Designing the Foothill Intermix
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Impacts of Development in El Dorado County
Designing the Foothill Intermix |
Robin Marose
GIS Manager
Fire and Resource Assessment Program
PO Box 944246
Sacramento, CA 94244
(916) 324-1646
Fax: (916) 324-1180
robin.marose@fire.ca.gov
Economic diversification and population growth will largely determine the nature and sustainability of social and ecological systems in the Sierra Nevada over the foreseeable future. The Sierra Nevada Ecosystem Project found that population in the Sierra doubled from 1970 to 1990 and will triple again before 2040. Most of that growth will occur on the western slope of the Sierra as a result of continued growth in adjacent Central Valley cities.
These landscapes will change much more than the conversion to urban land use would suggest. As a percentage of total area, the area covered by houses and businesses with landscaping and roads will remain, even at buildout, far below that of major urban areas. Nonetheless, changes in settlement patterns at densities far below that associated with fully urbanized areas affect fire regimes and the watershed values associated with forest, shrub, and grassland.
The nature of rural development is therefore as important to the sustainability of Sierran ecosystems as the location of parks, natural areas, and other reserved lands. Privately owned rural lands in El Dorado County contribute the majority of oak woodland. Oak woodland now creates a partially connected mosaic of functional habitat stretching across a landscape with little or no reserved lands. The "wildland oak woodland" does not appear in a single large public reserve. Instead, it is found on adjacent undeveloped portions of thousands of private parcels built into the private settlement pattern. Biodiversity in oak woodlands is more a "backyard" than a "big wild" phenomenon.
Analytical methods that deal rigorously with intermix lands – both the threats they pose as well as the contributions they make – are poorly developed. Methods derived in areas where high-density urban development completely erases wildland habitat view the world in all-or-nothing categories of "reserved" or "developed." Even within methods that distinguish multiple levels of legal commitment to biodiversity goals such as gap analysis, all private lands are typically lumped together, thereby ignoring distinctions between different development densities, the regulations aimed at maintaining environmental values and the contribution that these lands already make to biodiversity.
The development of oak woodland conservation guidelines by El Dorado County provided an opportunity to develop such analytical methods. These methods generate a series of spatially explicit maps of land cover. They reflect the thematic density maps of General Plans, the existing parcelization, and specific policies and mitigation requirements. As such, they provide a basis for rigorous examination of policies such as riparian buffers, canopy retention guidelines, and clustering - the real world as experienced by county planners and supervisors. The methods generate fine-grain depictions of habitat resulting from such plans and policies. They quantify the contributions, express or inadvertent, of private landowners to the conservation of biodiversity.
Pixels
El Dorado County – Western Slope Land Cover and Planning Regions portrays vegetation life form (e.g., grass, shrub) with additional detail within oak woodlands (e.g. blue oak woodland, montane hardwood mix) as well as developed and agricultural land use. The data comprising the map are derived from satellite imagery and presented as 25-meter square, or 0.15 acre, pixels. The overall accuracy of the data, verified through several field checks, is quite good below the conifer-dominated portions of the county. CDF has such data for more than one-third of California (see Figure 2.1, Project Area Extent) including the areas likely to absorb most of California’s growth outside of Orange, Riverside, and San Diego counties.
Parcels
El Dorado County – Current Developed Areas Derived from Imagery and County Parcel Data portrays the "footprint" of human use on the western slope. While many activities affect oak woodlands, development is the factor most likely to cause widespread change in the woodlands over the foreseeable future. The El Dorado County General Plan regulates most development activities. Therefore, assessing the future of oak woodlands means generally assessing the impact of the General Plan on oak woodlands. The analysis began with an assessment of the current extent of development. The red areas on the map portray the extent of significant alteration of the habitat on the basis of both imagery and County Assessor’s data. Such habitat alteration frequently leaves considerable vegetation on the site. Nonetheless, it significantly changes its value to the full range of wildlife species associated with oak woodlands.
El Dorado County – Current Fragmentation of Wildland Oak Woodland portrays the connections between wildland oak woodland stands. Wildland oak woodlands are located more than 150 feet away from any urban or other developed area. They are arranged in blocks at least 250 acres in size and no narrower than 150 feet at any point. While wildland oak woodlands probably stretched across El Dorado County north to south, wildland oaks are currently concentrated in two large blocks. Each block is about 70,000 acres and located north and south of Highway 50. Smaller fragments exist around these large blocks as they grade into Sierra mixed conifer and valley grasslands. Several smaller blocks located between these large blocks provide islands in the gaps.
Plans
El Dorado County – Additional Development Influence at Buildout shows a "footprint" of development likely to result from buildout of the General Plan. This picture considers
This particular map corresponds to the addition of roughly 37,000 new housing units in the area.
El Dorado County – Projected Fragmentation of Wildland Oak Woodland at Buildout shows that the large island north of the highway fragments considerably with buildout. Two-thirds of the remaining wildland oak woodland consists of three fragments between 13,000 and 35,000 acres in extent. The fragments are smaller and the distances between them greater, particularly along the Highway 50 corridor.
Policies
Analyses of different policy scenarios, such as wider riparian buffers, more clustering or higher canopy retention standards within certain general plan land use zones, did not markedly mitigate the growing fragmentation of the wildland oak woodland. These policies may have considerable impact on the extent of oak woodlands in different development classes. Nonetheless, they did not target explicitly those areas critical to the maintenance of regional connectivity. Specific policies aimed at maintaining connections may not only achieve the objective but may do so at lower political and economic cost.
El Dorado County – Primary Corridor Areas for Wildland Oak Woodland Landscape Connectivity shows areas of wildland oak that will disappear at buildout. One possible set of zones is illustrated within which special efforts could be designed to maintain regional connectivity in a north-south direction across Highway 50. These efforts could be education and information for current residents and particular analyses required of new development projects.
California Department of Forestry and
Fire Protection
Fire and Resource Assessment Program (frap.cdf.ca.gov)
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