| Description |
Quantifying and understanding the spatiotemporal variability in gross primary production (GPP), a key component of the global carbon cycle, remain difficult. Therefore, devising means for improving estimates of GPP and its variability on different spatial and time scales and for different land cover types is crucial. Inter-annual variability in GPP for evergreen needleleaf (coniferous) forests in the western U.S. is a topic of significant scientific interest because coniferous forests constitute an important carbon reservoir whose annual GPP is highly dynamic due to drought and disturbance events. However, GPP in coniferous forests is difficult to infer from conventional vegetation greenness indices such as the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI). While satellite-based observations of solar-induced chlorophyll fluorescence (SIF) have been shown to correlate well with GPP from monthly to seasonal time scales, a knowledge gap exists for the potential of SIF as a proxy for GPP between years. We show here that annually-averaged SIF (retrieved from GOME-2) exhibits significantly stronger correlation with annually-summed tower-based GPP (GPPTower) than do NDVI, EVI, or satellite-based GPP (all retrieved from MODIS) at four eddy covariance sites in coniferous forests in the western U.S. (Sierra Nevada, Cascade, and Rocky Mountains). We discuss, however, some limitations that remain for SIF to serve as a reliable proxy for inter-annual variation in GPP of coniferous forests. |
