- 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
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.