Pascal Carrère

The ability of sheep at different stocking rates to maintain the quality and quantity of their diet during the grazing season

The degree to which grazers maintain the amount (organic matter intake) or the quality (organic matter digestibility) of their diet without adversely affecting the other component was addressed by investigating how sheep managed trade-offs between quantity and quality throughout the grazing season in an upland area of central France. Two groups of five dry ewes, grazing two plots of contrasting areas from April to the end of September 2000. were studied. On the smaller plot (1500 m 2 ), the application of a high stocking rate (HSR) produced a resource of good quality but in low quantity; and on the larger plot (3000 m 2 ),a low stocking rate (LSR) created a sward of low quality but in good quantity. In spring, in both conditions, the sheep maintained their intake of digestible organic matter (OM) at between 1000 and 1250 g/day. Both organic matter intake and digestibility remained high at both stocking rates. In summer, the intake of digestible OM decreased to between 750 and 1000 g/day. On HSR, this was mainly due to a decline of intake in relation to the decrease of intake rate and bite weight. On LSR a decrease in digestibility and to a lesser extent in intake was involved. At both stocking rates, the sheep maximized the digestibility of their diet by selecting the green laminae throughout the grazing season. In spring, the sheep modulated their daily grazing time to compensate the decrease in intake rate and maintained a high daily intake. In summer and autumn, the sheep failed to maintain their daily intake at the same level as previously observed. On both plots they modulated their daily grazing time to cover their needs (730 g/day), but they did not increase it further to maximize daily intake. This may be attributable to the costs involved in selecting (LSR) or taking (HSR) the best components from the sward.

Plant trait–digestibility relationships across management and climate gradients in permanent grasslands

1. Dry matter digestibility is a critical component of herbage nutritive value, a major service delivered by grasslands. The aim of this study was to test whether the dominance hypothesis applies to assess the impacts of environmental gradients and management regimes on thiscomponent of herbage nutritive value in permanent grasslands. 2. At the plant level, digestibility has been related to a number of functional traits, but whether this can be scaled up to the community level in species-rich grasslands and how such relationships are modulated by environmental conditions and management regimes remainunknown. Our primary objective was to test whether community-weighted means – species trait values weighted by the species abundance – of morphological, phenological and chemical traits could be used to explain variations in digestibility over a large range of climatic contexts,soil resource levels and management regimes. Our second objective was to explain variations in community digestibility within and among nine contrasting sites along large natural and man-induced environmental gradients.3. Over the whole data set, digestibility and most community-weighted means of traits responded to climatic factors and management regimes, but relations were not always significant when each site was considered separately. Community digestibility was significantly related to one or more plant traits within each site and to all of the measured traits when considering all the sites. Leaf dry matter content (LDMC) had the most consistent effects on digestibility, with a strikingly similar negative effect within each site. Potential evapotranspiration was negatively related to digestibility and contributed to explain a large part of the among-site variance. In addition, a low return interval of disturbance and a high disturbance intensity (biomass removal) were both associated with a high digestibility.4. Synthesis and applications. Disturbance regime, plant traits and local climate impacted dry matter digestibility roughly equally in grasslands. The effects of community composition on digestibility and its response to abiotic factors could be successfully captured by community weightedmeans of leaf dry matter content. This functional marker can be used to develop indicators and grassland management rules to support farmers in the refinement of their practices towards specific needs, such as target production outputs.

Identification of the environmental factors which drive the botanical and functional composition of permanent grasslands

SUMMARY Managed grasslands provide environmental and agronomic services that can be predicted from the botanical and functional composition of the vegetation. These areinfluenced by management, edaphic and climatic factors. The present report set out to estimate and analyse the relative importance of management, soil and climate factors on botanical and functional characteristics of grassland vegetation. A set of 178 French grasslands having a large pedoclimatic and management gradient was selected, and information collected on botanical composition, pedoclimatic factors and management. Six vegetation characteristics were considered: two botanical (floristic composition and species dominance) and four functional (proportion of entomophilous species, number of oligotrophic species, leaf dry matter content and date of flowering). First, the links between the characteristics of the vegetation were analysed to check for any redundancy among them; all were kept. Second, it was demonstrated that botanical and functional characteristics were not driven by the same factors: functional composition was characterized by management, edaphic and climatic factors, whereas botanical composition was influenced mainly by climatic and edaphic factors plus other factors. Interactions between factors also have to be taken into consideration to predict botanical and functional composition of grasslands. Functional and botanical characteristics of vegetation help to predict ecosystem services delivered by grasslands and may be used in combination.

