The life zones Merriam identified are most applicable to western
North America, being developed on the
San Francisco Peaks,
Arizona and
Cascade Range of the northwestern USA. He tried to develop a system that is applicable across the North American continent, but that system is rarely referred to.
List The life zones that Merriam identified, along with characteristic plants, are as follows: • Lower Sonoran (low, hot desert):
creosote bush,
Joshua tree • Upper Sonoran (desert steppe or
chaparral):
sagebrush,
scrub oak,
Colorado pinyon,
Utah juniper • Transition (open woodlands):
ponderosa pine • Canadian (fir forest):
Rocky Mountain Douglas fir,
quaking aspen • Hudsonian (spruce forest):
Engelmann spruce,
Rocky Mountains bristlecone pine • Arctic-Alpine (alpine meadows or tundra):
lichen,
grass The Canadian and Hudsonian life zones are commonly combined into a Boreal life zone.
Criticism This system has been criticized as being too imprecise. For example, the scrub oak chaparral in
Arizona shares relatively few plant and animal species with the
Great Basin sagebrush desert, yet both are classified as Upper Sonoran. However it is still sometimes referred to by biologists (and anthropologists) working in the
western United States. Much more detailed and empirically based classifications of vegetation and life zones now exist for most areas of the world, such as the
list of world ecoregions defined by the
World Wide Fund for Nature, or the
list of North American ecoregions defined by the
Commission for Environmental Cooperation. == Holdridge ==