rainforest

The Science
Although satellites with high spatial resolution have become available in the last decade, they have not yet been employed for the quantification of windthrow tree-mortality. Here, we address how increasing the spatial resolution of satellites affects plot-to-landscape estimates of windthrow tree-mortality. We combined forest inventory data with Landsat 8 (30 m pixel), Sentinel 2 (10 m), and WorldView 2 (2 m) imagery over an old-growth forest in the Central Amazon that was disturbed by a single windthrow event in November 2015.

The Impact
Although the three satellites produced reliable and statistically similar estimates (from 26.5% to 30.3%, p < 0.001), Landsat 8 had the most accurate results and efficiently captured field-observed variations in windthrow tree-mortality across the entire gradient of disturbance (Sentinel 2 and WorldView 2 produced the second and third best results, respectively). As expected, mean-associated uncertainties decreased systematically with increasing spatial resolution (i.e., from Landsat 8 to Sentinel 2 and WorldView 2).

Summary
Remote sensing estimates of windthrow tree-mortality were produced from Spectral Mixture Analysis and evaluated with forest inventory data (i.e., ground true) by using Generalized Linear Models. Field measured windthrow tree-mortality (3 20mx125m transects and 30 10mx25m subplots) crossing the entire disturbance gradient was 26.9 ± 11.1% (mean ± 95% CI).

Figure. (left) Windthrown forest located near Manaus, Central Amazon, Brazil, and inventory and virtual plots used to quantify tree mortality. (Right) Distribution of windthrow tree mortality (%) from field subplots and satellite data with varying spatial resolution.

Contact: Daniel  Marra, Max Planck (dmarra@bgc-jena.mpg.de)
Robinson Negron-Juarez, Lawrence Berkeley National Laboratory (robinson.inj@lbl.gov)

Funding
R.I.N.-J and J.Q.C. were supported by the Office of Science, Office of Biological and Environmental Research of the US Department of Energy, Agreement grant DE-AC02-05CH11231, Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics). This research is part of the INVENTA (Interação Vento-Árvore na Amazônia), and the ATTO projects funded by the German Federal Ministry of Education and Research (BMBF contracts no. 01LB1001A and no. 01LK1602A), the Brazilian Ministry of Science, Technology, and Innovation (MCTI/FINEP contract no. 01.11.01248.00), and the Max Planck Society (MPG). L.E. was funded by the Amazonas State Research Support Foundation (FAPEAM) (PhDgrant no. 41640.UNI739.1607.28032019-65939) and supported by the Instituto Nacional de Ciência e Tecnologia (INCT)Madeiras da Amazônia.

Publication
Emmert L, Negron-Juarez R, Chambers J, Santos J, Lima A, Trumbore S, Marra D. Sensitivity of Optical Satellites to Estimate Windthrow Tree-Mortality in a Central Amazon Forest. Remote Sens. 2023, 15, 4027. https://doi.org/10.3390/rs15164027.

While traditionally considered important mainly in hypoxic roots during flooding, upregulation of fermentation pathways in plants is highlighted to be an evolutionarily conserved strategy under aerobic conditions.

The Science
Upregulation of fermentation in plants has mainly been considered important in hypoxic roots during flooding. However, plant fermentation rates remain poorly characterized across diverse plant functional types in managed and natural ecosystems globally. Here, new studies are summarized that demonstrate the upregulation of fermentation pathways in plants during 1) Growth and development, 2) Root hypoxia associated with flooding, and 3) Defense processes during abiotic stress. While maintenance and growth respiration are often modeled separately in terrestrial models, here we propose the concept of “Defense Respiration” fueled by acetate fermentation where upregulation of acetate fermentation contributes acetate substrate for alternative energy production via aerobic respiration, biosynthesis of primary and secondary metabolites, and the acetylation of proteins involved in defense gene regulation.

The Impact
Fermentation processes, are now recognized to be tightly integrated into plant growth and development as well as responses to abiotic stress. While traditionally considered important mainly in roots during flooding, fermentation in roots, stems, and leaves is now recognized as a critical drought survival strategy. Acetate produced by fermentation may be used as an energy source through “Defense Respiration” and as a stress signaling molecule critical to drought survival. We highlight new frontiers in leaf-atmosphere emission measurements as a potential way to study plant fermentation responses of individual leaves, branches, ecosystems and regions. We conclude that new field studies are urgently needed to resolve the physiological and ecological roles of plant fermentation metabolism under a changing climate.

