Can you give me a hint of where the green stuff is? A greenspace analysis of Norfolk, Virginia

Section I:  Introduction

            In an increasingly urbanized and human-developed landscape, natural lands such as forests, meadows, and streams are increasingly being divided and separated into smaller and more isolated areas.  Growing population densities across major metropolitan areas in the United States are placing available acreage of open space for public use on a premium.  As McMahon notes, a growing community usually has plans to expand its “airport, sewage treatment plant, storm water facilities, fiber optics cables, and other community utilities,” yet often ignores or omits plans to “preserve their essential life sustaining natural infrastructure,” (2000).  Greenspace in an urban setting can not only serve as a vital resource to people, it can also be beneficial in protecting wildlife and other natural resources.

Norfolk, Virginia, one of the “Hampton Roads” cities in southeast Virginia, is a low elevation coastal city whose origins date back to early European colonization of the former colony of Virginia.  Presently, Norfolk has a population of 245,782 people spread across a landscape that is nearly entirely urban (U.S. Census Bureau, 2013, and Map 1).  The terrain is generally flat and low lying, with elevations only averaging 10-20 feet above mean sea level.  Its proximity to the Atlantic Ocean to the east, the Chesapeake Bay to the north, and its vast stretches of tidal water allow for a more moderate climate.  This marks Norfolk and the surrounding area an important stopover on the Mid-Atlantic flyway for migratory birds, as well as critical habitat for wildlife.

Conservation of natural resources and naturalized land in Norfolk has been somewhat limited, at least in terms of terrestrial resources.  Norfolk’s open spaces are for the most part “postage-stamp” parks such as corner playgrounds and recreational fields usually no larger than 10 acres in area (City of Norfolk recreation, parks, and open space, 2013).  Habitat for wildlife is often confined to habitat “islands” that consist of small, discontinuous greenspaces.  Habitat fragmentation of plant and wildlife habitat has become a chief concern among wildlife biologists in recent years.  As humans develop more and more of the landscape, movement and migration of wild animals has been increasingly restricted and sometimes inhibited by the profusion of inhospitable lands as a consequence of human development. 

Small habitat “islands” themselves can alter the dynamics of wildlife populations and their migration into a metapopulation pattern.  A metapopulation consists of “a discrete set of populations of the same species in the same general geographic area, that may exchange individuals through migration, dispersal, or human mediated movement,” (Akcayaka, Mills, & Doncaster, 2007).  Although metapopulations of wildlife can be a naturally occurring phenomena, others can be human caused.  Wildlife ecologists have noted that plants and animals can assume a metapopulation dynamic wherever landscapes are fragmented as a result of human activities and urban development (Akcayaka, Mills, & Doncaster, 2007).   The main components of a species metapopulation consists of sources and sinks.  Sources are larger areas of wildlife habitat where there is a general equilibrium of emigration and immigration of individuals, or where births rates exceed death rates.  Smaller habitat islands that are some distance away from sources are referred to as sinks.  Sinks a greater rate of immigration of individuals, or have death rates exceed birth rates (Akcayaka, Mills, & Doncaster, 2007).  It should be noted that the formation of habitat islands themselves are similar to islands in a large body of water, but in this context are in a “sea” of urban development. 

 The impacts of habitat fragmentation has necessitated the need for an ecosystem-based management approach to wildlife conservation.  This stands in contrast to managing a small nature preserve to protect only a single species (Chiras & Reganold, 2005).  Ecosystem management includes the challenge of how to best manage metapopulations in a manner that allows for population stability, genetic diversity, and minimal risk of extinctions, as well as movement of individuals (Akcakaya, Mills, & Doncaster, 2007). 

A knowledge of the distribution of fragmented land is an essential component of examining and managing an ecosystem, especially in a geographic area that is highly urbanized.  The use of a geographic information system (GIS) has become a valuable tool and resource in ecosystem management for both hydrological and terrestrial systems (Chiras & Reganold, 2005).  For example, a GIS can be used by wildlife biologists to monitor the migration of wildlife (Chiras & Reganold, 2005), or  it can be used to assist managers in determining which areas in a reserve offer suitable habitat for wildlife species based upon different geophysical characteristics such as elevation, land cover, or proximity to roads (Price, 2013).  A map can then be produced which can assist land managers and urban planners in making sound decisions based upon known habitat fragmentation and the relative proximity of urban areas. 

