Abstract
Livestock exerts direct and indirect effects on plant communities, changing colonization and extinction rates of species and the surrounding environmental conditions. There is scarce knowledge on how and to what extent these effects control the floristic and functional composition of plant communities in grasslands. We performed an experiment that included several treatments simulating trampling, defoliation, faeces addition and their combinations in a Mediterranean scrub community grazing-abandoned for at least 50 years. We monitored the plots for four years, and collected data on species composition, photosynthetically active radiation (PAR) and red∶far-red ratio (R∶FR), soil moisture and compaction. We estimated community weighted means (CWM) for height, habit, life cycle, seed mass and SLA. Neither compaction nor soil moisture were modified by the treatments, while PAR and R∶FR increased in all treatments in comparison to the Control and Faeces treatments. The floristic composition of all treatments, except for Faeces, converged over time, but deviated from that of the Control. The functional traits displayed the trends expected in the presence of grazing: loss of erect species and increased cover of short species with light seeds, with rosettes and prostrate habit. However, contrary to the results in literature, SLA was lower in all the treatments than Control plots. Like the results for floristic composition, all treatments except for Faeces converged towards a similar functional composition at the end of the four year period. The results of this study show the initial evolution of a Mediterranean plant community in the presence of grazing, driven primarily by the destructive action of livestock. These actions seem to directly affect the rates of extinction/colonization, and indirectly affect the light environment but not the soil conditions. However, their effects on floristic and trait composition do not seem to differ, at least at the small spatio-temporal scale.
Highlights
Livestock grazing influences vegetation through a series of direct and indirect effects on individual plants and on the environment, respectively, which have major consequences on the composition and structure of grassland communities at several hierarchical levels
The effect of grazing is reflected in changes in the species composition and richness of the grassland communities [3,4,5], these effects are often dependent on habitat productivity [6,7]
In contrast to previous studies in the same area, which found that the application of faeces in experimental plots produced an increase in species richness [61], our results showed no effect of the addition of excrement in this parameter, and a very marginal change in the floristic composition
Summary
Livestock grazing influences vegetation through a series of direct and indirect effects on individual plants and on the environment, respectively, which have major consequences on the composition and structure of grassland communities at several hierarchical levels. The effect of grazing is reflected in changes in the species composition and richness of the grassland communities [3,4,5], these effects are often dependent on habitat productivity [6,7]. The influence of grazing on the species composition and richness of grasslands has been studied by means of grazing exclusion experiments [9,10], comparisons between adjacent grazed and abandoned farms [5,11] and gradients of grazing pressure [7,12]. There is a growing interest in the study of plant trait responses to grazing [5,12,13,14,15]
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