Non-destructive assessing and monitoring of populations of Isoetes lacustris L

Extensive studies of Isoetes lacustris, performed throughout Europe, resulted in regressions between the number of leaves per rosette and (1) the number of spores per megasporangium, (2) length of seasonal growth, (3) Secchi depth and (4) water colour plus a relationship between pH and the number of spores per megasporangium. The evaluation of Isoetes populations requires measurements of the lake data Secchi depth, water colour, pH and conductivity, the establishment of climate data and leaf counts on 20-30 plants with the aid of SCUBA. The method may be applied to lakes in a range of situations, varying between lowland and highland, and between temperate and subarctic climate regions. The regressions are displayed graphically. The actual mean leaf number and corresponding megaspore number are compared with the numbers referred to in the environmental data. Consistent values point to the parameters which influence growth and vitality of the quillwort and to what extent, in a particular lake. Examples of evaluation and monitoring are given.