Can urban areas have ecological integrity?

Reed F. Noss

INTRODUCTION The question of whether urban areas can offer a habitat and wildlife within and around urban areas, semblance of the natural world – a vestige (at least) where most people live. But, if we embark on this of ecological integrity – is an important one to many venture, how do we know if we are succeeding? people who live in these areas. As more and more of There are both social and biological measures of the world becomes urbanized, this question becomes success. The social measures include increased highly relevant to the broader mission of maintain- awareness of and appreciation for native wildlife ing the Earth’s biological diversity. and healthy ecosystems. The biological measures are Most people, especially when young, are attracted the subject of my talk this morning; I will focus on to the natural world and living things, Ed Wilson adaptation of the ecological integrity concept to called this attraction “biophilia.” And entire books urban and suburban areas and the role of connectiv- have been written about it – one, for example, by ity (i.e. wildlife corridors) in promoting ecological Steve Kellert, who also appears in this morning’s integrity. program. Personally, I share Wilson’s speculation that biophilia has a genetic basis. Some people are Urban Ecological Integrity biophilic than others. This tendency is very likely Ecological integrity is what we might call an heritable, although it certainly is influenced by the “umbrella concept,” embracing all that is good and environment, particularly by early experiences. My right in ecosystems. It encompasses other conserva- own experience, which includes working many tion values, including biodiversity, ecological years as a camp counselor and environmental resilience, and naturalness. The first reference to educator early in my career, and having 3 children of integrity in the environmental literature was Aldo my own, suggests that most children are biophilic. Leopold’s famous statement in his essay on land They are fascinated by non-human life forms. Kids ethics: “A thing is right when it tends to preserve the that have abundant exposure to nature tend to be integrity, stability, and beauty of the biotic commu- more biophilic. As they get older, however, most nity. It is wrong when it tends otherwise.” Many kids seem to lose touch with nature. They are years later ecological integrity (specifically, chemical, socially conditioned to value television, computers, physical, and biological integrity) became a goal of and video games above bugs and salamanders. the U.S. Clean Water Act (1972), the bilateral Great Their teachers and parents reinforce whatever fears Lakes Water Quality Agreement (1978), and other they have about the outdoors (e.g. about snakes, environmental policies in the U.S. and Canada. The spiders, and poison oak) and their peers tell them development of ways to actually measure ecological that nature isn’t “cool. Only nerds are interested in integrity came later. Such measurements have been that stuff.” With few or no natural areas near their applied mostly to aquatic ecosystems. Most note- homes to offer alternative experiences, many young worthy is Jim Karr’s index of biotic integrity (the people let their biophilia dwindle away to nothing as IBI). they grow older. It is no wonder we have a populace The IBI is based on the idea that the biotic integrity distanced from nature and unwilling to support of an aquatic ecosystem is affected by 5 classes of meaningful conservation programs. environmental factors: water quality, habitat struc- I have just outlined what I believe is the major ture, energy source, flow regime, and biotic interac- challenge of urban wildlife conservation. What, then, tions. The IBI assumes that fish (or other taxa, such do we do about it? Basically, what we do is maintain as benthic invertebrate) communities tell us much and, where possible, restore a lot more natural more about integrity than chemical measures because

Author’s address: Biology Dept., University of Central Florida, Orlando, FL 32815

