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e c o l o g i c a l e n g i n e e r i n g 3 0 ( 2 0 0 7 ) 201–205

avai lab le at www.sc iencedi rec t .com

journa l homepage: www.e lsev ier .com/ locate /eco leng

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xploiting the attributes of regional ecosystems forandscape design: The role of ecological restorationn ecological engineering�

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eywords:

ative plant

nvasive species

estoration ecology

rban design

andscape design

a b s t r a c t

The application of the principles of ecological restoration has been underutilized by land-

scape designers. The reliance on a small palette of often non-native plant species combined

with limited application of sound ecological principles both limits design potential and

poses significant environmental risk. The principles of ecological restoration, which exam-

ine regional native ecology to guide landscape design, need not be limited to reparation or

restoration projects, but may equally apply to parks, parking lots, detention ponds, green

roofs, and roadsides, just as they do to re-establishing a prairie or wetland. We propose

that environmental designers, whether landscape architects, civil engineers or restoration

practitioners, investigate and exploit the ecological attributes of their native landscapes to

provide smarter tools for solving design problems. This will improve ecological value of

the project and reduce any collateral ecological damage caused by poor plant selection. We

suggest that this calls on the landscape design industry to focus on three core areas:

1. Exploration of the relevant science and principles of ecological restoration as applied to

landscape design issues.

2. Examination of regional native plants and their biology for specific landscape design problems.

3. Education about the threat that invasive plants pose both in short and long terms.

environment and, more importantly, the surrounding ecosys-

. Introduction

cological restoration has been criticized as being unrealisticnd a quaint hobby on a par with collecting antiques (Kirby,994). This criticism results, in part, from the fact that mostf the areas where the practice of restoration occurs haveeen outside the highly urbanized environment. This needot be the case, however, as fundamental ecological knowl-dge is indeed highly relevant to all aspects and scales ofandscape design. Skills drawn from ecological restoration can

elp to address these challenges, even if the result is not liter-lly a restoration of a locally historic system. Environmentalesigners, whether they are landscape architects, civil engi-

� Segments of this article were previously published in the May 2006

neers, or other professionals involved in landscape design andengineering face a wide range of challenges in both urbanand rural environments. However, a revegetation prescriptionbased on a limited appreciation of regional ecology and a lim-ited commercially available plant palette can generate latentecological problems. The same growth traits of the horticul-turally familiar species that might promote rapid revegetationin ecologically harsh settings might result in contributing toproblematic invasive species in both the immediate project

edition of Landscape Architecture.

tems. Conversely, beyond the risks of plant invasion, the valueof functioning natural resources is being recognized by thelandscape design industry, and restoration of this natural cap-

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ital is becoming an increasing priority (Aronson et al., 2006),Finally, the expansion of the scope of the project beyond bla-tant design goals may even improve overall project success(Gawlik, 2006).

Although regionally native plants might offer a moresustainable alternative, native substitutes for common land-scaping plants are often rejected by the landscape designindustry. This is not only due to lack of availability, but alsobecause of their perceived poor growth characteristics, in spiteof the fact that this has rarely been tested. Too often, the rele-vance of a plant’s geographic source is effectively eclipsed byits perceived ability to perform a specific function and estab-lish and thrive in sometimes harsh environments. We suggestthat by ignoring geographic provenance, we lose an oppor-tunity to take advantage of our rich, underutilized, nativefloral diversity and find more ecologically sensitive as well aspotentially cost-effective solutions. Furthermore, the applica-tion of principles and methods of ecological restoration offersreal solutions to the host of environmental design problemsencountered in both the wild as well as the urban landscape.The growing challenge to designers who pursue the objectiveof environmental sustainability is not only to strive for land-scapes that require fewer inputs in terms of water, fertilizer,and maintenance, but also to consider the effects that theirentire design, including their plant selection, will have bothon and off their project site.

We propose that environmental designers, regardless of thescale or scope of the project, need to investigate and exploittheir native regional floras and ecosystems to provide smartertools for solving design problems.

