Isolated coastal populations of Tilia americana var. Caroliniana persist long-term through vegetative growth

Abstract

PREMISE OF THE STUDY: Sprouting in woody plant species allows for the long-term persistence of small, isolated populations experiencing changing environments and can preserve genetic diversity in these populations despite the infrequent recruitment of sexually produced individuals. We examined demographic data collected over a 10-yr period for Tilia americana var. caroliniana populations in the context of genetic structure as an empirical case study of this concept. METHODS: Two back-barrier islands on the Georgia coast of the United States were completely censused for Tilia americana var. caroliniana. Recruitment, growth, and mortality of all stems were tracked over 10 yr. All genets were genotyped using eight nuclear microsatellite loci to assess population genetic structure among sampled stems and among populations in the region. KEY RESULTS: The two island populations differed in their ability to establish seedlings despite having similar patterns in flowering frequency. Seedling mortality was high throughout the 10 yr, and cycling of ramets within genets was common. Long-term recruitment in this system appears to be primarily a result of vegetative growth via basal sprouts. Genetic structure was limited, both between islands and among populations in the region. CONCLUSIONS: Long-lived woody species that persist by vegetative reproduction may unexpectedly influence regional forest responses to climate change, particularly on the trailing edge of a species' distribution.