Observations of satellite land surface phenology suggest that maximum
leaf greenness affects global vegetation productivity more than growing
season length
Abstract
Vegetation green leaf phenology directly impacts gross primary
productivity (GPP) of terrestrial ecosystems. Satellite observations of
land surface phenology (LSP) provide an important means to monitor the
key timing of vegetation green leaf development. However, differences
between satellite-derived LSP proxies and in-situ measurements of GPP
make it difficult to quantify the impact of climate-induced changes in
green leaf phenology on annual GPP. Here we used 1,110 site-years of GPP
measurements from eddy-covariance towers in association with time series
of satellite LSP observations from 2000-2014 to show that while
satellite LSP explains a large proportion of variation in annual GPP,
changes in green-leaf-based growing season length (GSL) had less impact
on annual GPP by ~30% than GSL changes in GPP-based
photosynthetic duration. Further, maximum leaf greenness explained
substantially more variance in annual GPP than green leaf GSL,
highlighting the role of future vegetation greening trends on
large-scale carbon budgets. We conclude that satellite LSP-based
inferences regarding large-scale dynamics in GPP need to consider
changes in both green leaf GSL and maximum greenness.