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Lars Eklundh

Professor

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Estimating local-scale forest GPP in Northern Europe using Sentinel-2 : Model comparisons with LUE, APAR, the plant phenology index, and a light response function

Author

  • Sofia Junttila
  • Jonas Ardö
  • Zhanzhang Cai
  • Hongxiao Jin
  • Natascha Kljun
  • Leif Klemedtsson
  • Alisa Krasnova
  • Holger Lange
  • Anders Lindroth
  • Meelis Mölder
  • Steffen Noe
  • Torbern Tagesson
  • Patrik Vestin
  • Per Weslien
  • Lars Eklundh

Summary, in English

Northern forest ecosystems make up an important part of the global carbon cycle. Hence, monitoring local-scale gross primary production (GPP) of northern forest is essential for understanding climatic change impacts on terrestrial carbon sequestration and for assessing and planning management practices. Here we evaluate and compare four methods for estimating GPP using Sentinel-2 data in order to improve current available GPP estimates: four empirical regression models based on either the 2-band Enhanced Vegetation Index (EVI2) or the plant phenology index (PPI), an asymptotic light response function (LRF) model, and a light-use efficiency (LUE) model using the MOD17 algorithm. These approaches were based on remote sensing vegetation indices, air temperature (Tair), vapor pressure deficit (VPD), and photosynthetically active radiation (PAR). The models were parametrized and evaluated using in-situ data from eleven forest sites in North Europe, covering two common forest types, evergreen needleleaf forest and deciduous broadleaf forest. Most of the models gave good agreement with eddy covariance-derived GPP. The VI-based regression models performed well in evergreen needleleaf forest (R2 = 0.69–0.78, RMSE = 1.97–2.28 g C m−2 d−1, and NRMSE = 9–11.0%, eight sites), whereas the LRF and MOD17 performed slightly worse (R2 = 0.65 and 0.57, RMSE = 2.49 and 2.72 g C m−2 d−1, NRMSE = 12 and 13.0%, respectively). In deciduous broadleaf forest all models, except the LRF, showed close agreements with the observed GPP (R2 = 0.75–0.80, RMSE = 2.23–2.46 g C m−2 d−1, NRMSE = 11–12%, three sites). For the LRF model, R2 = 0.57, RMSE = 3.21 g C m−2 d−1, NRMSE = 16%. The results highlighted the necessity of improved models in evergreen needleleaf forest where the LUE approach gave poorer results., The simplest regression model using only PPI performed well beside more complex models, suggesting PPI to be a process indicator directly linked with GPP. All models were able to capture the seasonal dynamics of GPP well, but underestimation of the growing season peaks were a common issue. The LRF was the only model tending to overestimate GPP. Estimation of interannual variability in cumulative GPP was less accurate than the single-year models and will need further development. In general, all models performed well on local scale and demonstrated their feasibility for upscaling GPP in northern forest ecosystems using Sentinel-2 data.

Department/s

  • BECC: Biodiversity and Ecosystem services in a Changing Climate
  • Dept of Physical Geography and Ecosystem Science
  • MERGE: ModElling the Regional and Global Earth system
  • Centre for Environmental and Climate Science (CEC)
  • ICOS Sweden

Publishing year

2023-06

Language

English

Publication/Series

Science of Remote Sensing

Volume

7

Document type

Journal article

Publisher

Elsevier

Topic

  • Physical Geography

Keywords

  • Enhanced vegetation index 2
  • Gross primary production
  • Light response function
  • Plant phenology index
  • Sentinel-2

Status

Published

Project

  • Upscaling carbon fluxes to a landscape

ISBN/ISSN/Other

  • ISSN: 2666-0172