Novel urban hardscape habitats showcase spontaneous vegetation that grows in designed or undesigned interstitial spaces within or atop impervious surfaces. These habitats form a disproportionately large area of the urban land available for spontaneous plant colonization. Parking lots are estimated to cover three times the area of parks within US cities. Parking lots host a confluence of physiologically stressful environmental factors affecting native as well as non-native plants with tolerances for drought, chemical pollution, and population fragmentation. Our objective was to determine the niche indicators, functional traits, and life history strategies associated with these plant communities. A trait-based approach to understanding habitat-specific urban floras can provide generalizable results and help develop mechanistic hypotheses for predicting future environmental change.
We generated a community list by surveying cracks of asphalted parking lots on Rutgers University New Brunswick, NJ, USA, for vascular plant species richness, and we developed a county-wide species list. We used plant trait data on Grime (CSR) species strategy, clonal reproduction, photosynthetic pathway, lifespan, woodiness, wetland status, and dispersal and pollination syndromes on all species and compared the frequencies of species with each trait state between the county-wide and parking lot communities using Bayesian modeling.
The parking lot communities contained 102 vascular plant species representing 93 genera and 39 families across all parking lots and microhabitats; the county list contained 2196 vascular plant species. Compared to the county-wide species pool, the parking lot community contained a significantly higher proportion of annual or biennial, ruderal, C4-capable, non-woody, and/or facultative upland plants but a lower proportion of clonal species. In addition, the parking lot community contained a significantly higher proportion of species that use six or more types of dispersal vectors and a lower proportion of species that use only one type of dispersal vector.
As urban areas are a dynamic mosaic of land use types with unpredictable disturbance regimes, plant species able to reproduce early in life and make use of a wide range of dispersal vector options may have colonization priorities and thus fitness advantages over perennials and specialized dispersers. Areas of high impervious surface cover and vehicle traffic in cities are hotspots for urban warming, altered hydrology, and carbon dioxide flux. Such high density zones in cities may be unique in creating an additional urban environmental filter that favors facultative upland and C4-capable species, potentially altering local ecosystem function.