Determination of Aboveground Net Primary Productivity and Plant Traits in Grasslands with Near-Infrared Reflectance Spectroscopy

Proposed links between biodiversity and ecosystem processes have generated intense interest in the linkage between aboveground net primary productivity (ANPP) and soil C storage. Quantity and quality of ANPP largely depend on plant functional groups and management practices. In a context of environmental change (that is, land-use and climate) long-term studies of ANPP and functional groups are gaining interest. However, rapid determination of ANPP and functional groups are often limited in time and money, resulting in less than ideal sampling schemes and replications. Near-infrared reflectance spectroscopy (NIRS) can relieve constraints of labor intensive hand-sorting by providing quick, non-destructive, and quantitative analyses of a range of organic constituents (for example, plant tissues). Here, we investigated the potential of a NIRS method to rapidly predict harvested green aboveground biomass, the proportion of dead material, and simple functional plant traits, necessary to determine ANPP and related ecosystem properties. The issue was investigated for two independent grassland experiments of contrasted long-term field management (high vs. low grazing and N fertilization). Our results show that NIRS analyses are well suited to determine ANPP (12 and 19% error of prediction) and simple plant traits (error 9%) of contrasted treatment of two independent multi-species grasslands. Moreover, we show that calibration may be simplified when compared to commonly used protocols, which offers ecologists enormous analytical power.

An open platform to assess vulnerabilities to climate change: An application to agricultural systems

Numerous climate futures are now available from global climate models. Translation of climate data such as precipitation and temperatures into ecologically meaningful outputs for managers and planners is the next frontier. We describe a model-based open platform to assess vulnerabilities of agricultural systems to climate change on pixel-wise data. The platform includes a simulation modeling engine and is suited to work with NetCDF format of input and output files. In a case study covering a region (Auvergne) in the Massif Central of France, the platform is configured to characterize climate (occurrence of arid conditions in historical and projected climate records), soils and human management, and is then used to assess the vulnerability to climate change of grassland productivity (downscaled to a fine scale). We demonstrate how using climate time series, and process-based simulations vulnerabilities can be defined at fine spatial scales relevant to farmers and land managers, and can be incorporated into management frameworks.

Complex plant community responses to modifications of disturbance and nutrient availability in productive permanent grasslands

Question(s) Do the effects of grazing and fertilisation on taxonomic and functional diversity follow the dynamic equilibrium model? Location Long-term observatory of permanent upland grasslands in Massif-central, France. Methods Over eight years, we monitored vegetation changes in 24 experimental plots in two productive grasslands after modification of grazing intensity (including abandonment) or fertilisation regime (including cessation of fertilisation). Botanical surveys and plant trait measurements (leaf dry matter content, LDMC; specific leaf area, SLA and reproductive plant height) were performed within each plot. We analysed taxonomic responses using principal response curves and functional responses from observed temporal changes of community-weighted mean traits and Rao index. Results Grazing abandonment led to significant reductions in species richness and functional convergence toward taller plants with higher LDMC in both grasslands. Intermediate and high grazing pressure did not differ but showed strong variations in taxonomic diversity between-years. Changes in functional vegetation structure were mostly driven by species turnover and weakly influenced by intraspecific trait variability. Community responses to modified fertilization regime were more complex with strong differences between the two mown grasslands. Species richness did not change significantly although species evenness decreased in the highly-fertilised treatments (NPK), particularly in the most productive grassland. Here, functional changes were largely driven by intraspecific trait variability. Both functional divergence and convergence were found for different traits. In NPK, grassland assemblages converged toward taller plants while SLA diverged. Conclusions In our upland study system, the different components of grassland diversity responded differently, in terms of direction or rate of change and mostly under extreme modifications of management. Following abandonment, the observed patterns suggest a prominent and consistent role of competitive exclusion as expected under the DEM. However, our findings also suggest the role of additional processes especially the importance of niche differentiation for our mown grassland under NPK. Timing and net effects of these combined assembly drivers were sensitive to even slight differences in initial productivity and species composition. This article is protected by copyright. All rights reserved.