The biogeography and historical ecology of Lobelia urens L.(r)(the heath lobelia) in southern England

This paper examines the past and present ecology and biogeography of Lobelia urens L. (the heath lobelia) which is threatened with extinction in southern England. A survey of the historical and documentary evidence of the distribution of the species is presented. Historical records exist for nineteen sites in the south but nowhere else in England. The status of L. urens is in decline in Britain with ten populations having been lost this century. The six remaining sites have been surveyed to describe the phytosociology of L. urens communities and the variability of the environmental factors controlling its distribution. A total of ninety-five quadrats containing 122 species were recorded and analysed using two-way indicator species analysis. Canonical correspondence analysis was used to assess the correlations between twenty-eight environmental variables and the floristic variation in the ninety-five quadrats. These were reduced to sixteen variables for the final analysis. L. urens is shown to be a member of rough, grass-heath communities (NVC M25 and W23) dominated by Molinia caerulea and situated on seasonally waterlogged, moderately acidic, nutrient-poor soils. The species is suited to both cyclical and sporadic soil disturbance regimes. The final discussion argues that existing populations will only be maintained and expansion of the species distribution occur, if conservationists prevent woodland succession in L. urens sites and periodically disturb the ground in locations where the species survives at present and also where it has been observed in the recent past. This link between historical ecology and present-day conservation management would appear very important. Further demographic and experimental work is needed to explore these predictions and their implications for the future conservation management of L. urens .