Provincial and cosmopolitan: floristic composition of a dryland urban river

Abstract

High rates of intercontinental exchange of plant species have caused scientists to ask whether floristic areas with similar environments are undergoing global homogenization. We focused on riparian forests of the urban Salt River (Sonoran Desert, USA) to ask: (1) Is the forest dominated by cosmopolitan or provincial elements? (2) Which trees planted in the irrigated cityscape have established along the river? (3) Which types of restoration interventions have favored provincial species? We surveyed tree abundance, size and vigor in belt transects among five reaches that differed in degree of restoration, and obtained data on tree species composition of the urban landscape and pre-development riparian zone. Our results reveal the urban riparian forest to have many cosmopolitan elements, owing in part to spillover of trees from the cultivated cityscape (e.g., Acacia stenophylla, Vitex agnus-castus). Global spread of some regional (Neotropical) riparian taxa (e.g., Parkinsonia aculeata, Prosopis) also has contributed to the cosmopolitan status. Yet, the forests retain a distinct regional signature. Unintentional restoration of winter floods has allowed for regeneration of Salix gooddingii, a vernally-adapted provincial pioneer, although its long-term survivorship is restricted to limited micro-sites (storm drain outfalls). Urbanization-related changes in stream hydrogeomorphology explain increases in some regional species (e.g., Washingtonia spp.) that historically were excluded from the river.Reaches restored by planting, weeding, watering, and geocountouring had the greatest abundance of provincial species and greatest floristic similarity to historic conditions.

An overview of non‐native species invasions in urban river corridors

“…Presence in the seed bank is also reflected in riverine and riparian community composition; for example, Stromberg et al () observed that many urban riparian species in the Salt River (United States) were trees cultivated in nearby cities, whereas Meek, Richardson, and Mucina () found that riparian non‐native plant cover was highest in areas bordered by urban land. In this way, urban areas directly contribute non‐native species to rivers from their component ecosystems (gardens, parks, brownfield sites, etc.…”

Who removes seeds in a heavily urbanized area?

“…The occurrence of native plants inside green areas in cities play critical roles in determining the quality and abundance of resources for wildlife that delivering ecosystem services [1]. Mostly in urban reserves conserve native species plants [2], while parks, corridors, and other types of urban green infrastructure more often contain cosmopolitan [3] and/or introduced species [4]. Besides, the spatial distribution of green infrastructure is relevant for determining ecosystem services [5].…”

Ecological implications of twentieth century reforestation programs for the urban forests of São Paulo, Brazil: a study based on litterfall and nutrient cycling

“…These trees, along with many other native species, such as Schinus terebinthifolius and Pleroma granulosum, are scattered throughout the city providing important ecosystem services (Lafortezza and Chen 2016;Arratia et al 2020). Exotic trees, such as Eucalyptus spp., are excellent competitors in the natural system because of allelopathy and their ability to alter floristic composition and soil properties (Suominien 2013;Yitaferu et al 2013;Gatto et al 2014;Sampaio and Schmidt 2014;Silva et al 2016;Shams 2016;Stromberg et al 2016). Some studies have shown that the decomposition rate of Eucalyptus leaves is slower than that of native species (Louzada et al 1997;Barlow et al 2007;Bala et al 2010;Demessie et al 2012;Martins et al 2013;Cizungu et al 2014).…”