The Real Vegetation of our Urban Landscapes
Driving down I-94 recently, I noticed a bright orange patch of butterfly milkweed, wild bergamot, and purple coneflower growing along the highway embankment. The plants were in bloom and stood out amongst the surrounding vegetation. At other times of year, the planting wouldn’t make an impact, but in July it jumps out at you even at 75 miles an hour. The plantings were so vibrant that we were inspired to exit the off ramp, climb down the retaining wall and get some close up pictures. Once on the ground we saw that there were spots throughout the planting where people had dug up plants for their gardens. This planting is the result of new methods for roadside vegetation planting, establishment, and maintenance specified in Native Seed Mix Design for Roadsides, a report prepared for MNDOT by Kestrel Design Group in 2010. This report reflects the rise of green infrastructure and native vegetation restoration as emergent paradigms for understanding urban ecology and landscape management, particularly at the macro-scale of transportation networks.
The stated purpose of this manual is to create plantings that meet the following design criteria.
- maintain visibility and safety for roadside travelers
- withstand harsh conditions
- minimize maintenance costs
- minimize erosion
- improve water quality
- infiltrate stormwater runoff
- maintain good public relations
Furthermore, the manual identifies some additional practical goals that really stand out for their down to earth sophistication.
- Empower users of varied backgrounds, including transportation engineers and maintenance workers with limited or no knowledge about native plants, to design reliable site-specific native grassland seed mixes that are well suited to their project and create grasslands that are resilient over time
- Allow for flexibility in species selection based on current seed availability and costs
- Maximize seed market demand/supply balance
- Result in the most diverse possible species use statewide to maximize resilience and biodiversity on a landscape ecological scale
What impressed me about this set of design objectives and practical considerations is that it is responsive to site context, user capacity, and is committed to accomplishing multiple social and ecological objectives. Beyond that, this guidance is applicable not just to roadsides, but to all of the landscapes of our cities as a whole. The tricky part about getting it to work is getting the last of the design criteria right – “maintain good public relations.”
Like many urban phenomena, people’s perception of vegetation and wildlife is dominated by narratives and preconceptions. Aside from a species’ appearance and ability to survive in a given location, our notions about why it is there is based on a story. On one hand you have lawns and landscaping, whose purpose is to soften the hard surfaces of our cities while conveying a sense of order and beauty. Native vegetation restoration is a newer concept, whose aim is to re-establish the wild vegetation that was present before the land was developed. Its principle goals are to improve wildlife habitat and to limit the chemical and nutrient inputs associated with traditional landscaping. Parallel to this is the idea of invasive species, typically exotic plants and wildlife that have naturalized and are out-competing the native species. Another narrative is the notion of green infrastructure, in which vegetation, soil, and water are managed as living systems to provide ecosystem services such as aquifer recharge, retaining stormwater runoff, urban heat island mitigation, carbon sequestration, etc.
Where these narratives really matter is how they govern the ways we set priorities for action, plan our interventions in the landscape, and allocate human and fiscal resources to accomplish specific goals. We are reaching a point in time, where many of the high maintenance / aesthetically oriented landscape design and maintenance practices are becoming wasteful and prohibitively expensive. Likewise, the effort associated with trying to restore native plant communities in disturbed locations can easily devolve into an endless struggle against the inevitable species that are most suited to dominate and rapidly reproduce in these areas. In the next few decades we will need to make decisions about the extent to which we wish to garden our landscape versus finding better ways to let our landscape happen.
Peter Del Tredici, a horticulturalist, recently published a very interesting book entitled Wild Urban Plants of the Northeast: A Field Guide. What makes this book particularly noteworthy is the respectful treatment that he gives to plants that typically are vilified as weeds and invasive species. He considers species like Broadleaf Plantain, and lionizes them for their prolific seeding habit, robust germination rates, and their ability to tolerate repeatedly being run over by cars. His essential point, aside from providing a top notch field guide to real urban vegetation, is that we have been too hung up on labels such as native or exotic. We should understand and respect these plants for what they can do in inhospitable human landscapes that can never be restored to what they were before they were turned into parking lots.
Despite the blows to biodiversity caused by human interventions in the landscape, urban ecosystems remain areas of high ecological contrast and patch diversity. They include intensively designed and maintained landscapes, remnant natural areas, degraded or neglected zones, urban forests, and areas subject to frequent and intense disturbance. Urban ecosystems are further differentiated by their inherent fragmentation as a result of human land use and transportation networks. This means that the species that can thrive and spread most readily are generalist species that can hang on in many different settings and those whose vectors can piggyback on human movement. This is true whether it is a seed stuck to a hiker’s boot, or a zebra mussel larvae riding in a boat’s ballast tank. Just as humans are most responsible for the spread of species beyond their native ranges, we also are responsible for selectively breeding (or genetically modifying) species to serve their desired role more effectively and we provide them with water, nutrients, and the microclimates they need to survive when they wouldn’t otherwise. As a result, urban landscapes are unique and diverse ecosystems that emerge through a parallel process of purposeful cultivation and spontaneous regeneration of plant and wildlife communities.
In his book, Principles of Ecological Landscape Design, Travis Beck advocates for a new style of planting design that is cognizant of how plant communities form, evolve, and grow particularly in the context of challenging human environments. At the core of Beck’s work is the idea that in order to be sustainable, the landscapes of the 21st century will need to provide environmental services beyond looking pretty while demanding fewer resources. His premise is that by harnessing ecological processes such as competition, disturbance, and succession, land managers can create lower input landscapes that can still have the aesthetic qualities that are expected by the public. In the work, Beck cites examples of how this approach is being implemented at the institutional, park, and corridor scale. In one example, the Storm King Art Center in Mountainville, New York has been strategically converting its turfgrass areas into simplified native grass communities since 1997. Their land manager has been experimenting with different seed mixes that contain many of the same core species in each mix, but by editing the mix to account for variables such as soil moisture, desired height, and solar aspect he has been able to create mixes that are very low maintenance, effectively suppress weed competition, are drought/burn tolerant, and provide a unified yet diverse backdrop for their landscape sculpture park.
The implementation of this kind of landscape approach tends to happen most intuitively with larger scale sites like Storm King, but the techniques involved with making it work can equally be applied to the micro-scale of a house lot. The problem is that there is a shift in terminology from management to maintenance as we move to the smaller scale. This speaks to the difference between endeavoring to maintain a static landscape condition through regular human input versus allowing a landscape to evolve under the application of targeted and minimal human interventions. The problem with this, as many people who have dabbled with native gardening know, is that without neatness and organization these landscapes look weedy and unkempt. High input landscapes will never disappear entirely, but we are going to see them shrink over time to the places where they make sense. So, the question then becomes: How can we can we move to more of a management paradigm within the urban landscape and still keep things looking sharp?
The plantings on I-94 show that even though erosion control and stormwater management are priorities, so are flowers that inspire people to jump over a highway embankment and dig plants out of the ground. This is even truer in residential and commercial landscapes where the expectation is mown lawns and showy perennials. According to Beck, the sensible design approach is to keep it simple and proportional to the scale of the site. Picking a limited palette of the right species that can dominate a space against opportunistic undesirables and persist through stressful periods is one basic recipe for success. However, the ultimate goal in all of this is to develop a design approach that not only works, but is able to self-propagate and establish itself in the complex landscape of human perception. What I find appealing about the “green infrastructure” narrative is that it is about landscape performance and placemaking. This narrative appeals to planners and landscape architects, but it is lost on the general public unless it is intuitively apparent and looks really great. For that to happen, the proof needs to jump out at you even when you are going 75 miles an hour.