A 38-year study of relations between weather and vegetation dynamics in road verges near Bibury, Gloucestershire

The Bibury long-term data set contains information on annual fluctuations in the abundance of over 100 grasses and forbs in roadside verge vegetation over the period from 1958 to the present. Monitoring has been carried out every July by the same individual. The data set represents a unique long-term record of the dynamics of a complete plant community. Records for the most abundant taxa (including bare ground and litter) were used to determine the effect of climate variability on the year-to-year performance of the selected species. Residuals about the long-term mean log biomass of each species (detrended where the species showed a significant increase or decrease in abundance over time) were correlated against indices of interannual climate variability. Plant and weather records were compared over 3-month seasonal periods (March-May, June-August, September-November, December-February) or 6-month seasonal periods (March-August. September-February), with time lags of 0, 1 and 2 years. Principal components analysis (PCA) was used to formulate annual weather indices, using either conventional weather variables (temperature, rainfall and sunshine) or the Lamb catalogue of daily weather types. Between 5% and 70% more correlations were observed than might be expected to occur by chance, depending on the season and the PCA index, indicating markedly non-random plant-weather relationships. Total vegetation production was positively correlated with minimum spring temperature. The distribution of correlations was generally evenly distributed across the three lag periods. In general, those species favoured by environmental stress or disturbance were promoted following warm dry springs and summers, whereas those favoured by more productive conditions were promoted following a wet growing season.