Chlorophyll fluorescence variation in two Mediterranean forest species over a 21-year drought treatment period.

This article focuses on a 21-year precipitation exclusion experiment investigating the effects of prolonged drought and climatic variables on photochemical activity and chlorophyll fluorescence in two co-dominant Mediterranean forest species, Quercus ilex L. (holm oak) and Phillyrea latifolia L. The study found that despite drought treatment reducing stem density, leaf biomass, and basal area due to increased mortality, drought had no significant effect on the maximum potential quantum efficiency of photosystem II (Fv/Fm) in either species, which instead increased over time in parallel with rising temperatures. Photochemical efficiency (yield) was higher in Q. ilex and under drought conditions, while non-photochemical quenching (NPQ) was higher in P. latifolia; these differences may relate to species-specific drought tolerance and reduced competition in drought-treated plots. The results suggest that reductions in stem density could enhance forest resilience to climate change-induced drought, and that light thinning may mitigate the displacement of Q. ilex by P. latifolia under warming and drying Mediterranean conditions.