Identifying Significant Ecological Hubs
in Watauga County, North Carolina
David Ponder
Geographic Information Systems
for Environmental and Social Science
Appalachian State University
December 2005
Introduction
North Carolina was the ninth fastest growing state between 1990 and 2000, with a net increase of more than 1.4 million residents (CensusScope). While most of North Carolina’s population growth occurred in urban and urban-adjacent areas significant growth also occurred in high-amenity areas such as the High Country (NC Rural Center). During the same period, Watauga County experienced a 15.5% increase in population while notably Boone, the county’s largest municipality, experienced only a 4% increase in population, suggesting much of this growth occurred in unincorporated parts of the county (High Country Council of Governments). Furthermore, the rate of land consumption for the county, the conversion of undeveloped to developed lands, between 1986 and 1999 was nearly 52% while the consumption rate in unincorporated portions of the county was 66% (MountainKeepers).
These recent trends have many residents concerned that development pressures will result in undesirable changes to the character of the landscape and deterioration in the quality of life. Furthermore, the fragmentation of landscapes due to rapid development may result in threats to the integrity of ‘ecosystem services,’ those benefits people derive from healthy ecosystem functioning such as the procurement of clean drinking water (Daily). Given the value of these services, local communities across the country are seeking to protect the integrity of natural landscapes, through both voluntary and mandatory conservation techniques.
Both public agencies and private organizations play an active role in land conservation in Watauga County. Public agencies participate through the acquisition and ownership of property, the sponsorship of temporary binding agreements, and by providing funding and technical support. Private land trusts and conservancies also play an important role through the acquisition of private property, the purchase or donation of conservation easements, partnering with developers to mitigate impacts, and collaborating with government agencies. All told at least four federal agencies, six state agencies, two local government agencies, two private land trusts working exclusively in the region, three regional or national land trusts, as well as, a number of other conservation organizations play a role in land conservation efforts in Watauga County While, these groups and agencies work towards common ends and opportunistically collaborate, they tend to pursue their objectives in isolation (Trew and Coffey 2005).
The lack of a shared comprehensive strategy among private organizations and public agencies stands in contrast to the trend among land preservation advocates toward ‘smart’ conservation planning that is “proactive not reactive; systematic not haphazard; holistic not piecemeal; multifunctional not single purpose; multi-jurisdictional not single jurisdictional; and multiple scale not single scale” (Benedict, and McMahon p14). Such comprehensive approaches are intended to maximize protection of the most vulnerable and valuable landscapes and the ‘ecosystem services,’ they support.
The purpose of this project therefore is to construct a Geographic Information System (GIS) model that begins to identify an interconnected network of open lands that conserves significant ecosystem values and function which can serve as a strategic guide toward future conservation planning in Watauga County, North Carolina.
Rationale
While ad hoc approaches to conservation can yield protection for some sensitive lands, absent a guiding framework, such efforts may result in a patchwork protected lands that fail to sustain critical ecosystem functions, due to size and relative isolation. Increasingly communities are moving away from piecemeal approaches and towards “strategic and comprehensive open space protection” within a framework of planning for ‘green infrastructure’ (Hopper 8). Green infrastructure is an “interconnected network of green space that conserves natural ecosystem values and functions and provides associated benefits to human populations” (Benedict and McMahon p12).
The conservation planning principle of maintaining ecosystem services through the designation and management of a linked network of areas of particular ecological significance is rooted in conservation biology scholarship and in particular the notion of ‘conservation area networks’ (CANs). CANs (see Figure 1) are networks of core areas, or hubs, which have been prioritized for protection based on biodiversity value surrounded by buffer areas that allow for restoration and sustainable resource use. These core zones in turn are connected by natural corridors to allow for flows between the zones (Tukel 67).
Figure 1: Conservation Area Network
Almost all methods used in conservation planning assume that data are recorded in a GIS model. GIS facilitates the delineation of these networks through its ability to layer multiple features. When these layers are superimposed upon one another patterns in the landscape begin to emerge. These patterns in turn can be used to identify significant ecological hubs.
