A bioregion is an area constituting a natural ecological community, with distinct natural systems, flora, fauna, geology, etc., often defined by one or more watersheds. A bioregion is defined by natural rather than man-made borders and has unique requirements for human inhabitation so that it will not be disrupted and damaged. One major impetus for Cascadian independence is to enable Cascadians to protect the integrity of the bioregion they live in.
A similar, though distinct concept is that of the ecoregion. Ecoregions are areas of similar environment, which support a unique set of endemic species throughout, such as the Columbia Plateau or the coastal subalpine of the Olympic Mountains. Bioregions are often composed of many dozens of distinct ecoregions, each of which exchanges nutrients, water, and air (including pollution) with other adjacent ecoregions. Whereas ecoregions are defined by areas of consistent populations, bioregions are areas of interdependent relationships based on water cycles, animal migrations, and atmospheric exchange. As an example of a trans bioregional ecoregion, the Rocky Mountain alpine splits along the hydrologic divide between the Cascadian and plains/continental bioregions.