Another potential management application with respect to a fragmented landscape is the creation of or enhancement of wildlife corridors.  A wildlife corridor is a linear-shaped area of natural land that can link natural areas together and provide necessary migration routes between source and sink wildlife populations (Chrias & Reganold, 2005; Akcayaka, Mills, & Doncaster, 2007).  A habitat corridor can be essential for natural resource management in an urban landscape, since urban areas can serve as a dispersal barrier to most wildlife (Akcayaka, Mills, & Doncaster, 2007).  Norfolk’s urban landscape makes it challenging to manage for wildlife corridors, because most of the greenspace parcels shown in Maps 1 and 2 are widely separated from one another.  Yet as Akcayak and others note, wildlife corridors can be artificially created, which can still help reduce extinction of many species (2007).  Conservation easements and other private land conservation areas have the potential to protect natural resources on non-public greenspaces (Chrias & Reganold, 2005). 

The cartographic experiment presented in this paper is an attempt to begin examining habitat fragmentation in Norfolk’s urban landscape by analyzing areas within the city that are within a certain distance of  green space islands.  An effort to better understand which areas are a long versus short distance from larger greenspaces within Norfolk city limits will be estimated based upon a Euclidean (straight-line) distance calculated with a GIS.  Parcels of land that are 5 acres or larger in size and those that are 10 acres or larger in size will be the baseline areas for the calculations. These area sizes were chosen based upon the fact that most public parks in Norfolk are more than 10 acres in size (Table 1).  Only non-militarized land spaces were included in this analysis because of their accessibility or management by the public. 

Section II: Methodology

Parcel attribute data acquired from the City of Norfolk’s GIS department[1] that contained information on park locations, acreage, and type was examined.  A copy of the parks parcel data was created and then each parks feature class (a digital, georeferenced polygon) was edited to only include park areas that had forest, meadow, old field, wetlands, small freshwater ponds, and/or passive-use grassy areas on at least part of each polygon.    Land cover in this manner was determined visually via an orthophoto mosaic of Norfolk.  Park and greenspace polygons that included buildings, athletic fields, large parking lots, major roads and other urbanized features were edited to exclude those features, or were eliminated if urban features were the only land cover contained in a polygon.  This task was accomplished by using heads-up digitizing tools in the ArcGIS 10.0 geographic information system (GIS) software.  The park type classification scheme employed by the city of Norfolk was ignored, and all greenspaces from the city’s data were treated as a single category (greenspace).  It should be noted that large bodies of open water, or bodies of water not completely surrounded by public greenspace, were omitted from this analysis.

            The original parks data only included public greenspaces under the jurisdiction of the city’s parks, recreation, and open space department, and did not include a publicly accessible greenspace managed by a private organization, the Cape Henry Audubon Society, which manages a small nature preserve known as the Weyanoke Bird Sanctuary[2].  This was added into the greenspace data.  Additionally, public beaches were added into the greenspace data layer which included beaches from the swash zone to the dunes, and any other adjacent greenspace not already included in the city’s data.  High and low tides were ignored in the creation of beach features.   

            Once all of the needed data was compiled, acreage of each greenspace parcel was calculated using a geometric calculator built into GIS.  Then, greenspace parcels that were ≥ 5 acres and those that were ≥ 10 acres were isolated and then placed into their own data layer, resulting in two GIS vector layers containing public greenspace parcels for the different acreage criteria.  Next, a Euclidean-distance (straight-line distance) algorithm was performed on each data layer that calculated the distance in feet (U.S.) that each area was from the nearest greenspace of 5 or more acres and 10 or more acres in size within the city of Norfolk.  The greenspace parcels, formatted as a vector polygon layer, was automatically converted to a raster layer by the GIS.  The distance categories were divided into thirteen classes for each map, and then the results were displayed on two separate presentation maps (see Maps 2 and 3). 

