Concrete Jungles of the Noyce Courtyard and North-Western France

      From song lyrics to film titles, the term concrete jungle is often used ironically to refer to urban areas filled with buildings and sidewalks rather than trees or other plants. However, given the many plants to be found in urban landscapes, it is clear that the two are not mutually exclusive. The relationship between urban environments of concrete and steel and the species of plants that continue to grow in them is the subject of plenty of research by urban ecologists. Many people expect that the diversity of plant species and the well-being of the plants themselves would decrease as environments develop from wild forests to towns and cities, but research suggests that those assumptions don’t capture the complexity of plants’ abilities to occupy urban landscapes. The paper Plant species response to urbanization: comparison of isolated woodland patches in two cities of North-Western France explores the relationship between plants and their urban and rural environments in depth, and also connects to research I’ve done on Grinnell’s campus examining the effect of pavement on which plant species occur in a courtyard in the Noyce Sciencec Building.

      The aforementioned paper by Vallet et al. built off of previous research showing that urban environments tend to be home to more non-indigenous species and plants adapted to high levels of disturbance. The researchers in Vallet worked in 22 sites across two cities in France, all of which were then characterized along an urban to rural gradient. The classification of each site is shown in Fig. 1.  Scientists measured each site for species abundance, as well as measurements of light, moisture, soil pH, and soil nitrogen content. The researchers found a marked difference in plant composition across proportion of sites with impervious surfaces (i.e. concrete); namely three non-native species and seven native species were associated with larger cover of impervious surfaces. Vallet et al. mentioned research by other teams showing that concrete can increase nitrogen content and affect pH, causing some plants to perform quite well when growing near concrete. They concluded that some plant species, both native and non-native, are able to withstand changes to their environment due to urbanization, and many urban plants thrive in the conditions caused by abundant concrete.

      These findings also have applications to a much smaller concrete jungle: the courtyard near the elbow of the Noyce Science Center in Grinnell (Fig. 2). The courtyard serves as a study space in the science building, and many plants were introduced to populate the garden spaces, but some species colonized the pavement cracks on their own. We surveyed the cracks to see if the presence and abundance of certain plant species are affected by the width of the sidewalk cracks (a measure of both permeability and soil space). The research by Vallet et al. shows that we shouldn’t be looking at the concrete in the courtyard purely as an obstacle to plant growth; some species thrive better near concrete than in rural environments. Although the analysis of native and introduced species is not as applicable to our research, since many of the plants in the cracks of the sidewalk are descendants of the ornamental plants in the courtyard, and although our research space is of a much smaller scale, their findings on the effects of concrete still have implications for us. Concrete jungles exist all around us, and the plants that live there are often doing just fine.

Figure 2. We took to the Noyce Courtyard to measure the species abundance and width of sidewalk cracks                        

Vallet, J., H. Daniel, V. Beaujouan, F. Roze. 2008. Plant species response to urbanization: comparison of isolated woodland patches in two cities of North-Western France. Landscape Ecology 23:1205-1217.