Studies in the population dynamics of some Teesdale plants

Abstract

The study was essentially a demographic one. Few studies of this kind have been carried out on rare plant populations. Permanent quadrats (selected subjectively for the presence of some Teesdale plants, including Gentlana verna and Polygala amarelle) were established on Widdybank and Cronkley Fells in the Northern Pennines. The quadrats were all established on the grazed or eroding areas of sugar limestone grassland. For each quadrat the grid positions of all the individuals of the species being recorded were plotted on a chart. The fate of the initially recorded mixed-age population and that of all subsequent additions was noted at each visit. Larger permanently marked sample sites, usually adjacent to a permanent quadrat, were recorded once a year for the number of flowering and non-flowering individuals. Individuals which flowered were then recorded for the number of flowers, fruits and seeds they produced. From these data the population flux, mortality, survival and age-distribution of the individuals in the quadrats were obtained. The relative importance of sexual reproduction was ascertained by closely following the appearance of seedlings and vegetative shoots in each of the quadrats where a species produced both.