Proceedings 4th International Urban Wildlife Symposium. Shaw et al., Eds. 2004 3 biotic communities tell us much more about integrity We might justifiably ask if it is even possible for than chemical measures because biotic communities urban landscapes to have ecological integrity. Ecologi- integrate the effects of numerous environmental cal integrity is typically measured with respect to factors. Generally, as human disturbance increases, some undisturbed reference condition. As defined by total species richness, number of intolerant species, Karr, the IBI value for a site is a measure of the and number of trophic specialists decline, while the deviation of the biological community at that site from number of trophic generalists increases. a baseline condition that represents “a biota that is the Attempts to develop terrestrial indices of ecological product of evolutionary and biogeographic processes integrity, or indices for entire landscapes including in the relative absence of the effect of modern human terrestrial and aquatic components, have been less activity.” Although I do not wish to dilute the concept successful. Nevertheless, a number of potential of ecological integrity, I suggest that reference sites in indicators and indices are emerging. One attempt to urban landscapes might be a bit different from those in develop a terrestrial IBI is in progress at the U.S. wildlands. We cannot expect an urban landscape to Department of Energy’s Hanford Nuclear Reservation meet the same standards for ecological integrity as in Washington. This work, by Jim Karr and colleagues, rural or wildland areas. Instead, we might establish a is examining species, taxa, and ecological groups of gradient of reference sites corresponding to the invertebrates and plants in the shrub steppe to deter- gradient in naturalness from urban areas to wildlands. mine their utility as indicators of human disturbance. The reference site for an urban landscape in a particu- Among the preliminary results, are that species lar biogeographic region would represent the best richness of invertebrates and native forbs declines in possible condition that an urban landscape in that response to increasing disturbance, as does shrub region might achieve. “Best possible,” in turn, would density and cover. On the other hand, exotic annual be defined according to degree of similarity to refer- plant taxa and density increase with disturbance. ence sites in wildland landscapes in the same region. Other examples of potential indices of ecological Thus, we recognize that although urban areas will integrity that are promising but not yet well tested never have the biodiversity, naturalness, and ecologi- include a multi-metric assessment of the conservation cal resilience of pristine wilderness areas, there are value of redwood forest landscapes developed by Jim reasonable standards they can meet. Nevertheless, Strittholt and me, and a broad assessment of the meeting those standards will require significant ecological integrity of the Interior Columbia Basin changes in habitat apportionment and management in undertaken by the USDA Forest Service and cooperat- our cities and suburbs. ing agencies. In the latter study, each of the 164 sub- The question of how one might measure ecological basins were rated as having high, medium, or low integrity in urban landscapes is beyond my scope in ecological integrity for a maximum of 5 components: this paper. I believe an adequate index would consider forestlands, rangelands, forestland hydrology, range- the composition, structure, and function of the urban land hydrology, and aquatic systems. ecosystem. An initial list of indicators should probably No study, to my knowledge, has investigated the include representatives of all these groups, ideally at ecological integrity of entire urban landscapes. several levels of organization. On the other hand, the However, biotic integrity has been evaluated in urban interdependence of composition, structure, and stream segments, for example with respect to riparian function suggests that indicators in one group might vegetation. In the Toronto area, a threshold of degra- be surrogates for the others. We might, for instance, dation of streams was reached under conditions get a good handle on the structure and function ranging from 75% removal of riparian vegetation in simply by monitoring the biota (i.e. composition). areas with no urbanization to 0% removal of riparian Conversely, it might be faster and cheaper to measure vegetation in areas with 55% urbanization. Ongoing habitat structure directly, especially at the landscape work in the Georgia Piedmont is showing lowest IBI scale where remote sensing and geographic informa- scores for streams in urban areas with the greatest tion system (GIS) technology permits rapid, quantita- amount of impervious surface from commercial, tive measurements. industrial, and transportation land uses. In this study Importantly, indicators of one attribute can be used correlations between IBI scores and percent forest to test and validate the others. For example, the only cover within 50 m of streams or whole watersheds are way we will know if indices of habitat structure or similar; suggesting that restoration of urban water- landscape pattern correspond to ecological integrity is sheds should consider land-use and land-cover of the by measuring responses of the biota to changes or whole watershed, not just the riparian areas. Studies differences in pattern. Although ecological processes such as these demonstrate that the ecological integrity (i.e. function) ultimately determine the integrity of any of aquatic communities is closely tied to the integrity ecosystem, the sensitivity of organisms to the rate, of the surrounding terrestrial landscape. magnitude, and other characteristics of natural

