Demographic modeling of the invasive tree Ailanthus altissima

Background/Question/Methods Demographic modeling is typically utilized to aid in species conservation, however this can also be applied to invasive species to learn about invasive population growth, vulnerable stages, and population persistence. Ailanthus altissima, the tree-of-heaven, is a widespread invasive species originally from China that colonizes a large range of habitats. Ailanthus altissima readily forms root sprouts in addition to producing seeds, giving the opportunity to determine which form of reproduction is more vital to population growth and persistence. This research examined the growth of A. altissima populations and the importance of sexual versus asexual reproduction. Forty by forty meter plots were established in five A. altissima populations outside Morgantown, WV and censused for four years. These populations were representative of A. altissima habitat and included agricultural fields, disturbed habitats along roadways, and an intact forest. Plants were classified into five stages: new seedlings; new root sprouts; juveniles; small, sexually non-reproductive adults shorter than 3m; and large, sexually reproductive adults taller than 3m. Populations were pooled for analysis to calculate combined annual population growth rate (λ), sensitivity analyses, and elasticity analyses. Results/Conclusions Combined population annual growth rate was 1.04 indicating a slight increase in combined population size. The elasticity analysis indicated the transitions contributing the most of λ were remaining small adults, transitioning from small to large adults, remaining large adults, and formation of root sprouts from large adults. Seedling survival was 30% while root sprout survival was 57%. Furthermore, elasticity analyses indicate the transition from root sprout to juvenile was more influential on λ than the transition from seedling to juvenile. While invasive plant populations are typically thought to grow very rapidly, these data indicate growth is slower. The seedling and root sprout data concur with previous research suggesting asexual reproduction is key in the growth of populations.