Effects of revegetation methods on wild-boar-rooted semi-natural pastures in the eastern Italian Pre-Alps

Alpine semi-natural pastures are highly appreciated for their agronomic and environmental value. Recent wild-boar recolonisation represents an important risk to their conservation. Agronomic value is reduced due to decreased vegetation cover and ground surface becoming difficult to transit by animals and machinery. Vegetation natural value can significantly change due to species establishing in the bare soil niches created by rooting and soil properties can be impacted by the increased bulk density and organic matter decomposition. The research was conducted in 16 summer farms, where the middle-term effects of three revegetation methods not yet sufficiently evaluated were studied: natural regeneration (NR), no intervention at all; rotary tillage (RT), with clods displaced by wild boars broken up with rotary tillers and redistributed on the ground surface; and RT plus mechanical sowing of mixtures of forage cultivars for fertile-soil pastures (RTS). Pasture traits analysed were ground cover (stones and bare soil cover and vascular plants' cover), vegetation, forage quality and carrying capacity. All revegetation methods affected negatively the pasture natural value which transformed into vegetation typical for more fertile soils, with lower biodiversity, less forbs and more grasses. Changes in grassland natural value and productivity differed greatly by revegetation type. In NR, the species loss was the lowest and ecological recovery was fastest. However, the negative effect on the carrying capacity in the first 2 years after rooting was the highest, and the unlevelled ground surface made the pasture difficult to transit. RTS and RT could quickly re-establish a full, levelled (easy-to-transit) herbaceous cover and, especially RTS, better control weed establishment. In RTS species loss was highest and no trend of ecological recovery was observed. The introduced, highly competitive forage cultivars nearly doubled the pasture productivity. IN RT, the species loss was intermediate between that of NR and RTS, the ecological recovery was fast and the pasture productivity became rapidly similar to that of pre-rooting. A pros-and-cons balance suggests that RT is the most suitable method for revegetating rooted alpine pastures, as it recreates an easy-to-transit pasture surface with good agronomic quality and does not introduce non-native ecotypes.