Life Zones

In late 1800s Clinton Merriam studied the distribution patterns of plants and animals along a transect deep within the Grand Canyon to the top of San Francisco Mountains (Humphreys Peak, elevation 12,760 ft) above the city of Flagstaff in Arizona. Merriam used his observations to develop the concept of a Life Zone, an orderly change in the assemblage of plant and animal life with an increase in altitude in a manner similar to how assemblages of plants and animal life changes with an increase in latitude (from the equator to the poles).

The Life Zones according to Merriam were:

• Lower Sonoran (low, hot desert) includes producers like the Creosotebush, Joshua Tree
• Upper Sonoran (desert steppe or chaparral) includes producers like the Sagebrush, Scrub Oak, Colorado Pinyon, Utah Juniper
• Transition (open woodlands) includes producers like the Ponderosa Pine
• Canadian (fir forest) includes producers like the Douglas-fir, Quaking Aspen
• Hudsonian (spruce forest) includes producers like the Engelmann Spruce, Bristlecone Pine
• Arctic-Alpine (alpine meadows or tundra) includes producers like the Lichen, Grass

Contemporary as well a present day ecologists found Merriam's concept useful but not very applicable outside of Merriam's study area. In the mid 1900s Dr. Leslie Holdridge, an American botanist and climatologist, suggested that the concept of a Life Zone could be better delineated using average annual temperature(between 0° C or above 30° C), she called “biotemperatures”, the total annual precipitationand the ratio of average annual potential evapotranspiration to average total annual precipitation. Using these indicators, Dr. Holdridge came up wit the following diagram:

This model of the Life Zone concept would redefine Merriam's Altitudinal Life zones as follows:

• Lower Sonoran (low, hot desert) would become Super Arid, Pre Montane, Subtropical Desert
• Upper Sonoran (desert steppe or chaparral) would become Semi Arid, Pre Montane Desert Scrub/Steppe
• Transition (open woodlands) would become Semi Arid to Arid, Pre- to Lower Montane, Dry Scrub /Dry Forest
• Canadian (fir forest) would become Sub-Humid, Sub-Alpine Wet Forest
• Hudsonian (spruce forest) would become Sub-Humid to Humid, Sub-Alpine Wet Forest
• Arctic-Alpine (alpine meadows or tundra) would become a Sub-Humid to Humid, Alpine Moist or Wet Tundra

Using Google Earth, examples of these Life zones can be virtually viewed along a transect here in Southern California between the Imperial Valley and the summits of San Jacinto Peak (10834 feet (3302 m) and San Gorgonio Peak, 11, 503 feet (3,506 m). "Getting your ticket" for this virtual field trip will require you to download and/or open Google Earth (GE) on your computer. It will open in a different window and will require an active internet connection to operate. After opening GE, go to the "View" option and make sure all the options EXCEPT Grid, Sun and Historical Imagery are checked. Next, go to Preferences, under the Google Earth and make sure the Show Lat/Long preference is set to Degrees, Minutes, Seconds, click ok and proceed.

Lets start our trip in the Lower Colorado Desert of Southern California. Assuming that you have opened GE and made the changes addressed above, find the Search arrow in the upper left corner of the GE window and open it by clicking on it. Once open click on the "Fly To" option. To travel on GE, copy and paste the following latitude and longitide (lat, long) of 33°15'9.97"N, 115°52'23.43"W into the text box in GE's Fly To search engine (click on the magnifying glass/or tap the enter key to activate your search). You will be "flown" to the west shore of the Salton Sea. Once you have arrived, zoom out using the "-" minus key (zoom in using the "+" key) and explore around this area, getting close enough to see some of its surface features and plant life. The arrow keys will also help you navigate in any compass direction (ie. NEWS). Use some of the features of GE to "mess around" a bit and see what GE can add to your experience before leaving this biome and "hopping to another". Use the red text adjacent to the following "Life Zones" to "fly to" the locations.

• Super Arid, Pre Montane, Subtropical Desert (32°54'12.64"N, 115°14'21.94"W)
• Semi Arid, Pre Montane Desert Scrub/Steppe ( 33°39'31.85"N, 116°22'24.67"W)
• Semi Arid to Arid, Pre- to Lower Montane, Dry Scrub /Dry Forest (33°34'13.67"N, 116°32'35.68"W)
• Sub-Humid, Sub-Alpine Wet Forest (33°49'6.28"N, 116°44'14.73"W)
• Sub-Humid to Humid, Sub-Alpine Wet Forest (33°48'41.20"N, 116°40'39.67"W) on San Jacinto Peak (10834 feet (3302 m)
• Sub-Humid to Humid, Alpine Moist or Wet Tundra (34° 6'3.17"N, 116°49'44.54"W) on San Gorgonio Peak, 11, 503 feet (3,506 m)

To view on GE examples of Merrriam's original Life Zones between the Grand Canyon and the top of San Francisco Mountains use the following lat and long datum points:

• Lower Sonoran (low, hot desert) (36° 5'12.51"N, 111°51'12.98"W)
• Upper Sonoran (desert steppe or chaparral) ( 36° 4'30.16"N, 111°47'43.05"W)
• Transition (open woodlands) (35°32'4.23"N, 111°51'30.25"W)
• Canadian (fir forest) ( 35°21'5.02"N, 111°42'3.26"W)
• Hudsonian (spruce forest) (35°20'23.83"N, 111°41'17.51"W)
• Arctic-Alpine (alpine meadows or tundra) (35°20'48.02"N, 111°40'40.15"W)