Piqueras J. & Klimeš L. 1998. Clonal growth and population dynamics in the pseudoannual plant Trientalis europaea L.
Some species of clonal plants exhibit a pseudoannual growth habit, i.e. the individual ramets die at the end of the growing season after having produced vegetative propagules that must overwinter before they emerge. The clonal growth pattern and demography of clonal fragments (aggregation of ramets derived from a common parent ramet) in the pseudoannual plant Trientalis europaea were studied in field conditions from 1991 to 1993. During this period the population of clonal fragments declined, with a half-life of 7.4 years. Number and size of the clonal progeny and stolon length were positively related to ramet size. Survival rates of ramets increased with ramet size. The rate of clonal growth was low; after three years, about 70% of the clonal fragmets had only one ramet. This suggests that the pseudoannual growth habit in Trientalis europaea is more important as mechanism of perennation than of ramet multiplication in the studied area.
To simulate population dynamics of clonal fragments an architectural simulation model has been developed, based on the field data. The spatial arrangement of ramets of simulated clonal fragments varied greatly, but the most common pattern resembled a "guerrilla" growth form. About 10% of the clonal fragments survived to the end of the simulation (15 years) and the mean survival was 4.7 years. The model predicted a positive correlation between persistence of the clonal fragment and the number of ramets produced. A sensitivity analysis showed that the production of a daughter ramet of at least the same size as the parent ramet, was the most important pathway for the survival of the clonal fragment, whereas the production of additional small ramets had a very small effect. This confirms the interpretation of the pseudoannual life-cycle as a mechanism of ramet replacement in this species. The sensitivity analysis also revealed that changes in the survival probabilities of the smallest ramets had the largest impact on the clonal fragment dynamics. This reflects the important role of this size class of ramets as a source of new vegetative propagules, maintaining a hierarchy in the size structure of the population.