Development of a land evaluation and site assessment (LESA) model for forestry in Lane County, Oregon Public Deposited


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  • A Land Evaluation and Site Assessment (LESA) Model was developed for the forested soils of Lane County, in western Oregon, based on soil potential ratings and indexes of parcel size and adjacent and surrounding land use conflict. Lane County's economy is heavily dependent on resource production uses of land for forestry. At the same time, population growth around metropolitan areas creates pressure to convert rural land from large resource use parcels to smaller rural residential parcels. Planning for future allocation of land among competing uses promoted the county to develop an objective method for determining the relative quality of any parcel of land for forestry. Parcels of lower quality could then be considered for conversion to rural residential uses. LESA was developed by the SCS for use by state and local governments as an objective method of evaluating the resource production quality of land for planning purposes. Land evaluation (LE) measures the relative suitability of the soils of a given parcel for forestry. Site Assessment (SA) measures the relative suitability of the setting in which the parcel occurs. The soil potential ratings (SPR's) were developed from soil map unit characteristics defined in the Soil Survey of the Lane County Area. SPR's are indexes of the net return to soil management for forestry. Each soil is assigned an expected output, or yield, to soil management for forestry using a computer model called DFSIM. Management practices required to achieve that yield also are specified. Monetary values are determined for both yields and management practices, and the difference between price received and total costs is a measure of soil potential. The soil having the highest net return to soil management is assigned an arbitrary value of 100 points. All other soils are rated by expressing their net return as a percent of the maximum. Management practices in each of four categories - site preparation and stand establishment, thinning, harvest, and road construction and maintenance - were prescribed, and their costs determined, based on their interactions with soil slope, erodibility, depth, bedrock hardness, and coarse fragment content. Land evaluation was completed by overlaying a soil map of the land parcel of interest, determining the fractional amount of each soil present, and multiplying that amount by the corresponding soil potential rating. The sum of all the products is a weighted average soil potential rating for a parcel. Development of the Site Assessment (SA) portion of the model was guided by a technical committee of forest management professionals and land use specialists. The committee chose the factors that were considered important in site assessment and how much weight to give to each factor. For this LESA model, two factors were identified: compatibility with other land uses, and parcel size. The concept of compatibility implies that large scale forestry uses are compatible with each other but are not compatible with small scale residential uses. Generally, the more non-resource related dwellings in forestry areas, the greater the potential conflict due to noise, chemical spraying, dust, smoke, and vandalism. Two empirical formulas were developed to measure compatibility effects. One accounts for the number and density of non-compatible parcels adjacent to the parcel of interest. The other measures the density of non-compatible parcels within a specified distance of the target parcel, which was 1/2 mile. Parcel size implies that large parcels are more suitable for resource uses than small ones, and that parcels surrounded by a few large parcels are more favorable than parcels surrounded by many small parcels. An empirical formula was derived to measure these effects. Optimum parcel sizes depended on slope, parcel shape, and the number of streams running through the parcel. The final step in the LESA model development was to specify a total point value, and to decide on the proportion of that total that would go to each of the factors, soils, compatibility, and parcel size. In previous LESA models the point total has been 300. This total was allocated to each of the factors as follows: soils 105, adjacent use 75, surrounding use 45, and parcel size 75. Validation is a critical part of the development of a LESA model, and it is done by applying the LESA criteria to several parcels that represent a range of soil resource quality, sizes, and land use settings. Each parcel must then be examined in the field by the LESA development committee. Field examination is essential in order to make needed adjustments in empirical formulas. Through the repeating of this validation process, the model is fine tuned and its accuracy for planning purposes is validated. LESA scores can be used to distinguish between primary and secondary land resources. Primary resource lands are sufficiently valuable for forest uses that land use controls are justified to prevent the introduction of non-resource development. Secondary resource land is of lesser quality and is a more appropriate site for smaller scale resource uses and certain non-resource uses. Information from the test parcels was used to set primary/secondary thresholds for each factor and to develop empirical criteria for classifying each parcel.
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