Biodiverse permanent pastures, composed of Mediterranean Basin native species mixtures rich in legumes, have been implemented in Portugal as a management tool to increase soil fertility, grassland productivity and animal carrying capacity and were later selected as a national land-use change strategy for increasing carbon sequestration and climate change mitigation. These sown, legume-rich improved pastures, now occupying more than 4% of the national agricultural land and being implemented in other countries, are commonly found in the understory of Mediterranean-type agroforestry systems – the Montados - with cork oak (Quercus suber) as the dominant tree species, often co-occurring with stone pine (Pinus pinea). However, the sustainability of these sown pastures and their long-term consequences for the ecosystem are not completely understood. We examined the effects of pasture diversification on C, N, P stoichiometry along a sequence of paired improved biodiverse and natural pasture plots in cork oak-pine stone savanna, as a means to assess the potential nutrient-related services provided by this management technique.
Soil nitrogen and carbon concentrations were similar across pastures under oak and pine canopies, but were slightly lower in improved pastures than natural pastures for open field samples. On the contrary, total soil phosphorus was higher in improved pastures under pine canopies only. Magnesium and calcium contents were higher in improved pastures (ca. 40% increase for Mg and 20% for Ca) compared to natural pastures across all plots, likely reflecting specific management actions (e.g., fertilization) associated with the establishment of these biodiverse swards. Across all plots and vegetation types, plant N and P concentrations were higher in improved pastures (1.56% N; 0.19%P) compared to the natural pastures (1.44% N; 0.16%P), with no differences in C concentration, leading to higher C:N and C:P ratios, but also N:P ratio, in natural pastures vegetation. These differences were mainly driven by changes in the herbaceous layer nutrient status with little or no differences observed in tree leaves. Further understanding the linkages between the local management actions and ecosystem biogeochemistry will helps promote long-term sustainability of these agroecosystems.