Session: The Wildland-Urban Interface

April 2, 10:15 AM

Wayne C. Zipperer
USDA Forest Service

Other papers from this session:

The Wildland-Urban Interface: An Introduction

Policy in the Wildland-Urban Interface

The wildland-urban interface is a zone of rapid land use change. Through planning, urban effects can be minimized so that ecosystem goods and services can still be utilized for this and future generations. The conservation of ecosystem goods and services must be a guiding principle when making land use decisions. Otherwise, the quality of goods and services will be significantly compromised. Similarly, natural disasters and their influence in shaping landscape patterns must be considered during the planning process. Without understanding how disturbances function over time, risk to both ecosystems and humans increase, and significant losses to ecosystems and human life and property may occur.

The wildland-urban interface, as described by Hermansen et al. (this session), is a zone of rapid ecological, economical, and social change. Planning plays a key role in the interface by conserving and protecting critical ecological, economic, and social elements of the landscape. To direct this planning, we propose that the conservation of ecosystem goods and services guide land use decisions. This paper overviews the concept of ecosystem goods and services, describes urban effects ecological systems, overviews how urbanization alters disturbance regimes, and describes how urbanization affects natural resources management.

Continuous forest cover or large patches of forest cover often characterize the interface in the eastern United States. In these areas, an extractive economy provided incomes for many of the local residents. With development and changes in land ownership patterns, this extractive economy shifts to more of a service-oriented economy. With that shift, there are corresponding shifts in the ecosystem goods and services.

Ecosystem goods and services are benefits that humans derive from natural ecosystems (Christensen et al. 1996). Examples of goods include forest products, wild genes, medicinal plants, and recreation. These goods often have an economic value associated with them. For example, timber is a forest product that is bought and sold on an open market. Because of proximity to development, timber often is not harvested (Hull and Stewart 2002, Hull et al. 2003). An assessment of the effect of development on timber resources in the Highlands Region, a productive forested area in northern New Jersey and southern New York, revealed that only 10 percent of the growing stock is being removed (Koten and Horn 1993).

Recreation provides another example of how development alters ecosystem goods. With development, large land ownerships are divided into smaller land ownership parcels, a process called parcelization. Often new landowners are less likely to permit use of their land for recreational purposes (e.g., hunting and trapping) (Dawson and Zipperer 1992). These decisions cause greater recreational pressures on public lands. With changes to habitat conditions and lack of harvesting, local populations of herbivores (e.g., white-tail deer) and omnivores (e.g., raccoons) may increase, which can significantly affect forest structure and population dynamics of other species.

Examples of ecosystem services include clean air and water, soil production, and detoxification of pollutants (see Christensen et al. 1996). It is important to recognize that these services result from ecosystem processes. For example, clean water results from the movement of water through the soil profile. Soil production results from decomposition and nutrient cycling by soil organisms, and weathering of parent material. Soil organisms also detoxify pollutant washed into the soil. Development alters the soil profile and subsequently the organisms, thus changing the services derived from them.

Land use transformation by humans for food, shelter, and products is one of the most significant ecological effects of humans (Dale et al. 2000). Land-use planners must reconcile the conflict between the benefits of economic development and the loss of goods and services provided by ecosystems. To do so, we need to understand how urbanization alters ecosystems.

Urbanization directly and indirectly affects ecosystem goods and services. Direct effects result from land use changes and are characterized by deforestation and fragmentation. With deforestation, a patch of forest (or any other natural habitat) cover is converted to urban use, and there is a corresponding increase in amount of forest edge and a loss of forest cover and interior habitat. Fragmentation is an element of deforestation and occurs when a forest patch is split into two or more smaller parcels. Together, deforestation and fragmentation decrease habitat size and increase habitat isolation. A study in Arundel County, Maryland showed that between 1973 and 1980 deforestation and fragmentation increased forest edge by over 30 miles and decreased interior habitat by over 5,800 acres (Zipperer 1993). These losses are compounded further when one considers losses of ecosystem services. For example, in the Gwynns Falls watershed, Baltimore County, Maryland, between 1994 and 1999 deforestation and fragmentation removed 641 acres of forestland, which resulted in the loss of over 46 thousand pounds of pollutants being removed from the air by trees (Zipperer in review).

Indirect urban effects are secondary influences from urbanization, deforestation and proximity to urban sites. Examples include alteration of microclimates and ecosystem processes, introduction of non-native species, disruption of migration corridors, and increase in environmental stresses from air pollution. For example, with ornamental and horticultural plantings, we often plant non-native species. Some of these species may eventually become invasive (e.g., purple loose-strife) (Reichard and White 2001). By developing in the interface, we increase the exposure of forests to colonization by invasive species. Similarly, by building roads and adding impervious surfaces, we increase storm runoff (Arnold and Gibbons 1996). This increase has significant effects on stream biota and stability. Just a 10 percent increase of impervious surface can affect stream biota (Schueler 1994). An increase of 35 percent or greater can alter the stream biota and stability permanently. Likewise, research on forest fragments in the Northeast revealed that urban forest patches received more nitrogen and heavy metal deposition than similar rural forests (McDonnell et al. 1997). This increase deposition alters soil fauna, rates of nitrogen mineralization and the amount of nitrogen leached from the soil profile.

