Phylogenetic and functional characteristics of household yard floras and their changes along an urbanization gradient

Abstract

Abstract. Urban areas are among the most heavily managed landscapes in the world, yet they harbor a remarkable richness of species. Private yards are common habitats in urban areas and are places where cultivated species manage to escape cultivation and become part of the spontaneous species pool. Yards are novel ecosystems where community assembly is driven by both natural and anthropogenic processes. Phylogenetic diversity and functional traits are increasingly recognized as critical to understanding processes of community assembly. Recent evidence indicates that urban areas may select more closely related plant species from the pool of regionally occurring species than do nonurban areas, and that exotic species are phylogenetically clustered within communities. We tested whether phylogenetic diversity and functional trait composition in privately managed yards change along a gradient of housing density in the Minneapolis-Saint Paul metropolis, Minnesota, USA, in accordance with these predictions. We also identified characteristics of the spontaneous yard flora by comparing its phylogenetic diversity and functional composition with the ''natural-areas'' species pool represented by the flora of nearby Cedar Creek Ecosystem Science Reserve. Along the urbanization gradient, yards had more species per hectare in densely built regions than in lower-density regions, but phylogenetic diversity and functional composition did not change with housing density. In contrast, in comparison to species in natural areas, yard species were more closely related to each other and functionally distinct: They were more often short-lived, self-compatible, and had higher specific leaf area than species of Cedar Creek. The high number of exotic yard species increased the yard flora's phylogenetic relatedness in comparison to species of Cedar Creek, causing a degree of phylogenetic homogenization within yards. The urban environment and homeowners' preferences select for trait attributes and phylogenetic lineages that can colonize and persist in yards. As yard species disperse beyond household boundaries, their functional attributes will affect ecosystem processes in urban environments and beyond, such as accelerating decomposition rates. Limited phylogenetic diversity may reduce the potential of ecosystems to respond to environmental changes. As cities continue to expand globally, understanding the impacts of yard management for biodiversity and ecosystem services becomes increasingly important.

Native and exotic woody vegetation communities in domestic gardens in relation to social and environmental factors

“…Native species are also usually outnumbered in private gardens: across five UK cities 30% of the garden flora and about a third of the 50 most frequently occurring species were native (Thompson et al 2003, Smith et al 2006b, Loram et al 2008a, Knapp et al 2012. Native representation in gardens in this study was even lower than in the UK.…”

“…Exotic plant species of all types are very common in urban landscapes: 40% of plant species richness in Europe, 43% in Burundi, 45% of species in home gardens in Brazil, and between 18% and 34% in U.S. cities (Pyšek 1998, Wania et al 2006, Akinnifesi et al 2010, Bigirimana et al 2011, Knapp et al 2012. Native species are also usually outnumbered in private gardens: across five UK cities 30% of the garden flora and about a third of the 50 most frequently occurring species were native (Thompson et al 2003, Smith et al 2006b, Loram et al 2008a, Knapp et al 2012.…”

A review of urban ecosystem services: six key challenges for future research

“…Several studies did, however, mention difficulties in obtaining permission for research in private areas (e.g. Davies et al, 2011;Knapp et al, 2012;.…”

Changes in Plant Species Composition and Structure in Two Peri-urban Nature Preserves over 10 Years

“…This increase will add to the unique challenges facing flora and fauna in and around cities. The expected increase in global urbanization is predicted to have especially negative consequences for biodiversity during the next few decades (Knapp et al, 2012). This challenge to biodiversity and the ecological services ecosystems provide will likely be further exacerbated by global climate change (Seto et al, 2012).…”