Section III:  Results

For both outputs, a visual examination reveals that most areas of the city are a moderate to far distance from the nearest greenspace.  Greenspace parcels are showsn as green polygons. Areas closer to a greenspace are shaded with a yellow-green hue.   As areas progress further from the nearest greenspace polygon, the hue transitions into a pink and purple shading, with areas furthest from a greenspace shaded in blue.  In Map 2, there is a small section of the city in the middle that is a far distance from a given public greenspace, as indicated by the pink to purple shading.  This same section is considerably larger in Map 3, indicating a lack of nearby greenspace that is at least 10 acres in size.  The middle section of both maps is part of Norfolk characterized with a landscape of dense urbanization with many housing communities, shopping malls, parking lots, industrial complexes, and busy roads.  There is also a large section in the Northwest corner of the city that has blue-tinted shading, indicating that this region is the furthest distance from a public greenspace.  This is a militarized section of Norfolk that is a part of the Norfolk Naval Base, and no militarized greenspace areas were inputted into this analysis, as mentioned earlier. Land areas in the northern sections of each map were shaded with a light green because of the presence of linear greenspace in the form of public beaches and city-managed sand dunes along the Chesapeake Bay.  Areas of each map that are shown as a smooth, black surface are bodies of open water. 

Section IV:  Discussion and Conclusion

            This greenspace analysis of Norfolk provides a general visualization of the distribution of public, naturalized lands in a congested coastal city in terms of distance in each area of the city to the nearest open space.  It also reveals the extent of habitat fragmentation of terrestrial wildlife habitat.  Although about half of the area in both maps is categorized as being close to a greenspace, it should be noted that the minimum acreage criteria of ≥5 acres and ≥10 acres is a modest size.  Certain communities of flora and fauna may need larger spaces and reserves to ensure population stability.  In theory, a large[3] reserve can hold a stable population of a given wildlife species and insulate it from the effects of human disturbances (Akcayaka, Mills, & Doncaster, 2007).  In contrast, smaller reserves are thought to be more vulnerable to the “edge effect” of a weedy, polluted condition as a result of its proximity to human disturbances such as urbanized areas (Akcayaka, Mills, & Doncaster, 2007).  The output maps of this analysis could potentially serve a starting point for terrestrial ecologists and wildlife managers to begin examining the extent of habitat fragmentation in Norfolk, as well as determine which areas serve as sources or sinks for wildlife metapopulations. 

            Another potential application as a result of this study pertinent to natural resource conservation is determining suitability of wildlife corridor locations.  Prioritizing areas of the city that have greenspace parcels close to each other may be a more cost-effective and logistically realistic approach to developing and maintaining urban wildlife corridors.  The Euclidean distance output displayed in Maps 2 and 3 can perhaps help narrow down a search for wildlife corridor development in Norfolk by choosing greenspace parcels that are close to each other.  For example, in Map 2 there are two greenspace areas in the north-central section of the map are nearly adjacent to each other, and are not far from several other greenspace parcels and a beach, located just to the north.  The land area separating these areas is primarily a residential neighborhood.  Although a residential neighborhood is technically a part of an urban land cover category, the yards in these areas could be managed as backyard wildlife habitat to help mitigate the adverse ecological effects of habitat fragmentation.  Backyard wildlife habitat usually consists of incorporating environmental features into a front or back yard of a residential complex (Figure 1).  Native landscaping, manmade ponds, rain gardens, butterfly gardens, and sustainable energy technologies are some examples of what can be incorporated into backyard wildlife habitat project.  Maps 2 or 3 could assist environmental activists with seeking out the best sites for coordinating a neighborhood-wide backyard wildlife habitat initiative based upon number of residential parcels, cost, or other project management factors. 

