Effects of grazing vs mowing on the functional diversity of sub-Mediterranean productive grasslands
In order to preserve the ecosystem functioning of semi-natural sub-Mediterranean calcareous grasslands of the Central Apennines, it is vital to understand how functional diversity (FD) changes in relation to different types of disturbance. To compare the effects of sheep grazing and those of late-summer mowing, we asked: do different types of disturbance (grazing and mowing) affect FD; are FD and species diversity positively correlated in both grazed and mown grasslands; do FD and species diversity take different paths in the two disturbance regimes; and are different FD values related to changes in the composition of traits linked to competitive ability, resource acquisition and resistance strategies?
Grazed and mown sites in the Central Apennines (Italy).
We performed redundancy analysis and indicator species analysis to characterize the trait composition of the two disturbance regimes. We calculated FD for each selected trait and a compound FD for multiple traits, using Rao's quadratic entropy index. Differences in FD between disturbance regimes were tested with a nested ANOVA. We performed a regression analysis between FD and species diversity indices under the two disturbance types.
Species and functional diversity were positively correlated in both disturbance types. FD was generally less correlated with species diversity variations in mown grasslands than in grazed ones, suggesting that late mowing leads to higher levels of functional redundancy (i.e. to a wider overlap of species functional composition). Late mowing promoted higher species and functional diversities and a wider variety of functional traits in the plant community. Grazing, besides negatively affecting the species diversity of grasslands, reduced their FD by favouring the dominance of traits related to avoidance and tolerance strategies.
The continuation of late mowing is recommended to preserve the richness and variability of functional groups and the ecosystem functioning of sub-Mediterranean grasslands.