Future Viable Plant Palettes for Metropolitan Areas, Part 5

Figure 1: Bush Center south Terrace on opening day in 2013 image: David Hopman

Figure 1: Bush Center south Terrace on opening day in 2013
image: David Hopman

Part 5: Lessons from the Bush Presidential Center: Local Consultants and Urban Prairies

The G. W. Bush Presidential Center landscape is a good point of departure for a discussion of a variety of strategies for future viable plant palettes, as there were three relevant strategies employed for selecting plant species:

  1. Using local consultants to check species for regional appropriateness,
  2. Recreating a local prairie ecosystem in an urban context using ecological restoration consultants, and
  3. Using an aesthetically qualified native polyculture.

The Bush Center is a 23-acre campus near downtown Dallas that features four distinctly different plant palettes. Almost the entire campus, designed by Michael Van Valkenburgh Associates, Inc., was designed with sophisticated sustainable strategies. A small internal Rose garden, however, uses a more traditional green industry plant palette and demonstrates a good balance of a small area of resource-intensive exotic species within a large, biologically diverse, resource-efficient landscape—with many species of native plants.

Strategy 1: Using local consultants to check species for regional appropriateness

The South Terrace of the Bush Center (figure 1 above) is a transition zone from the cultural landscape of primarily lawn on the north side of the campus to the prairie re-creation on the south side (see the plan). As part of their design process, the landscape architects were referred to three local plant experts by the Dallas Chapter of the Native Plant Society of Texas. They were Carol Feldman, PLA, David Hopman, PLA, ASLA, and Dr. Peter Schaar.

Texas, as in many parts of the country, has a very complex and diverse matrix of biomes that reflect the rapid drop in rainfall as one moves west, and the frequent changes in soil conditions that mirror the interlaced fingers of the underlying geology. It is a difficult area to understand ecologically without the benefit of considerable study and experience. Large landscape architecture firms with a broad national practice frequently design projects here since it is one of the most rapidly developing areas of the United States. These firms often make questionable plant palette decisions, so I was very pleased when the three of us were invited to participate in a portion of the design process.

At the beginning of the process, it was evident that the lead designers were focusing on a plant palette more appropriate for the much drier climate west of the Dallas-Fort Worth area. With a relatively small amount of effort, we were able to steer them towards more regionally appropriate species for the native and adapted plant palette on the South Terrace (figure 1) without impinging on the control of the planting design by the prime consultants. This effort showed that for a very nominal expenditure of time and money, it is possible to use local consultants to fine tune a regional plant palette in a location distant from the home base of a designer.

The barriers to adoption of this important practice are not financial. They are ideological (i.e., is it important enough to make the effort to find the best consultant for the project?) and, perhaps, competitive. Either way, to make a native and adapted plant palette more future viable, we must find a way around the obstacles and find qualified forward-thinking regional consultants. Perhaps we need a new category of consultants that understand landscape architecture and development, but are not inclined to poach clients or biased to promote their existing plant inventory or other green industry business. A brief survey of North Texas firms and my personal office experience indicates that local consultants are frequently used. This raises a number of important questions:

  1. Who are the most appropriate local professionals to consult who understand and can balance the horticultural requirements of development conditions and the poetics of the local native plants and natural systems?
  2. Are currently used local consultants moving the plant palette in a more future viable direction or are they a force that is maintaining the status quo?

Responses to these questions, and other experiences with regional plant consultants, are welcome in the Comments section below. I will summarize the comments in a future post.

Strategy 2: Recreating a local prairie ecosystem in an urban context using ecological restoration consultants

The Bush Center features 8.6 acres of restored prairie plants consisting of Prairie and Savannah, a Wildflower Meadow, a Wet Prairie, and Bioswales [1]. The entire system of plants was aided in the design process by the Ecosystem Design Group at The Ladybird Johnson Wildflower Center at The University of Texas at Austin as well as regional native plant growers. The Design Group provided an initial site assessment, reviewed soil specifications, recommended plants, and developed a 5-year maintenance and operation plan to control invasive species. The prairie restoration has been successful from a plant establishment standpoint. It does, however, raise a number of important issues related to the idea of utilizing a high use area in a densely populated city as a restoration opportunity.

The Problem with Prairies in Metropolitan Areas

Using a complete prairie plant palette to accomplish a prairie restoration in metropolitan areas can be highly problematic. Prairies are hazardous to traverse on foot because of insects, and inhospitable to most forms of human activities that are a feature of urbanizing areas. For example, there is a microscopic insect in prairies called a chigger that appears in the summer months. The chigger larvae (about 1/100 inch in diameter) are parasitic. Once a larva finds a host, it typically feeds for 3 days before dropping off to digest its meal and molt into its next life stage [2]. Unprotected people can suffer with hundreds of bites if a particularly dense infestation is encountered. Unfortunately, there is no way to tell if you are infected until two to four hours after exposure when the itching and swelling on the skin begins. Chiggers can be controlled using an insect repellent with DEET or by using sulfur as a repellent, but this requires forethought and constant vigilance, and may represent a larger human health problem than the chiggers themselves.

Chiggers are not life threatening, but they are very uncomfortable and one of the elements that add to the general perception of prairies as places that are best avoided. Preference studies using photo elicitation have shown that the grasslands that were once the predominant biome of the Great Plains region of the Unites States area are one of the least popular types of natural landscapes, compared with the favorability ratings for mountains, rivers, forests, and large water bodies [3]. Figure 2 below was photographed during opening day at the Bush Center when tens of thousands of people were passing through the new Presidential Center. On the same day and with perfect weather, the prairie park was almost completely deserted and I had to wait over 15 minutes to capture the scene with people in it.

