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1. Ecohydrological Response of a Tropical Peatland to Rainfall Changes Driven by Intertropical Convergence Zone Variability

   https://doi.org/10.1111/jbi.15051  

   Swindles, Graeme T ; Whitney, Bronwen S ; Gałka, Mariusz ; Mullan, Donal J ; Low, Rob ; Gallego‐Sala, Angela ; Lopez, R Omar ; Kilbride, Elliot ; Graham, Conor ; Baird, Andy J ( December 2024 , Journal of Biogeography)

   Tropical peatlands are globally significant carbon stores, increasingly threatened by human activities and climate change. However, their ecohydrological responses to shifting water availability remain poorly understood. In this study, we investigate the connections between climate change, hydrology and vegetation dynamics in a coastal tropical peatland in Panama, aiming to understand the effects of future drying on peatland dynamics.

   Bocas del Toro, Panama (9°22′54″N, 82°21′59″W).

   Angiosperms.

   High‐resolution multiproxy palaeoecological data, including pollen and plant macrofossils (vegetation), testate amoebae (water‐table depth) and physical peat properties, are used to explore the relationships between climate change, hydrology and vegetation in a coastal tropical peatland over the past 700 years. Downscaled climate simulations are integrated with this process‐based understanding to project the likely future responses of this coastal peatland to climate change.

   We identify a clear connection between precipitation variability, driven by shifts in the Intertropical Convergence Zone and water‐table dynamics, which subsequently influence changes in the peatland vegetation mosaic. Historical drier periods are marked by the expansion of shrub communities into the open peatland plain.

   Palaeoecological studies incorporating climate and hydrological proxies are essential for understanding both recent and future ecohydrological dynamics of tropical peatlands. Our findings suggest that in response to future climate change, water tables will lower and shrub communities will expand due to rising temperatures and reduced precipitation. Additionally, future sea‐level rise, combined with declining rainfall, may result in seawater intrusion and significant vegetation shifts in coastal tropical peatlands.

    

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2. Characterizing Boreal Peatland Plant Composition and Species Diversity with Hyperspectral Remote Sensing

   https://doi.org/10.3390/rs11141685  

   McPartland, Mara ; Falkowski, Michael ; Reinhardt, Jason ; Kane, Evan ; Kolka, Randy ; Turetsky, Merritt ; Douglas, Thomas ; Anderson, John ; Edwards, Jarrod ; Palik, Brian ; et al ( July 2019 , Remote Sensing)

   Peatlands, which account for approximately 15% of land surface across the arctic and boreal regions of the globe, are experiencing a range of ecological impacts as a result of climate change. Factors that include altered hydrology resulting from drought and permafrost thaw, rising temperatures, and elevated levels of atmospheric carbon dioxide have been shown to cause plant community compositional changes. Shifts in plant composition affect the productivity, species diversity, and carbon cycling of peatlands. We used hyperspectral remote sensing to characterize the response of boreal peatland plant composition and species diversity to warming, hydrologic change, and elevated CO2. Hyperspectral remote sensing techniques offer the ability to complete landscape-scale analyses of ecological responses to climate disturbance when paired with plot-level measurements that link ecosystem biophysical properties with spectral reflectance signatures. Working within two large ecosystem manipulation experiments, we examined climate controls on composition and diversity in two types of common boreal peatlands: a nutrient rich fen located at the Alaska Peatland Experiment (APEX) in central Alaska, and an ombrotrophic bog located in northern Minnesota at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment. We found a strong effect of plant functional cover on spectral reflectance characteristics. We also found a positive relationship between species diversity and spectral variation at the APEX field site, which is consistent with other recently published findings. Based on the results of our field study, we performed a supervised land cover classification analysis on an aerial hyperspectral dataset to map peatland plant functional types (PFTs) across an area encompassing a range of different plant communities. Our results underscore recent advances in the application of remote sensing measurements to ecological research, particularly in far northern ecosystems. 

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3. Two Decades of Experimental Manipulation Reveal Potential for Enhanced Biomass Accumulation and Water Use Efficiency in Ponderosa Pine Plantations Across Climate Gradients

   https://doi.org/10.1029/2019JG005183  

   Liles, G. C. ; Maxwell, T. M. ; Silva, L. C. R. ; Zhang, J. W. ; Horwath, W. R. ( July 2019 , Journal of Geophysical Research: Biogeosciences)

