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The Willamette River Basin drains an area of approximately 12,100 square miles, or roughly 12.5% of the state of Oregon. The basin is home to 1.8 million people - almost 70% of the state's population (ODOT 1993).
The study of large land areas such as the Willamette River Basin (WRB) is difficult both because of the amount of data required to represent important features and because of the variability of landforms and human land use practices present. There are two common methods for dealing with this predicament:
The first approach typically suffers from lack of detail as physically small landscape features and processes are difficult to represent. The second approach allows better representation, but at the expense of generalization.
Of course, both approaches are complementary. Our approach in this study was to use the best available data on chosen indicators of landscape condition at the WRB scale. We used this initial "geoscoping" analysis to select an appropriate subarea which we examined in detail.
Our broad criteria for study area selection were that the chosen area be both
Of course no land area is representative of all possible uses or changes. In this study, we chose to use aggregate measures of
We do not mean to imply that these criteria are necessarily the most important under all circumstances, only that some measurable criteria must be chosen, and that it is useful to make these as explicit as possible. The use of other criteria may be appropriate in determining a study area, based on interests or qualities specific to a given region, such as a fire-shed boundary or economic measures such as Standard Metropolitan Statistical Areas.
In part because of land ownership patterns, otherwise similar parcels of land may be on widely varying landscape trajectories, that is, there may be different forces effecting how different portions of the landscape change over time. For example, a forested area of private industrial timberland is on a different landscape trajectory than a forested area in a public county park. The natural processes that shape a landscape, in concert with recent and current human activities, determine that landscape's trajectory. The agents of change, whether originating with people or not, have the potential to alter the future trajectory of a landscape as well.
Considering past and plausible future landscape trajectories for a study area helps to define the structure of the study process described in this report. Doing so requires researchers to explicitly characterize how a study area has changed over time and to examine how the agents of change may interact to produce significantly different landscapes in different possible futures. This enables people to focus attention on areas that are likely to experience significant land use transformations in the future, as well as places where shifts in natural processes have been most evident in the past. |
Another important preliminary question in defining any study area is the choice of its boundary. Boundaries can be drawn based on many criteria; political, managerial, ecological, economic, or statistical all being common. While the use of political boundaries, such as city limits, counties, or states, instead of natural process boundaries, like a watershed, may facilitate data gathering and integration, a strict political framework may focus attention on political processes at the expense of ecological processes.
In the Pacific Northwest, water-based processes, like stream and river flow, form a common and well understood link between otherwise separate activities, such as forestry and agriculture practices. Farmers in the lowlands often have an acute awareness of how streams have been treated in the uplands. Foresters and other residents in higher elevations may notice landscape changes that effect stream suitability for aquatic life use and recreational purposes, as well as prospects for flooding, hillside erosion and landslides. Given the goals of this project, a watershed boundary was chosen as the most appropriate boundary unit.
As to spatial extent, a watershed approximately 100 to 200 square miles in area was determined to be preferable for several reasons. This extent is large enough to encompass many of the key hydrological processes and biodiversity qualities of interest, as well as a range of land uses and ownerships typical of the larger Willamette River Basin, yet small enough to be recognized as a discrete, distinct place and to allow examination and exploration of land use change in parcel-level increments, corresponding to the scale at which land use decision making frequently occurs.