Early plant community dynamics following overseeding for the rehabilitation of a Mediterranean silvopastoral system

The sowing of selected seeds is often applied as post-fire rehabilitation practice in Mediterranean silvopastoral systems. Often, the topography of these silvopastoral systems is sloppy and irregular, requiring low input and easy pasture rehabilitation practices, such as no tillage, low seed and fertilizer rates. In this paper, we studied the vegetation changes over 4 years, after a low-input overseeding (broadcasting) of non-native pasture species, within a post-fire rehabilitation program of a silvopastoral system in Sardinia (Italy). The main objective was to assess the effect of overseeding on the early plant community dynamics and on the relationship between topography, soil pH, and soil nitrogen content on the spatial and temporal dynamics of the grassland composition. Understorey vegetation was classified into nine "functional classes", three corresponding to the oversown species (subclovers, burr medic and annual ryegrass) and six belonging to the native community, i.e. grasses, legumes, Cistus spp., spiny Carduaceae, spiny Rubus spp. and other forbs. The oversown species showed a rapid establishment, contributing from 30 up to 50% to the floristic composition of the oversown pasture. The overseeding reduced the abundance of post-fire invasive shrubs and spiny forbs by up to about 70% compared to the unsown pasture. The spatial patterns of the functional classes were only weakly influenced by nitrogen content, with a higher impact on introduced species in the first 2 years after overseeding, while the topographic variables had a desultory influence over the 4 years. Overseeding proved to be effective for the rehabilitation and improvement of semiarid Mediterranean grasslands without substantially constraining the ecological succession of floristic composition towards the native vegetation.