The Greening of the Great Basin
The bleak landscapes of the American West have often been used as shorthand for both the imagined freedom of the wild west and the dangerous barrenness (see: the last film Don’t worry dear). If there is a direct opposite to this eremophobia, it may be specifically the American desire for grass and all its suggestions of order, abundance, and prosperity. These tropes, however, are being tested in the face of rapid climate change and globalized plant exchange, where shifting biomes and invasive species are forcefully reshaping entire ecosystems.
The arid and semiarid Great Basin of the western United States includes parts of California, Nevada, Utah, Idaho, and Oregon and may be described differently by its hydrology, topography, or biology. Biologically, the area has historically been defined by native fungi and shrubs that thrive in the dry valleys of the Sierra Nevada and Cascade Mountains. But as a recent study undertaken by researchers at the University of Montana and the Department of Agriculture points out, these native plant communities are rapidly being colonized by non-native annual grasses such as cheatgrass (Bromus tectorum), red bromide (B. rubens), and Medusahead (Taeniatherum caput-medusae) to the detriment of wildlife and humans.
To the casual observer, the greening of a desert may not seem like a problematic development. Global efforts such as the Great Green Wall in the Sahara and China’s reforestation of the Gobi suggest that native desert ecologies are unsafe and unfit for human habitation. But desert ecosystems are delicately balanced webs among the global patchwork of biomes, and exotic vegetation that replaces native biotic communities—such as non-native grasses in the Great Basin—can fundamentally disrupt plant, animal, and plant populations. and people. According to Smith et al., “among diverse ecosystems across several continents, the consequences of grass invasions include increased risk to human life and property from larger and/or more frequent fires. […] disruption of hydrological and nutrient cycles [….] and reduced biodiversity at all trophic levels.”
The conversion of vegetation in the Great Basin to herbs “also includes [a] significant loss of biomass carbon’ and eliminates key species such as They also make the area more flammable: grasses form a path between different groups of native grasses and shrubs, allowing fires to break out. Grasses are then among the first species to reestablish in the environment after fire, creating a cycle of invasion, fire, and exclusion of native competitors. And as the climate has warmed, conditions have allowed grass to thrive at higher and higher elevations in the upland areas of the Great Basin.
Using high-resolution Landsat satellite imagery in a program known as the Rangeland Analysis Platform, Smith et al. determined the dominance of annual exotic grasses for each year between 1990 and 2020 for three regions of the Great Basin. The program sorted each pixel of the images into visible clusters, allowing the researchers to calculate and map the areal spread of grass over thirty years, revealing a greater than eightfold increase in annual grass cover between 1990 and 2020 at a rate of more than 2300 km2 each year—a rate proportionally greater than the recent deforestation of the Amazon. Smith et al. conservatively estimate that exotic grass accounted for 77,617 km2 of the Great Basin in 2020, or about one-fifth (19.8 percent) of the historically defined range areas.
Recovery of scrub from exotic grasses would require sustained and aggressive intervention. Given the limited material resources and social support for this type of entrepreneurship, Smith et al. advise that the best course of action will be to prevent any further land conversion. “Without increased investment and a paradigm shift in management mindset,” they warn, “the archetypal Great Basin shrubland ecosystems could be largely transformed into highly flammable, impoverished, year-over-year dominated grasslands and forests.”
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By: Joseph T. Smith, Brady W. Allred, Chad S. Boyd, Kirk W. Davies, Matthew O. Jones, Andrew R. Kleinhesselink, Jeremy D. Maestas, Scott L. Morford, and David E. Naugle
Diversity and Distributions, vol. 28, No. 1 (January 2022), p. 83–96