C. Hart Merriam
Clinton Hart Merriam (December 5, 1855 – March 19, 1942) was an American zoologist, mammalogist, ornithologist, entomologist, ecologist, ethnographer, geographer, naturalist and physician. He was commonly known as the 'father of mammalogy', a ...
in 1889 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 a constant latitude.
The life zones Merriam identified are most applicable to western
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
, being developed on the
San Francisco Peaks
The San Francisco Peaks (Navajo: , es, Sierra de San Francisco, Hopi: ''Nuva'tukya'ovi'', Western Apache: ''Dził Tso'', Keres: ''Tsii Bina'', Southern Paiute: ''Nuvaxatuh'', Havasupai-Hualapai: ''Hvehasahpatch''/''Huassapatch''/''Wik'hanbaja'', ...
Cascade Range
The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...
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.
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
Chaparral ( ) is a shrubland plant community and geographical feature found primarily in the U.S. state of California, in southern Oregon, and in the northern portion of the Baja California Peninsula in Mexico. It is shaped by a Mediterranean c ...
Utah juniper
''Juniperus osteosperma'' (Utah juniper; syn. ''J. utahensis'') is a shrub or small tree native to the southwestern United States.
Description
The plant reaches , rarely to 9 m, tall. The shoots are fairly thick compared to most junipers, i ...
* Transition (open woodlands): ponderosa pine
* Canadian (fir forest):
Rocky Mountain Douglas fir
''Pseudotsuga menziesii'' var. ''glauca'', or Rocky Mountain Douglas-fir, is an evergreen conifer native to the interior mountainous regions of western North America, from central British Columbia and southwest Alberta in Canada southward through ...
lichen
A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.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
The Great Basin is the largest area of contiguous endorheic basin, endorheic watersheds, those with no outlets, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja California ...
sagebrush desert, yet both are classified as Upper Sonoran. However it is still sometimes referred to by biologists (and anthropologists) working in the westernUnited 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
The Commission for Environmental Cooperation (CEC; es, Comisión para la Cooperación Ambiental; french: Commission de coopération environnementale) was established by Canada, Mexico, and the United States to implement the North American Agree ...
.
Holdridge
In 1947, Leslie Holdridge published a life zone classification using indicators of:
* mean annual
biotemperature
The Holdridge life zones system is a global bioclimatic scheme for the classification of land areas. It was first published by Leslie Holdridge in 1947, and updated in 1967. It is a relatively simple system based on few empirical data, giving obj ...
(logarithmic)
* annual precipitation (logarithmic)
* ratio of annual potential evapotranspiration to mean total annual precipitation.
Biotemperature refers to all temperatures above freezing, with all temperatures below freezing adjusted to 0 °C, as plants are dormant at these temperatures. Holdridge's system uses biotemperature first, rather than the temperate latitude bias of
Merriam Merriam can refer to:
People
* Alan P. Merriam (1923–1980), American ethnomusicologist
* Charles Edward Merriam (1874–1953), American political scientist
* Charles W. Merriam (1877–1961), American insurance businessman and politician
* Clinto ...
's life zones, and does not primarily use elevation. The system is considered more appropriate to the complexities of tropical vegetation than Merriam's system.