Prescribed burning is a management tool used in the last years to prevent the invasion of woody vegetation in pastureland, decreasing the risk of extensive wildfires in vulnerable areas. Nevertheless, the effect of this practice in the soil is not yet fully understood, and more information is needed to ameliorate management practices. In order to understand how prescribed fire affect soil fertility, and the carbon (C) and nitrogen (N) cycles in pastures invaded by shrubs in Mediterranean areas, we carried out an experiment in Montseny, an acidic pre-littoral mountain range northern Barcelona (NE Iberian Peninsula). This area has experienced a decrease in traditional sheep stocks and therefore pastures endure strong shrub encroachment. We wanted to know: 1) what are the effects of prescribed burning on soil fertility in acidic Mediterranean pastures? and 2) are there legacy effects of the previous vegetation patches on the soil C and N cycles after prescribed burning? To answer those questions, we sampled soils before and after prescribed burning of a pasture heavily invaded by shrubs. Soils were sampled under six canopy types: Erica scoparia-dominated patches, Calluna vulgaris-dominated patches, Cytisus scoparius-dominated patches, Pteridium aquilinum-dominated patches and Cladonia-dominated biological crusts. The exact soil sampling point was recorded by a highly precise GPS, and each point resampled few days and six months after burning. As expected, soil fertility parameters varied with burning, including losses in soil phosphorus and nitrogen. In addition, several soil C and N parameters responded to the previous vegetation patches, including shifts in soil C and N concentration.

Dehesas are mosaics of open grassland and standalone trees that are diversity reservoirs. However, they have recently faced abandonment and intensification, being replaced by plantations of fast-growing trees or subject to encroachment. Following a change in dehesa communities and structure, a change in soil microbial diversity and functionality in dehesas is expected, but dehesas’ microbial diversity is still a big unknown. In this work, we bring to light the soil prokaryotic taxonomic diversity in dehesa ecosystems and present a first approach to assessing their metabolic diversity through metabarcoding data. For this, we compared three dehesas dominated by different tree species: (i) one dehesa dominated by Quercus ilex; (ii) one dominated by Pinus pinea; and (iii) one dominated by a mixture of Q. ilex and Q. suber. At each dehesa, samples were taken under the canopy and in the open grassland, as well as through two seasons of peak vegetation productivity (autumn and spring). Our results show the following findings: (1) seasonality plays an important role in prokaryotic richness, showing higher values in autumn, and higher evenness in spring; (2) the effect of seasonality on the soil’s prokaryotic diversity is often modulated by the effect of tree species and canopy; (3) taxonomic diversity is driven mainly by the site effects, i.e., the opposite of the metabolic diversity that seemed to be driven by complex interactions among seasons, tree species, and canopies.