• Hay-meadows production and weed dynamics as influenced by management

      Magda, Daniele; Theau, Jean-Pierre; Duru, Michel; Coleno, François (Society for Range Management, 2003-03-01)
      Managers of extensive livestock systems generally have 2 goals for permanent grassland management: to obtain sufficient dry matter to feed animals and to avoid the establishment and dominance of unpalatable species. Hay production to French Pyrenean meadows is dependant on the need to balance grazing and cutting dates to produce maximum biomass for hay stock and to prevent seed recruitment of Chaerophyllum aureum L., one of the major invasive unpalatable species. Experiments and observations on a set of meadows within farms show that optimal dates calculated from degree-days for cutting or spring grazing of C. aureum fitted to see production and apex development, respectively, decreases hay yield. This decrease is related to the earliness of the cut in regard to sward growth or to the biomass loss by senescence due to the vegetative regrowth of the sward after spring grazing. Compromises and choices have to be made for each meadow by the farmer according to its potential production, the risk of invasion by C. aureum, and its role in the forage system.
    • Leaf Traits as Functional Descriptors of the Intensity of Continuous Grazing in Native Grasslands in the South of Brazil

      Cruz, Pablo; De Quadros, Fernando Luis F.; Theau, Jean Pierre; Frizzo, Adriana; Jouany, Claire; Duru, Michel; Carvalho, Paulo Cesar F. (Society for Range Management, 2010-05-01)
      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 long- term 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 species3traits, paddocks3grass 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 C4 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. 
    • Using Leaf Traits to Rank Native Grasses According to Their Nutritive Value

      Khaled, Raounda Al Haj; Duru, Michel; Decruyenaere, Virginie; Jouany, Claire; Cruz, Pablo (Society for Range Management, 2006-11-01)
      Leaf traits (leaf dry matter content [LDMC], specific leaf area [SLA] and leaf life span [LLS]) previously proposed to predict plant strategies for resource use, were studied to test if they can be used to rank grasses for digestible organic matter (DOM). On 14 native grass species from natural meadows in the French Pyrenees, leaf blade chemical components (fiber, cellulose, hemi-cellulose and lignin) and DOM were estimated for two growing periods using two different methods (chemical-enzymatic and Near Infrared Reflectance Spectroscopy). The ranking of species based on LDMC, SLA and LLS was conserved. Fiber content and DOM were significantly correlated even though the data were obtained in different years (2001 and 2002), on different organs (youngest adult blades in 2001 and all the green blades of tillers in 2002) and by different analytical methods. LDMC seems to be the most suitable trait to rank native grasses according to their nutritive value because it ranks species as well as leaf traits and it is the easiest to measure. We suggest using LDMC as an indicator to rank grassland communities for herbage nutritive values.