RESUMO
In spite of their recognized ecological value, relatively little is known about the nutritional value of species-rich rangelands for herbivores. We investigated the sources of variation in dry matter digestibility (DMD), neutral detergent fibre content (NDF) and nitrogen concentration (NC) in plants from species-rich Mediterranean rangelands in southern France, and tested whether the dry matter content (DMC) was a good predictor of the forage quality of different plant parts. Sixteen plant species with contrasting growth forms (rosette, tussock, extensive and stemmed-herb) were studied, representative of two management regimes imposed in these rangelands: (i) fertilization and intensive grazing and (ii) non-fertilization and moderate grazing. Among the 16 plant species, four species were found in both treatments, allowing us to assess the intraspecific variability in forage quality and DMC across the treatments. The components of nutritional value (DMD, NDF and NC) as well as the DMC of leaves, stems and reproductive plant parts, were assessed at the beginning of the growing season and at peak standing biomass. All components of nutritional value and DMC were affected by species growth form: rosettes had higher DMD and NC than tussocks; the reverse being found for NDF and DMC. As the season progressed, DMD and NC of the different plant parts decreased while NDF and DMC increased for all species. DMC was negatively related to DMD and NC and positively to NDF, regardless of the source of variation (species, harvest date, management regime or plant part). Path analysis indicated that NDF was the main determinant of DMD. Better assessment of forage quality in species-rich systems requires consideration of their growth form composition. DMC of all plant parts, which is closely related to NDF, emerged as a good predictor and easily measured trait to estimate DMD in these species-rich systems.
RESUMO
⢠Variations in leaf life span (LLS), construction cost (CC) and dynamics patterns (periods of leaf production, tp , and loss, tL , time lag separating the end of leaf production and the beginning of leaf loss, t) were investigated in species differing in successional status and life forms. We tested how those traits varied along the succession and how these were interrelated. A new graphical framework is proposed to assess the influence of dynamics traits on LLS. ⢠The study was conducted on 42 species of contrasted life forms, typical of various stages of secondary succession, under the Mediterranean climate of southern France. ⢠LLS increased along the succession, tp was shorter and t longer in species from the later stage, without significant change in CC or tL . Herbaceous species, mostly of early successional status, had short-lived, low-CC leaves, produced and lost continuously. Woody species, of later successional status, had long-lived leaves, with slightly higher CC than herbs. LLS and CC or payback time were weakly correlated. ⢠Variations in LLS and leaf dynamics along the succession were related to changes in plant stature and growth potential of species, captured by leaf traits. Whether this is the consequence of a decrease in frequency of disturbance or of a change in the level of resources remains an open question.