Fringe Ecosystems: Ghost Grass and the Sonoran Desert

"One day, Ghost Grass will cover everything, and that's the way the world will end"

-Ser Jorah Mormont, quoting a Dothraki legend, Game of Thrones. 

 On a recent hike through the Sonoran desert, the warm air and fantastic shapes of the cactus around me made it easy to imagine I was diving on a tropical reef. At the same time, I had a strange feeling I was in Africa. Numerous acacia trees created classic Africa skyline sillouettes, and beneath them waved a sea of amber grass. The grass was fully cured, the air was 110 degrees, and monsoonal lightning storms were approaching. Minus the cactus, it looked just like West Africa during the harmattan/fire season.

 But, unlike many Sahel ecosystems, the Sonoran Desert is not fire adapted. It seemed like this impossibly combustible cocktail should have done in the slow-growing saguaros and other cacti long ago. Some research proved the resemblance to Africa wasn't coincidental; African and Mediterranean fire-adapted grasses have invaded the Sonoran Desert, threatening ecological catastrophe. 

 The real-world equivalent of Game of Throne's Dothraki Ghost Grass consists of a sinister trio: Cheat Grass, Buffle Grass, and Red Brome. For Western Deserts, the 19th-century introduction of these old-world grasses was, arguably, the most ecologically consequential event since the last Glacial Period.

 Adapted to Mediterranean and African conditions, inluding drought and wildfire, these grasses outcompete American species, such as sage and native bunchgrass. Cheatgrass, Red Brome, and Buffel grass create soil characteristics unfavorable for native desert plants. Drying out early into continous fuel bed, they carry wildfire across desert landscapes, where plant spacing used to prevent fire from spreading. Invasive grasses have spread throughout the West, from Texas to California, and the Dakotas to Arizona. Below, a field of invasive red brome fills in the spaces between saguaros.

The NPS publishes the guide, seen below, to identifying and eradicating Red Brome. The eradication options (hand-pulling bunches of grass, or five years of annual herbicide application) may work for individual homeowners. Unfortunately, the idea of implementing these on a large-enough scale to protect the vast stretches of Sonoran Desert which have been invaded by Red Brome is laughable.

Arizona and New Mexico are home to the southern fringe of many landscapes, including Ponderosa Forests, Pinyon-Juniper forests, and the Sonoran Desert. These fringe forests represent species inhabiting the southern end of their range- a range that is shifting northwards due to climate change. These days, the unhappy theme of each of my wildfire assignments here seems to be the complete destruction- by fire- of fringe ecosystems that were already stressed by climate change, pollution, and overgrowth, and competition with invasives. Natural forest succession cycles and climactic range shifts occur at too rapid a pace for nature's coping mechanisms to keep up. A forest that used to burn in a mosaic of 5-acre fires over 100 years burns today in a single, 500,000-acre blaze. No refuges for wildlife are left, the soil is baked to clay. When the rains return, no animals remain to greet it from unburned refuges, no green islands of trees are left to reseed the soil. Without roots to retain it in place, the soil is washed away into vast, destructive debris flows. 

 Fringe forests convert to fields of brush, deserts to fields of Ghost Grasses- and fire is the final catalyst.