Effects of irrigation on the vegetation of permanent grassland in a mountain region of Switzerland

In a dry region of Oberwallis (Martisberg) changes in the vegetation of permanent grassland were observed during eight years following the introduction of spray irrigation. Botanical records on eleven plots of 25 m2 show that no fundamental changes occurred from 1988 to 1996. On the most fertile and freshest meadows the number of species slightly decreased and the proportion of good fodder plants increased after the introduction of irrigation. On the driest plots which have not been irrigated the vegetation has not changed. More evident changes following the introduction of irrigation were observed on meadows with an intermediate botanical composition compared with the two previous types. Year by year their botanical composition developed towards that of the most fertile and freshest meadows. These botanical changes do not lead to a decrease in the botanical diversity, but the fodder value of these meadows increases.