Relative growth-rate: its range and adaptive significance in a local flora.

Laboratory experimentation in plant ecology has evolved very largely as an attempt to pursue investigations which began with fieldwork. With the widespread development of plant growth-room facilities an alternative approach is possible. This is to measure the characteristics of plants under a variety of controlled conditions, and to use the results to predict their field ecology (Grime & Hodgson 1969). One advantage of this approach is that predictions can be tested against descriptions of the field ecology obtained by independent field investigation. In the long term, however, the most important advantage of the predictive approach is that many growth-room investigations can be reproduced or extended wherever there are adequate facilities: hence data collected on different species or genotypes and in various laboratories can be compared directly. When comparable data are available for a large number of species drawn from a wide range of habitats it may be possible to estimate the limits of variation of a particular plant attribute, to place an individual measurement in context and to attempt to judge its ecological significance. The investigation described in this paper is an attempt to examine the range and pattern of variation in a local flora of one particular plant attribute-the maximum potential rate of dry matter production. Although most data have been obtained from only one field population per species the number of species is large and includes representatives from all the major dry terrestrial habitats of the area. Uncertainty concerning the extent to which each sample is representative of the species does not, therefore, invalidate the exercise either as an estimate of the range of variation or as an attempt to recognize differences between groups of species of contrasted ecology.