Population growth and viability analyses of the clonal woodland herb, Asarum canadense

1 Long-term demographic field studies combined with simulation models that incorporated two types of stochasticity were used to investigate the relative impact of reproduction and survival on the persistence of populations of the North American woodland herb, Asarum canadense. 2 Field data were collected over 7 years in replicate plots located in early and late successional forest habitat. By following marked ramets from year to year it proved possible to investigate the demography both of ramets and of groups of genetically identical ramets (clones). 3 A. canadense exhibited considerable temporal and spatial variation in reproductive success, survivorship, and population growth rates. Populations of ramets and clones in late successional forest habitats held their own, while those in early successional forest habitats declined. 4 Sexual and clonal reproduction had less impact on population growth than did survival. Nonetheless, seedling recruitment was important, as indicated by the relatively high rates of genet turnover in A. canadense populations. 5 Results from simulations indicated that the vast majority of genets in both habitat types failed to reproduce. Over their lifetime, simulated genets produced a maximum of 44 and 77 seedlings in early and late successional forest habitat, respectively. 6 Although A. canadense genets are potentially immortal, the maximum life span for 2000 simulated genets was 104 years. Simulated genets lived a mean of 3.0 and 4.8 years in early and late successional forest habitat, respectively. 7 Simulated A. canadense populations only persisted in late successional forest habitat. Within simulated late successional forest populations, the number of ramets tended to decrease over time, while the number of genets tended to increase over time. 8 The minimum viable population size for A. canadense ramets in late successional forest was 25 individuals with environmental stochasticity only, and 1000 individuals with both environmental and demographic stochasticity; for genets in late successional forest, the corresponding numbers were 20 and 25, respectively. 9 Ramet and genet dynamics differed greatly in A. canadense, highlighting the importance of long-term demographic studies at each of these levels.