Ecosystem-based Models

Ecosystem-based habitat suitability models are conceptual and expert-based rather than empirically derived. Ecosystems are initially defined based on the concept of Holdridge life zones (HLZ’s). HLZ’s are discrete classifications of vegetation communities (similar to ecoregions) mapped using 30-year normal temperature, precipitation, and aridity data from climate models. They are based on observed global patterns of vegetation that co-vary with climate (e.g., decreasing precipitation drives transitions from forests to shrublands to grasslands that can be predicted from climate data). TerrAdapt aggregates the HLZ’s from our region (n=38 globally) into 4 broad ecosystem classes (temperate forests of the coastal lowlands, montane wet forests of the Cascades, Coast Range, and Rockies, montane dry forests in the interior east of the Coast Range and Cascades, and shrubsteppe in the Columbia Basin and Okanagan). These ecosystems closely track current and historical vegetation communities across the region and can be projected into the future given future climate scenarios. Once the climatic niche of an ecosystem has been mapped, we define habitat suitability for an ecosystem based on 1) the similarity to the preferred HLZ climate, the degree to which the landcover matches the preferred landcover for the ecosystem (e.g., forest ecosystem habitat suitability is highest in forest landcover classes and lower in more open non-forest habitat), and the degree of human modification based on a human footprint model (described below).

Validation of the ecosystem-based habitat model is not strictly possible because it is expert-based rather than empirical. However, the four ecosystems align strongly with current and historical patterns of vegetation as well as the known ranges of many species tied to each ecosystem.