Urban Plant Diversity

May 31, 2018

60 students from Narbonne High School in Los Angeles teamed up with over 40 volunteers from Lowe’s, as well as staff from the school and the Conservancy, for a significant work day at the school’s campus garden. Photo © Devan King/The Nature Conservancy

It’s spring and a young man’s fancy may turn to…….gardening. Across the country, weekends are spent selecting plants at the local nursery to bring home for the yard. Of course, it is tempting to find ornamental plants that no one else has in the neighborhood, so a significant fraction of the nursery trade focuses on exotics—species that do not occur locally.

As a result of such plantings, affluent neighborhoods often have greater plant diversity than the regional flora outside the city limits. Several studies have found a direct correlation between household income and plant diversity in yards.

The problem with exotics is, of course, that they are not necessarily adapted to the local conditions, versus native plants that have evolved in the face of droughts, insect attack and other variations of nature that they have endured. Many exotic garden plants need a lot of tender loving care. Exotic plants are not likely to harbor the insects of their native habitat, so that they can be biological deserts for birds and other organisms that feed on insects.

A pollinator garden. Photo © London Permaculture/Flickr through a Creative Commons license.

Of course, the occasional exotic species, not subject to its native pests, can outcompete native species and expand its population and range explosively in a new habitat. Barberry (Berberis vulgaris), which is native to Europe, has escaped cultivation and now occurs rampantly as an understory shrub in eastern forests. The Tree of Heaven, Ailanthus, brought to the U.S. from Asia, is now a widespread invading tree in eastern cities. A recent analysis suggests that the onslaught of exotic species is not over; 25% of the first-records of species during 2000-2005 were for species that were not previously recorded as alien.

I am not recommending that we leave our yards barren. In cities, crime rates drop when vacant and abandoned lots are given landscaping. But, the purchase and upkeep of exotic plantings is often misguided. Native species are cheaper, require less maintenance and harbor a greater diversity of nature in their canopy. Native species are likely to be more resistant and resilient to disturbance.

Go natural.

This post originally appeared on William H. Schlesinger’s blog Citizen Scientist, published by Duke’s Nicholas School of the Environment.

William H. Schlesinger

William H. Schlesinger is one of the nation’s leading ecologists and earth scientists and a passionate advocate for translating science for lay audiences. A member of the National Academy of Sciences, he has served as dean of the Nicholas School of the Environment at Duke and president of the Cary Institute of Ecosystem Studies. More from William H.

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  1. Volunteer native plant nurseries do help, (I volunteer in one run by the local CNPS chapter) but are just a drop in the bucket as it is hard to find natives in regular nurseries, much less big-box stores. And the natives need to be the right varieties for the urban landscape.