Part 1: Grass-Dominant Meadow Communities
Estimates indicate that grasslands, or meadows, once covered 42% of the earth's land surface.[1] Today, these fertile zones are home to a new family of grass species critical to grain production such as wheat, barley, corn, sorghum, millet, rice, oats and sugarcane; and, in smaller scales to the grazing needs of the livestock industry. Still, grasslands cover 25% of the earth’s surface and serve important ecological functions.[2]The intersection of agriculture and urbanization remains critical as the meadow is making its way back into the city and has the capacity to engage with infrastructural corridors and established landscapes. "Cosmopolitan urban meadow" communities that have developed tolerance to drought and poor soil structures have particular relevance within the urban fabric by way of their ability to handle environmental stress, provide erosion control, enhance wildlife, engender economies of mass production and maintain an aesthetic agenda.[3]
Meadow plant communities are largely comprised of grasses and forbs, herbaceous perennials with life spans that can reach decades and root systems that can extend deep into the soil in response to fluctuations in available resources. Precipitation, geology and disturbance regimes become parameters by which each community becomes defined. Microbial, invertebrate and herbivore communities interact with herbaceous plant structures in a process that advances species development and cycles nutrients in habitats that encourage burrowing and grazing.
Three types of meadows span the core of the United States and Europe: they are the Tallgrass, Mixed and Shortgrass. Though largely eliminated in their natural context, a better understanding of the ancestry of these communities provides a starting point for understanding the conditions undergirding the success of herbaceous material in the urban environment. In North America, these meadow typologies developed on the flat and rolling terrains created by the craton during the Cambrian period, a defining feature the Plains and the Midwest. Eroded materials blown into the Midwest from the Rocky Mountains and glacial activity from the Pleistocene period determine the more topography-specific composition of plants revolving around soil moisture.[4]Meadows are drought and fire resistant, have soils that are rich in organic matter, fertile and slightly alkaline.
At 20 to 50 percent, grasslands exhibit the highest index of productivity per unit of standing crop among terrestrial systems.[5] Biomass productivity increases as a function of precipitation, as water stress is reduced and nutrient intake is increased.
Meadow systems interact at three levels including the root, ground and herbaceous layer.[6] Because the subsurface root zone comprises over half of the plant's biomass, Brown has aptly named this critical environment the "invisible prairie."[7]Microbes and invertebrates process nutrients from detritus left by herbivores and other invertebrates in the root zone. According to Grime, ectotrophic mycorrizas "are strongly associated with conditions of mineral nutrient stress" and operate as a surrogate to a process of root establishment and decay that requires a large amount of plant photysynthate as the mycorriza store nutrients that are available to the plant without a large investment by the plant.[8]
Nurseryman and author Roy Diblik offers a poetic that "weeds heal the Earth," functioning to enable microorganism activity that creates arable soil. The maintenance practices of mulching or mowing and removing thatch destroys soil quality and perennial plant longevity. Diblik equates this thinking with an agricultural tradition that considers all plants "annual" and fails to allow critical growth cycles, sometimes hidden, to unfold over time.[9]Indeed, according to Brown the total weight of microorganisms in a given area in a meadow is about equal to the total weight of vegetation,[10]with nematodes accounting for "90, 95 and 93 percent of all belowground herbivory, carnivory, and saprophagous activity, respectively."[11] In short, the meadow primarily functions as a soil-manufacturing and remediation machine.
