A 38-YEAR STUDY OF RELATIONS BETWEEN WEATHER AND VEGETATION DYNAMICS IN ROAD VERGES NEAR BIBURY, GLOUCESTERSHIRE

1 The Bibury long-term data set contains information on annual fluctua tions in the abundance of over 100 grasses and forbs in roadside verge vegetation over the period from 1958 to the present. Monitoring has b een carried out every July by the same individual. The data set repres ents a unique long-term record of the dynamics of a complete plant com munity. 2 Records for the most abundant taxa (including bare ground an d 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 sp ecies 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-m onth seasonal periods (March-August, September-February), with time la gs of 0, 1 and 2 years. 3 Principal components analysis (PCA) was used to formulate annual weather indices, using either conventional weathe r variables (temperature, rainfall and sunshine) or the Lamb catalogue of daily weather types. 4 Between 5% and 70% more correlations were o bserved than might be expected to occur by chance, depending on the se ason and the PCB index, indicating markedly non-random plant-weather r elationships. Total vegetation production was positively correlated wi th minimum spring temperature. The distribution of correlations was ge nerally evenly distributed across the three lag periods. 5 In general, those species favoured by environmental stress or disturbance were pr omoted following warm dry springs and summers, whereas those favoured by more productive conditions were promoted following a wet growing se ason.