Climate change may alter the signal of plant facilitation in Mediterranean drylands

Facilitation is an ecological interaction that has allowed plant lineages
to survive past climate aridification. This same interaction can be
expected to buffer the effects of current climate change, which is tending
to become more arid in the Mediterranean basin. However, facilitation may
wane when stress conditions are extreme. Here we argue that the erosion of
the facilitation signal between Quercus ilex and its nurses detected by
García-Fayos et al. (2020) along 50 years in the eastern Iberian Peninsula
may have been due to the reversion of facilitation to competition imposed
by an increasingly arid climate. To support this speculation, we
reconstructed the climatic niche of Q. ilex and its nurses as well as the
local climate change occurring in the populations studied. We found that
the decreasing trend in precipitation is pushing Q. ilex out of its
climatic optimum in the stressful (semi-arid) but not in the mild
(sub-humid) habitats. These results suggest that facilitation will be
unable to mitigate the effects of climate change, especially those related
to aridification. However, other scenarios linking climatic change with
herbivory and rural abandonment should be considered to fully understand
the past, present and future of facilitation interactions. Reconstructing
past interactions can serve as an early warning signal about the future of
populations in the face of climate change.