What is a Life Zone
Life Zone Overview
In 1889, the life zone concept was developed by C. Hart Merriam (an American zoologist, mammalogist, ornithologist, entomologist, ecologist, ethnographer, geographer, naturalist, and physician – he was commonly known as the ‘father of mammalogy’, a branch of zoology referring to the study of mammals) as a means of describing areas with similar plant and animal communities.
Merriam observed that the changes in these communities with an increase in latitude at a constant elevation are similar to the changes seen with an increase in elevation at constant latitude.
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.
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.