Nitrogen fertilizer enhances vegetation establishment of a high-altitude machine-graded ski slope

Machine grading is frequently required to prepare the terrain when building high-altitude ski slopes in the Alps. However, this kind of disturbance alters the natural environment, destroying the vegetation and hampering its reestablishment. Thus, specific restoration plans are necessary to encourage the recovery of vegetation, which is already affected by different natural constraints in this harsh environment. One of the main critical factors affecting plant growth in high-altitude areas is the lack of available nitrogen (N) in the soil. In this context, the addition of a slow-release N fertilizer was carried out in an experimental revegetated ski slope between 2,800 and 2,900 m above sea level in the western Italian Alps. Both vegetation and soil were monitored during a 5-year period in order to test the effectiveness of N addition on the restoration process. Even if effects on soil carbon and N contents were negligible, vegetation was remarkably affected by the fertilization, since the total vegetation cover and the species richness significantly increased. Against the expectations, there was a remarkable increase in spontaneous forbs, rather than in most of the sown graminoids, which slightly varied during the experimental period. Actually, graminoids responded in different ways, mostly increasing (likewise forbs), but the slight decrease of the dominant Festuca nigrescens (Chewing's Fescue) masked their spread. This study confirms the noteworthy role of N in high-altitude alpine soils and consequently its importance to improve the restoration process of degraded ecosystems.