Quantitative vs qualitative vegetation sampling methods: A lesson from a grazing experiment in a Mediterranean grassland

Question: How well does a time-saving, qualitative sampling method compare with an intensive, quantitative sampling method in identifying the effects of reduction and cessation of cattle grazing on compositional change in a Mediterranean grassland? Location: Upper Galilee, northern Israel. Methods: Experimental treatments involved two levels of grazing intensity and protection from grazing for different time periods. Sampling methods included a quantitative method, involving harvesting of vegetative biomass from small (25 × 25 cm) quadrats within 10 × 10 m exclosures, and a qualitative method, involving recording presence only of plant species within the same exclosures. Results: Both sampling methods revealed differences between protected vegetation and grazed vegetation; however they were not comparable in the way they described differences in species composition between grazed and ungrazed vegetation, and neither method could discriminate between the two levels of grazing intensity. The discrepancy between the two methods in the number and identity of species recorded ranged from 37% to 51% per plot for species recorded by both methods. Conclusions: Qualitative sampling highlighted species that are indicative of protection from grazing; however it did not satisfactorily describe alteration in community composition, since the studied grassland is characterized by changing dominance of common species among treatments, instead of major species turnover. Suitable methods of data collection and monitoring will depend primarily on manpower and the specific characteristics of the studied community.