The Santa Catalina Island Conservancy's mission is to preserve the native plants, animals, biotic communities and natural landscapes on the 17,000+ hectares of the island which it owns. In addition to its conservation mission, there is a mandate for reasonable public access to the island through a recreational easement with Los Angeles County. An existing network of more than 200 miles of interior roads facilitates access both for public recreation and management activities by the Conservancy's employees and volunteers.
This extensive road network poses an interesting dilemma in that roads are necessary to provide access for ecological management activities, but also constitute a disturbance to the ecological landscapes they intrude upon. It is therefore necessary to evaluate the ecological costs and benefits of these roads. To do so requires an accurate road map. Although several previous maps of the island's road network exist, no single map nor even a compilation of all the maps represents all the roads. In addition, some roads were mapped in locations as much as 2 km from their true position.
The Conservancy has developed an enterprise geographic information system (GIS) as part of its ecological management program. An integral part of the GIS is the collection of field data using global positioning system (GPS) receivers. The donation of a Trimble Pathfinder Pro XR GPS receiver allowed the Conservancy to accurately map the island's road network in the field. By incorporating this road layer into the GIS, the network can be better evaluated relative to access needs, ecological impacts, road maintenance frequency and other questions. The road layer is also an integral part of the Conservancy's planned GIS-based Land Use Plan and Recreation Plan which will assist its management efforts.
Santa Catalina Island is one of eight Channel Islands located off the southern California coast (see Figure 1). The island is about 34 km long and is oriented in a NW-to-SE direction with a high (450-600 m) central ridge running nearly its entire length. A series of secondary ridges and valleys extend from the main ridge on either side resulting in an extremely rugged topography. Island elevations range from sea level to more than 600 m within a short distance. There are also significant geographic differences in the underlying geology and soils. This diversity in the abiotic environment results in a wide range of conditions affecting the surface and stability of the island's extensive road network.
The Santa Catalina Island Conservancy was established in 1972 as a 501(c)3 non-profit organization with an initial gift of about 600 acres of the island. Based on its Articles of Incorporation, the Conservancy's mission is to "preserve native plants and animals, biotic communities, geological and geographical formations of educational interest"; to promote the study of ecology, natural history and conservation; and "to promote the ecologically-sound and appropriate recreational and educational use" of the island.
In 1974 a 50-year recreational easement was established between Los Angeles County and the Santa Catalina Island Company (SCICo), former owner of the island. This agreement allowed for recreational access to the island by the public. The Conservancy's Articles condition such access "subject to reasonable restrictions concerning the needs of the land."
In 1975 the Conservancy acquired more than 88% (17,000+ ha) of the island from the SCICo. The Conservancy's mission of ecological management and restoration of the island, coupled with increasing public recreational use of the island, poses a complex challenge. Its lands include a number of endemic plants and animals found nowhere else in the world, including two federally endangered plants. Approximately one million people visit the island each year due to its close proximity to one of the largest metropolitan areas in the world.
Catalina's extensive road network began in 1892 when the Banning family, then owners of the island, started the first road from Two Harbors to Little Harbor. By 1903, the primary road extended from Avalon to Two Harbors and was used for sightseeing in stagecoaches operated by concessionaires. Secondary roads were also established over the past 100+ years for various purposes including livestock ranching and to manage fence lines associated with these operations. Currently, the historic road network is used for ecological management activities (ecological restoration, weed control, non-native animal removal) and recreation (hiking, mountain biking, horse riding, sightseeing tours). Reasonable annual or daily fees are charged for commercial and non-commercial vehicular use of the roads to help cover maintenance and safety-related costs.
While roads may be necessary for ecological management and recreation, they also represent a disturbance to the ecological landscapes they impinge upon, posing an interesting dilemma for the Conservancy. Roads create ecological impacts, and therefore new ecological management challenges, through increased erosion, the dispersal of non-native weeds, and actions related to public access such as litter and fire danger. The island's steep terrain coupled with often heavy seasonal rainfall results in an annual cycle of damage and repair to the roads. Road maintenance activities entail high labor and capital costs to the non-profit Conservancy. Despite their importance, it is more difficult to raise money for such expenses than for conservation programs.
