Long‐term effects of grazing intensity on strategies and spatial components of functional diversity in subtropical grassland

Abstract

AbstractQuestionHow does grazing intensity affect plant community functional traits and the spatial components of functional diversity in subtropical grasslands?LocationLong‐term cattle grazing management experiment in subtropical Campos grassland, southern Brazil.MethodsFourteen experimental units (paddocks) maintained under seven grazing intensity treatments for 26 years. In each paddock, we recorded plant species cover and species functional traits in nine systematically located plots of 1 m2. Nineteen functional traits were used in the ordination of species to identify main axes of trait variation. Functional diversity measured by Rao entropy was partitioned into alpha, beta and gamma components. We tested, by linear models, for the effects of grazing intensity on community‐weighted mean traits and functional diversity components, using as traits the species scores on the PCA axes.ResultsThe two main axes of trait variation suggest a separation in species by their functional strategies (acquisition–conservation and tolerance–avoidance trade‐offs). Acquisitive and tolerant species increased while conservative and avoidant species decreased with grazing intensity. Rao quadratic entropy, considering the three spatial components, decreased with grazing intensity, but this trend was more accentuated with beta‐diversity.ConclusionsThe long‐term, strictly‐managed grazing experiment allowed us to reveal the effect of not only grazing disturbance per se, but also of different grazing intensities. Under high grazing intensity, frequent and severe defoliation allows only the persistence of species similarly adapted to regrowth. Under low grazing intensity, the lack of frequent defoliation enables the development of species with high investment in strong and long‐lived leaves. The partitioning of functional diversity revealed that the increase in functional diversity in areas with low grazing intensity is mostly due to an increase in heterogeneity among patches (beta‐component). The double stratum vegetation structure: tussocks, which escape grazing control, and short‐grazed patches often overgrazed, is maintained by grazer selectivity.