MORPHOLOGICAL PLASTICITY IN CLONAL PLANTS - THE FORAGING CONCEPT RECONSIDERED

1 Studies of morphological plasticity in clonal plants have analysed r esponses to habitat quality in terms of spacer (stolon or rhizome inte rnode) length and branching intensity. The capacity for these paramete rs to respond to environmental quality has been interpreted as an expr ession of foraging behaviour, as it confers the potential to intensify the placement of ramets in the more favourable microhabitats (patches ) of a heterogeneous environment. This plasticity in clonal morphology is compared with similar responses of individual shoots and roots to habitat quality that have also been accepted as manifestations of fora ging behaviour. 2 The most consistent morphological response shown by clonal species is a higher branching intensity - an increased propensi ty of lateral meristems to grow out and form lateral rhizomes and stol ons - under conditions of higher resource supply. In contrast, spacer lengths show a variety of responses to light and nutrient availability , and many species exhibit no significant response. Even in stolonifer ous species, where stolon internodes tend to shorten under higher phot on flux densities, the degree of shortening may often be insufficient to elicit a significant concentration of ramets in favourable habitat patches.3 Many clonal and nonclonal species have however, been shown t o be very efficient in placing leaves and roots in areas of high resou rce supply within their environment. This is achieved by a high level of morphological plasticity of the shoot and root branches. 4 We there fore suggest that it is the highly plastic changes in the morphology o f individual ramets that enable effective exploitation of local concen trations of essential resources once they have been located. The unres ponsive spacer lengths of many clonal species may permit a continuous search of habitat space by the plant, rather than a selective placemen t of ramets. 5 The foraging concept is reformulated in more general te rms relating to resource-acquisition strategies, so that it is applica ble to both clonal and nonclonal species of plants.