Habitats found in the herbaceous and ground layer privilege hopping and leaping, speed, digging, burrowing and social behavior amongst predators and prey, with grasshoppers making up the majority of an invertebrate denizen of 1 to 50 grams per square meter compared to mammals that comprise 2 to 5 grams per square meter of biomass. Feeding activity in the herbaceous and ground layer contributes to plant regeneration and mulch formation, which contributes to the nutrient cycling process. The relationship between grazing and growth has developed in grasses the capacity to have culms reduced to the crown without damaging the plant. Grasses and forbs have developed the ability to relocate nutrients from roots to stems and remove inefficient tissue to foster the growth of young tissue and increase light intensities. As such, moderate grazing of grasslands increases overall primary production, up to levels twice that of un-grazed meadows.[12]
The impact of mowing on a meadow community is one that deserves a closer look as meadow communities attempt to make their way into constructed landscapes that require maintenance by mowing. In an excellent early comparative study of root and shoot development in prairie grasses in response to the clipping of grass tops, Biswell and Weaver show that in some grass species (Bouteloua gracilis/Andropogon gerardii, for example) the width of the rhizomatic sphere and depth of roots in grasses that are repeatedly clipped are signficantly less than their unclipped counterparts, though flowering may continue unabated in repeatedly cut grasses.[13] This finding supports the possibility that forbs can be sown into an established meadow community that uses mowing as a technique to increase species richness. Seedling recruitment is increased with less competition below the surface and more light above the surface, making establishment in a closed canopy of grasses possible after mowing. Findings confirm this notion, with forbs developed from seedlings in mowed conditions demonstrating significantly higher biomass, healthier root structure and significantly higher over-wintering rates that those seedlings established under closed-canopy, unmown conditions.[14]
The act of mowing the meadow can become a participant in the development of the meadow's richness. Interestingly, many studies examine how agricultural machinery used to mow the ditches and hedgerows are responsible for acting as an agent in the seed dispersal, to the extent that they are indicated as a possible source for fragmented patches of remnant native landscapes in old fields.[15] While mowing of these remnant patches typically occurs after crop planting on traditional farms, there is a fair deal of research that indicates the relationship between species-richness and mowing date.[16] Studies of mowing ditches in the Netherlands, for examples, have found that mowing twice annually on July 1 and September 1 contributes to the highest seed dispersal. By alternating mowing dates in consecutive years more tender species are more likely to flourish. Of course, this knowledge must consider the flowering time and seed establishment times of species within the meadow to produce the richest effects.
Part 2: Proposal for an Urban Meadow at the Charles River Esplanade
"Any future improvements to the Esplanade should be done with an understanding of the original intent of the founders and in a way that reinforces the purpose and character of the Esplanade. We are lucky to have Charles Eliot, Guy Lowell, and Arthur Shurcliff to look back to for inspiration even as we look ahead to meet the needs of 21st century park visitors.
Evolution and change in a park over time to meet modern needs is natural and even essential but can be accommodated in a way that respects the core purpose and meaning of an historic landscape."[17]
"We want to serve history only to the extent that history serves life: for it is possible to value the study of history to such a degree that life becomes stunted and degenerate-a phenomenon we are now forced to acknowledge, painful though this may be, in the face of certain striking symptoms of our age."[18]
Landscape Architecture has the unique capacity to use time as a variable within its scope of services; indeed, the opportunity to collage natural systems with diverse evolutionary tracts into coherent patterns that are entirely constructed for the purpose of achieving a designed landscape system is considered by many as an identifying feature of a successful project. In this regard, directing the evolution of large, historic parks should be a major topic in the training of any landscape architect that intends to work in the public realm of established cities. These are the sacred places within which an established ecological trajectory can merge with new principles that redirect our relationship with nature, while creating a rich dialogue between the past and future.
The Charles River Esplanade, designed by Guy Lowell and Arthur Shurcliff from 1931 into the early 1950's was to become the public landscape that brought the Charles River to life in the core of Boston's Back Bay. Today, this vision has been realized to varying degrees with the park proving to be a major attraction to joggers, walkers and bikers and to a lesser extent, a place where massive crowds of the public come to participate in cultural events on the Charles River.
In many ways, the criterion by which design success can be measured at the Esplanade are inseparable from the status of its vegetative structure. The Spartan park concept, like many in the mid-20th century, conveys meaning by varying open and closed spaces that create "natural" moments along the river, with little attention paid to ecological function. In a paradox typical of mature landscapes, the original tree distributions employed to provide shade throughout the park creates the conditions responsible for its current decline.
A leitmotif of Shurcliff's planting strategy at the Esplanade was to use vegetation to define rooms within the park and to locate gathering locations within these transition points. The canopy, largely consisting of Tilia,Quercus, Acer platanoides, Salix and Zelkova was to provide shade within these borders. Mass plantings of Berberis thunbergi, Forsythia fortunei, Forsythia suspensa, Ligustrum ibotaand Lonicera morrowi[19]were to be a shrub layer that defined pathways and created thresholds into shaded "rooms" that visitors would proceed through as the river and the city it framed unfolded before them.
