As a followup to a previous post, here are some earlier results on drought impacts on tree growth. The Vicente-Serrano paper had looked at the response of tree growth to droughts of different lengths globally. This one was just for Spain.
While less extensive, the summary figure is neater and looks at the timing of drought better.
Here they integrated precipitation over different lengths of time with different starting points.
Top to bottom is xeric to humid gradient.
All sites respond most mid-season precipitation, but integrated drought over the past ~10 months is most relevant for trees in xeric sites and only a few months for humid sites.
Pasho, E., J. J. Camarero, M. de Luis, and S. M. Vicente-Serrano. 2011. Impacts of drought at different time scales on forest growth across a wide climatic gradient in north-eastern Spain. Agricultural and Forest Meteorology 151:1800-1811.