Shift from short-term competition to facilitation with drought stress is due to a decrease in long-term facilitation

Disentangling short- and long-term neighbour effects, using both removal and observational methods within a single experiment, has strongly improved our understanding of the driving mechanisms of plant-plant interactions. However, there has been no attempt to assess two important underlying processes of their changes along gradients, environmental-severity (changes in target performance without neighbours) and neighbour-traits (changes in performance with neighbours) effects, the former previously shown in alpine communities to be involved in competition and the latter in facilitation. We addressed this goal in an experiment conducted in continental saline depressions (sebkhas) from the Mediterranean arid climate of central Tunisia. We quantified short- and long-term effects of dominant shrubs, transplanting three target grass species in open, nurse and removed-nurse microhabitats of two habitats of different salinity levels in height sebkhas. The design extended geographically from cen...