Demography and Growth Forms of the Clonal Perennial Rubia Peregrina in Mediterranean Vineyard and Unmanaged Habitats

Abstract

SUMMARY (1) During a two-year study, the dynamics of genets, ramets and aerial metamers (leaf whorl+ internode) and the growth forms of three populations of Rubia peregrina, a mediterranean rhizomatous perennial, were compared in a vineyard, a degraded open sward and under a Quercus ilex canopy. (2) The weedy vineyard population increased in size (the relative rate of change of ramets over the period of study was 1 8) whereas the two non-weedy populations were in a more-or-less steady-state (relative rates of change were -01 1 and 0-23 for the sward and oakwood populations, respectively). No establishment of new genets was observed. (3) In the three habitats, the production of ramets and metamers was maximal during spring and autumn; during summer, it stopped in unmanaged habitats, while a small rate of production was still observed in the vineyard. In all habitats, mortality was high during active growth periods and, especially in the sward, during summer drought. Death of ramets was density independent in the vineyard and sward. (4) In the vineyard, R. peregrina showed a phalanx growth form, with a high density of closely packed ramets; under the oak canopy it showed a guerrilla growth form with lower density of more widely spaced ramets; in the degraded open sward, an intermediate growth form was observed. The results show that the compact architecture of the phalanx type is enhanced by the high degree of branching of modules bearing short and numerous metamers, and that opposite traits predominate in the guerrilla type. In addition, half-lives of metamers were inversely related to their size. Thus, it is suggested that the morphology of ramets and demography of aerial metamers should be integrated in the definitions of growth forms. (5) For the whole data set, a positive linear relationship (P < 0 001) was found between half-lives of metamers and internode length and a negative linear relationship (P < 0 003) between internode length and degree of branching of ramets. (6) The differences in growth forms between the unmanaged and agricultural habitats may be due to competition and resource availability. It is suggested that species tolerant of herbicides and displaying a phalanx growth form are potentially injurious weeds in vineyards and orchards where minimum tillage is practised.