Bridging the gap between ecological succession of fleshy-fruited shrubs and restoration frameworks in semiarid oldfields.

Abandoned agricultural areas (i.e. oldfields) represent an opportunity for natural vegetation recovery, increasing soil carbon sequestration and lessening the impacts of climate change and desertification. Ecological succession in oldfields can be hampered by the harsh conditions of semiarid and arid ecosystems, and hence, restoration actions may be needed in some contexts to reactivate the ecosystem functioning. Fleshy-fruited shrubs are indicators of progression in the ecological succession, which can shift notably across environmental gradients, making difficult to obtain robust conclusions at regional scales. Other poorly studied aspects at such scales (agricultural legacy, structural features and local landscape effects) add to this knowledge gap. Here, we study the species-specific natural colonization patterns of fleshy-fruited shrubs in semiarid oldfields across environmental gradients in the Southeast of the Iberian Peninsula taking into account specific traits of plants. We used Hierarchical Modelling of Species Communities (HMSC) to test the influence of the time since the abandonment and the past land-use history of the oldfields, and the effect of local structural factors, such as the presence of remnant trees and natural patches of vegetation, on the shrub recolonization patterns. We found that altitude and lithology conditioned the structure of shrub communities, allowing the selection of different focal species for making recommendations for restoration. Time since abandonment was not relevant for the colonization process. The persistence of remnant trees in the oldfields showed a positive effect on the occurrence of several shrub species. Close sources of propagules (terrace edges and/or natural vegetation patches) benefited the occurrence of certain species mainly at lower altitudes. Traits of species (growth form, root depth, dispersal mode, fruit length and water content) helped to explain the performance of species along the environmental gradients. We identified the main drivers of natural colonization of fleshy-fruited shrubs in semiarid oldfields across environmental gradients, providing ecological knowledge to guide scientists and practitioners to develop nature-based restoration frameworks. Different management actions are recommended according to the environmental gradient.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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