Variability in Urban Soils Influences the Health and Growth of Native Tree Seedlings

Reforesting degraded urban landscapes is important due to the many benefits urban forests provide. Urban soils are highly variable, yet little is known about how this variability in urban soils influences tree seedling performance and survival. We conducted a greenhouse study to assess health, growth, and survival of four native tree species growing in native glacial till, coal ash, urban fill, and sandy clean fill soils collected from urban forest restoration sites in New York City. Using a multifactorial design, nine replicates of silver maple (Acer saccharinum), black birch (Betula lenta), red oak (Quercus rubra), and Canadian serviceberry (Amelanchier canadensis) were planted in four urban soil types and one greenhouse mix. We hypothesized that: 1) urban soil type would influence growth, health, and survivorship; 2) each tree species would respond differentially to each soil type; and 3) seedling stress and mortality would be higher for soils with more anthropogenic disturbance. After one growing season, we found that seedlings were less healthy and grew less in soils with a history of greater anthropogenic disturbance. Seedling mortality was low (< 3% overall) except for red oak seedlings in urban fill soil from one location. These results demonstrate that urban soil conditions can impact tree growth and health while supporting high survivorship. Species × soil type interaction for height growth and stress indicate that native tree species may not respond to urban soil conditions consistently. Consequently, matching tree species to soil type could help optimize establishment and growth of urban forest restoration projects.