It was early learned that North America is divisible into seven transcontinental belts of life zones and a much larger number of minor areas of faunas, each characterized by associations of animals and plants.

H. Merriam 1898

Clinton Hart Merriam was born into a wealthy family like many successful naturalists. As a result, Merriam was free to follow his interests without having to work for a living. He grew up on his family’s estate in Locust Grove, New York. By age 18, he was publishing papers on animals. Like Charles Darwin and Alfred Russel Wallace, Merriam was a born naturalist. He studied biology at Yale and received a medical degree from Colombia in 1879. All the while, Merriam continued to publish papers on natural history. He practiced medicine briefly, but the lure of a career in natural history brought him to become the administrator of the newly established Section of Ornithology in the Entomological Division of the United States Department of Agriculture in 1885. The agency became the Bureau of Biological Survey in 1905, with Merriam as the administrator. Merriam had a 25-year career with the Bureau and made many significant contributions to the natural history of the United States.

In 1889, Merriam visited Arizona’s Colorado Plateau and published the results of his survey of the San Francisco Mountain region and the desert of Little Colorado, Arizona. He chose this region because “of its southern position, isolation, great altitude, and proximity to an arid desert.” He believed a new scientific understanding of the diversity of physical and climatic conditions and how they related to life forms could be obtained. The extensive plant and animal collections he made included elevational data. The research let him build his “life zones” concept.

Merriam set up camp at Little Spring, at the base of the San Francisco Mountain. He was accompanied by his wife, the botanist Frank H. Knowlton, the museum collector Vernon Bailey, and herpetologist Leonhard Stejneger. The camp was in an aspen grove at about 2525 m, and the team stayed there for about two months. San Francisco Mountain is an extinct, Pleistocene strato-volcano in a volcanic field of over 600 smaller cinder cone volcanos. After it formed, it was estimated to be 4800 m tall before an eruption blew off the side or a glacier eroded the top. The mountain’s crest line has a series of peaks, the tallest of which is Humphreys peak.

The peaks have spiritual significance to the Havasupai, Navajo, Hopi, Zuni, and other tribes. The Hopi associate the San Francisco Mountain with the intercardinal direction southwest and consider the peaks ritually pure sacred spaces. They use the peaks as sources for ceremonial objects and landmarks for calculating the winter solstice and other calendar events. In addition, the peaks are the home of the Kachina spirits, Hopi ancestors who became clouds following their deaths.

The volcanic cone is also of scientific interest for its role in understanding basic ecological principles. Merriam realized that the vegetation zones on the mountainside were like the north-south latitudinal distribution patterns of vegetation. Temperature and precipitation differences at various altitudes produced different vegetation, and similar changes in vegetation could be seen as you move from north to south. Building on Alexander von Humboldt’s efforts, Merriam wanted to understand plant distribution and turned Humboldt’s ideas into ecological principles. At the time, this approach differed from creationist Louis Agassiz, who viewed the north-south pattern in plants because of geographic barriers and a higher intelligence responsible for placing the plants.

Merriam considered migration, dispersal, and colonization significant. Species moved with changing conditions. Finding the high-altitude tundra in Arizona that corresponded with the arctic tundra convinced him of the movements of flora and fauna. In 1890, he wrote,

“The present biological survey of the San Francisco Mountain region has demonstrated that mammals, birds, reptiles, insects, and plants so coincide in distribution that a map showing the boundaries of an area inhabited by an association of species in one group serves equally well for other groups. The reason for this coincidence in distribution is that all terrestrial forms of life inhabiting the same area are exposed to the same surroundings and governed by the same general laws…At high elevations, an abbreviated growing season combined with strong winds and heavy snowfall (about 100 mm) creates an environment hostile to most plants and animals. Only tundra-adapted species grow in such a harsh climate. Tundra plants evolved their flat, ground-hugging stems and leaves to avoid the wind and obtain heat from the ground.”

Arizona’s Alpine Tundra is the most restricted plant community in the state and covers about 650 ha in area. It can be found about 10 miles north of Flagstaff on the isolated San Francisco Mountain summit in the Kachina Peaks Wilderness Area of the Coconino National Forest. At its base, San Francisco Mountain is at 2156 m ASL on the Colorado Plateau, rising to 3902 m ASL, making it the most prominent landmark in northern Arizona.

Of the 82 species of plants found in the alpine tundra, about half can be found in the Arctic tundra or have close relatives there. The same species or close relatives also occur on the high summits of the Rocky Mountains that range northward into Canada.

At least one plant, the San Francisco Peak Ragwort, is likely endemic. Nearby areas have been closed to travel to protect this rare plant. The tundra has an alpine rock field flora, which consists mainly of lichens, and an alpine meadow dominated by Ross’s Avens (Rosaceae). Its yellow blossoms are in alpine and arctic tundra communities from Arizona to Alaska and northern Canada. Near the meadow’s edge at about 3500 m are the gnarled “Krumholtz trees,” the stunted and deformed woody plants in subarctic and subalpine timberline landscapes. These twisted plants are shaped by continual exposure to fierce, freezing winds.

Merriam observed the Desert Bighorn Sheep and the Long-tailed Weasel on the alpine tundra. He suggested that these and other species occasionally investigated the tundra and described seeing Say’s Squirrel (now called the Golden-mantled Ground Squirrel), the Gray-collared Chipmunk, and the Montane Shrew above the timberline.

Merriam’s legacy was his effort to classify life zones based on climate. The life zone concept developed by Merriam in 1889 provided a framework for describing areas with similar plant and animal communities. He saw changes in communities followed an increase in latitude at a constant elevation and that the changes were like those seen with an increase in elevation at a continual latitude.

The life zones Merriam identified apply to western North America, but his system did not work well across the North American continent. In addition, Merriam’s system was criticized for being too imprecise. For example, the scrub oak chaparral in Arizona shares relatively few species with the Great Basin Sagebrush Desert, yet Merriam’s system classifies both as Upper Sonoran. However, his observations and system were changed and improved by others. This early research has resulted in the scheme of life zones, biomes, and ecoregions today.