4 Proceedings 4th International Urban Wildlife Symposium. Shaw et al., Eds. 2004 processes suggests that measuring processes directly scapes. Many species of forest and grassland without information from the biota will not be too birds, for example, are progressively more helpful for assessing integrity. likely to be found as habitat area increases. Some species are present only in large blocks of Landscape Design for Urban Ecological Integrity habitat. Hence, species richness increases as Our society’s criteria for what makes a good urban habitat area increases. This is the well-known design, largely has to do with aesthetics and efficiency. species-area relationship. Of course, in urban How can we get from place to place easily and safely areas no truly large blocks of habitat may be and see pretty things along the way? Wildlife is rarely available. Nevertheless, the bigger the better. considered in urban design, much less the grander The larger blocks of natural or semi-natural concept of ecological integrity. This must change. habitat in an urban landscape should be Fortunately, with the increasing ecological literacy of priorities for protection. landscape architects and planners, it is changing. Furthermore, we don’t have to start from scratch with (3) Blocks of habitat close together are better than each new design. The science of conservation biology blocks far apart. The idea here is that blocks of offers a few principles (perhaps better described as habitat close together may function as one empirical generalizations) for maintaining biodiversity larger, contiguous habitat block for those and ecological integrity, which can be applied to a species that can move between areas. What is variety of situations. Although developed mostly from “close together” must be considered from the case studies in wild landscapes (in fact, first for the standpoint of the species of concern. Habitats conservation of the northern spotted owl), these close together form the standpoint of humans principles apply with minimal modification to urban or birds might as well be thousand miles apart and suburban settings. Among the best established for animals incapable of crossing the interven- principles are the following: ing barriers. For instance, many forest mam- mals, salamanders, and flightless invertebrates (1) Species well distributed across their native seldom or never cross roads. range are less susceptible to extinction than species confined to small portions of their (4) Habitat in contiguous blocks is better than range. This principle is most directly applicable fragmented habitat. Habitat fragmentation has to large-scale conservation planning. The idea is been documented to have deleterious effects in to maintain multiple populations of imperiled countless studies across the globe. Natural and or potentially imperiled species. By so doing, semi-natural habitats in urban as well as we maintain the natural range of among- agricultural landscapes are usually quite population genetic variability within the fragmented. But again, this principle is relative. species and minimize the chances that environ- The less fragmented the better. mental variability will drive all populations of the species to extinction within a given period (5) Interconnected blocks of habitat are better than of time (i.e. the farther apart, the less likely that isolated blocks. You may have noticed by now populations will fluctuate in synchrony). For that each of these principles is pretty much a urban settings, this principle suggests that corollary of the others. Connectivity allows habitat protection must have some redundancy. organisms to move among habitat patches. A Species associated with a particular habitat collection of habitat patches may be individu- must be represented in many places across the ally too small to maintain populations of area- urban landscape, both within and among sensitive species. But if connected, these metropolitan areas, so that local extinctions do patches may provide sufficient habitat for these not eliminate the species from the urban setting. species to maintain viable populations. Hence, the whole can be greater than the sum of its (2) Large blocks of habitat, containing large popula- parts. tions, are better than small blocks with small populations. This is probably the best docu- The Role of Connectivity in Urban Wildlife Conservation mented of all the empirical generalizations of Let’s now focus on the issue of connectivity in more conservation biology. All else being equal, detail. Wildlife corridors are something of a fad in larger populations are less susceptible to conservation these days. Many conservationists and extinction. This is especially true when habitat planners draw corridors into their designs with little patches are more or less isolated from each awareness of their potential utility or consequences. other, which is often the case in urban land- What conservation biologists are interested in is not

