The Effects of Waterlogging on the Growth of Molinia Caerulea and Eriophorum Vaginatum

It is well known (Jefferies 1915; Fraser 1933; Pearsall 1950) that Molinia caerulea is usually associated with situations which have moving soil water whereas Eriophorum vaginatum is found in more stagnant places, but the reasons for this difference are little understood. Pearsall (1938) concluded that under acid peat conditions (pH 4 Molinia occurred in reducing conditions (Eh5 110-270). Rutter (1955) showed that the best development of Molinia on a heathland site occurred in places with the greatest amplitude of water table fluctuation, and suggested that fluctuation in the water table may result in the sweeping away of toxic products or renewal of soluble nutrients. Webster (1962) showed that Molinia was adversely affected by hydrogen sulphide and carbon dioxide concentrations in the soil which were apparently not harmful to Erica tetralix. Conway (1940) drew attention to the possible importance of root distribution with depth. Molinia caerulea appears to be more sensitive to some anaerobic peat conditions than Eriophorum vaginatum but it is not clear what these conditions are or how they operate differentially on these two species. The work described here has examined a differential growth response of possible relevance to this problem using redox potentials as the method of characterizing soil aeration. Gillespie (1920) and van Raalte (1944) have shown this method to be useful in waterlogged soils containing organic matter.