2. The constraints of landscape design andhorticulture

The creation of a landscape requires designers to apply appro-priate plant species to a broad spectrum of environmentalconditions (Lindig-Cisneros and Zedler, 2000). In most situ-ations, the original vegetation has been greatly changed oreven eradicated, the soils have been physically and chemicallyaltered, and the microclimate transformed. Economics andproject success encourage environmental designers to selectspecies that demonstrate strong survival and growth traitsand the ability to establish with variable levels of resources in awide range of climate and soil conditions. A further constraintis imposed by horticulture which demands characteristics ofease of propagation, transport, and growth performance. Theresulting limited inventory of plants gathered from aroundthe world constitutes the species typically used in designedlandscapes. Unfortunately, many of these species have thepotential to be invasive and therefore ecologically and eco-nomically destructive. Of the 235 woody species that areinvasive in the US, 85% were introduced for ornamental andlandscape purposes (Reichard and Campbell, 1996). Simi-larly, many herbaceous plants promoted by the horticulturalindustry, such as water hyacinth and purple loosestrife, have

escaped cultivation and resulted in major negative impactson water supply, recreation, and forage production, while alsoincreasing the probability of wildfires and flooding. Moreover,from the design perspective, the overuse of a small number

3 0 ( 2 0 0 7 ) 201–205

of plant species has promoted a homogenization of designedlandscapes that do not exhibit a sense of place or a local designaesthetic. This practice effectively compromises the intrin-sic (e.g. aesthetic appeal, site function) and extrinsic (e.g. lowenvironmental impact, reduced heat-island effect) landscapedesign goals in return for the convenience of the commonlyutilized species selection.

Fortunately, there is growing evidence that native speciesare capable of outperforming their exotic counterparts bothin aesthetic and establishment attributes, and this shouldencourage us to further investigate the many species thatcharacterize our native ecosystems. The key to using theuntapped resources of our regional floras is the understand-ing that each ecoregion has species adapted to a wide range ofenvironmental conditions and ecological processes. The chal-lenge is to match regionally appropriate native plant speciesto the designed site conditions.

Promotion of such a shift of emphasis for the landscapedesign industry requires focus in three core areas:

1. Exploration of the relevant science and principles of eco-logical restoration as applied to landscape design issues.

2. Examination of regional native plants and their biology forspecific landscape design problems.

3. Education about the threat that invasive plants pose bothin short and long term.

3. The patterns and consequences of plantinvasion

In the United States, plant invasion has been responsiblefor significant ecological (40 million acres invaded) and eco-nomic (currently $38 billion annually) damage (Pimentel etal., 2000). Ecosystem diversity is also threatened. Along withhabitat loss, invasive species are considered a major causeof loss of biodiversity and species extinction. The invasabil-ity of a non-native species is, however, difficult to predict, andthe illusion of ecological benignancy encourages a dangerouscomplacency. While some characteristics, such as high seedproduction, the lack of predators or ecological disturbance,broad ecological niche, and the presence of suitable pollina-tors, can indicate invasive potential, it is still very difficult todetermine in advance which species will be a problem in thefuture. Those species that do become invasive typically followa predictable growth pattern after introduction. The popula-tion establishes and increases slowly, followed by colonizationthat is marked by exponential population increase until it nat-uralizes or saturates the plant community. Because the timefrom introduction to colonization varies for many reasons,the invasive species can ‘simmer’ in the background at theintroduction phase for years, even decades, before emergingas a real ecological threat. One review of 184 invasive woodyplants found that 6% spread within the first 50 years followingintroduction, 25% took 100 years, 51% took 200 years, and 14%lagged up to 300 years (Kowarik, 1995). By the time invasion is

recognized, effective control is often economically prohibitive.

Therefore, it is widely recognized that thwarting the prob-lem in the introduction phase should be the priority fortackling invasive species, and the horticultural industry has

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een identified as one of the most damaging pathways ofeliberate introduction of invasive plants (Lodge et al., 2006).his implies several things. Primarily, the design and horti-ulture professions must share that responsibility for thesentroductions. Secondly, if the relationship between the twondustries is interactive, then designers who demand alter-atives to conventional plant palettes could initiate positivehanges. Finally, it is incumbent upon those professionals whoave knowledge of native plant material and basic ecologi-al principles to become more involved in the design of notnly restoration projects, but also more urban projects evenhen the goal might be a landscape far removed from anyast historical condition.