   In this study, we report 20 years of data from three ponderosa pine plantations in northern California. Our sites span a natural gradient of forest productivity where climate variability and edaphic conditions delineate marked differences in baseline productivity (approximately threefold). Experimental herbicide application and fertilization significantly reduced competition and improved tree growth by 1.4‐ to 2.2‐fold across sites. At the site of lowest productivity, where soils are poorly developed and water limiting, tree growth increased strongly in response to understory suppression. Small but significant improvements in tree growth were observed in response to understory suppression at the moderate‐productivity site. At the site of highest productivity, where climate is favorable and soils well developed, fertilization increased productivity to a greater extent than did understory suppression. In most cases, the effect of understory suppression and fertilization caused an unexpected growth release, exceeding the anticipated maximum productivity by >5 m of additional height and 60–100% more basal area. At the site of highest productivity, however, understory suppression caused a weak increase on late‐season growth compared to fertilization alone, suggesting a beneficial effect of understory vegetation on long‐term growth at that site. Tree ring cellulose carbon isotopes indicate a negative relationship between intrinsic water use efficiency (iWUE) and tree growth in control stands, which shifted to a positive relationship as both iWUE and tree growth increased in response to management. Cellulose oxygen isotope ratios (δ¹⁸O) were positively correlated with iWUE and negatively correlated with vapor pressure deficit across sites, but δ¹⁸O was not a strong predictor of tree growth.

    

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4. Nitrogen Cycling Feedback on Carbon Dynamics Leads to Greater CH 4 Emissions and Weaker Cooling Effect of Northern Peatlands

   https://doi.org/10.1029/2023GB007978  

   Zhao, Bailu ; Zhuang, Qianlai ( April 2024 , Global Biogeochemical Cycles)

   Northern peatlands have been a carbon sink since their initiation. This has been simulated by existing process‐based models. However, most of these models are limited by lacking sufficient processes of the N cycle in peatlands. Here, we use a peatland biogeochemistry model incorporated with N‐related processes of fixation, deposition, gas emission, loss through water flow, net mineralization, plant uptake and litterfall to project the role of the peatlands in future radiative forcing (RF). Simulations from 15‐ka BP to 2100 are conducted driven by CMIP5 climate forcing data of IPSL‐CM5A‐LR and bcc‐csm1‐1, including warming scenarios of RCP 2.6, RCP 4.5 and RCP 8.5. During the Holocene, northern peatlands have an increasing cooling effect with RF up to −0.57 W m⁻². By 1990, these peatlands accumulate 408 Pg C and 7.8 Pg N. Under warming, increasing mineral N content enhances plant net primary productivity; the cooling effect persists. However, RF increases by 0.1–0.5 W m⁻²during the 21st century, mainly due to the stimulated CH₄emissions. Northern peatlands could switch from a C sink to a source when the annual temperature exceeds −2.2 to −0.5°C. This study highlights that the improved N cycle causes higher CO₂‐C sink capacity in northern peatlands. However, it also causes a significant increase in CH₄emissions, which weakens the cooling effect of northern peatlands in future climate.

    

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5. Large stocks of peatland carbon and nitrogen are vulnerable to permafrost thaw

   https://doi.org/10.1073/pnas.1916387117  

   Hugelius, Gustaf ; Loisel, Julie ; Chadburn, Sarah ; Jackson, Robert B. ; Jones, Miriam ; MacDonald, Glen ; Marushchak, Maija ; Olefeldt, David ; Packalen, Maara ; Siewert, Matthias B. ; et al ( August 2020 , Proceedings of the National Academy of Sciences)

   Northern peatlands have accumulated large stocks of organic carbon (C) and nitrogen (N), but their spatial distribution and vulnerability to climate warming remain uncertain. Here, we used machine-learning techniques with extensive peat core data ( n > 7,000) to create observation-based maps of northern peatland C and N stocks, and to assess their response to warming and permafrost thaw. We estimate that northern peatlands cover 3.7 ± 0.5 million km 2 and store 415 ± 150 Pg C and 10 ± 7 Pg N. Nearly half of the peatland area and peat C stocks are permafrost affected. Using modeled global warming stabilization scenarios (from 1.5 to 6 °C warming), we project that the current sink of atmospheric C (0.10 ± 0.02 Pg C⋅y −1 ) in northern peatlands will shift to a C source as 0.8 to 1.9 million km 2 of permafrost-affected peatlands thaw. The projected thaw would cause peatland greenhouse gas emissions equal to ∼1% of anthropogenic radiative forcing in this century. The main forcing is from methane emissions (0.7 to 3 Pg cumulative CH 4 -C) with smaller carbon dioxide forcing (1 to 2 Pg CO 2 -C) and minor nitrous oxide losses. We project that initial CO 2 -C losses reverse after ∼200 y, as warming strengthens peatland C-sinks. We project substantial, but highly uncertain, additional losses of peat into fluvial systems of 10 to 30 Pg C and 0.4 to 0.9 Pg N. The combined gaseous and fluvial peatland C loss estimated here adds 30 to 50% onto previous estimates of permafrost-thaw C losses, with southern permafrost regions being the most vulnerable. 

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