Point-quadrat vs Phytosociological Method to Assess the Pastoral Value of Dry Grasslands in NW Alps

The pastoral value (PV) is a synthetic index summarizing forage yield and quality for livestock. It is largely used in rangeland management to determine sward carrying capacity. The computation of PV is based on a specific survey procedure (i.e. point-quadrat method) conceived by Daget & Poissonet (1971). This method allows an accurate estimate of the abundances of the main species in the sward, whereas it underestimates the overall species richness as occasional species can be missed. On the other hand, the Braun-Blanquet phytosociological method (1932) allows to precisely determine species richness, whereas the estimation of species abundances is rather subjective because they are visually determined. The objective of this research was to evaluate the suitability of the phytosociological method to assess the PV, when compared to the point-quadrat method. The study was carried out in dry grasslands in the NW Italian Alps and 140 vegetation surveys were performed. Then, paired t-tests were performed to assess the differences in species richness and PV between the two survey methods. The phytosociological method recorded higher values of species richness than the point-quadrat one. The PV did not significantly differ between the two methods for all the grassland types, except for the Bromus erectus one. In the phytosociological surveys, the abundance visual estimation could have been facilitated by the open vegetation structure and short herbaceous layer of dry grassland communities. Future studies should compare the computation of PV also in other grasslands, such as in more productive and mesophilic ones.