Today, these shrub borders have been eliminated by the overwhelming shade produced by the successful growth of the existing canopy; in particular, the advantageous Norway maple has outcompeted the growth of less aggressive species and made difficult the establishment of understory and herbaceous plant material. The shade created by mature trees has caused turf to fail, soil to become compacted and, ultimately, reduced the horticultural variety of the thickened edges that the park showcased during the early years of tree growth. This condition is typical throughout the park; with exceptions including the Ellipse (band shell), ball fields and the island landscape adjacent Storrow Lagoon. Limited maintenance due to reduced landscape budgets only compound existing stressors, though a recent survey of trees has been completed by the Esplanade Association in an effort to prioritize the pruning, removal and transplanting of trees based on their current condition in hopes of directing piece-meal financial contributions to the trees that need most care.[20]
These circumstances create a challenging scenario that confront many mature landscapes that require nudging when the need to intervene with their stage in succession becomes more pressing than relying on and adherence to the design's original intent. Out of this emerges a unique set of parameters that will likely continue to be a major factor in park (re)design; namely, a field condition that demands acupunctural solutions rather than wholesale demolition of the past in the process of building for the future. Planting as a redevelopment strategy can be a driving force in promoting a new understanding of time and ecology within this framework.
In an October 2011 meeting with Esplanade Association Project Manager, Jessica Peterson, it became clear that moving forward, the limitations of the park would also have to become guiding factors in its renovation. The following proposal to the Esplanade Association results from a synthesis of their 50-year vision for the park and my own ambitions to examine the extent to which "sustainable" planting approaches can engage with mature urban landscapes. In the process of this exploration, my intention is to respect Arthur Shurcliff's vision while simultaneously positing a new relationship between the park, plant communities and its users.
The following summary enumerates strategies that respond to the needs of the park, acknowledge existing site conditions and respect the maintenance resources available to the Esplanade Association (these aims are detailed in the attached drawings) The remaining content of this paper will explore how the creation of a grassland biotope, or "cosmopolitan urban meadow," operate.
0. Set a Goal for Alternative Turf at the Esplanade
John Greenlee, author of The American Meadow Garden, a book dedicated to looking at alternative plant species capable of taking the place of conventional turf using lower resource-inputs has conceded that the love for turf is largely driven by its simplicity as a "green panel" that can be easily accessed.[21] While the island at the Esplanade is a public space that requires a dependable surface cover, there is no indication that using alternative species for this purpose is less durable. Studies have indicated that native and non-native polycultures have up to 30% higher leaf density during the early season and 50% less weed cover by mid season when compared to a non-native monoculture.[22] In general, slower growth rates of "native" grass species can be seen as an inherent savings in maintenance that also reduces the carbon footprint of the park while allowing for the integration of other perennials and herbs that offset any perception of weak performance due to lower leaf density early in the season.
1. Mowing is Design:
The jogging and biking community forms the largest user group of the corridor landscape between the Charles River and Storrow Lagoon. The site provides a rare opportunity within the park to easily establish diverse plant communities at the ground level due to the scattering of trees that allow greater light penetration. This stretch of landscape is primarily trail-oriented which creates an opportunity for its maintenance regime to enter into an associative relationship with meadow development and programmatic potential.
An existing toe path that runs parallel to the Charles River varies in width from 24" to 48." Using this width as a parameter, new mowing patterns through the established meadow communities can be determined by the width of cutting machinery; using standard riding mower dimensions, this allows for easy width adjustments that allow for 30", 48", 60" and 72" pathway dimensions. These can be shifted to accommodate user intensity, for example, be cut at 30" width during the fall mowing and 72" width during the early summer mowing.
According to Steven Bernhardt, maintenance supervisor at Millennium Park in Chicago, IL, mowing times in this condition (grasses with a few existing trees) will likely range from 1 to 2 hours per acre at a labor cost of $35/HR. Bernhardt points out that once grasses reach about 36" in height, the pathway may need to be double or triple mowed in order to cut material that flops upon being mowed; however, line trimming (which requires more intensive manual labor) is unlikely necessary for this application.[23]
By altering mowing patterns and converting a "turf" landscape to a maintained "cosmopolitan meadow" the strategy effectively a.) Reduces mowing costs for the parkb.) Creates shifting trail networks and thus provides opportunities for new experiences with the landscape for daily users; and c.) Encourages the establishment of a dynamic ground plane that displays herbaceous and perennial competition within their matrices.