To ensure continued access for management and recreation, it is necessary to assess the ecological costs and benefits of the existing road network. The Conservancy's board and the Ecological Restoration Element of its Long-Range Plan recently called for the development of a Road Use and Maintenance Plan to accomplish this task. Because the historic ranching activities have been terminated, some of the roads may no longer be necessary. Current roads need to be evaluated relative to their present and future value, and those determined unnecessary need to be ecologically decommissioned. Remaining roads need to be prioritized for maintenance to contain costs and reduce ecological impacts.
To assess the road network requires an accurate road map. Although several earlier maps of the island's roads exist, no one map nor even a compilation of them, represents all the roads. In addition, some roads were mapped in locations as much as two (2) km from their true position. The logical tool to analyze the road network is the Conservancy's enterprise geographic information system (GIS). An integral part of the GIS is the collection of field data using global positioning system (GPS) receivers.
The donation of a Trimble Pathfinder Pro XR GPS receiver allowed the Conservancy to accurately map the island's road network in the field. By incorporating this road layer into the GIS, the network can be better evaluated relative to access needs, ecological impacts, road maintenance frequency and other questions. The road layer is also an integral part of the Conservancy's planned GIS-based Land Use Plan and Recreation Plan which will assist its management efforts.
Mapping of the island's road network was done with the Trimble Pathfinder Pro XR differential GPS (dGPS) receiver using an integrated GPS/beacon/satellite antenna for real-time data collection. A Trimble TD C2 Asset Surveyor was used to log the GPS data due to its memory capacity (3 MB RAM). Software used to download, process and export the GPS data was Trimble Pathfinder Office version 1.10.
Most roads were mapped during November of 1997, an appropriate window of opportunity. The majority of the island's roads were in drive able condition following the previous winter's rains, thanks to the efforts of the Conservancy's road crew. The predicted (and realized) El Niño rains during the winter of 1997-1998 suggested a large percentage of the roads would be (and were) closed later.
Based on trial field experience, factory set defaults were changed to reflect signal reception problems associated with the island's extreme relief and deep canyons. These conditions restricted the visible horizon, limiting the number of GPS satellites in view and the resulting satellite geometry, and occasionally blocking the real time correction (RTCM) signal from the U.S. Coast Guard radio beacon at Point Loma near San Diego. An elevation mask of 15 was used to eliminate satellites near the island's obstructed real horizon. The position dilution of precision (PDOP) mask was increased from the factory default 6.0 to 8.0 based on field tests.
Although the dGPS RTCM mode generally functioned well and PDOP values were below the mask setting, the topographic limitations resulted in the occasional acquisition of uncorrected data. This required post-processing using base station data available from Trimble's World Wide Web site. This data source was chosen based on ease of access from the island. However, the significant distance (~650 km) between the island and Trimble's base station in Sunnyvale (CA) undoubtedly introduced some error in the resulting values.
During mapping the Pathfinder Pro XR's antenna was extended from the passenger side of a Conservancy ranger vehicle (Ford Explorer). Antenna height was set at six feet (1.8 m) to reflect its distance from the surface as it was driven along the roads. Two individuals were required, a driver and an assistant who managed the antenna and data logger. This assured greater safety while mapping, and this team effort resulted in cleaner data requiring less editing after acquisition.
A data dictionary was created using Trimble's Pathfinder Office software. The data structure included one linear feature (road) and several point features (sign, gate, bridge, trail marker, culvert, utility pole, erosion problem, plant, animal and other). The road feature was categorized by two fields: type and year constructed. Road types were designated based on public access and surface type as primary surfaced, primary dirt, secondary dirt, tertiary dirt, unused and hiking trail.
Primary roads are those on which public vehicle access is allowed through the Conservancy's road permits or sightseeing operations. Secondary roads are significant routes used for non-vehicular recreational access (hiking, horse riding, mountain biking) and by utility or Conservancy vehicles. These categories do not reflect their importance relative to mission-related activities. Tertiary roads are short, dead-end roads used for mission-related activities, recreational, public utility or emergency services access.
