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Harvard Forest Symposium Abstract 2012

• Title: Population persistence of a riparian plant Silene tatarica in Northern Finland
• Primary Author: Rui Zhang (Harvard Forest)
• Additional Authors: Elizabeth Crone (Tufts University); Anne Jakalaniemi (University of Oulu, Thule Institute, Oulanka Reseach Station)
• Abstract:

  Persistence of populations in dynamic landscapes depends on both demographic processes and habitat dynamics (i.e. 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 a flooding river (e.g. scouring, erosion, and deposition) and succession towards closed canopy where S. tatarica cannot establish. Unlike previously described systems with temporally varying environments where disturbances only promote population persistence by improving habitat quality (e.g. Pascarella and Horvitz 1998 or Valverde and Silvertown 1997), disturbance in our system has both positive and negative effects on population dynamics. Erosion kills S. tatarica; accumulation due to river deposition creates newly suitable habitats; scouring not only kills S. tatarica and other vegetation, but also opens up new habitats for S. tatarica to colonize. We are interested in testing whether existing mega-matrix framework, which is developed based on systems where positive effects of disturbance dominate, can be applied to our more complex riparian system.
  
  
  
  We classify habitats in our system into three types based on their openness (open: >80%; intermediate: 30%-80%; closed: <30%). To evaluate the quality of each habitat type, we construct a size-based Integral Projection Model (IPM) using five years’ demographic data of fifteen populations. We find that 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. Deterministic 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).
  
  
  
  Using historic aerial photos, we estimate annual habitat transition rates due to erosion, scouring, deposition, and succession, respectively. Combining the habitat transition matrix with demographic IPMs for each habitat, we plan to build a mega-IPM, which can be used to explore population growth, the contribution of each habitat or of each life stage to population growth, and the importance of river dynamics in the system. Our study will not only improve our understanding of population persistence in dynamic landscapes, but also provide insights for conservation of this endangered species.
  
  

• Research Category: Conservation and Management
  Ecological Informatics and Modelling