Plant functional types (PFT) have been used to describe the response of native vegetation to environmental factors (i.e., fertility) and to livestock disturbance, but rarely under conditions of continuous grazing. In this work we investigate whether the longterm response of grassland communities submitted to a gradient of continuous grazing pressure can be described with such an approach. After 15 yr of differentiation of the grazing pressure applied to native grasslands we measured leaf dry-matter content (LDMC) and specific leaf area (SLA) of Poaceae populations of the communities. A grazing pressure gradient was created by levels of daily forage allowance: 4, 8, 12, and 16 kg of dry matter per day per 100 kg of animal live weight, monitored monthly. PFTs were defined by numerical analysis, where an algorithm finds the optimal trait subset based on the agreement between matrices of species 3 traits, paddocks 3 grass biomass, and environmental variables (levels of forage allowance and soil characteristics). The results show that it is possible to describe a gradient of grazing pressure by means of LDMC and/or SLA measured only on the Poacea contributing at least 80% of the total Poaceae biomass. Four PFTs were differentiated by these leaf traits. PFTs having low LDMC and high SLA are characteristic of high intensity of use and are made up largely of stoloniferous C 4 species typical of rapid resource capture strategies. Conversely, PFTs characterized by high LDMC and low SLA include species that are representative of low grazing pressure. Variations in the aggregate value of traits are due to changes in the species proportions and not to leaf-size adaptation as hypothesized. We conclude than in the absence of a gradient of fertility, plants with strategies of resource capture tend to be more represented under high grazing pressures. This situation results in a loss of functional diversity, but in particular a reduction in forage availability, which is incompatible with high animal production. Resumen La noción de grupos funcionales de plantas (GFP) ha sido utilizada para describir la respuesta de la vegetación nativa a los factores del medio (fertilidad) y al disturbio del pastoreo, pero pocos de dichos estudios han sido conducidos bajo condiciones de pastoreo continuo. En el presente trabajo se trata de verificar si dicho enfoque puede utilizarse para analizar la respuesta de la comunidad a un gradiente de presión de pastoreo continuo. Al te´rmino de 15 añ os de diferenciación continua de la presión de pastoreo ejercida sobre una pradera nativa, se midió el contenido de materia seca foliar (CMSF) y el área foliar específica (AFE) de las poblaciones de gramíneas presentes en la comunidad. El gradiente de pastoreo fue establecido según los niveles de oferta de forraje: 4, 8, 12, y 16 kg de materia seca por 100 kg de peso vivo por día, oferta ajustada mensualmente. Los GFP fueron definidos según un análisis numérico, donde un algoritmo identifica un subgrupo óptimo de características basado en la correspondencia e...

Question: Are leaf dry matter content, specific leaf area and leaf life span relevant plant traits to discriminate the fertility gradient in species‐rich natural grasslands? In other words, is species ranking conserved when nitrogen availability or growing periods change? Location: Toulouse Research Centre, France; 150 m a.s.l. Methods: Fifteen grasses and nine dicotyledons were sown in pure stands in a random block design with three replicates. Each species was cultivated at two levels of nitrogen supply, limiting and non‐limiting for growth, with three replications per nitrogen level. Leaf traits were measured across both levels of nitrogen supply and growing periods over the year. Results: Leaf dry matter content values separated the species into three life‐form classes (grasses, rosette forbs and upright forbs, P < 0.001). This was not the case for specific leaf area and leaf life span. The three leaf traits were variable across growing periods and nitrogen levels, but the ranking of species was conserved over N‐levels and growth periods. Furthermore leaf dry matter content was always less variable than the other leaf traits. Conclusion: We conclude that leaf dry matter content measured only on grasses could be used as an indicator to describe the N‐richness of the habitat where native herbaceous vegetation develops.

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.

The PFT composition and the Ni were more reliable than the plant functional traits measured in the field for evaluating herbage growth pattern and digestibility in spring.

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