Of the point data features, only the gates and trail markers were mapped in this effort. Gate features included a type attribute based on whether they were locked, unlocked, "bump" (a unique type of gate opened by vehicular contact) or other. Trail marker features represent hiking trail signage installed for orientation by the public and included the attributes of route abbreviation and mileage along route. Using the Trimble's "nesting" feature, these point features were easily collected as the linear road features were mapped.
To accurately capture the island roads, the data logging interval for road features was set to a two (2) second interval. Safe driving speeds on the island range from five to 25 mph (8-40 km/hr) depending on visibility, road surface, width and steepness. At these speeds the Trimble Pathfinder Pro XR was usually able to collect adequate data along the winding mountain roads. When the RTCM signal was lost or PDOP exceeded the mask around curves, vehicle speed was reduced or halted to ensure adequate data collection to represent the road's curvature. When data collection in regions shadowed from signal was poor, these roads were remapped several times and the most accurate data was consolidated to represent that portion of road. Mapping of several hiking trails was done on foot. The data logging interval in these cases was set to a ten (10) second interval due to slower travel speeds. The minimum number of positions collected for the point features was set at ten (10) to give a good positional fix for gates and trail markers.
The acquired data was downloaded each day from the Trimble Pathfinder Pro XR using the Pathfinder Office software. Correction files were obtained from Trimble's base station archive, and the data was post-processed. The corrected data was exported using Pathfinder Office software to the ARCView shape file format. The coordinate system and projection used was Universal Transverse Mercator Zone 11 North (UTM-11), North American Datum 1927 (NAD27) for consistency with the Conservancy GIS base data layers derived from the United States Geological Survey (USGS) 1:24,000 quad maps.
The initial data collection was done by Conservancy Vice-President Dr. Bill Bushing and ranger Jim Fellows. Later, Director of Ecological Restoration Peter Schuyler joined them. After the interior roads most subject to potential damage by winter rains were recorded, reserve ranger Bob Kopolow was trained to use the equipment and mapped the surfaced roads near and in the incorporated City of Avalon. A total of more than 200 "person hours" was required to collect, post process, export and edit all the data.
Following acquisition, the GPS road network data layer was compared with earlier road maps to assess both their and its accuracy. These maps included the road network from the 1:24,000 USGS quad maps; a 1:24,000 road map produced by the Santa Catalina Island Company in the 1970's; an emergency road map produced by Los Angeles County in the 1980's; a map of selected roads acquired using non-differentially corrected GPS data from a Garmin 12XL receiver in 1997; and a very accurate Avalon road map contracted by the City in the 1990's using surveyor grade GPS mapping and provided by the City in AutoCad format. The hard copy maps were all manually digitized using a Calcomp 9100 digitizing tablet.
The result of this effort was the production of the island's first truly accurate road map (see figure 9). Despite the island's extreme relief and deep canyons, the Trimble Pathfinder Pro XR performed well. PDOP values ranged as low as 1.7, but were generally in the 2.8 to 6.0 range. Although PDOP occasionally exceeded the 8.0 mask and RTCM signals were lost in steep, signal shaded areas of the island, this was accommodated by waiting until signal quality improved or remapping at another time.
Prior to this mapping effort, estimates of the total road mileage on the island miles by
Conservancy, public utility and emergency services employees ranged from less than 100 to in
excess of 1,000. The actual mileage in the island's interior was recorded at about 204 miles
(328,400 m) with an additional 17.5 miles (28,200 m) of roads in the incorporated City of
Avalon and vicinity and about 19 miles (30,590 m) of roads and hiking trails from previous maps
that have yet to be surveyed with the Trimble GPS, resulting in a total of nearly 241 miles
(387,650 m). The breakdown of road mileage by category is presented in the following table.
|Historic but not mapped with GPS||30,590||19.0|
The acquired Trimble dGPS data was compared with the previous road maps to assess their accuracy. The linked images below show the road network in the vicinity of a hunting road known as Herman's Trail in Middle Canyon and the Sweetwater Canyon road.
