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Identifying optimal cloud cover for enhanced forest carbon uptake: Periodic-case NEE-overshoot modelling
On certain kinds of cloudy days, many forested ecosystems exhibit enhanced carbon uptake and water-use effi-
ciency-the cloudy-day forest flux anomaly. Using ensemble methods to analyze eddy-covariance fluxes, we have
diagnosed net ecosystem exchange (NEE) and water-use efficiency (WUE) of a temperate broadleaf forest and a
tropical evergreen forest as they responded to natural fluctuating-light regimes. Here we apply average NEE and
evapotranspiration solutions of a first-order dynamic model to describe the observed whole-canopy sensitivity to
periodic light. On partly-cloudy days, maximum overall NEE enhancements over conventional steady-state equi-
librium estimates are ≈ 25% for a midlatitude deciduous forest and ≈ 15% for a tropical evergreen forest. This
finding supports our conclusion that in many cases the cloudy-day anomaly is a consequence of a dynamic re-
sponse by the trees responding to fluctuating-light regimes occasioned by passing cumulus clouds.