This unique idea was proposed by collaborators from Germany's University of Oldenburg, the Helmholtz Centre for Environmental Health, and the Institute for Environmental Modeling. Their recommendations were based on a series of models, which were, in turn, based on data collected from 133 sampling plots on brownfield sites in Bremen, Germany. Within each plot, they counted the incidence and abundance of plant and insect species (specifically, leaf-hoppers, grasshoppers, and one species of bush-cricket). These data were used to create species distribution models, which related the biodiversity data to environmental factors such as soil properties, age of the site (indicating degree of succession, or colonization by, and growth of, different species), and, in the case of insects, vegetation parameters.
(The Market Square in Bremen, Germany)
Once the researchers had an idea of the temporal and spatial variation that could be observed among different brownfield sites within a single city, they used modeling techniques to examine how variations in environmental parameters might affect brownfield communities; their goal was to determine which conditions would yield maximal biodiversity--information that could be used by city architects to improve urban planning efforts. The scientists performed the modeling using an actual industrial area as their framework--a 550-hectare site in southwestern Bremen that had seen various levels of development (and, later, abandonment) since 1974. Various simulations explored how biodiversity at the industrial area would be impacted by differences in proportion of developed lots, turnover rate of built-up lots to brownfields (and vice versa), and lot size.
When brownfield areas were left undisturbed, both plant and insect species richness declined over time; this process began at about 3 years for plants, and at about 20 years for insects. This is a result of succession, since "climax species"--or those that can sustain themselves continually--eventually replace the primary and secondary species that initially colonize a new habitat. The opposite of this "static" condition is "dynamic"--in this case, a continual presence of brownfield areas, but spread over space as different sections of the industrial site are developed or abandoned. Under these conditions, richness was much higher, peaking for plants after approximately 15 years, and for insects after about 10-15 years. This process would be facilitated by the species' ability to colonize a new brownfield area prior to being extinguished from a newly-developing site, thus continually maintaining their presence in the industrial complex; under a static condition, the species would have nowhere to go once they went extinct locally, and would therefore vanish from the industrial area altogether.
(Example of a brownfield site--one that has already experienced several years of succession)
For the focal industrial site, the researchers investigated which of 4 lot layouts best fostered biodiversity: the original (current) arrangement, one with a fewer number of larger lots, one with many small lots, or one with a few larger and many small lots. This is an interesting urban spin on a debate that ecologists--and, particularly, conservationists--have been having for years: Is biodiversity enhanced/maintained better with the creation of a few large habitats, or several small ones? In this case, the simulations showed that large lot sizes should have the lowest levels of biodiversity. The other three layouts were quite similar, with only small differences between predicted biodiversity levels.
Based on their findings, the authors recommend that urban areas contain 50-60% of open space, with site turnover occurring every 15 years or so. Although these figures may seem like a tall order, the researchers say that they are achievable. For instance, analyses of a time series of aerial photos taken over 6 German cities suggest that turnover time between brownfield and developed areas is already approximately 15 years. The 50-60% open space suggestion may be a bit more difficult to achieve--and, given current regulations, may actually be impossible in some areas--but is a goal that future policies can work towards.
(One example of a temporary building, which could facilitate temporary biodiversity by enabling dynamic management of urban areas)
The results also have broader implications. First, they suggest that the traditional "stationary protection" technique--underlying the creation of national parks and reserves, for instance--may not be useful in certain areas, or for certain species (especially those that thrive on, or require, environmental disturbance). Thus, it may be important for managers and conservationists to consider more "dynamic plans," or to incorporate dynamically-managed areas into larger, otherwise stationary, sites. Second, the authors recognize that current attitudes towards brownfield areas are generally not positive; many people view these places as "wastelands creating social problems." Temporary building would allow these former industrial sites to find new lives as green areas that "support human well-being" and provide ecosystem services. One thing that will be needed for this is high-quality, short-term, reusable, and dismountable temporary buildings that can be relocated at regular intervals in order to promote the dynamic environment that appears to foster urban biodiversity. The authors suggest that it may also be helpful to use incentives to landowners and space-users in order to advocate this style of urban planning. This could have the further advantage of encouraging businesses to stay within city limits, thus preventing city shrinking and promoting a thriving urban community--not just for wildlife, but for humans, too.
Kattwinkel, M., Biedermann, R., Kleyer, M. 2011. Temporary conservation for urban biodiversity. Biological Conservation 144:2335-2343.
Thanks to the following websites for providing the images used in this post: