Biological processes dominate seasonality of remotely sensed canopy greenness in an Amazon evergreen forest

Jin Wu, Hideki Kobayashi, Scott C. Stark, Ran Meng, Kaiyu Guan, Ngoc Nguyen Tran, Sicong Gao, Wei Yang, Natalia Restrepo-Coupe, Tomoaki Miura, Raimundo Cosme Oliviera, Alistair Rogers, Dennis G. Dye, Bruce W. Nelson, Shawn P. Serbin, Alfredo R. Huete, Scott R. Saleska

Research output: Contribution to journalArticle

16 Scopus citations

Abstract

Satellite observations of Amazon forests show seasonal and interannual variations, but the underlying biological processes remain debated. Here we combined radiative transfer models (RTMs) with field observations of Amazon forest leaf and canopy characteristics to test three hypotheses for satellite-observed canopy reflectance seasonality: seasonal changes in leaf area index, in canopy-surface leafless crown fraction and/or in leaf demography. Canopy RTMs (PROSAIL and FLiES), driven by these three factors combined, simulated satellite-observed seasonal patterns well, explaining c. 70% of the variability in a key reflectance-based vegetation index (MAIAC EVI, which removes artifacts that would otherwise arise from clouds/aerosols and sun–sensor geometry). Leaf area index, leafless crown fraction and leaf demography independently accounted for 1, 33 and 66% of FLiES-simulated EVI seasonality, respectively. These factors also strongly influenced modeled near-infrared (NIR) reflectance, explaining why both modeled and observed EVI, which is especially sensitive to NIR, captures canopy seasonal dynamics well. Our improved analysis of canopy-scale biophysics rules out satellite artifacts as significant causes of satellite-observed seasonal patterns at this site, implying that aggregated phenology explains the larger scale remotely observed patterns. This work significantly reconciles current controversies about satellite-detected Amazon phenology, and improves our use of satellite observations to study climate–phenology relationships in the tropics.

Original languageEnglish (US)
Pages (from-to)1507-1520
Number of pages14
JournalNew Phytologist
Volume217
Issue number4
DOIs
StatePublished - Mar 2018

    Fingerprint

Keywords

  • LiDAR canopy structure
  • MODIS EVI
  • WorldView-2
  • canopy phenology
  • leaf age
  • leaf optics

ASJC Scopus subject areas

  • Physiology
  • Plant Science

Cite this

Wu, J., Kobayashi, H., Stark, S. C., Meng, R., Guan, K., Tran, N. N., Gao, S., Yang, W., Restrepo-Coupe, N., Miura, T., Oliviera, R. C., Rogers, A., Dye, D. G., Nelson, B. W., Serbin, S. P., Huete, A. R., & Saleska, S. R. (2018). Biological processes dominate seasonality of remotely sensed canopy greenness in an Amazon evergreen forest. New Phytologist, 217(4), 1507-1520. https://doi.org/10.1111/nph.14939