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- Title
A Study of Dominant Vegetation Phenology in a Sphagnum Mountain Peatland Using In Situ and Sentinel‐2 Observations.
- Authors
Garisoain, Raphael; Delire, Christine; Decharme, Bertrand; Ferrant, Sylvain; Granouillac, Franck; Payre‐Suc, Virginie; Gandois, Laure
- Abstract
Peatlands store more than a third of the global soil organic carbon stock. Bryophytes, more specifically Sphagnum mosses, play a major role in the carbon and water cycles of these ecosystems. There is a need to include Sphagnum mosses into Earth system models to better simulate the dynamics of peatlands in a changing environment. Leaf area index (LAI) is a key plant trait that characterizes the plant photosynthesizing capacity. Moreover, LAI is a variable calculated by land surface models used in climate models, allowing control of the exchange of matter and energy between vegetation and the environment. There is extremely little data on Sphagnum LAI and none on its seasonal change. We monitored Sphagnum mosses LAI phenology in a mountainous peatland site (altitude of 1,343 m) from June to December 2021 using two methods: 2D scans of monthly Sphagnum moss samples and analysis of Sentinel‐2 images. LAI derived from field campaigns and the remote sensing approach show a strong seasonality, with high peak values reaching 10 and 7 m2·m−2, respectively. The Sentinel‐2 images were also used to derive common vegetation indices. The moisture soil index effectively discriminates Sphagnum‐dominated areas in the peatland. Satellite‐derived LAI of Sphagnum mosses is directly correlated to gross primary production monitored by gas exchange measurements (R2 = 0.83) but also to physical drivers of the environment such as air temperature (R2 = 0.74) or water table depth (R2 = 0.61) over the 2017–2021 period. It is therefore highly suitable to investigate ecosystemic functions. Plain Language Summary: Sphagnum mosses are the main organisms inhabiting Northern Hemisphere peatlands. Peatlands play a major role in the evolution of the global carbon cycle over the long term. Numerical models of continental surfaces do not correctly model the functioning of peatlands. This study aims therefore at improving carbon cycle modeling by providing needed knowledge on Sphagnum phenology. Vegetation indices are used to monitor the development of vegetation over time. Here, vegetation indices are measured from the harvesting of Sphagnum on a Pyrenean peatland. These field indices are compared to vegetation indices acquired through satellite imagery. The two types of measurements show a marked seasonality of Sphagnum, with a rapid growth phase in June–July. The second part of the study highlights the links between environmental parameters (air temperature, water table height, and solar radiation), satellite vegetation indices, and Sphagnum photosynthesis, allowing us to understand the functioning of the ecosystem. Finally, the remote sensing method performs well at mapping Sphagnum mosses. This will be useful to study peatlands on larger scales, especially for still unknown or inaccessible peatland sites, as well as for the monitoring of these ecosystems in the context of climate change. Key Points: Sphagnum leaf area index seasonality—in situ and derived from Sentinel‐2 (with the SL2P10 algorithm)Sphagnum vegetation index dynamics (chlorophyll activity, green chromatic coordinate, moisture soil index, normalized difference index) and Sphagnum gross primary production driversPotential use of Sentinel‐2 vegetation indices for Sphagnum mapping
- Subjects
PEAT mosses; LEAF area index; CARBON cycle; PHENOLOGY; REMOTE-sensing images; PEATLANDS; PLANT phenology
- Publication
Journal of Geophysical Research. Biogeosciences, 2023, Vol 128, Issue 10, p1
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2023JG007403