Eastern-flowering Dogwood population genetics and ecological/environmental data

Forest fragmentation and introduced pathogens are negatively impacting
trees and forests globally, including the Carolinian forest of southern
Ontario, Canada. Multiple species-at-risk live in this threatened but
biodiverse forest, including the endangered Cornus florida (Eastern
flowering dogwood), which is now limited to fragmented woodlots, and has
been decimated by the introduced fungal pathogen Discula destructiva
(dogwood anthracnose). Ongoing management of C. florida in Canada is
challenged by multiple knowledge gaps, two of which we aimed to address in
this study. We first evaluated the association between anthracnose disease
prevalence and a suite of ecological and environmental variables across 21
sites. Across our sites, larger trees tended to have the highest disease
incidence, and trees on shallow slopes had the most crown dieback. We then
quantified genetic diversity and gene flow and found that genetic
structure has not been substantially impacted by habitat fragmentation,
although dispersal typically covers short distances. However, genetic
diversity is relatively low in smaller populations, and in younger trees.
Localized dispersal and eroding genetic diversity may limit future
adaptation and hence exacerbate population declines. We recommend that
managers prioritize plantings in small populations, avoid shallow slopes,
and track younger trees to evaluate age-related mortality.