Ecoregions - The Conditions that Determine Native Adaptation

         by Lauren Vanier

The understory in the footprint of the Museum Fire has exploded with wildflowers, likely lying dormant in the seed bank until better conditions arose. In this case, the area is no longer densely shaded.

            Everybody always asks "what is native?" or even "where is it native?" The less frequently asked question is "how is it native?” How is it that there are over 250 species of Penstemon in North America - the largest genus of plants found only on this continent? How do the conditions in our region determine which plants pass along their genetic material? What drives speciation? For a better understanding, we can look to ecoregion mapping to understand the differences in regions, and therefore, how plants have evolved to withstand different environments.

            Between the sun’s “broil” setting at 7,000 feet, the thin air, thin soils, short growing season, and increasingly unpredictable precipitation regime, the plants that have historically grown here in northern Arizona are tough. Plants have evolved over millions of years to withstand these conditions as a requirement for existence. They’ve coevolved with other plants, insects, fungi, birds, and mammals, whether in mutualistic relationships or in response to predation, to create the rich tapestry of diversity that we see today.

            These are some of the features of what is called an “ecoregion.” Ecoregions are geographically defined regions, delineated at multiple resolutions (called ‘levels’), where the type, quality, and quantity of environmental resources are generally similar. They can be identified by the composition of biotic and abiotic phenomena that define differences in ecosystems, including geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology.

United States Geological Survey’s map of the Ecoregions of Arizona.

            The life zone concept, a related approach for ecological mapping, was conceptualized at the base of the San Francisco Peaks - one of the Flagstaff area’s long list of contributions to modern scientific understanding. It was developed by C. Hart Merriam in 1889 during the infancy of the science of ecology. Base camping at Little Spring on the northwest flank of the San Francisco Peaks, Merriam inventoried flora and fauna from the top of the mountain to the Little Colorado River, developing a system that classifies plant and animal life as communities defined by abiotic factors associated with altitudinal and latitudinal gradients.  While this concept proved to be too coarse, it was a solid predecessor to today’s ecoregion delineation.

An assemblage of plants, including a native Elderberry, found at Little Spring, the location of C. Hart Merriam’s basecamp during his expedition where he developed the life zone concept.

            According to the U.S. Geological Survey’s ecoregion map of Arizona, Coconino County alone contains four Level III ecoregions, which are divided into 36 subregions at the Level IV resolution. Flagstaff is within the Level III region called Arizona/New Mexico Mountains that extends along the Mogollon Rim, and at the more specific Level IV resolution, the Montane Conifer Forests. The USGS ecoregion map defines these regions as being “distinguished from neighboring mountainous ecoregions by their lower elevations…indicative of drier, warmer environments, due in part to the region’s more southerly location… These mountains are the northern extent of some Mexican plant and animal species. Surrounded by deserts or grasslands, these mountains in Arizona and New Mexico can be considered biogeographical islands…The region’s plateaus, valleys, and deep canyons are geologically diverse with volcanic, sedimentary, and some intrusive and crystalline rocks.”

            As Gary Nabhan and co-authors wrote in 2002, the Colorado Plateau is considered to be one of the top five American regions north of the Tropic of Cancer in biologic, linguistic, and cultural diversity and endemism, and we are blessed to live within it. However, the region’s diversity is vulnerable to threats, including the encroachment of invasive species and the fragmentation of wild habitats by increasing urbanization. This is where gardeners and non-gardeners alike can step in. Ecoregions can help narrow the focus on how we support the specific biodiversity of our area; by planting even a few natives, our yards, balcony window boxes, roadside strips, and other city infrastructure can become part of the mosaic of evolutionary history of our unique region.

            With the native plant movement gaining traction, resources are getting better and more specific. The City of Flagstaff has developed native plant lists, while most recently, local author Julie Crawford published a guide on Flagstaff area plants complete with illustrations. The Arboretum and Museum of Northern Arizona both boast extensive native plantings. Organizations such as the Arizona Native Plant Society, Homegrown National Park, and the Audubon Society are great resources for regional native plant lists as well. Tucson’s Dunbar/Spring Neighborhood Foresters (neighborhoodforesters.org) is a fantastic example of how neighborhoods can come together to create reciprocal environments within our cities. Flagstaff is an exceptional city in many ways, and together, we can give back to the environments that enrich our lives.

Lauren Vanier, Master Gardener, hopes to promote the idea of mutualism between our landscapes, plants, watersheds, and communities to inspire better stewardship within Flagstaff and beyond. Gardening Etcetera is written for the community by certified Master Gardeners of the University of Arizona's Coconino County Cooperative Extension Master Gardener Program. To learn more visit https://extension.arizona.edu/programs/coconino-county-master-gardener.