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A comprehensive assessment of Liatris helleri demography: Insights from 16 years of observations and modeling

Abstract:

We analyzed demographic data for the endangered Blue Ridge endemic Liatris helleri (16 years, 6 sites, 982 plants, and 15,697 annual transitions). We recorded survival, growth, flowering, and recruitment. We evaluated effects of poaching, trampling, browsing, and fire which are potential population drivers for this species. Population size exhibited quasi stable trends, with some population changes attributable to fire or browsing. Survival, growth, and number of heads per plant varied among populations, increased with plant diameter, and were affected by browsing and fire (including overcompensation). Recruits were rarely observed but their numbers increased after fire. We built a projection model including seedlings, second year recruits, adults, and dormant plants. Populations were projected for 50 years. Decadal fires maintained sustainable recruitment rates. Browsing probabilities varied among populations and years; browsing increased the uncertainty of stochastic population growth and boosted extinction probability. Consideration of long-term, spatially replicated data and multiple drivers permitted us to evaluate demographic threats of a relatively long-lived species. Overall, these models suggested that L. helleri populations are likely to persist in the near term under current conditions. However, given their population growth rates near one and poor recruitment, any drivers that reduce their survival are threats to this species.