Climate and management effects on the herbaceous layer productivity of a cork oak woodland.

Cork oak woodlands are highly biodiverse silvopastoral systems, economically and socially relevant to rural communities in many Mediterranean areas. The installation of legume-rich pasture mixtures became a common practice in these woodlands aiming to obtain higher productivity, to improve soil fertility, and to increase the amount of protein for forage. The predicted impacts of climate change will affect pasture productivity either by altering the biomass total amount or its seasonal productivity. We analysed an 8-years data series of meteorological variables and herbaceous biomass productivity collected in a certified cork oak ecosystem with a moderate tree density (177 trees ha⁻¹) to investigate how understorey herbaceous biomass is affected by inter annual and seasonal climate variability. The field collections were carried out in two contrasting understorey management systems: a natural understorey vegetation (NU) subject to shrub clearing every 5 years, without grazing; and a sown improved pasture, installed in 2009, grazed by cattle (IP). Results have shown that herbaceous biomass productivity was on average 8 times higher in IP than in the NU most likely due to the positive effects of the initial fertilization and the legume rich seed composition which increased N soil availability. The main climatic driver explaining the biomass productivity was the cumulative precipitation from February to May. The proportion of grasses increased in response to drought with a pronounce decrease in legumes, regardless of the management system. Nonetheless, the NU system was more resilient to drought compared to IP suggesting a need to better understand the role and contribution of each native species to resistance, resilience and recovery to drought in order to improve future forage mixtures. These results may support better management decisions by forest producers which are mostly based on empirical procedures and might provide some directions for further studies. [ABSTRACT FROM AUTHOR]