Proceedings 4th International Urban Wildlife Symposium. Shaw et al., Eds. 2004 5 corridors per se but functional connectivity, which Urban wildlife populations probably often exist as must be defined according to the potential for metapopulations – systems of subpopulations movement and interchange between populations. connected by at least occasional dispersal. Connec- Connectivity is generally a species-specific property. tivity can lower the chances of extinction for small, What a corridor to one species may be a barrier to local populations by providing a “rescue effect,” another. We don’t need to be concerned about every whereby dispersing individuals augment resident individual species, however. Many species get populations. If a local population goes extinct, that around just fine without our help – in the case of site (if the habitat remains suitable) can be recolo- many exotics and other weeds; they get along much nized if sufficient landscape connectivity exists. On too well. In planning for connectivity, we need to be the other hand, an isolated habitat patch that loses a concerned most about species that are particularly population will not be recolonized if dispersal sensitive to anthropogenic habitat fragmentation. corridors have been severed. As more and more We need to know something about the mobility of habitat patches become isolated by fragmentation, species, and what constitutes potential barriers to the metapopulation as a whole may go extinct. their movements, in order to plan effective corri- Not only do corridors provide movement routes dors. What looks like a corridor to us may or may for animals between parks and other habitat not provide functional connectivity to the species of patches, they also constitute important habitats in interest. Nevertheless, a recent review paper by Paul their own right, particularly when they are located Beier and me showed that most well-designed studies in riparian areas. In the arid West, riparian areas of corridors show they do, in fact, provide for connec- typically are the most species-rich habitats. Some tivity; furthermore, no deleterious effects of corridors 80% of vertebrate species in Arizona and New have been documented. This does not mean that Mexico depend on riparian habitat for at least a deleterious effects never occur. Narrow edge-domi- portion of their life cycles. Maintaining intact nated corridors could conceivably do more harm than riparian areas not only contributes to terrestrial good, for example by encouraging a proliferation of ecological integrity, but as noted earlier, aquatic edge-adapted species and their invasion into remnant biotic integrity increases as adjacent riparian natural areas. habitats are preserved. Just how wide a corridor must be to avoid edge In urban areas most wildlife corridors will also be effects and provide security and habitat-interior corridors for people. That is, these urban greenways conditions for sensitive species is highly variable. It will have trails and will be used for recreation and depends on the nature of the surrounding habitat, the other purposes, not all of which are desirable. For life history characteristics of the species involved, the example, when I lived in Gainesville, Florida we length of the corridor, and other factors. For some had a heck of a time establishing an urban species, corridors less than a few hundred meters wide greenway system because many residents were are too narrow, unless the constricted portions are concerned that these greenways would serve as fairly short. For example, Paul Beier’s work has shown corridors for thieves and degenerates, which, that mountain lions in southern California can use frankly, is not all that unlikely. In any case, urban quite narrow corridors if they are short and connect greenways must be designed with the needs of both much wider swaths of habitat. Creating effective people and wildlife in mind. In Colorado, a Trails underpasses or tunnels to allow animals to cross safely and Wildlife Task Force recently released an excel- beneath or over roads is usually the greatest challenge, lent handbook for trail planners, called “Planning as roadkill is often the greatest category of mortality trails with wildlife in mind.” The handbook notes for large mammals in developed and sometimes that trails have zones of influence and that an area even in wildland landscapes. crisscrossed with trails could end up with few The key point is this: in urban settings, most places undisturbed by human activities. Hence, patches of natural and semi-natural habitat are too sensitive wildlife could be eliminated. Among the small to maintain populations of many species. handbook’s recommendations are to 1) leave Countless examples exist of small urban parks, for untouched large, undisturbed areas for wildlife, 2) example, Rock Creek Park in Maryland on the route trails around edges of high-quality areas, 3) outskirts of Washington D.C., losing their diversity keep density of trails lower near high-quality areas, of native species over time, especially as they 4) do not route trails continuously close to riparian become isolated from other natural and semi- areas, 5) use public support of trails to protect natural habitats. Connectivity is the only way to riparian corridors, 6) plan how to manage a trail’s maintain a rich diversity of wildlife in many urban wildlife issues before the trail alignment is set, 7) settings. don’t depend on management to resolve wildlife