2. Plant Selection
Horticulturalists, Researchers and Nurserymen have dedicated a considerable amount time into finding the appropriate plants for urban meadows (see attached drawings for my suggestions) and in general suggest using plants that thrive in low-nutrient soils. I think it is critical that these recommendations remove self-seeding or wind-dispersed material off of these lists in order to maintain a dynamism and aesthetic to the urban meadow. For instance, a mistake like including Knautia macedonica, Oenertha sp., Campanula sp., could skew a perception of orderliness that is part and parcel of a secret code with the public. Meadow does not mean formless and at the Esplanade this guiding principle can keep out plant material that gets untidy, even with mowing.
3. Nursery Development & Distribution
The conversion of existing to turf to meadow will require that forbs be introduced into the grass-dominant matrix at some point. In an effort to reduce the cost of these forbs and focus maintenance staff and supplemental resources such as the provision of irrigation connections and applications of fertilization, the park should designate a parcel to the growing of herbaceous material. I have proposed this nursery to be placed at the main entrance into the island and to be bound by clipped hedges at various heights in an effort to signify that this element of the landscape is a unique location. A new bituminous jogging path courses through this nursery, increasing the public interaction with the plants that they will see repeated throughout the island.
In terms of plant material, the objective is to blur the definition of "cultivated" and "weedy" plant material by treating both as equals. In this way, the public views certain, less favorable plants as new additions to the perennial palettes with which they are familiar. Indeed, the lots in which plants are raised and maintained are developed in polycultural matrices based on physiological structure rather than in monocultural swaths based on cultivar, an artifact of traditional agricultural production prevalent in the ornamental nursery industry. This could be best understood as a recipe that represents plant communities within the area as a combination of "Foundation + 2," where "Foundation" includes one of any number of dominant grasses and "+2" means the inclusion of supporting plant structures. (See attached drawings for details).
Take for example, a 20' x 20' parcel composed of 60% Amsonia hubrichtii(foundation) interplanted with 30% Parthenium integrifolium (umbellifier) and 10% Verbascum thapsus (spire). This permutation (foundation + umbellifier + spire) would demonstrate the suitability of associates based on aesthetic sensibilities based on vegetative structure and flowering form rather than highlighting their biogeography or value as a "sustainable" plant prima facia. Educational signage would not discuss plant origins, but instead focus on the possible associates found within the nursery that could be an associate of Amsonia, for instance, based on structural compatibilities (i.e., umbellifier + spire, etc.)
This type of organization has been discussed extensively by owner of Northwind Perennial Farm in Geneva, Wisconsin, Roy Diblik, who now provides these ratios based primarily on form to Midwest Groundcovers, Chicago's largest whole-sale perennial nursery. The work of Piet Oudolf is seminal here, and in his book Designing with Plants, Oudolf plants the seed of distributing plants based on their form. The Esplanade could greatly benefit from this forward-thinking strategy.
After the third growing season when plant material is divided and planted elsewhere in the park, combinations within the nursery area can shift as well, creating a dynamic landscape of production in addition to stocking the site. Programmatic possibilities include selling the plants to the public or creating an exchange network that includes other public parks.
Works Cited
Bernhardt, Steve. Senior Maintenance Manager, Christy Webber Landscapes, Chicago, IL. Personal Communication. 16 December 2011.
Biswell, Harold and J.E. Weaver. "Effect of Frequent Clipping on the Development of Roots and Tops of Grasses in Prairie Sod." Ecology. Vol. 14, No. 4 (1933).
Brown, Lauren. The Audubon Society Nature Guides: Grasslands. New York: Knopf, 1985.
Coulson, Sarah et. al. "Colonization of Grassland by Sown Species: Dispersal Versus Microsite Limitations in Responses to Management." Journal of Applied Ecology. Vol 38 (2001).
DelTredici, Peter. Wild Urban Plants of the Northeast: A Field Guide. New York: Cornell University Press, 2010.
Diblik, Roy. Owner Northwind Perennial Farm; Author Roy Diblik's Small Perennial Gardens: The Know Maintenance Approach.Personal Communication. 10 December 2011.
Grime, J.P. "Evidence for the Existence of Three Primary Strategies in Plants and Its Relevance to Ecological and Evolutionary Theory." The American Naturalist, Vol. 111, No. 982 (1977).
