Population dynamics and the influence of blight on American chestnut at its northern range limit: Lessons for conservation

- We track changes in American chestnut demography in its northern range over 13 years.
- Chestnut blight is widespread and affects tree size, reproduction and mortality.
- Northern population differs in tree size and reproduction compared to central populations.
- The chestnut population is in decline (λ = 0.817) due to a lack of recruitment.
- Conservation action should target recruitment to reverse population decline.

Species of conservation concern may require special management consideration at their range limits where population vulnerability can be exaggerated by environmental stress. American chestnut, dramatically affected by chestnut blight in the early 1900s, has received extensive conservation attention especially in the central (U.S.) portion of its native range. However, relatively little is known about the population dynamics and the demographic effects of blight at the northern edge of its range, in Canada. Here we measure changes in tree size, reproduction, blight symptoms, and survival since a survey in 2001-02 and estimate the effect of chestnut blight on vital rates and population growth rates using a projection matrix model. Currently, chestnut trees in Canada range from <2 to 77.8 cm DBH. The incidence of reproductive trees (11%) decreased while frequency of blight (36%) and dieback (37%) increased since the 2001-02 survey. Mortality was 21.3% overall (41% for trees with blight) with few trees producing viable nuts or having established recruits (0.014 recruits per tree). Chestnut in Canada is in decline (λ = 0.817), but tends to differ in blight incidence, tree size, and reproduction compared to surveys in the central part of the range. Efforts to elevate recruitment may be necessary to mitigate extirpation in the northern population.