Assessing Potential Hardwood Loss in the Northern Sacramento Valley Using GIS Technology

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The human population of the northern Sacramento Valley is forecast tomore than double by the year 2040. This implies that additional land inthe region will be under increasing development pressure for urban and ruralresidential uses. If this pattern of development is projected beyond the15- to 20-year time frames of local-area plans, significant oak woodlandacreage will be affected.

Since early 1994, the Northern Sacramento Valley Sustainable LandscapeProject (SLP), covering Butte, Colusa, Glenn, Shasta, and Tehama Counties,has focused on facilitating informed discussions between public policy makersand resource stakeholders-including the general public-on long term managementof the extensive oak woodland landscape. As part of its goal to developan acceptable framework for discussing issues related to sustainability,the SLP has chosen to use geographical information system (GIS) technology.By incorporating land-use and population projections into a GIS, spatialassessments of present and future growth patterns can be conducted.

A review of past and present population patterns and growth trends inthe SLP region resulted in a series of maps depicting future land-use andpopulation density. Paper maps of each of the five counties were prepared(using key factors including the 1990 Census, county assessors records,an estimate of build-out potential described as average population density,and the estimated average annual population growth rate to be expected withineach area) and digitized into one of five general land-use categories. Thesecategories included incorporated city spheres of influence, areas specificallydesignated for future urban growth and expansion; unincorporated communities,where water and/or sewer services are provided and residential build-outdensity is less than one dwelling unit per acre; rural residential lands,generally located on agricultural, grazing and range, and timber-producingland, where build-out density is between one and 40 acres per dwelling unitand resource production from the parcel is not the primary land-use; agriculturallands; and other resource producing lands, including lands used for grazing,timber production, mining, wildlife habitat, and open space.

Map information showing California hardwood types was obtained as a digitalfile from the California Department of Forestry and Fire Protection. UsingGIS software, spatial statistics were generated showing the total acreageof hardwood rangelands in the SLP region (Table 1).

To examine the potential effect of population growth on the oak interface,the land-use map layers were overlayed on the hardwood coverage. Initialanalyses were limited to incorporated city pheres, unincorporated communities,and foothill rural residential areas because they have the greatest effecton oak woodlands.

The effects of potential buildout within the oak woodland interface arevery apparent (Table 1). Further, when examined on a regional scale, itbecomes apparent that not all counties are similarly or significantly affected.In the SLP region, major impacts are tied to land-use and will occur wheremajor growth is projected; i.e., in Butte and Shasta Counties.

To better quantify effects in these two counties, a breakdown of hardwoodrangelands by type can be used to quantify effects by land-use type or bydevelopment density (Table 2).

From this information, other questions can be formulated and new GISinquiries made. For example, total affected acreage in this study is basedon development densities of 40 acres per unit and greater. If these densitythresholds are changed, changing the numbers and generating new maps isrelatively easy.

Also, maps can be updated when new land-use policy decisions are made.Affected areas can then be adjusted upward or downward to reflect thesechanges. By illustrating potential land-use conflicts in the oak woodlandinterface, resulting maps help facilitate "what if?" scenariosthat can lead to better management decisions.

This information was based on growth projections and should not be usedto stop development in Butte and Shasta counties or anywhere in the five-countySLP region. Rather, it should be used to guide responsible growth. Mapsand statistical information merely give planners, decision makers, and theinterested public the ability to examine potential effects of development,initiate discussion, and to try to formulate workable strategies to managegrowth.

The ability to graphically illustrate growth projections in a GIS givesthe SLP an important planning tool. The potential uses for this type ofdata are great. For instance, this information can be used as a tool tohelp counties formulate general plan policy regarding oak woodland sustainabilityin the hardwood rangelands. It also can be used to assess population growthon other natural resource components like riparian zones, wetlands, andvernal pools, and may lead to more related research in the region. Importantly,mapping provides a clear visual format for residents to understand relationshipsbetween land-use and population growth.

prepared and edited by Richard B. Standiford and Pamela Tinnin