Overview

Biodiversity was the first criterion we used in our search for a study area within the Willamette River Basin. This portion of the project relied entirely on best available existing data. Two types of analyses were performed. First, a complementary set analysis determined the minimum number of subunits that best represented the biodiversity regionally and statewide. In the subsequent cluster analysis, species lists for hexagonal subareas within the Willamette River Basin were compared to determine which were the most representative of the Basin as a whole.

Complementarity Set Analyses of Species Data

To identify subunits within the Willamette River Basin of particular interest from a biodiversity perspective, data and prioritizations for Oregon were obtained from the Biodiversity Research Consortium (BRC) (Kiester et al 1993.). The BRC data consist of a list of bird, mammal, amphibian, fish, and reptile species occurring in each of 441 hexagons in the state. Each hexagon covers 650 km2 and includes information on the presence of vertebrates, butterflies, selected freshwater invertebrates, and trees known to exist within that hexagon during the past 30 years. First, a set of complementarity set analyses were performed at the state scale. This produced the minimum sized sets of hexagons which contained populations of all terrestrial vertebrate species found in the state (Csuti et al 1995.).

Statewide and Regional Complementarity Analyses of BRC Species Data

A set of complementarity analyses were performed at the state scale. This produced the minimum sized sets of hexagons which contained populations of all terrestrial vertebrate species found in the state (Csuti et al.). The five of these hexagons occurring within the mid Willamette Valley are shown with a striped pattern at left. Next, the same analysis was performed for the 30 mid Willamette Valley hexagons. A set of 7 hexagons selected from a total of 10 hexagons contain 239 of 244 terrestrial vertebrates. These are shown in bright yellow at left. Four hexagons (striped yellow) were both statewide and regional priority areas and were further investigated.

Cluster Analysis of Relative Similarity Between Species Lists

BRC Hexagons within the Lower Elevation Willamette River Basin Clustered to Depth 7

In this map, hexagons of the same color have relatively similar species lists. Mean Percent Similarity: 84% Most similar pair: 94% Least similar pair: 75% Cluster analyses were conducted to assess the similarity of species among hexagons and the extent to which individual hexagons were representative of the mid-Willamette Valley's biodiversity. The priority hexagons in the Portland area (gray borders) were atypical of most of the mid-Willamette Valley. In contrast, hexagons near Albany and Corvallis (shown with darker border) were characteristic of much of the valley.