Dynamics of Tundra and Taiga Populations of Herbaceous Plants in Relation to the Tihomirov-Fretwell and Kalela-Tast Hypotheses

Abstract

The Tihomirov hypothesis, according to which microtines have a strong impact upon the reproductive performance of northern plant populations, and the hypothesis of Kalela and Tast, stating that northern environments are characterized by strong, synchronous pulses of generative and vegetative reproduction, which create microtine cycles, were tested by studying fluctuations in the flowering intensity and population size of orohemiarctic populations of Solidago virgaurea, Trollius europeaus and Carex bigelowii and in middle boreal populations of S. virgaurea during 1977-84 in relation to microtine herbivory. The orohemiarctic populations failed to show any clear and widespread synchrony in reproduction between species or habitats, except for a synchronous low in 1983, associated with the highest vernal vole densities during the whole period and with high rates of injury in marked shoots of herbs. For boreal S. virgaurea populations, fluctuations in numbers of floral shoots were only pronounced in nutrient-poor habitats and were mainly attributable to fluctuations in survival rates. The results suggest that apparent flowering cycles in northern areas are mainly a consequence of fluctuations in microtine populations, as proposed by Tihomirov. A review of available productivity data does not support the assumptions of the Kalela-Tast hypothesis. The field layer of subarctic habitats tends to be more productive than that of more southern forests. Thus, there is no obvious reason why subarctic herbs would need to accumulate resources over several years in order to reproduce, as proposed by Kalela and Tast.