Planted hedgerows and fenced perches speed up the slow woodland recovery in continental Mediterranean farmland

Abstract

Natural forest regeneration is slow in abandoned continental Mediterranean cropland due to several abiotic and biotic factors. We aim at assessing the rates and limiting factors of woodland recovery following passive and assisted restoration of cropland by combing observational, quasi-experimental and experimental approaches. We quantified spontaneous plant recruitment, particularly of holm oak (Quercus ilex), after (1) 46 years of cropland abandonment and (2) 1–2 years of halted plowing in field strips with and without planted hedgerows and with introduced perches for birds, and (3) the effects of the protection with tree shelters of 1–2-year-old oak seedlings spontaneously established. The recruitment rate at the old-field plots was 2 oaks ha−1 yr−1 only. Field strips with planted hedgerows favored the spontaneous recruitment of oaks (rate was 22.7 ind. ha−1 yr−1) compared to unplanted strips (7.8 ind. ha−1 yr−1) hinting to the attraction of dispersers. Perches favored the recruitment of bird-dispersed species only in the long term provided they were fenced (up to 224 ind. ha−1 yr−1). Protection of oak seedlings did not increase survival, pointing out that herbivory was not a limiting factor of their early establishment. We conclude that, in continental Mediterranean environments, (1) natural regeneration is a slow but efficient nature-based solution to produce multifunctional and resilient landscapes provided there are abundant, nearby seed sources and (2) the recovery of woody vegetation is speed up by hedgerows in the short term and by fenced perches in the mid- to long-term, leading to enhanced biodiversity of agroecosystems.