Species dominance rather than complementarity drives community digestibility and litter decomposition in species‐rich Mediterranean rangelands

Questions Management practices in permanent grasslands affect plant community structure and thus resources for both the herbivore and the decomposer subsystems. While their effects on digestibility or litter decomposition had been studied separately, few, if any, studies have tested the responses simultaneously and the underlying relationships with community functional structure. We tested whether the mass ratio hypothesis or the niche complementarity hypothesis held in scaling up from species to community level. Location Dry calcareous rangelands of southern France on a limestone plateau. Methods We measured digestibility and litter decomposability of 24 communities in three management regimes representing an intensification gradient corresponding to a combination of increased fertility and grazing. Key structural leaf traits (e.g. leaf dry‐matter content, LDMC) and chemical traits (e.g. leaf nitrogen content, LNC, and leaf neutral detergent fiber, LNDF) were measured as well as communities’ mean (i.e. community‐weighted mean, CWM) and variance (i.e. community‐weighted variance, CWV). Results Digestibility and litter decomposability were higher in intensively grazed and fertilized than in lightly grazed and abandoned communities. Increased nutrient availability combined with more intense grazing induced an increase in CWM LNC and a decrease in CWM LDMC and CWM LNDF. Communities in these regimes were less functionally diverse, with lower CWV LDMC and lower CWV LNDF. Conclusions The close relationship between digestibility and decomposability was maintained at the community level. Relationships between CWM, community digestibility and decomposability were more consistent across the management regimes than relationships with CWV, supporting the dominance rather than the complementarity hypothesis.