Implications of the spatial pattern of Vigur's Eyebright (Euphrasia vigursii) for heathland management

Abstract

Summary Euphrasia vigursii is a rare, endemic plant of heathland in South West England. Its numbers have declined markedly in recent years. The great majority of plants in modern times has been found on Lydford High Down, and this site has recently undergone a change in management to encourage a greater cover of dwarf-shrubs, and this may have consequences for the E. vigursii population. The shrub-grass mosaic structure was quantified using line transects and mapped. Associations with other species were investigated with 0.25 m2 samples. Relationships with Ulex gallii dwarf-shrubs were examined by detailed mapping within four 100 m2 sampling areas and second-order spatial analysis with Ripley's K/L and Wiegand-Moloney's O-ring statistics. Height and canopy dimensions of the dwarf-shrubs were also recorded. Individuals of E. vigursii were normally found in areas with 35–50% gorse cover, and with the shrubs about 30 cm tall. At finer scales, within the subpopulations, E. vigursii plants were found in patches of up to 0.9 m in diameter, and were positively associated with Euphrasia anglica. E. vigursii plants were located around the edges of U. gallii shrubs more than expected by chance. A parasitic relationship is possible, or the dwarf-shrubs might have a facilitative effect on the arrival, establishment and/or growth of E. vigursii. Any significant increase in dwarf-shrub cover from current levels might cause a further reduction in the population size of E. vigursii. The population has declined on Lydford High Down from an estimated 21,000 individuals in 2002 to less than 500 in 2004. Areas where small populations of E. vigursii have recently disappeared do show an increased cover and height of dwarf-shrubs, compared to areas where the population has survived. While increasing the cover of dwarf-shrubs on Dartmoor may be a laudable objective in general terms, it may not be the most appropriate way to manage populations of E. vigursii on Lydford High Down. Often conservation priorities are set to meet large-scale, habitat-orientated objectives, but fail to recognise the fine-scale needs of rare populations that may need somewhat different management regimes.