Summary
Plant fermentation is an ancient metabolic pathway that may be critical in surviving hypoxic conditions experienced by roots during flooding. However, emerging evidence suggests that rather than a strict dependence on oxygen availability in tissues, fermentation can also be active under aerobic conditions linked to a drop in cellular energy status. Key adaptations to root hypoxia in flood tolerant species, including enhanced uptake of atmospheric oxygen in aerial tissues and delivery to roots, is lacking in flood intolerant species. This likely explains why much higher foliar emissions of ethanol and acetaldehyde have been observed from some flood intolerant species during flooding compared with flood tolerant species, in contrast to early predictions. Moreover, high tissue concentrations and atmospheric emissions of fermentation volatiles have been observed under aerobic conditions in well drained soils associated with temperature-linked growth processes as well as drought stress. Further, genomic and transcriptomic studies have revealed that a metabolic shift towards acetate fermentation occurs in roots and leaves which coordinates drought tolerance in plants via protein acetylation and the activation of the jasmonate signaling pathway. Additional studies revealed that acetate fermentation under aerobic conditions improves plant growth and that co-occurrence of acetate fermentation, aerobic respiration, and the utilization of acetate in biosynthetic pathways helps plants meet the high energetic and carbon demands of fast growth rates. This recent research appears to resolve the paradox from earlier work of why fermentation enzymes are so abundant in leaves when they are the least likely tissue to experience hypoxia. While destructive methods are mainly used to study fermentation patterns in plants, the emerging frontier of quantifying biosphere-atmosphere fluxes of fermentation volatiles and atmospheric vertical concentration gradients may provide a means to study dynamic fermentation responses in plants during growth and environmental stress from leaves, branches, ecosystems, landscapes and whole regions. This may enable studies aimed at improving the quantitative understanding of the plant physiological and ecological roles of fermentation under hypoxic and aerobic conditions. This includes potential critical roles in supporting productivity during favorable conditions for net carbon assimilation and growth, as well as defense processes linked to survival during abiotic stress in a changing climate.

Although field observations to quantify plant fermentative metabolism patterns across diverse plant functional types are in general lacking, ecosystems regularly exposed to root flooding like mangroves and low-lying tropical forests may be considered to have high rates of fermentative metabolism. For example, in Amazonian floodplain forests, more than 1000 tree species are exposed to extended annual submergence lasting up to 9 months each year, with full submergence of young trees. Despite hypoxia, restricted photosynthesis rates, and extremely low light levels during the submergence, leafed seedlings survival rates are high. Aerobic fermentation metabolism coupled to respiration in fast growing tropical pioneer tree species like Vismia guianensis, may also be important in the re-growth of tropical forests following a disturbance. In addition, high temperature and drought stress characteristic of desert ecosystems may also stimulate high rates of fermentative metabolism as a key survival trait. For example, creosotebush (Larrea tridentata), which grows in well drained sandy soils, is vastly distributed in North American deserts, and was reported to have large temperature-stimulated leaf emissions of the fermentation volatiles acetaldehyde, acetic acid, acetone, ethanol, and methyl acetate during the summer monsoon in the Sonoran desert. Thus, plant fermentation studies across diverse plant functional traits like photosynthetic types (C3, C4, and crassulacean acid metabolism), growth rates, wood density, specific leaf area, etc. may lead to improvements in our predictive understanding of the roles of plant fermentative metabolism in the establishment and resilience of ecosystem structure and function.

Figure. Graphical representation of acetate fermentation metabolism in plant cells and whole trees during root flooding and drought. Also shown are emerging methods of biosphere-atmosphere studies of fermentation volatile emissions from leaf to global scales, and an ecosystem pizza showing globally important ecosystems and the main processes anticipated to dominate fermentation processes in plants. Image credit: Kolby Jardine.

Contact: Kolby Jardine, Research Scientist (LBNL: Earth and Environmental Sciences Area, Ecology Department), kjjardine@lbl.gov

Funding
This material is based upon work supported by the US Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research (BER), Biological System Science Division (BSSD), Early Career Research Program under Award no. FP00007421 to KJJ and at the Lawrence Berkeley National Laboratory (LBNL). Additional DOE support was provided by the Coastal Observations, Mechanisms, and Predictions Across Scales (COMPASS) project and the Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics) through contract no. DE-AC02-05CH11231 as part of DOE’s Terrestrial Ecosystem Science Program.

Publications
Jardine K and McDowell N. (2023) Fermentation-mediated Growth, Signaling, and Defense in Plants. New Phytologist, Tansley Review. https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.19015.