. The application of ecological restorationn landscape design

estoration ecology as applied to environmental designhould not be distracted by the desire to achieve a high levelf ecological function within the project site itself (Lindig-isneros and Zedler, 2000). Restoration, rehabilitation, andepair are all target goals along a continuum. Subsequently,nstallations of a solitary native tree among a suburban street,ative turf in a parking lot, biofiltration pond, or monoculturef native shrubs on an urban green roof are equally qualifiedo be worthy of the application of sound ecological principles.oreover, such projects should not be perceived as isolated

lantings, but rather a positive contribution to the ecologicalunction of the broader environment (Thompson et al., 2003).his approach removes any perceived constraints of the appli-ation of the principles of restoration ecology by broadeninghe project scope to include the wider ecological impact of theesign.

Ecological restoration draws on decades of cumulativenderstanding of ecology, biology, climate, and soil science,nd attempts to pull the relevant parts together to reconstructr repair the system. In the process, it has become increasinglypparent that solutions to landscape-scale problems are notlways simple and often require a thorough understanding ofhe ecosystem components and dynamics. There is little doubthat human influence on global vegetation is significant andrreversible. The contemporary environment is largely com-osed of altered landscapes that have been exposed to such

ntense disturbance that it is difficult to overcome the ecologi-al ratchet that would permit restoration of these sites to someormer pre-Columbian state. While ecological restoration touch a target condition may in some cases be possible, inost landscape situations the redesign and repair of ecosys-

em function are perhaps the only desirable and practical goalseft. A current description of ecological restoration as definedy the Society for Ecological Restoration implies (re)creationf process as well as form: “Ecological restoration is the processf assisting the recovery of an ecosystem that has been degraded,amaged, or destroyed” (SER, 2002). The restoration ecologypproach is to derive a workable model through the study

f existing, functioning plant communities and then applyhis knowledge of plants and ecological process to produce

designed system that has attributes (plant composition,cological function and integrity) that mimic some identified

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reference system elsewhere. While this definition is useful forachieving many restoration endpoints, it does not readily cap-ture all potential goals within the realm of many landscapechallenges, where a single engineering or aesthetic problemdemands a specific, sometimes ecologically simple solution.Nevertheless, the overall approach of ecological restoration,which emphasizes the links between plant assemblage andecological process, offers valuable insights and guidelines forlandscape design. The extent to which the final design sim-ulates a natural native plant assemblage with its inherentecological mechanisms is highly variable and dictated by thedesign goal. Viewed this way, the practice of ecological restora-tion is perhaps a subset, albeit, occasionally, a critical one, ofecological engineering. Furthermore, this might prompt a callfor the evolution of a greater range of attributes of ecologicalrestoration which might be among core elements in all qualityenvironmental design practice.

From the landscape design perspective, successful designand manipulation of an ecosystem or plant community,however simple, is assisted by an understanding of severalelements: plant biology, abiotic conditions (climate, hydrol-ogy, and soils), and the ecological processes which influencethe interaction of these components. Knowledge of one or twoof these elements may enable the successful landscape plant-ing, but an understanding of all three elements provides theinsight and opportunity to improve both the appropriatenessof design as well as its ecological function and long-term suc-cess. An understanding of ecological process can help to createan ecologically functioning landscape—even one that is totallysynthetic and without a historical equivalent. Many designersfrequently practice this concept. For example, investigationof local dominant native vegetation may direct and inspirethe designer to select suitable candidate trees and shrubsfor an urban landscape. However, a deeper knowledge of thefull range of native plants which exist, or formerly existed,regionally, and not just the few conspicuous species, gives thedesigner more planting options with a wider range of applica-tions. Compare reliance on only the dominant plant speciesto the use of subdominant species of the same ecosystemwhich upon first glance might be effectively invisible and eas-ily overlooked. In most plant assemblages only a few speciesare common and therefore dominant. The majority of speciesthat comprise plant communities are uncommon and oftendispersed intermittently or temporally absent (Gaston, 1994).Such species are often adapted to temporary, aberrant, ecolog-ical disturbance such as canopy openings or the conditionsfollowing a wildfire, and may be ideal candidates for otherdesign applications such as rapid revegetation, permanentground cover, or for seasonal color.