Leng, Xin, et. al."Effects of Mowing Date on the Opportunities of Seed Dispersal of Ditch Bank Plant Species Under Different Management Regimes. Journal for Nature Conservation. Vol. 19 (2011).
Lehmusvirta, Linda. "Get off the Grass." Organic Gardening. Vol. 58, No. 3. April/May 2011.
Massachusetts Department of Conservation and Recreation. "Request for Response for Goods or Services: Charles Eliot Memorial Revitalization Project, Charles River Esplanade, Boston MA DCR MSA No. 323-Landscape Architectural Services-DCR Contract No. P10-2582-D1A." May 26 2011.
Peterson, Jessica. Charles River Esplanade Association, Project Manager. Personal Communication. 14 October 2011
Simmons, Mark et. al. "The Performance of Native and Non-Native Turfgrass Monocultures and Native Turfgrass Polycultures: An Ecological Approach to Sustainable Lawns. Ecological Engineering. Vol. 37 (2011).
Smith, Robert Leo. Ecology and Field Biology 5th edition. New York: HarperCollins College Publishers, 1996.
Williams, Dave et. al. "Effects of Frequent Mowing on Survival and Persistence of Forbs Seeded into a Species-Poor Grassland." Restoration Ecology. Vol. 15. No. 1. (2007).
[1]Smith, Robert Leo. Ecology and Field Biology 5th edition. New York: HarperCollins College Publishers, 1996, pg. 226.
[2]Brown, Lauren. The Audubon Society Nature Guides: Grasslands. New York: Knopf, 1985. p. 19.
[3]DelTredici, Peter. Wild Urban Plants of the Northeast: A Field Guide. New York: Cornell University Press, 2010, p. 21.
[4]Brown, p. 33.
[5]Smith, p. 223.
[6]Smith, p. 231.
[7]Brown, p. 28.
[8]Grime, J.P. "Evidence for the Existence of Three Primary Strategies in Plants and Its Relevance to Ecological and Evolutionary Theory." The American Naturalist. Vol. 111, No. 982 (1977), p. 1181.
[9]Diblik, Roy. Owner Northwind Perennial Farm; Author Roy Diblik's Small Perennial Gardens: The Know Maintenance Approach.Personal Communication. 10 December 2011.
[10]Brown, p. 29.
[11]Smith, pgs. 233-234.
[12]Smith, 234.
[13]Biswell, Harold and J.E. Weaver. "Effect of Frequent Clipping on the Development of Roots and Tops of Grasses in Prairie Sod." Ecology. Vol. 14, No. 4 (1933).
[14]See Williams, Dave et. al. "Effects of Frequent Mowing on Survival and Persistence of Forbs Seeded into a Species-Poor Grassland." Restoration Ecology. Vol. 15. No. 1 (2007).
[15]Coulson, Sarah et. al. "Colonization of Grassland by Sown Species: Dispersal Versus Microsite Limitations in Responses to Management." Journal of Applied Ecology. Vol 38 (2001).
[16]Leng, Xin, et. al."Effects of Mowing Date on the Opportunities of Seed Dispersal of Ditch Bank Plant Species Under Different Management Regimes. Journal for Nature Conservation. Vol. 19 (2011).
[17]Massachusetts Department of Conservation and Recreation. "Request for Response for Goods or Services: Charles Eliot Memorial Revitalization Project, Charles River Esplanade, Boston MA DCR MSA No. 323-Landscape Architectural Services-DCR Contract No. P10-2582-D1A." May 26 2011, pg. A-1.
[18]Nietzche, Friedrick. "On the Uses and Disadvantages of History for Life," in Untimely Meditations pg. 59.
[19]Massachusetts Department of Conservation and Recreation, pg. A-5.
[20]Peterson, Jessica. Project Manager, Charles River Esplanade Association. Personal Communication. 14 October 2011.
[21]Lehmusvirta, Linda. "Get off the Grass." Organic Gardening. Vol. 58 (3) April/May 2011.
[22]Simmons, Mark et. al. "The Performance of Native and Non-Native Turfgrass Monocultures and Native Turfgrass Polycultures: An Ecological Approach to Sustainable Lawns. Ecological Engineering. Vol. 37 (2011).
[23]Bernhardt, Steve. Senior Maintenance Manager, Christy Webber Landscapes, Chicago. Personal Communication. 16 December 2011.
Comments