            There are some limitations to this greenspace analysis that would need to be taken into consideration by any decision maker or natural resource manager.  The areas designated as greenspaces for maps 1 and 2 were subjectively chosen by the researcher based upon their knowledge of known locations public parks and nature preserves.  Areas managed for their natural resources and open space in militarized zones or on private land were neglected in this study, although these lands may offer the same benefits to people and wildlife that public lands provide.  Data collection of greenspace parcels were imperfect, as well.  Because a “heads-up” digitizing approach was used as a primary data collection method, some of the greenspace parcels may include urbanized land or buildings, which are not considered authentic greenspaces.  The selection criteria for greenspaces assumed that each parcel was the same in its suitability for wildlife conservation as well as quality of wildlife habitat, when in fact some of the greenspaces had land covers that consisted of mowed lawn, manicured park land, athletic fields, and other areas not supportive of most wildlife populations.  This analysis also did not take into account the amount and variability of wildlife cover and other essential habitat components.  Finally, the Euclidean distance calculations were limited to areas within and near the city limits of Norfolk; there may have been  nearby greenspaces in adjacent communities that were not accounted for in the results.  

            Despite its drawbacks, the deliverables for this study revealed the urbanized geography of Norfolk, as well as illustrating a potentially daunting challenge in regards to managing terrestrial wildlife and planning more open space in an urban coastal community. 

Section V:  References

Akcakaya, H. R., Mills, G., & Doncaster, C. P. (2007). Chapter 5: The role of metapopulations in conservation. In D. Macdonald & K. Service (Eds.), Key Topics in Conservation Biology.

Betts, L. (Photographer). (2011, October 04). File:NRCSIA03057 - Iowa (2525)(NRCS Photo Gallery).tif [Print Photo]. Retrieved from http://commons.wikimedia.org/wiki/File:NRCSIA03057_-_Iowa_(2525)(NRCS_Photo_Gallery).tif

Chiras, D., & Reganold, J. (2005). Natural resource conservation. (Ninth ed.). New Jersey: Pearson Prentice Hall.

City of Norfolk recreation, parks, and open space, (2013).  Parks. Retrieved from http://www.norfolk.gov/index.aspx?NID=836

McMahon, E. T. (n.d.). Green infrastructure. (2000).  Planning Commissioners Journal, 37, 4-7.

Price, M. H. (2012). Mastering ArcGis. (5th ed.). New York, NY: McGraw-Hill.

U.S. Census Bureau. U.S. Department of Commerce, U.S. Census Bureau. (2013). State & county quickfacts, Norfolk city, Virginia. Retrieved from U.S. Census Bureau: State and County QuickFacts website: http://quickfacts.census.gov/qfd/states/51/51710.html

Section VI:  Acknowledgements

I would like to thank Mr. Paul Anderson, lab instructor at the Geographic Information Systems laboratory at Old Dominion University, for giving me access to the City of Norfolk’s parcel data for use in this study. 

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[1] For details and metadata regarding the city of Norfolk’s geospatial data, please contact Paul Anderson at pbanders@odu.edu. 

[2] More information on the Weyanoke Bird Sanctuary can be found at <http://www.chasnorfolk.org/weyanokesanctuary.html>.

[3] There is no formal definition of ‘large’ in terms of reserve design and management.  The term ‘large’ in this context has relative meaning. 

 

Map 1:  Orthophoto of a section of Norfolk, Virginia showing dense urban development.  

 Table 1: Summarized descriptions of Norfolk’s public parks and greenspaces.  Source:  City of Norfolk recreation, parks, and open space, 2013

Park Type	Description	Count
Festive Parks	Specially designated parks for festive events	2
Community Parks	Parks 10 acres in size or larger	6
Neighboorhood Active Parks	Recreational parks that are usually 10 acres or less	37
Neighboorhood Passive Parks	Passive-use areas that are usually 10 acres or less	27
School sites with park amenities	Recreational or passive use.  Some are shared with the city	53
Community Centers with open space areas	Has recreational and passive amenities	7
Other	Dog parks, large road medians, golf courses, fee-based areas, etc.	21

                     

           

 

Map 2

 

Map 3

 

Figure 1:  Backyard wildlife habitat.  By Photo by Lynn Betts, USDA Natural Resources Conservation Service. (USDA NRCS Photo Gallery: NRCSIA03057.tif) [Public domain], via Wikimedia Commons.