Ecological Studies on Growth-Form in Bryophytes: IV. Growth-Form Distribution in a Deciduous Wood

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Abstract
In culture, direction of growth and branching in some mosses may be modified by direction and intensity of light supply, and correlations have already been suggested between representation of certain growth-forms and illumination in the natural habitat. To examine this, the distribution of Rhytidiadelphus triquetrus, Thuidium tamariscinum and Eurhynchium praelongum in a deciduous wood in Kincardineshire, Scotland, was investigated in relation to variation in habitat factors. At localities in which each of these species were abundant the community structure and stratification of the woodland were recorded and comparative measurements made of illumination, duration of canopy of the various strata, evaporation, rela-tive humidity of the atmosphere, soil moisture, drainage etc. Full analysis of the bryophytic communities was also carried out. Moisture and soil conditions were found to differ less than illumination between localities, suggesting that light supply may be of prime importance in determining bryophytic distribution here. Where light intensity falls in summer to between 5 and 13% of that in the open, communities in which the weft form predominates are found; where the value is 1% or less the more slender thread-like forms are of greater importance. The field stratum is largely responsible for these variations, by its shading effects. Where it is sparse and the tree and shrub canopies are open, robust wefts without rhizoids (e.g. R. triquetrus) are prominent. When shading is dense, though of short duration (pre-vernal), there is luxuriance of wefts in which a more creeping habit is associated with tufts of rhizoids on the stems (e.g. T. tamariscinum). If, however, a field stratum persists throughout the summer, the habitat appears to be most favorable to the slender thread-like form represented by E. praelongum.