1 Plant age is an important but less accessible parameter in population ecology and lifehistory strategy. For most plants, notably perennial herbaceous species, the possibility to determine calendar age has been regarded to be restricted to only exceptional cases, if at all possible. We therefore have only a poor understanding of plant age and life-span for many species, which renders quantitative comparisons of life-history strategies difficult.
2 Our recent studies suggest that annual growth rings in the roots of perennial dicotyledonous herbs are far more widespread than hitherto accepted and could be used for age determination (herb-chronology). Furthermore, as in trees, variations in annual ring width may indicate ontogenetic changes in growth and fluctuations in past growth conditions that could be used in ecological studies.
3 In this project we experimentally test the following hypotheses: (i) growth rings in the stem bases or roots of perennial forbs are truly formed annually, irrespective of growth conditions and (ii) xylem growth responds sensitively to variations in relevant environmental factors so that the patterns of growth ring width can be used to compare growth conditions among sites and to infer changes in past growth conditions.
4 The development of growth rings will be analyzed in a multi-year field experiment at two locations differing in climatic conditions. The experiment will involve competition intensity and simulated herbivory (clipping) as treatments and will include nine species of perennial forbs from different plant families, which differ in the clarity of growth rings and in longevity.
5 We expect our project to yield the first "hard" results on the factors determining the development of growth rings in the roots of perennial herbs. These results are indispensable for a sound evaluation of the potentials and limitations of herb-chronology in current and future studies. Analysis of annual rings can generally contribute to our understanding of processes in plant ecology for a wide variety of forb species and may also be valuable in taxonomic studies.