Changing wetland soils in the Peruvian Amazon threaten global climate with more greenhouse gas emissions

The Science
Amazonian wetlands, including wet peatlands, are a major carbon and nitrogen sink but also sources of methane (CH₄). Additionally, Peruvian rainforests are home to an impressive diversity of species, including 5% of globally known amphibians and 16% of butterflies. However, these ecological capacities are increasingly vulnerable to the impacts of global warming, droughts, and land use changes. The changes are turning the Amazonian peatlands to sources of dangerous greenhouse gases – carbon dioxide (CO₂) and nitrous oxide (laughing gas; N₂O). To better understand the environmental drivers of CO₂, methane (CH₄) and N₂O fluxes in Peruvian peatlands across a wide range of land uses, an international team lead by Dr. Jaan Pärn and Prof. Ülo Mander from the University of Tartu, in collaboration wihh Dr. Robinson I. Negron-Juarez of Lawrence Berkeley lab, conducted a measurement campaign in Iquitos, the Peruvian Amazon. The campaign took place from the end of dry season in September 2019 to late rainy season in March 2020. The team investigated three sites:

1. A pristine swamp forest in the Quistococha lake floodplain.
2. A young secondary swamp forest grown on fallow pasture and banana plantation on an alluvial toe slope.
3. A slash-and-burn manioc (Manihot esculenta) field.

The team measured CO₂, CH₄, N₂O fluxes, denitrification (N₂O and N₂) potential from intact peat cores, and auxiliary environmental characteristics (soil temperature, water table, O₂ and other chemistry) from the soil. In the pristine swamp forest, CO₂, CH₄, N₂O fluxes were also measured from palm and Symphonia hardwood trunks.

The Impact
The peat swamp forests under slight water table drawdown emitted large amounts of both CO₂ and CH₄. Much of the CH₄ was released through palm trunks, which is a novel addition to current knowledge. A heavy post-drought shower created a hot moment of N₂O in the pristine swamp forest. The analysis revealed nitrifiers – a group of soil microbes – as responsible for the N₂O production. Several indirect signs of temporary oxygen intrusion in the swamp forest soil were noticed, facilitating the aerobic microbes. The manioc field, in no surprise, emitted relatively high amounts of CO₂ and N₂O.

Summary
Peruvian Amazonia is a global sink of carbon but a hotspot of CH₄ and N₂O emissions. With an objective to identify environmental drivers of CO₂, CH₄ and N₂O fluxes of Peruvian wetland soils under a broad range of land use, an international team lead by Dr. Jaan Pärn and Prof. Ülo Mander from the University of Tartu and involving Dr. Robinson I. Negron-Juarez of Lawrence Berkeley lab held a measurement campaign in Iquitos, the Peruvian Amazon. The investigation showed that even small changes in soil moisture can create ‘hot moments’ of GHG emissions from microbes in Amazonian wetland soils, and should therefore be carefully monitored.

Figure. The left figure shows the site location and experimental design. The right figure shows carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes in from the Peruvian wetland soils, and their box plots. Significant differences according to Wilcoxon test are shown with asterisks as follows: * – p<0.05; ** – p<0.01; *** –p<0.001. Asterisks directly above box without brackets denote significant difference from all other sites in the plot. Images: courtesy of Jaan Pärn. Peat core image: Anna Macphie, Uni. St. Andrews

 Contact: Jaan Pärn (University of Tartu), jaan.parn@ut.ee 

Funding
The study was supported by the Estonian Research Council (PRG352 and MOBERC-20 grants) and the EU through the European Research Executive Agency (HORIZON-WIDERA Living Labs for Wetland Forest Research Twinning project No 101079192), European Regional Development Fund (ENVIRON and EcolChange Centres of Excellence, Estonia and the MOBTP101 returning researcher grant by the Mobilitas Pluss programme), the European Social Fund (Doctoral School of Earth Sciences and Ecology), LIFE programme project “Demonstration of climate change mitigation potential of nutrients rich organic soils in Baltic States and Finland” (LIFE OrgBalt, LIFE18 CCM/LV/001158), Czech Science Foundation (17-18112Y), and project SustES – Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0 .0/16_019/0000797).

Dr. Negron-Juarez was supported by the Next Generation Ecosystem Experiments – Tropics funded by the U.S Department of Energy, Office of Biological and Environmental Research

 Publication: Parn et al. “Effects of Water Table Fluctuation on Greenhouse Gas Emissions from Wetland Soils in the Peruvian Amazon”, Wetlands, 43:62 (2023). https://doi.org/10.1007/s13157-023-01709-z.