What those who practice ecological restoration are learn-ing is that we have underestimated the ecological engineeringpotential of our diverse floras by focusing on dominant or cli-max species composition. It is likely that there is a native plantsuitable for almost any landscape situation encountered, butto date we have not thoroughly investigated or taken advan-tage of this full range of species. Texas, for example, has

approximately 5400 native species, but less than 3% are avail-able commercially even within the state. Obviously, not all ofthe remaining 97% will have design applications or exhibitgood propagation characteristics, but it seems likely that many

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will. We are mistaken and naive to assume that existing,commercially available species are the only ones biologi-cally, horticulturally, or aesthetically suitable for a particularfunction. Given the risks posed by introducing a potentiallyinvasive species, if there is a suitable native alternative thatcan perform as well, if not better than the non-native in termsof the desired design characteristics, would that not be prefer-able? Clearly, native floras need closer examination.

5. Native plants can provide specificsolutions for landscape design

It is sometimes perceived that because some native species arepoor performers in some designed environments, all nativesmust be similarly inferior performers. In truth, this perceptionmerely reflects how little effort we have put toward under-standing the ecophysiological attributes of our regionallynative floras. Looking closer, there are numerous examples ofnative plants that are well adapted to harsh environments andcan establish quickly even under harsh conditions. Riparianspecies, adapted to anoxic conditions on riverbanks, functionwell in compacted soils of paved urban sites. Alternatively,competitive ‘weedy’ native species are well suited to heavilydisturbed sites. On Staten Island, NY, the construction of park-land on the Fresh Kills Landfill was accomplished using suchnative species as hackberry, Virginia creeper, sumac, sassafras,blackberry, and blueberry (Millar, 2005).

Sometimes it is not a single species that is needed toaddress a single design problem but an entire plant com-munity. The Texas Department of Transportation, chargedwith managing 1.1 million acres of right of way, has longrelied on a few species to provide for revegetation along road-sides (Texas Department of Transport, 2004). Based on earlyefforts using common native grass species, it was believedthat native grasses could not be used for rapid revegetation.However, a recent roadside study demonstrated that after60 days from sowing, the seedling densities of two purelynative mixes (some selected based on their “weedy” nature)were up to five times greater than the recommended non-native mix (Tinsley et al., 2006). This suggests that judiciouslyselected native plants adapted to these disturbed conditionsmight not only do as well as standard non-native mixes inrevegetation projects, but also dramatically outperform them.Both of the non-native grasses tested exhibited relatively poorestablishment traits in this application, which implies thattheir suitability for revegetation projects may have been over-rated. Furthermore, these two non-native species have beendesignated invasive or noxious weeds in several regions byeither federal or state authorities, and their use thereforecould be perceived as an unnecessary threat to ecosystemhealth.

Designs that utilize native plants also positively con-tribute to general ecological function and diversity, and henceecosystem services of the entire landscape. Even incremen-tal ecological contributions (small areas or few species) can

improve overall ecological function by introducing corridorsor islands of habitat in an increasingly fragmented landscape(Thompson et al., 2003). A similar positive ecological impact isless likely with non-native species.

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Aside from arguments about the ecological suitability ofnative or non-native species, native plants can also provide asense of place and regional identity. In the battle against thehomogenization of the landscape, the use of natives encour-ages an ecological patriotism. In an apartment complex inKirkby, in the industrial north of England, a public surveyshowed that 97% of respondents said they wanted more nativewildflowers, and 64% said they were more likely to take awalk outside as a result of the vistas of wildflowers. They alsosaid they probably had little chance ever of seeing this nativelandscape in the surrounding rural areas countryside. As aconsequence, the surrounding grounds were converted intonative wildflower meadows at a lower cost than conventionalurban landscaping solutions. The resulting design receivedhigh praise from residents, the press, and even unsolicitedletters from local health centers (Landlife UK, 2006).

