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Mediterranean oak-dominated agro-silvo-pastoral systems of southwestern Europe (called montado in Portugal and dehesa in Spain) are semi-natural, savannah-style High Nature Value farmlands (HNVfs) shaped by centuries of anthropogenic (e.g., cultivation, grazing) and natural (e.g., drought) disturbances. Therefore, changes in grazing and precipitation may alter their vegetation composition and ecosystem properties and impact upon their long-term viability. We quantified the responses of soil organic carbon (SOC) and plant taxonomic and functional trait diversities to cattle grazing and inter-annual changes in precipitation across three open-woodland sites within the montado landscape in Alentejo, southern Portugal. The sites are characterised by the presence or absence of cattle grazing and different amounts of mean annual precipitation (ranging from semiarid to dry subhumid). Three different precipitation periods were used: a shorter autumn-to-spring period and longer 12- and 18-month periods before sampling. Specific leaf area, plant height and seed mass were used to estimate single-trait community weighted means and a multi-trait measure of community functional diversity (Rao's Q). SOC and plant species richness responded negatively to the presence of cattle grazing but positively to increase in precipitation (and its interaction with cattle grazing), while trait-based measures were largely unresponsive to cattle grazing and precipitation (though RLQ analysis revealed strong controls of the environmental variables on plant life cycle, growth form, leaf phenology and dispersal strategies). SOC was most responsive to longer-term (18-month) changes in precipitation, whereas plant species richness was most responsive to shorter-term (autumn-to-spring) changes in precipitation. These results suggest that different components of plant diversity respond differently to external drivers in montado HNVfs, while the response time of soil properties may be longer than that of plant taxonomic diversity. • We assessed three sites in oak woodlands under different amounts of precipitation. • Taxonomic and functional diversity respond differently to grazing and precipitation. • Plant species richness is most responsive to autumn-to-spring precipitation. • Soil organic carbon is most responsive to 18-month changes in precipitation. • Soil organic carbon responds negatively to grazing but positively to precipitation. [ABSTRACT FROM AUTHOR]

Shrub encroachment influences several ecosystem services in drylands worldwide. Yet, commonly used strategies to reduce encroachment show a low medium-term success, calling for a better understanding of its causes. Previous works identified multiple drivers responsible for this phenomenon, including anthropogenic and environmental causes. However, the relative effect of climate, topography and edaphic factors on shrub encroachment is not fully understood nor has been properly quantified in Mediterranean Basin drylands. Also, understanding how these drivers lead to changes in plant communities' functional traits associated to shrub encroachment is crucial, considering traits influence ecosystem processes and associated ecosystem services. Here, we studied the understory of a Mediterranean dryland ecosystem composed of savanna-like Holm-oak woodlands, along a regional climatic gradient. We specifically assessed (i) how climatic, topographic and edaphic factors influence understory relative shrub cover (RSC) and (ii) their direct and indirect effects (via RSC) on plant functional traits. We studied the mean and diversity of 12 functional traits related to plant regeneration, establishment, and dispersal, at the community-level. We found that, under similar low-intensity land use, topographic and edaphic factors, namely slope variations and soil C:N ratio, were the most important predictors of shrub encroachment, determining communities' functional characteristics. Climate, namely summer precipitation, had a much lesser influence. Our model explained 52% of the variation in relative shrub cover. Climate had a stronger effect on a set of functional traits weakly involved in shrub encroachment, related to flowering and dispersal strategies. We show that shrub encroachment is largely predicted by topo-edaphic factors in Mediterranean drylands subject to conventional low-intensity land use. Hence, management strategies to reduce encroachment need to take these drivers into account for efficient forecasting and higher cost-effectiveness. Our results suggest that climate change might not greatly impact shrub encroachment in the Mediterranean Basin, but may affect functional structure and reduce functional diversity of plant communities, thus affecting ecosystem functioning., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)