6 Proceedings 4th International Urban Wildlife Symposium. Shaw et al., Eds. 2004 conflicts that could have been avoided by thought- other people. Wildlife corridors have been impli- ful alignment in the first place, and 8) balance cated in bringing both deer and lions into Boulder, competing wildlife and recreation needs across a Colorado which has created some problems. Person- landscape or region rather than trying to accommo- ally, I was thrilled to see a mountain lion track in our date all uses within specific areas. All of these driveway a couple years ago. Sure, we had to take a recommendations depend on having competent few precautions, especially regarding the children, biologists involved in the early stages of greenway but that’s part of living in a region that still has some planning and throughout the trail development wildness left. Our neighbors were not so thrilled, process. however, and animal control agents soon arrived to trap the animal (I don’t know if they succeeded, but Networks from Urban Areas to Wildlands we no longer saw tracks). In the long run, or maybe sooner, many wildlife I suggest that wildlife agencies, instead of inten- species will persist in urban areas only if there are tionally maintaining a superabundance of deer in connections to the surrounding rural and wildland rural and wildland areas, which is their usual policy, landscapes. Urban areas may be population sinks for instead direct hunters to particular corridor areas some of these species, places where mortality where deer may be proliferating. Properly managed, exceeds reproduction. Species will occur in these this policy should keep deer problems to a minimum urban areas only if there are source populations without eliminating deer from the suburban and within dispersal distance that can supply colonizing urban settings, and probably would also result in individuals. Hence, I envision a hierarchy of con- fewer conflicts between humans and large predators nected habitat networks comprising 1) relatively in these landscapes. small habitat patches and narrow corridors within the urban zone, connected to 2) a network of larger habitat patches and wider corridors in suburban and CONCLUSION rural areas, which in turn connects to 3) the wildlife People generally want wildlife in urban and subur- landscape, with its still larger habitat patches, lower ban areas, even if they are ambivalent about some of road density, and greater overall connectivity. the potential conflicts. Having a rich assemblage of There are 2 potential problems with this “network native plants and animals around us is an indication of networks” design. One, corridors leading from the that nature still prospers in the places where we dwell. more developed zones of the network might funnel It is a sign that our habitat still retains some of its exotics and other opportunistic, weedy species into ecological integrity. In the long run, the greatest benefit wildland areas. We know that roads and roadsides, of having a well-connected system of habitats in our for example, are frequent avenues for the invasion of cities and suburbs is one I alluded to in the introduc- these pests. I predict, however, that the wildlife tion to this paper: children as well as adults will have corridor network is unlikely to facilitate weedy abundant opportunities for contact with wild nature. species invasion of wildlands beyond that already Hence, they will be more likely to retain their biophilia facilitated by roads. In fact, well-designed corridors, despite all the social conditioning in the opposite especially if wide, may provide habitat for predators direction. And with a positive attitude toward nature of these weedy species. In addition, corridor bottle- they will more likely be good citizens willing to necks could be used to trap weedy species (for support strong conservation measures for their example, brown-headed cowbirds) and possibly broader environment. reduce their spread. A potentially more serious concern is that of corridors connected to wildlands or rural areas Further Reading funneling problematic large mammals into suburban Adams,L.W. and L.E. Dove. 1989. Wildlife reserves and urban areas. This is already a problem in the and corridors in the urban environment a guide to case of deer. Many people like to have deer near ecological landscape planning and resource conser- their homes, but may get quite angry when those vation. National Institute for Urban Wildlife, same deer eat their gardens. I have mixed feelings Columbia, Maryland. about the deer in the semi-rural neighborhood where Beier, P. and R.F. Noss. 1998 Do habitat corridors I live, but my family and have decided that the provide connectivity? Conservation Biology 12:1241- benefits of watching the deer generally outweigh the 1252 damage to our flowers and vegetables. Following the Dramstad, W., J. Olson, and R Forman. 1996. Land- deer into suburban areas, however, may be a natural scape ecology principles in landscape architecture predator of deer – mountain lions. Unfortunately, and land-use planning. Island Press, Washington these predators sometimes also attack joggers and D.C.

Proceedings 4th International Urban Wildlife Symposium. Shaw et al., Eds. 2004 7 Forman, R.T.T. 1995. Land mosaics: the ecology of Noss, R.F. and L.D. Harris. 1986. Nodes, networks, landscapes and regions. Cambridge University and MUM’s: preserving diversity at all scales. Press, Cambridge, UK. Environmental Management 10: 299-309. Hudson, W.E., ed. 1993. Landscape linkages and Simberloff, D., J.A. Farr, J. Cox, D.W. Mehlman. 1992 biodiversity. Island Press, Washington, D.C. Movement corridors: conservation bargains or Noss, R.F. 1993 Wildlife corridors. Pages 43 – 68 in poor investments? Conservation Biology 6: 493- D.S. Smith and P.C. Hellmund, eds. Ecology of 504. greenways. University of Minnesota Press, Minne- Smith, D.S., and P.C. Hellmund, eds. Ecology of apolis, Minnesota. greenways. University of Minnesota Press, Minne- Noss, R.F. and A Cooperrider. 1994 Saving nature’s apolis, Minnesota legacy: protecting and restoring biodiversity. Trails and Wildlife Task Force. 1998 Planning trails Defenders of Wildlife and Island Press, Washing- with wildlife in mind: a handbook for trail plan- ton, D.C. ners. Trails and Wildlife Task Force, Colorado State Noss, R.F. and B. Csuti. 1997 Habitat fragmentation. Parks, and Hellmund Associates, Denver, Colo- Pages 269 – 304 in G.K. Meffe And R.C. Carroll, rado. eds. Principles of conservation biology. Second edition. Sinauer Associates, Sunderland, MA.

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