Ecological subregions of the interior Columbia basin, USA.

Abstract

Land evaluations are not always conducted with adequate understanding of the relevant geologic and climatic contexts and their appropriate scales. This understanding is essential for developing representative sampling, monitoring, and conservation designs, and for pooling results of landscape analysis. To provide context for several regions of the interior northwestern United States, we conducted an ecoregion classification of the interior Columbia River Basin and vicinity (‘the Basin’). We grouped land units that are influenced by the same higher order geology and landform features, and share similar areal composition of potential vegetation and climate attributes. We used the TWINSPAN procedure to group 7496 watersheds of the Basin into 53 ecological subregions. We evaluated the contribution of attributes to group separation by discriminant analysis, and evaluated subregion robustness to prediction by cross-validation. Classification accuracy ranged from 80 - 97% across the subregions. All watersheds were classified to a subregion, and there were strong resemblances between members of adjacent subregions. Subregions with strong resemblances shared a similar composition of attributes, but differed in relative abundance and attribute combinations. We evaluated the geologic and climatic context of each subregion considering four levels in a nested land unit hierarchy. Most subregions nested at one of at least four scales, but some overlapped. Our results suggest that observation levels for a given ecological phenomenon need not be nested within their appropriate context levels, and across broad geographic areas context of the same phenomenon occurs at different scales.

Citation

Hessburg, P.F.; Salter, R.B.; Richmond, R.B.; Smith, B.G. 2000. Ecological subregions of the interior Columbia basin, USA. Applied Vegetation Science. 3: 163-180