Methodology
Based on these principles, between 1998 and 2001 the University of Florida’s GeoPlan Center conducted a region wide GIS “landscape analysis of ecological significance and the identification of critical landscape linkages” (SEF, i). While the resulting Southeastern Ecological Framework (SEF) is most appropriately used to guide conservation decisions at a regional scale, the final project report includes a case study on how the framework methodology might be applied at a local scale. Given my limited experience with ArcGIS, the project methodology relies heavily on the methods advanced in the SEF report. Indeed, I sought to follow the work as closely as possible, supplementing with additional research and trial and error.
The SEF report outlines a four stage process for identifying a local scale ecological network: 1) determining the model parameters, 2) identifying ecological hubs, 3) identifying links between hubs, and 4) combining hubs and linkages. In turn, each of these stages consists of a series of sub-process (SEF 101). The analysis presented in this paper completes the first two of these stages (Figure 2).
Stage One: Determining model parameters
The first step in creating the local ecological network was to determine the conservation goals and objectives. The second step was to collect and asses the data that would serve as a proxy for goals and objectives. Based on the recommendation in the SEF report, the availability of suitable proxies, consideration of local newspaper accounts, as well as, review of local watershed planning documents this analysis established the following parameters:
Goal 1: Protection of Water Resources:
Objective 1.1 Protection of drinking water resources
Drinking water supplies, especially those reliant on surface resources, are under increasing pressure as a direct result of the recent rapid development experienced in the county (Nicholson). Any deterioration to existing supplies from contamination or sedimentation would only serve to increase this scarcity. Therefore protection of water supply watersheds, those drainage basins above water supply intakes, was included in the GIS model. The location of water supply watersheds in Watauga County was acquired by clipping a statewide shapefile produced by the N. C. Center for Geographic Information and Analysis (NCGIA) and the The North Carolina Department of Environment and Natural Resources (NCDENR), Division of Water Quality (NCDWQ).
Objective 1.2 Protection of High Quality and Outstanding Resource Waters
NCDWQ has designated certain water bodies as High Quality or Outstanding Resource Waters (HQW or ORW) based on their exceptional water quality. These resources are among the few pristine in the state and deserve special consideration as a result of the exception ecological and recreational significance. HQW and ORW streams in Watauga County include the headwaters of four major river networks and wild trout waters. NCGIA has created a GIS data set representing the location of waters surrounding regions of stream or bodies of water identified as HQW or ORW by NCDWQ. For this analysis these zones were clipped to Watauga County.
Goal 2: Protection of Ecological Processes:
Objective 2.1 Protection of wetlands
Wetlands are areas typically inundated or saturated with water for periods long enough to support vegetation adapted to these types of conditions to thrive. Wetlands, such as bogs and marshes, support healthy ecosystem functioning through the filtration of sediment and other contaminants, the recharge of water supplies, the mitigation of flood waters, and the provisioning of habitat (EPA). The wetlands data used in the GIS model was acquired from the U.S. Fish and Wildlife Services National Wetlands Inventory and buffered by 300 feet per the SEF methodology.
Goal 3: Protection of Biodiversity:
Objective 3.1 Protection of Significant Natural Heritage Areas
The NC Natural Heritage Program (NCNHP), a division of DENR, identifies Significant Natural Heritage Areas (SNHAs) as the most important areas for natural diversity of the state.
A SNHA may derive its significance from the presence of rare species, rare or high quality natural communities, or other important ecological features. Biological inventories have identified 136 species of concern known to occur in Watauga County (NCNHP). The boundaries of SNHAs in Watauga County were derived from NCGIA shapefiles.
Objective 3.2 Protection of existing conservation lands and areas immediately surrounding them
Local land trusts as well as federal and state agencies have already worked to protect x acres of sensitive lands in Watauga County. Since these areas already enjoy protection from development they tend to have high densities of biota, however in order to maintain the integrity of these systems from negative edge effects the SEF methodology recommends buffering these lands by 300 meters. No single data source existed for all conservation lands in Watauga County so one had to be created. This was accomplished by merging several shapefiles and adding additional parcels known to be under conservation easements. The result is a shapefile that includes federally and state managed lands (Blue Ridge Parkway and associated parks, , Elk Knob State Natural Area, Appalachian State University’s Tater Hill Bog Research Area, state managed gamelands, etc.) as well as private lands managed for conservation (private parcels receiving conservation easement tax credits, Grandfather Mountain, etc.).
