An empirical test of neighbourhood effect and safe-site effect in abandoned Mediterranean vineyards

The importance of both neighbourhood effect and safe-site effect for the colonization of Mediterranean old fields by woody plants was investigated. Using a transect approach, we recorded colonization of 21 species of woody plants on abandoned, terraced vineyards on Pantelleria Island (Sicily) in dependence from neighbouring terraces in older succession stages (Maquis) and available safe sites for seedling establishment (former crop plant, terrace wall). With a paired design of four treatments, including presence/absence of adjacent older successional stages, and North-/South-facing slopes, a neighbourhood effect could be shown for both expositions if the transect started from an adjacent field with a more advanced succession stage. The safe-site effect was clearly detectable on N-facing terraces in the vicinity of both remaining crop plants and wall bases, while on S-facing terraces it was observed only under crop plants. It was most pronounced for zoochorous species. Underlying mechanisms are passive facilitation (especially former crop plants are used as shelter and perches by animals dispersing seeds) as well as active facilitation due to improved site conditions. Both the neighbourhood effect and the safe-site effect act in synergy and can considerably accelerate the pace of succession.

Research highlights
► Mediterranean old fields can be subject to rapid secondary succession dynamics.
► Woody colonization is a synergistic action of neighbourhood and safe-site effect.
► Zoochorous dispersal is a key mechanism for the initial passive facilitation process.
► Succession is slower on South-facing slopes for less efficient active facilitation.