Jing, Q. and Bélanger, G. 2012. Short Communication:Yield trend analysis of an ageing timothy sward using a modelling approach. Can. J. Plant Sci. 92: 1263-1266. Observed and simulated potential dry matter (DM) yields of the timothy (Phleum pratense L.) primary growth were compared to disentangle the yield trend from the effect of year-to-year climatic variations in an ageing sward (1 to 7 yr). Observed DM yields were close to simulated potential DM yields in the first 4 yr, but they were around 60% of simulated potential DM yields in the last 3 yr. This confirms that variations in air temperature and/or solar radiation could not explain the lower DM yield observed in the last three production years.