Little research has been done on the nutritive value of species-rich permanent grasslands in spite of their recognized ecological value. We proposed a new method based on the concept of plant functional type (PFT) to rank grass species and grasslands according to the organic matter digestibility (OMD) of the plant material. Th e PFTs are based on leaf dry matter content (LDMC). Th e objectives of this study were: (i) to see if there were signifi cant diff erences between PFTs for the three components of plant OMD (leaf and stem digestibility and leaf proportion [L%]) in a set of 19 grasses growing in pure stand under two contrasting levels of N supply (Exp. 1); (ii) to see whether grassland vegetation types (GVT) diff ering in their PFT composition have diff erent digestibility values; investigations being made on the leaf, stem, and whole plant OMD of fi ve and eight plant communities (Exp. 2 and 3, respectively). In pure grass stands (Exp. 1) as well as in grassland communities (Exp. 2 and 3), there was a signifi cant eff ect of PFT or GVT on leaf and stem OMD. Th e greatest diff erences in L% were observed when there were large diff erences in nutrient availability. At the leafy stage, the whole plant digestibility was higher for GVTs composed of PFTs with a low LDMC. However around the time of fl owering there was a convergence in whole-plant OMD between all grassland communities because L% decreased faster for those composed of PFTs having the lowest LDMC. At this stage, plots with low LDMC had higher plant component digestibility but lower L%. Our results show that the decrease in plant digestibility over time is the result of two processes, an ontogenic one, due to a decrease in leaf proportion, and an ageing one. For the latter, we show that PFT had an eff ect of leaf and stem digestibility at an early stage of plant development, then they decreased at a rate depending on plant development. Both processes explained the convergence between GVTs in plant digestibility at fl owering time.

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