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What is a Life Zone

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. 

Mountain biomes with altitude and Merriam’s life zones axis outline diagram. Educational climate and flora ecosystem description with labeled educational Arizona vegetation types vector illustration.

The life zones that Merriam identified, along with characteristic plants, are as follows:

  1. Lower Sonoran (low, hot desert): creosote bush, Joshua tree
  2. Upper Sonoran (desert steppe or chaparral): sagebrush, scrub oak, Colorado pinyon, Utah juniper
  3. Transition (open woodlands): ponderosa pine
  4. Canadian (fir forest): Rocky Mountain Douglas fir, quaking aspen
  5. Hudsonian (spruce forest): Engelmann spruce, Rocky Mountains bristlecone pine
  6. 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.

References Used

What is a Life Zone