6. Implications and opportunities of choice

The operational envelopes of environmental design aredemanding, and the function and the design goals should notbe compromised by self-limited constraints. Native plants andtheir inherent ecological functions can provide equally prac-tical and sometimes superior options to the designer, whichmight improve the quality of the project, significantly lowerthe ecological risks to the larger landscape, contribute posi-tively to broader landscape ecological function, and improveoverall project success. We should not accept the broader neg-ative environmental and economic consequences of crudeplant selection. Instead, the landscape design industry – whichmust begin to tap more extensively into the existing localecological knowledge base – should take responsibility forthe role of all designed landscapes in the greater biolog-ical function of the entire ecosystem. If we, as designers,accept this responsibility, then we should call on ecologicalengineering and restoration scientists and practitioners, thehorticultural and agricultural industries, and our federal andstate agencies to investigate and provide suitable native alter-natives to potentially harmful exotic species. Through thecourse of project implementation design practitioners are con-stantly exposed to plant–environment interactions, many ofwhich were not predicted. Further, as naturalists we observebiological processes across spatial and temporal scales thatwe intellectually absorb to incrementally add to our under-standing of natural systems. We suggest that this wealth ofinformation most likely holds solutions for specific designproblems and should be integrated into even the most urban ofdesign projects. The challenge for designers is to take advan-tage of these rich regional floras to create truly “sustainablelandscapes” in such a way that neither design objectives norbroader ecological health are compromised. Our created land-scapes are calling for smarter environmental solutions andthe principles of ecological restoration have much to offer.We should seek out those landscape problems where we can

edge of native ecology. The bottom line is that a successfullandscape needs innovation not only with respect to designbut also ecological vigor. We should not settle for anythingless.

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aston, K.J., 1994. Rarity. Chapman and Hall, London.awlik, D.E., 2006. The role of wildlife science in wetland

ecosystem restoration: lessons from the Everglades. Ecol. Eng.26, 70–83.

irby, J.T., 1994. Gardening with J. Crew: the political economy ofrestoration ecology. In: Baldwin Jr., A.D., Luce, J.D., Pletsch, C.(Eds.), Beyond Preservation: Restoring and InventingLandscapes. University of Minnesota Press, Minneapolis, pp.234–240.

owarik, I., 1995. Time lags in biological invasions with regard tothe success and failure of alien species. In: Pysek, P., Prach, K.,Rejmanek, M., Wade, M. (Eds.), Plant Invasions, GeneralAspects and Special Problems. SPB Academic Publishers, TheHague, pp. 15–38.

andlife, UK, 2006. URL http://www.landlife.org.uk/projects/projects.htm, accessed June 2006.

indig-Cisneros, R., Zedler, J.B., 2000. Restoring urban habitats: acomparative study. Ecol. Restor. 18, 184–192.

odge, D.M., Williams, S.L., MacIsaac, H., Hayes, K., Leung, B.,Reichard, S., Mack, R.N., Moyle, P.B., Smith, M., Andow, D.A.,Carlton, J.T., McMichael, A., 2006. Biological Invasions:Recommendations for U.S. Policy and Management. PositionPaper. Ecological Society of America, Washington, DC.

imentel, D., Lach, L., Zuniga, R., Morrison, D., 2000.

Environmental and economic costs of non-indigenous speciesin the United States. BioScience 50, 53–55.

illar, H., 2005. Talkin’ trash: let a billion flowers bloom: an urbanecologist is turning New York City’s largest dump into one ofits finest natural destinations. Sierra 90, 44–67.

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Reichard, S., Campbell, F., 1996. Invited but unwanted. AmericanNurseryman 184, 39–46.

SER, 2002. The SER Primer on Ecological Restoration. SER WorkingGroup.

Texas Department of Transport, 2004. Standard Specification forConstruction and Maintenance of Highways, Streets, andBridges. TxDOT, Austin, TX.

Thompson, K., Austin, K.C., Smith, R.M., Warren, P.H., Angold,P.G., Gaston, K.J., 2003. Urban domestic gardens (I): puttingsmall-scale plant diversity in context. J. Veg. Sci. 14, 71–78.

Tinsley, M.J., Simmons, M.T., Windhager, S., 2006. Theestablishment success of Native versus non-nativeherbaceous seed mixes on a revegetated roadside in CentralTexas. Ecol. Eng. 26, 231–240.

Mark T. Simmons ∗

Heather C. Venhaus 1

Steve Windhager 1

Lady Bird Johnson Wildflower Center, University of Texas atAustin, 4801 La Crosse Avenue, Austin, TX, United States

∗ Corresponding author. Tel.: +1 512 292 4200;fax: +1 512 292 4627.

E-mail addresses: msimmons@wildflower.org(M.T. Simmons), hvenhaus@wildflower.org (H.C. Venhaus),

stevew@wildflower.org (S. Windhager)1 Tel.: +1 512 292 4200; fax: +1 512 292 4627.

5 September 2006

0925-8574/$ – see front matter© 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.ecoleng.2007.01.007