Objective 3.3 Protection of roadless areas
Roads are a leading cause of habitat fragmentation and loss because in addition to creating physical barriers between habitats they bring with them negative edge effects such as noise, contaminated runoff, and the proliferation of invasive species. Therefore roadless areas are important for biodiversity because they offer unfragmented patches of habitat. To determine roadless areas all primary, secondary, and local road centerlines from NCGIA were merged, buffered by 100 feet, and clipped to the study area. Resulting polygons greater than 1000 acres were designated roadless.
Objective 3.4 Protection of areas important for endangered aquatic species
The N.C. Wildlife Resource Commission in conjunction with NCGIA has mapped the extent of extent of endangered or threatened aquatic species populations and the tributaries and headwaters of their habitats. These waterways were then buffered by 100 feet and clipped to Watauga County.
Stage 2: Identifying Ecological Hubs
Identify Significant Ecological Areas
After data layers were created to represent all of the conservation goals and objectives they were merged into a single shapefile and polygon boundaries were dissolved, creating a single polygon called Significant Ecological Areas or SEA (Figure 3).
Exclusion of Unsuitable Land Uses
After the identification of SEAs those portions overlapping incompatible land use were removed.
The determination of exclusion areas again closely follows the methodology set out in the SEF report and included:
Primary road exclusion
U.S. 421, U.S. 321, U.S. 221, and Highways 194, 105, 88, and 188, were selected from the NCGIA primary road data ad buffered by one quarter mile. These highways are the backbone of the transportation infrastructure in Watauga County with average daily traffic counts typically exceeding 10,000 vehicles. The heavy traffic volume and associated negative edge effects are the reason for their exclusion.
Areas with high road densities
Areas with road densities greater than or equal to three miles per square mile were excluded because they exceed road density thresholds for sensitive species. A line density analysis was preformed on a combined (primary, secondary, and local) road file. Those areas that exceed the standard were reclassified and converted into a shapefile for exclusion.
High intensity land use
High intensity land uses were extracted from a land cover file obtained from Highland Mapping of Banner Elk, NC and prepared for the MountainKeepers Forces of Change Report. The land use raster was based on satellite imagery from 1999. Those areas designated as ‘developed’ or ‘cultivated’ were reclassified and converted into a shapefile for exclusion.
Areas in close proximity to urban land uses
Per the SEF methodology, all areas within "neighborhoods" with extensive urban land use in 90-meter 3X3, 9X9, and 27X27 windows that exceed greater than or equal to 50% urban land use were identified and converted into shapefiles for exclusion. This addition to the exclusion layer
is intended to mitigate the influence of clusters intensive land use. Additionally all clusters of intensive land use greater than 100 acres were buffered by 270 meters.
The exclusion values were merged into a single shapefile and overlaid on the SEA to produce a new layer, Significant Ecological Area after Exclusion, or SEAX (Figure 4).
Identification and Optimization of Ecological Hubs
After SEAX are identified they were ‘optimized’ by filling internal gaps and smoothing outside edges where compatible land uses occurred. This was accomplished by reclassifying suitable land use data (forest and grassland cover) and converting it to a shapefile then a select by location. Those areas of suitable land use that intersected with gaps were then merged into the SEAX shapefile. Edge smoothing was accomplished by applying a 10 meter buffer to the new SEAX.
All contiguous SEAX polygons greater than 1000 acres were then selected and designated Ecological Hubs. A final optimization and is preformed to add back in all currently protected conservation lands and all resulting polygons greater than 1000 acres constitute the final set of ecological hubs (Figure 5).
Discussion
Nine ecological hubs emerged from the analysis. Below is a description of each hub and its primary SEAs components. Names were given to each hub in order to better conceptualize the location of each.