Oaks ‘n’ Folks – Volume 13, Issue 1 – February, 1998
The human population of the northern Sacramento Valley is forecast to more than double by the year 2040. This implies that additional land in the region will be under increasing development pressure for urban and rural residential uses. If this pattern of development is projected beyond the 15- to 20-year time frames of local-area plans, significant oak woodland acreage will be affected.
Since early 1994, the Northern Sacramento Valley Sustainable Landscape Project (SLP), covering Butte, Colusa, Glenn, Shasta, and Tehama Counties, has focused on facilitating informed discussions between public policy makers and resource stakeholders-including the general public-on long term management of the extensive oak woodland landscape. As part of its goal to develop an 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, spatial assessments of present and future growth patterns can be conducted.
A review of past and present population patterns and growth trends in the SLP region resulted in a series of maps depicting future land-use and population 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 within each area) and digitized into one of five general land-use categories. These categories included incorporated city spheres of influence, areas specifically designated for future urban growth and expansion; unincorporated communities,where water and/or sewer services are provided and residential build-out density is less than one dwelling unit per acre; rural residential lands,generally located on agricultural, grazing and range, and timber-producing land, where build-out density is between one and 40 acres per dwelling unit and resource production from the parcel is not the primary land-use; agricultural lands; 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 digital file from the California Department of Forestry and Fire Protection. Using GIS software, spatial statistics were generated showing the total acreage of hardwood range lands 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. Initial analyses were limited to incorporated city pheres, unincorporated communities, and foothill rural residential areas because they have the greatest effect on oak woodlands.
The effects of potential build out within the oak woodland interface are very apparent (Table 1). Further, when examined on a regional scale, it becomes apparent that not all counties are similarly or significantly affected. In the SLP region, major impacts are tied to land-use and will occur where major growth is projected; i.e., in Butte and Shasta Counties.
To better quantify effects in these two counties, a breakdown of hardwood rangelands by type can be used to quantify effects by land-use type or by development density (Table 2).
From this information, other questions can be formulated and new GIS inquiries made. For example, total affected acreage in this study is based on development densities of 40 acres per unit and greater. If these density thresholds are changed, changing the numbers and generating new maps is relatively 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 these changes. By illustrating potential land-use conflicts in the oak woodland interface, resulting maps help facilitate “what if?” scenarios that can lead to better management decisions.
This information was based on growth projections and should not be used to stop development in Butte and Shasta counties or anywhere in the five-county SLP region. Rather, it should be used to guide responsible growth. Maps and statistical information merely give planners, decision makers, and the interested public the ability to examine potential effects of development,initiate discussion, and to try to formulate workable strategies to manage growth.
The ability to graphically illustrate growth projections in a GIS gives the SLP an important planning tool. The potential uses for this type of data are great. For instance, this information can be used as a tool to help counties formulate general plan policy regarding oak woodland sustainability in the hardwood rangelands. It also can be used to assess population growth on other natural resource components like riparian zones, wetlands, and vernal pools, and may lead to more related research in the region. Importantly,mapping provides a clear visual format for residents to understand relationships between land-use and population growth.
Table 1. Acres of hardwood rangeland and acres affected by projected potential development in five northern California counties.
|County||Total Hardwood Rangland||Potential Development|
|Total Acreage||% of County||Affected Acres||% of Hardwood Rangeland|
Table 2. Acres in different hardwood rangeland types and percent of acres affected by potential projected development in Butte and Shasta counties.
|Hardwood Type||Butte County||Shasta County|
|Acres||% Affected||Acres||% Affected|
|Blue oak/foothill pine||
|Blue oak woodlands||
Charles W. Nelson
Director, Geographical Information Center, CaliforniaState University, Chico
prepared and edited by Richard B. Standiford and Pamela Tinnin