ECOLOGICAL APPLICATION OF HERBCHRONOLOGY - COMPARATIVE STAND AGE STRUCTURE ANALYSES OF THE INVASIVE PLANT BUNIAS-ORIENTALIS L

The age structures of stands of the herbaceous perennial forbs Bunias orientalis and Rumex crispus were determined in different habitats in the vicinity of Wurzburg (Unterfranken, Germany). Plant age was determ ined by counting annual rings in the secondary root xylem (herbchronol ogy). In rarely-disturbed (unmown, not disrupted) habitats, stands of B. orientalis showed a high proportion of older (greater than or equal to 4-year old) individuals, whereas comparable stands at frequently-d isturbed habitats were dominated by 1- or 2-year old plants. Plant siz e was positively and linearly related to plant age at frequently-distu rbed sites and plants in the reproductive stage were younger than at t he rarely-disturbed sites. Thus, the age structure data indicate favou rable effects of anthropogenic disturbance on stand development of B. orientalis. At recently-disturbed, productive sites, B. orientalis sho wed narrow age distributions for a few years after the disturbance eve nt, apparently resulting from a strong decline in seedling establishme nt after canopy closure. Stand development of the co-occurring species R. crispus was less affected by vegetation density at such productive sites, but seemed to suffer more from relatively dry soil conditions. Besides being markers of plant age, annual rings may be sensitive rec ords of past growing conditions, as suggested for B. orientalis by the relationship between annual ring width and position in a gradient of light supply. These results suggest that age structure data obtained b y 'herbchronology' can provide valuable supplementary information for studies on the population ecology of perennial dicotyledonous herbs wi th clearly-demarcated annual rings. (C) 1998 Annals of Botany Company