Figure 2: Bush Presidential Center prairie restoration on opening day, May 4, 2013 image: David Hopman

Figure 2: Bush Presidential Center prairie restoration on opening day, May 4, 2013
image: David Hopman

Another problem with prairies is their general incompatibility with most human activities. One cannot throw a Frisbee, play a ball game, or walk a dog on a prairie. The prairie is, in effect, a large ecologically constituted view garden. There is not a way to inhabit a prairie with its mix of grasses and forbs without trampling them. Additionally, many prairie plants need full sun—not the ideal condition for human comfort in hot Midwestern areas with increasingly warm urban heat islands. Treeless prairies are also not compatible with the imperative to cover hard metropolitan paving surfaces with biomass (trees and vines) for shade, thereby helping to mitigate the urban heat island, air pollution, and urban hardscape stormwater runoff.

The duration of prairie plants is another significant impediment to prairie restoration in metropolitan areas. Many of the more than 200 species of plants typically found in a mature prairie are annuals that survive the extreme disturbances in the Great Plains as seed. These seeds have strategies for widespread disbursement by ingestion, wind, attachment to fauna, etc. These strategies are very effective for large areas of prairie where there is room for these dispersal mechanisms to be effective. However, metropolitan planting areas tend to be in small patches that are mostly edge conditions, and the edges are where aggressively reseeding exotic invasive species are most likely to take hold.

The combination of exotic invasive species pushing in from the edges and the problematic dispersal systems of many of the native annuals makes a historic mix of native prairie plants only suitable for areas of sufficient size. For smaller patches, the aggressive exotic annuals often outcompete the native prairie annuals, which will quickly disappear. Encroaching native annuals can also be an issue as the planting designer loses control of such basic urban imperatives as the height of the planting and the erosion control of small planting areas. The creative aesthetic components of the design will also be impossible to maintain with a plant palette that changes dramatically from year to year, especially with the relatively unsophisticated maintenance work force used in most landscapes.

Finally, the economics of restoring prairies in urban areas create a missed opportunity to make a more significant impact on regional ecology. For the exorbitant cost of a single problematic acre of restored prairie in an urban area, it may be possible to restore 500 or even 1,000 acres in a rural area—patches that are of sufficient size to support the diverse biology required for a true prairie ecosystem (see figure 3).

Midwestern prairies are beautiful, fascinating, and critically important biomes for environmental services and ecological diversity. The Bush Library is providing a service to the people of Texas and visitors from throughout the world by serving as a museum for this important and endangered feature of the native Texas landscape. The contention here, however, is that this prairie restoration should not be a model for more widespread use throughout the DFW area in the same way that the large ornamental display gardens from part 2 of this series should not be a model for widespread adoption.

Figure 3: 13.5-square mile Konza Prairie in Kansas—late March during a spring burn. Pictured is Kansas State professor Chip Winslow. image: David Hopman

Figure 3: 13.5-square mile Konza Prairie in Kansas—late March during a spring burn. Pictured is Kansas State professor Chip Winslow.
image: David Hopman

Figure 4 documents the relative balance of a prairie restoration plant palette in an urban area showing very good environmental and ecological performance but a lower emphasis on human use and enjoyment.

Figure 4: Aesthetic, environmental, and ecological balance in a prairie plant palette image: David Hopman

Figure 4: Aesthetic, environmental, and ecological balance in a prairie plant palette
image: David Hopman

Next month’s post will begin the discussion of using aesthetically qualified native urban polycultures as a means to bridge the gap between the problematic functionality of urban prairies and other regional native plant communities and the missing ecological performance of the contemporary native and adapted plant palette.

References

[1] See the Bush Center’s website for a complete listing of plant species.

[2] Moore, Glen C. and M.E. Merchant. Chiggers.

[3] See Bourassa, Steven C. The Aesthetics of Landscape. London: Belhaven Press, 1991, 121-132 for a discussion on landscape preferences.

Missed parts 1-4 of this series? See below for the links to previous installments, and stay tuned for the next post:

Future Viable Plant Palettes for Metropolitan Areas

Part 1: Aesthetics, Environment, and Ecology in the Creation of Plant Palettes
Part 2: Fine Gardening
Part 3: The National Green Industry ‘Utility’ Plant Palette
Part 4: Contemporary Native and Adapted Plant Palette

David Hopman, ASLA, PLA, is an Associate Professor of Landscape Architecture at The University of Texas at Arlington, a registered landscape architect, and a research associate at The Botanical Research Institute of Texas (BRIT).

2 Responses to “Future Viable Plant Palettes for Metropolitan Areas, Part 5”

  1. Bejamin Vogt Says:

    I hope you’re not saying that prairie perennials don’t play a role, perhaps even a significant role, in managing urban stormwater, cleaning the air, sequestering carbon, and even cooling the local area. Sure, a tree is going to provide superior shade, but does an equivalent biomass of urban prairie pale in comparison in other areas of environmental benefit? What happens when prairie beds are combined with trees and shrubs?

    • David Hopman Says:

      Very good point. The series is moving towards native polycultures that are carefully selected for urban conditions, particularly under trees, but also in other microclimates. The assertion is that restoration is a problematic model for urban conditions and that other models are needed that will provide the balance of human, environmental, and ecological benefits. We need more people like yourself advocating for native perennials and other groundcovers and not just trees, although trees are critically important.

      Thank you for the comment

      David


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