A meta-analysis of climate change effects on forage quality in grasslands: perspectives for mountain and Mediterraneann areas

Atmospheric carbon dioxide (CO2), global mean temperature and inter-annual variability in temperature and rainfall are expected to be significantly higher by the end of the 21 st century. In order to review the effects of these factors on forage quality, we carried out a meta-analysis based on climate manipulation experiments. A first original output is the absence of effect of elevated CO2 on structural carbohydrates (NDF,ADF, lignin), and digestibility. Elevated CO2 decreased by an average of 9% forage nitrogen (N) content, but the concentration of N in the harvested biomass could be maintained as the result of increased legume abundance. There were no consistent effects of warming on N, water-soluble carbohydrates, NDF, ADF and digestibility. We highlighted the continuum in the effect of water availability from drought to irrigation, with a curvilinear increase of forage N response as water availability decreased. Digestibility increased on average by 10% with drought, but with strong experimental variations. Special emphasis is placed on the discussion of the specificities of mountain and Mediterranean grasslands. Forage N content increased by an average of 9% as a response to warming in mountain areas compared with a 2% decrease in temperate plains. In Mediterranean areas, forage N content was only reduced by 1% as the result of elevated CO2. In conclusion, we did not observe any dramatic change in forage quality induced by each climate change factor, but further experiments should test for the effects of combined factors including extreme climatic events.