Note that none of the previous maps agrees completely with the newly acquired Trimble GPS data. Some of the maps indicate road locations as much as two km from the actual position. This comparison illustrates that it would have been impossible to compile a single, accurate road map based on the available sources given the errors resulting from the differing methods in their creation. The Trimble GPS data allows us to do a map reconciliation with the other sources to identify the errors in previous maps.
The Trimble dGPS data for the Avalon area was also compared with the very accurate City of Avalon surveyed roads. The linked image below shows the Trimble dGPS road layer (in red) overlain on the City of Avalon road and building features for an area in Hamilton Cove. Note the Trimble dGPS data generally falls within the surveyed road bed, with apparent errors of only 1-2 meters. These data suggest that the Trimble GPS mapping was a very cost-effective method and accurate method of mapping the road network across more than 19,000 ha of island.
The road map generated by the Trimble GPS receiver replaces the earlier incomplete and inaccurate maps in the Conservancy's GIS, and will serve as a basis for developing the Conservancy's Road Use and Maintenance, Land Use and Recreation Plans. The following discussion addresses some of the considerations involved in evaluating the road data relative to the often conflicting issues of access and environmental protection.
Although the road feature types were categorized based on the degree of public access and surface type, the road network must be assessed in terms of its value based on many different criteria including the ecological management mission of the Conservancy. The prioritization of road maintenance may be based on factors including access for ecological management (weed control, non-native animal removal, ecological restoration projects); education; security (ranger patrol); public access by non-commercial and commercial road permittees; recreational access (hiking, horse riding, mountain biking) and public safety or emergency services (fire, sheriff, paramedics).
Social and Legal Issues
The Conservancy's mission activities are a primary factor in evaluating the value of the road network, but social factors such as economics, public access and legal issues necessitate a broader perspective. Economic issues include the cost of maintaining roads accessible by the public relative to the revenue generated from road and other use permits. The level of maintenance also directly affects maintenance costs for the Conservancy's fleet of 50 vehicles that regularly travel the roads.
The island has a resident population of about 3,500 people, many of whom hold non-commercial road permits allowing them access to the "interior" from Avalon or access to the shops and services of Avalon if they reside in the interior. In addition, thousands of island visitors attend camps and educational programs in the island's leased coves. Telecommunications providers, regional and federal agencies utilize island antenna sites to provide communication services and require road access to them. Public utilities (Pacific Bell and Edison International) provide telephone, electric and water service to the interior and need access to pole and water lines, often during inclement weather when such access may be most damaging to the roads. Sightseeing tour operators carry about 200,000 visitors into the island's interior each year. The level of road maintenance affects the comfort of these travelers on Conservancy roads, and their perception of the island. It also affects the speeds at which private vehicles may comfortably travel, and therefore safety.
The road and trail network serves to "channel" or restrict access to designated areas. All-terrain vehicles (ATVs) are not permitted on Conservancy roads except for mission-related activities where roads are not passable otherwise, or where the ATVs create lesser impact on the environment than a conventional vehicle. Without such restraints, access into ecologically sensitive areas would be more common, and potential impacts more widespread. Despite these restraints, there is occasional off-road driving which requires monitoring by the Conservancy rangers. By restricting access to a well-defined road system, the Conservancy also restricts the level of services (e.g., camping areas and attendant sanitary services, public safety and emergency services).
A road system with a consistent naming scheme, signage and trail markers as facilitated with the GIS has benefits for recreational and other access. Clearly-identified roads enable better communications with potential users regarding road conditions and closures, especially during the winter rainy season. This system also clearly communicates travel routes for hiking through road maps being produced by the Conservancy ranger department using the GIS. Communications with Los Angeles County emergency personnel (fire, sheriff and paramedics), who are often only temporary summer residents, is also facilitated for faster response.