Another indirect effect of urbanization is the alteration of natural disturbances. A disturbance can be classified based on it characteristics such as frequency, severity, and magnitude. With urbanization, we change these characteristics. For example, we suppress wildfires, which alters the frequency of fires and causes a build-up of fuels. Similarly, we dam stream and alter the severity and magnitude of yearly flooding. Unfortunately, our actions often lead to greater catastrophic effects. We do not know when a particular spot will be disturbed; however, what is known is that such natural events will occur at some point in time (Bormann and Likens 1979, Dale et al. 1998). Because disturbances will occur, planners need to consider how planning decisions affect the disturbance regime and how disturbances affect planning objectives.

Altering disturbance patterns also alters the spatial configuration of habitat patches across a landscape. The type and juxtaposition of the different land covers (patches) across the landscape influence the movement of energy, species, and materials. Intuitively, altering the pattern of landscape cover by changing the disturbance regime will alter ecosystem components and fluxes (Clark 1986, Pickett 1998). Because energy, species, and material flow into and out of an ecosystem, ecosystems adjacent to a site being urbanized influence these fluxes. From a landscape perspective, planners are able to ascertain not only the potential effects of altering an ecosystem on adjacent ecosystems but also the cumulative changes within the individual ecosystems of the landscape (Turner 1989). Altering the ecological, social, and physical components of an ecosystem not only changes the flow of energy, species and materials within and among ecosystems, but also changes the amount and quality of the goods and services derived from that ecosystem and landscape (Christensen et al. 1996).

With development in the interface, parcelization occurs. Parcelization reduces forest ownership size and subsequently affects management operations and objectives (see Duryea and Hermansen 2002). One change is the shift from economic and utilitarian uses to more biocentric uses. People manage their lands for aesthetics, improved forest health, wildlife habitat, privacy, and recreational opportunities. Consequently, there is a reduction in traditional forest products taken from the land. If forest products are to be harvested, several actions need to be taken:

1. Markets within the interface need to be maintained,
2. Tax reform and cost-sharing incentives may need to be developed,
3. Technical assistance to forest professionals to learn new communication and forestry techniques, and
4. Educational programs for landowners to learn about forestry operations (Hull et al. 2003).

Development will occur. How it occurs depends on our actions—how well we plan. We know urbanization affects ecosystem goods and services, which we need to survive as a species. Accounting for these goods and services and for risks from disturbances, planners can minimize the effect of development on the landscapes and create a working landscape that is sustainable.

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Bormann, F. H. and Likens, G. E. 1979. Catastrophic disturbance and the stead-state in northern hardwood forests. American Scientist 67, pp. 660-669.

Christensen, N. L., Bartuska, A. M., Brown, J. H., Carpenter, S., D'Antonio, C., Francis, R., Franklin, J. F., MacMahon, J. A., Noss, R. F., Parson, D. J., Peterson, C. H., Turner, M. G. and Woodmansee, R. G. 1996. The report of the Ecological Society of America Committee on the Scientific Basis for Ecosystem Management. Ecological Applications 6, pp. 665-691.

Clark, J. S. 1986. Costal forest tree populations in a changing environment, southeastern Long Island, New York. Ecological Monographs 56, pp. 259-277.

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Dawson, C. P. and Zipperer, W. C. 1992. Impacts of land use change on recreation and open space in the New York-New Jersey Highlands Region. In Symposium on Social Aspects and Recreation Research. (D. Chavez, ed., Albany, CA, USDA Forest Service Pacific Southwest Station Gen. Tech. Rep. PSW-GTR-132, pp. 67-68.

Duryea, M. L. and Hermansen, L. A. 2002. Challenges to forest resource management and conservation. In Human Influences on Forest Ecosystems. (E. A. Macie and L. A. Hermansen, eds.), Asheville, NC, USDA Forest Service Southern Research Station General Technical Report SRS-55, pp. 9-113.

Hull, R. B., Robertson, D. P. and Buhyoff, G. J. 2003. Boutique forestry: a call for new forest practices in urbanizing landscapes of North America. Journal of Forestry IN REVIEW, pp.

Hull, R. B. and Stewart, S. I. 2002. Social consequences of change. In Human influences on forest ecosystems. (E. A. M. a. L. A. Hermansen, ed., Asheville, NC, USDA Forest Service Southern Research Station General Technical Report SRS-55, pp. 115-129.

Koten, D. E. and Horn, A. F. 1993. Forest resources and timber. In New York-New Jersey Highland Regional Study: Analysis of selected resources. (L. R. Neville and W. C. Zipperer, eds.), Radnor, PA, USDA Forest Service Northeastern Areas State and Private NA-TP-04-93, pp. 1-18.

McDonnell, M. J., Pickett, S. T. A., Groffman, P., Bohlen, P., Pouyat, R. V., Zipperer, W. C., Parmelee, R. W. and Medley, K. 1997. Ecosystem processes along an urban-to-rural gradient. Urban Ecosystems 1, pp. 21-36.

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Zipperer, W. C. 1993. Deforestation patterns and their effects on forest patches. Landscape Ecology 8, pp. 177-184.

Author and Copyright Information

Wayne C. Zipperer
USDA Forest Service
Southern Center for Wildland Urban Interface Research and Information
408 W. University
Suite 101
Gainesville, FL 32601
352-376-3213
wzipperer@fs.fed.us