# Life zone > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Life_zone > Markdown URL: https://mediated.wiki/source/Life_zone.md > Source: https://en.wikipedia.org/wiki/Life_zone > Source revision: 1286407246 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) Concept developed by C. Hart Merriam in 1889 Main article: [Altitudinal zonation](/source/Altitudinal_zonation) The **life zone** concept was developed by [C. Hart Merriam](/source/Clinton_Hart_Merriam) in 1889 as a means of describing areas with similar [plant](/source/Plant) and [animal](/source/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.[1] ## Merriam The life zones Merriam identified are most applicable to western [North America](/source/North_America), being developed on the [San Francisco Peaks](/source/San_Francisco_Peaks), [Arizona](/source/Arizona) and [Cascade Range](/source/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](/source/Creosote_bush), [Joshua tree](/source/Yucca_brevifolia) - Upper Sonoran (desert steppe or [chaparral](/source/Chaparral)): [sagebrush](/source/Sagebrush), [scrub oak](/source/Quercus_turbinella), [Colorado pinyon](/source/Colorado_pinyon), [Utah juniper](/source/Utah_juniper) - Transition (open woodlands): [ponderosa pine](/source/Ponderosa_pine) - Canadian (fir forest): [Rocky Mountain Douglas fir](/source/Rocky_Mountain_Douglas_fir), [quaking aspen](/source/Aspen) - Hudsonian (spruce forest): [Engelmann spruce](/source/Engelmann_spruce), [Rocky Mountains bristlecone pine](/source/Rocky_Mountains_bristlecone_pine) - Arctic-Alpine (alpine meadows or tundra): [lichen](/source/Lichen), [grass](/source/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](/source/Arizona) shares relatively few plant and animal species with the [Great Basin](/source/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](/source/The_West_(U.S.)) [United States](/source/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](/source/List_of_terrestrial_ecoregions_(WWF)) defined by the [World Wide Fund for Nature](/source/World_Wide_Fund_for_Nature),[2] or the [list of North American ecoregions](/source/List_of_ecoregions_in_North_America_(CEC)) defined by the [Commission for Environmental Cooperation](/source/Commission_for_Environmental_Cooperation).[3] ## Holdridge Main article: [Holdridge life zones](/source/Holdridge_life_zones) Holdridge life zone classification scheme. Although conceived as three-dimensional by its originator, is usually shown as a two-dimensional array of hexagons in a triangular frame. In 1947, [Leslie Holdridge](/source/Leslie_Holdridge) published a life zone classification using indicators of: - mean annual [biotemperature](/source/Biotemperature) (logarithmic) - annual precipitation (logarithmic) - ratio of annual potential evapotranspiration to mean total annual [precipitation](/source/Precipitation_(meteorology)). 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](/source/Clinton_Hart_Merriam)'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.[4] ## See also - [Biogeographic realm](/source/Biogeographic_realm) - [Biome](/source/Biome) - [Ecoregion](/source/Ecoregion) - [Köppen climate classification](/source/K%C3%B6ppen_climate_classification) ## References 1. **[^](#cite_ref-1)** McColl, R.W. (2005). *Encyclopedia of World Geography*. Vol. 1. Infobase Publishing. p. 961. [ISBN](/source/ISBN_(identifier)) [9780816072293](https://en.wikipedia.org/wiki/Special:BookSources/9780816072293). 1. **[^](#cite_ref-2)** Ricketts, Taylor H.; Dinerstein, Eric; Olson, David M.; Loucks, Colby J.; et al. (1999). *Terrestrial Ecoregions of North America: a Conservation Assessment*. Washington DC: Island Press. 1. **[^](#cite_ref-CEC_3-0)** ["Ecological Regions of North America: Toward a Common Perspective"](https://web.archive.org/web/20040104002650/http://www.cec.org/files/pdf/BIODIVERSITY/eco-eng_EN.pdf) (PDF). [Commission for Environmental Cooperation](/source/Commission_for_Environmental_Cooperation). 1997. Archived from [the original](http://www.cec.org/files/PDF/BIODIVERSITY/eco-eng_EN.pdf) (PDF) on 2004-01-04. 1. **[^](#cite_ref-4)** ["Holdridge's Life Zones"](https://web.archive.org/web/20080110110748/http://www.radford.edu/~swoodwar/CLASSES/GEOG235/lifezone/holdrdge.html). *Geology class notes*. Radford University. Archived from [the original](http://www.radford.edu/~swoodwar/CLASSES/GEOG235/lifezone/holdrdge.html) on 2008-01-10. --- Adapted from the Wikipedia article [Life zone](https://en.wikipedia.org/wiki/Life_zone) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Life_zone?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.