An additional consideration is the legal constraints on road development and maintenance. Many of the historic roadbeds exist in riparian corridors or other sensitive areas. Road work in these areas may require U.S. Army Corps of Engineers permits under section 404 of the Clean Water Act or a streambed alteration agreement with the California Dept. of Fish & Game. Roads in oak chaparral or woodlands may fall under the oak tree permit requirements of Los Angeles County. Borrow pits, used to obtain soil and gravel for road fill operations, may be subject to state mining and reclamation (SMARA) regulations. Dust generated by vehicular travel on dirt roads may fall under South Coast Air Quality Management District air pollution regulations for particulates. Under the Local Implementation Plan (LIP) for Catalina required by the California Coastal Act, no new roads are permitted without an amendment other than realignments for public safety or access to permitted new structures.
An issue somewhat unique to Catalina is the dual ownership of the island. Although the Conservancy owns 88%, the SCICo retained about 11% of Catalina. Their lands include several of the roads. Due to legal requirements relating to the formation of the Conservancy and its tax-exempt, non-profit status, the SCICo may not receive any direct or indirect economic benefit from Conservancy activities including road maintenance. The GIS provides a mechanism to determine what percentage of the roads are owned by, and what proportion of road maintenance expenses should be contributed by the SCICo.
Ecological and Resource Issues
The ecological and other impacts of the road network are judged based on resource-related factors including erosion; damage to native plants and animals; archaeological resources; pollution; and fire danger. The value and prioritization assessed based on social and legal issues must be weighed against the damage based on ecological and resource issues. The Conservancy's mission to preserve native plants and animals and biotic communities, requires impacts on them due to road use and maintenance to be an important factor in weighing the ecological costs and benefits of the road network.
Roads allow Conservancy employees easier access to some rare and ecologically sensitive plant populations to implement protection and recovery programs. However, those populations adjacent to roadbeds must be safeguarded when road maintenance is scheduled. Identifying these populations is facilitated through the incorporation of rare plant mapping data with the roads data in the GIS. For example, a population of Lepidium latipes latipes was recently mapped immediately adjacent to the roadbed leading into a designated campground. This species was believed locally extinct, having not been seen on Catalina since 1910. By mapping its location, future road maintenance on this access road can be done with its presence in mind. In the past unknowing bulldozer operators have destroyed stands of the endemic yerba santa (Eriodictyon traskiae) and the native bunchgrasses (Nassella spp.).
Another issue is the control and dispersal of alien plant species on the island (Bushing, et al., 1997). More than 30% of the island's plant species are non-native (Junak, et al., 1995). Roads serve as dispersal corridors for these often-weedy species based on observations of the spread of crystalline iceplant (Mesembryanthemum crystallinum), Russian thistle (Salsola tragus), Italian thistle (Carduus pycnocephalus) and other species. For this reason, heavy equipment brought to the island from the mainland is inspected by Conservancy employees for seeds and other plant material encrusted in mud on the undercarriage or in the tire treads. Despite this negative impact, roads facilitate bringing the Conservancy's "weed warrior" volunteers and herbicide spray rigs into weed-infested areas for control.
Several rare animal species are found adjacent to roads and may be impacted by road use and maintenance. The endemic ornate shrew (Sorex ornatus willetti) and rare two-striped garter snake (Thamnophis couchii) are both found in riparian areas along roadbeds. Roads and road maintenance activities may affect habitat quality for these species. Although not rare or threatened, the endemic Beechey ground squirrel (Spermophilus beechyi nesioticus) is often found as road kill. For other species the presence of roads may fragment available habitat and disrupt normal dispersal corridors. However, roads are necessary for ecological restoration activities such as the reintroduction of the bald eagle (Haliaeetus leucocephalus) by the Institute for Wildlife Studies, and the removal of non-native goats and pigs from the island.
Archaeological sites are another resource specifically called out for protection by the Conservancy. Road maintenance activities may expose Native American midden or burial sites. Roads offer public access to these and other sites which may result in the theft of artifacts or vandalism. However, roads are also important for transporting archaeologists to these sites for research, and educating visitors about the island's Native American history.
