Population persistence of a riparian plant Silene tatarica in Northern Finland

Background/Question/Methods

Population persistence in dynamic landscapes depends on both local demographic processes and transitions between habitats of different qualities. We study the population dynamics of an endangered perennial plant, Silene tatarica, on the riverbanks of a meandering river in Northern Finland. The study system is characterized by disturbances caused by the flooding river (e.g. scouring, erosion, deposition) and succession towards closed canopy. We classified habitats into three types based on their openness (open: >80%; intermediate: 30%-80%; closed: <30%). For each habitat type, we constructed a size-based Integral Projection Model (IPM) using five years’ demographic data of fifteen populations.  We also estimated annual habitat transition rates using historic aerial photos. We then built a mega-IPM which incorporates both demographic transitions and habitat transitions. We calculated intrinsic population growth rate and performed sensitivity/elasticity analyses for habitat-specific IPMs as well as for the mega-IPM.

Results/Conclusions

Survival is higher in open and intermediate habitats than in closed habitats for plants of the same height. Seedling recruitment is highest in intermediate habitats and lowest in closed habitats. Plant growth and reproduction are different in all three habitats. Population growth rate is the highest in intermediate habitats (λ=1.21), followed by open habitats (λ=1.13), and then closed habitats (λ=0.93). The long-term intrinsic population growth rate of the mega-IPM is 1.18, suggesting an increasing population size under current environmental conditions. Results from the sensitivity/elasticity analyses suggest that intermediate habitats play a predominant role for the overall population growth, and so are the habitat transition rates leading to changes in intermediate habitats.