A role for vegetation phenology in shaping patterns of ecosystem sensitivity to drought.

Phenology, as the study of the timing and rhythms of vegetation activity, has traditionally emphasized trends in phenological responses to gradual climate change. Consequently, we lack understanding of phenological responses to concurrent increases in the frequency and intensity of climate extremes. Here, I advance a viewpoint that vegetation phenology is not just altered by drought, but that such alterations frequently generate compensatory dynamics that provide a mechanistic explanation for observed variation in ecosystem sensitivity to drought. I first review a growing body of literature on how vegetation phenology is altered during drought. I then develop hypotheses for how such phenological dynamics during these extremes can underpin and drive patterns of drought sensitivity among ecosystems. Finally, I test predictions of these hypotheses across a large grassland ecoregion, empirically demonstrating that variation in phenological responses during extreme drought can explain cross-ecosystem variation in drought sensitivity of annual net primary productivity. Deeper consideration of vegetation phenology under drought intensification can improve our understanding and ability to anticipate the ecological consequences of climate change.