COS 107-10
Influence of New York City soils on native tree seedling growth, health and survival
For the MillionTreesNYC campaign, New York City (NYC) has undertaken large-scale afforestation to establish native urban forest stands. Little is known about the success of these plantings, often established on soils made up of construction debris covered by gravel fill. In order to ensure sustainability of these forests we must understand how urban soil conditions effect the growth, health and survival of native tree species currently being planted. In this study we examine performance of red oak, silver maple, black birch, and serviceberry seedlings planted in several NYC soils in a controlled greenhouse setting. The soils were collected from areas currently undergoing afforestation, representing a range of soil nutrient quality and anthropogenic disturbance. Using a multi-factorial design, we planted the tree species into thirteen soils: one custom-made greenhouse soil and twelve urban soils from four categories—native glacial till, coal ash, urban fill, and sandy clean fill. We measured soil chemical and physical characteristics, seedling survival, height, leaf chlorosis, chlorophyll fluorescence (Performance Index, Fv/Fm), and seedling biomass. We hypothesized that soil type would influence growth, health and survivorship of native tree species; and that individual tree species would exhibit different growth, health, and survivorship characteristics on the same soil type.
Results/Conclusions
Overall seedling survival was high: silver maple survival was highest at 100% and red oak survival was lowest at 87%. However, one urban fill soil had only 39% survival across all species and 0% red oak survival. Preliminary data analysis indicates that native seedling height growth varied significantly (p<0.001) among soil types with the greatest growth found in coal ash and native till soils and lowest growth in urban fill and sandy clean fill soils. Seedling health variables (growth, chlorophyll fluorescence, and leaf chlorosis) were statistically combined into z-scores. This single stress rating variable allowed us to compare seedling health across soil types; we found significant differences among tree species and soil types (p<0.001). We also found there to be a significant soil x species interaction indicating species perform differentially across soil types (p<0.001). However, we also found that the four broad soil categories contained variation in chemical and physical properties as well as seedling performance, reflecting the heterogeneous nature of urban soils and challenge of characterizing them. These results will inform future restoration efforts by allowing managers to select species that can best tolerate the sometimes harsh conditions of urban soils.