Plant and animal species and habitat quality can be affected by environmental impacts related to roads including fire, erosion, and pollution. Roads may contribute to increased fire frequency. Several wildfires in recent memory were caused by passengers in vehicles who discarded cigarettes or matches in the interior. There is also a potential fire hazard due to uncleared vegetation adjacent to roads from sparks and hot catalytic converters. The use of roads to access unpermitted camping sites opens the potential for fire caused by unauthorized campfires in ecologically sensitive areas. However, roads are also critical for emergency access and control by fire fighting personnel.
Although a natural element associated with steep terrain in semi-arid landscapes like Catalina, erosion is accelerated by roads and their maintenance. These impacts may include sheet erosion of the unvegetated road surface, gully erosion from excessive runoff due to poor road drainage or road culverts and bladed water diversions. This increased erosion may impact downslope vegetation or introduce additional siltation into the adjacent riparian watercourses. In addition, bladed water diversions open up new areas for alien weed colonization.
Roads in the softer alluvial soils of canyon bottoms, riparian zones and landslide areas are usually more affected than those following ridgetops or on other hard substrate. The former environments are usually more dynamic in response to water. The influence of erosion is largely cyclical due to seasonal rainfall, allowing repair of the damage to roads during the dry summer and fall months. Many of these potential impacts may be anticipated by visualizing the road, topographic, geologic, soils and stream drainage layers in the GIS.
Finally environmental pollution is a consequence of road use and maintenance. The
increased siltation due to erosion on roads in riparian corridors affects both the water quality of
runoff into potable water reservoirs and habitat quality for aquatic species. Oil and other
vehicular pollutants are deposited on the roadbed where they may wash off into riparian streams.
Litter is often associated with roads due to public access and improper disposal of waste paper.
The GIS can target areas where some of these pollutants may have potential impact. Finally roads
have a visual impact on the natural landscape contrary to the Conservancy's mission to preserve
the scenic beauty of open-space lands. Viewshed analysis using the GIS may help limit the
intrusion of existing roads on the landscape.
The Conservancy's GIS will be an important tool in evaluating the level of access and
maintenance required for the various road segments. Only with the help of such a "large-scale,"
island-wide tool can we assess the myriad of factors and constraints identified in this paper. The
GIS will help identify roads that are no longer needed and that may be decommissioned and
ecologically restored. By defining appropriate maintenance methods, this process may be assisted
with future road closures by limiting negative impacts on roads which do not require high levels
of maintenance. By incorporating rare and ecologically sensitive plant and archaeological site
data, sections of road where maintenance may have negative impacts may be readily identified
before crews go into the field. The crews may then be educated regarding the particular species
or sites of concern. Roads in areas of high potential for erosion (landslide or stream crossings)
may be identified based on the topographic and stream drainage data layers.
Bushing, W. W., J. N. Takara and H. Saldaña, 1997. Integration of GPS locational data in a GIS to manage native plants, and control non-native invasive plants, on Santa Catalina Island. Proc. 17th Esri User Conference, San Diego, CA, July 7-11, 1997.
Junak, S., T. Ayers, R. Scott, D. Wilken and D. Young, 1995. A Flora of Santa Cruz Island. Santa Barbara Botanic Garden (Santa Barbara, CA). 397 pp.
The authors would like to thank the following: Trimble Navigation, Ltd. (especially Robert A. Trimble) for their donation of a Pathfinder Pro XR GPS unit and Pathfinder Office software to the Santa Catalina Island Conservancy; Environmental Systems Research Institute, Inc. (especially Jack Dangermond and Charles Convis) for contributions to the Conservancy's GIS program through the Conservation Support Program; the Offield Family Foundation for financial support of the Conservancy GIS; and the Conservancy volunteer program, especially reserve ranger Bob Kopolow and Director of Volunteer Services Annette Shears, for its contribution in the collection of data for the GIS. In addition the Conservancy's Facilities Management road crews, supervised by Oden Vanderwiel, deserve substantial credit for maintaining the island's road network for the organization's mission activities and public access.