Long‐term demographic study reveals stabilizing mechanisms of salt marsh plants under climate change

Abstract Despite its critical importance for biodiversity conservation, population persistence in multiple habitats under climate change has rarely been evaluated using long‐term demographic data. Furthermore, the drivers of population growth and the contributions of different demographic rates to population growth rates are likely to vary across habitats. Here, we parameterized size‐dependent integral projection models (IPMs) using 23 years of data on the clonal salt marsh plant Spartina alterniflora in two habitats at eight sites in coastal Georgia (USA) to investigate spatiotemporal variation in population dynamics and the driving mechanisms. Compared with environmental factors, population density was the strongest predictor of asymptotic population growth rates ( λ ) of S. alterniflora in nearly all creekbank and mid‐marsh habitats, with population dynamics exhibiting pronounced negative density dependence. Creekbank populations compensated for a low contribution of clonal reproduction number to population growth by increasing recruit size, resulting in effective demographic compensation and similar population fitness between habitats at most sites. Together, negative density dependence and demographic compensation acted as key mechanisms promoting population persistence, allowing most S. alterniflora populations to maintain positive cumulative population growth rates ( λ c ) across habitats. This study highlights the value of demographic analyses in clarifying population trends of species exhibiting high spatiotemporal variability and provides robust evidence for population persistence of salt marsh plants under climate change, emphasizing the crucial role of intrinsic population regulatory mechanisms in maintaining population stability. Read the free Plain Language Summary for this article on the Journal blog.