The Growth of Sphagnum: Experiments on, and Simulation of, Some Effects of Light Flux and Water-Table Depth

SUMMARY (1) Experiments were made to determine the effects of both shading and of water-table depth on the growth of three species of Sphagnum. The species (and their usual habitats) were: S. capillifolium (hummocks); S. papillosum (lawns); and S. recurvum (pools and flushed lawns). (2) Water-table depth had little effect on growth measured as increase of dry matter; shading reduced growth and there were specific differences associated with plant size. There were no significant interactions between water-table depth and shading. (3) For growth measured as growth in length, there were highly significant interactions, individual species behaving differently in response to shade and, to a lesser extent, in response to water-table depth. (4) In Sphagnum lawns in two natural habitats there was a negative correlation between depth of the water-table and surface-roughness. In experimental conditions surface-roughness increased both as the water-table was raised and as shade increased. (5) A computer simulation of growth of Sphagnum in a lawn was able to reproduce the observed variations in surface roughness. In mixed lawns of two species, the one in its 'natural' habitat out-grew the other.