Last fall, when I rolled down the leeward side of the Sierra Nevada and landed in the Mojave Desert, I finally understood why the word “enchanted” is so often used to describe the southwestern landscape. To someone born and raised east of the Mississippi, the desert looks impossible, a landscape too strange to exist. Bare ground dotted here and there with lonely shrubs; enormous, rounded boulders piled haphazardly together like toys; the eerie sight of Joshua trees, arms outstretched, waiting for some unknown sign that may never come. I was only able to stay for a few days, but I had a feeling that I would be back sooner rather than later. Lo and behold, here I am, beginning my 24th year as a Las Vegas local, and an intern of the US Geological Survey.
The Mojave Desert, just south of the Hoover Dam.
Compared to the cold desert of the Intermountain West, the warm southwestern deserts of North America have a remarkable history of escaping postcolonial mass disturbance. The Mojave and Sonoran regions are too hot and dry to support large-scale livestock operations, and are not as rich in fossil fuels as their northern counterpart. In short, the landscape didn’t have much to offer, so there was little reason to tear it up. However, in the last several decades rising incidence of severe wildfires and the development of renewable resource infrastructure in the southwest has made ecological restoration a priority, particularly in regards to desert tortoise critical habitat. The Mojave Desert and Sonoran Basin and Range Native Plant Programs were created to begin developing native seed sources for restoration needs in accordance with the national Native Plant Materials Development program. This is a massive, long-term undertaking involving seed collection, genetic and ecological experimentation, and collaboration with an assortment of interest groups, from public land managers to private business owners.
Before any of these steps can be taken, however, land managers must first determine which species to use for landscape-scale restoration. In desert ecosystems, where succession takes place on a scale of decades to centuries, it is particularly important to carefully select pioneer, mid-, and late-seral assemblages that can transition smoothly from one to the next. This is where I come in. My job is to develop lists of priority restoration species for both the Mojave Desert and the Sonoran Basin and Range ecoregions. Both of these programs are in their infancy, so while this internship project is a hefty responsibility, I also have considerable room for creativity.
The first item on my plate is to enhance the Mojave Desert list. For the first few weeks of my internship, I educated myself on the ecology of North America’s smallest warm desert, particularly in regards to succession of disturbed communities and the impact of invasive annual grasses such as Bromus madritensis. Once I felt I had a good working knowledge of the ecosystem, I set to work. Researchers at my field office had already developed a species list regarding the diet and cover plant needs of desert tortoise, but other important taxa, namely pollinators, had been neglected. Using this original list and other literature on diet and cover plants used by G. agassizii as my baseline, I compiled a list of candidates. I then researched each species individually to assess its potential use in restoration projects; this involved researching traits like successional stage, ease of collection, propagation, and seed storage, and whether or not each plant hosted native pollinators.
Desert Globemallow (Sphaeralcea ambigua) with some insect visitors.
Unfortunately, I quickly learned that there is a great dearth of information on pollinators of the Mojave Desert. Aside from a few highly impressive natural history papers from the 1950’s – 70’s, very little research has been conducted on native insects and their relationships with desert plants. Considering that the desert southwest is a hotspot for bee diversity, I found this surprising, not to mention frustrating! A 2006 USDA study found that in Carbon County, NV alone, there are nearly 600 species of native bees, over 30 of which are endemic (for more information, look up the Pollination Ecology Final Report for the Clark Co., NV 2003 Biennium). Environmental heterogeneity in desert regions promotes evolutionary divergence, and speciose taxa range from pupfish to insects to cacti. Combined with a high incidence of monolecty (ecological relationships in which a host species is visited by only one pollinator species), this makes the Mojave Desert a difficult but imperative environment in which to conduct pollinator research.
Much of what pollinator research has been done in the Mojave focuses on Larrea tridentata, the iconic creosote bush. As a ubiquitous, dominant presence throughout the Mojave, Larrea is visited by over one hundred species of bee, twenty of which are specialists. With such a massive guild and widespread distribution, one wonders if creosote facilitates pollination of other desert plants, acting as a pollen “pit stop” of sorts. While L. tridentata already performs many services to its community, if this idea is correct, creosote bush may turn out be even more important to warm desert ecosystems than we realize!
The iconic creosote bush (Larrea tridentata) at the Eureka Dunes in Death Valley National Park.
After several weeks of work, my principal investigators and I are in the revision stages of the Mojave Desert priority species list. Our ultimate goal is to craft a tool that land managers can use in conjunction with seed transfer zones, a novel and instrumental tool to help land managers effectively source native seed for use in revegetation and restoration projects, to make the best choice of a species suite for use in restoration projects. Such tools would expedite the process of restoring public lands with seeds that are best suited to each project restoration site.
In addition to reading papers and writing species profiles, I have had the opportunity to assist with ecotype research at the USGS greenhouse and a few of the common gardens that are established in the Mojave Desert. This spring, we have been growing Chylismia brevipes and Plantago ovata in the greenhouse. Chylismia will be outplanted in a garden south of Las Vegas as part of a study of native plant transplantation methods. The Plantago seeds will be harvested and used in other restoration experiments. Much of the greenhouse work involved daily hand-pollinating sessions for the Chylismia (as we cannot allow it to cross-pollinated between populations and genetically muddy our research specimens) and bagging the P. ovata to ensure that we don’t lose any seed to natural dispersal. In the gardens, I have assisted with monthly plant assessments, conducting morpho- and phenological measurements of Ambrosia dumosa, L. tridentata, Sphaeralcea ambigua, and Achnatherum hymenoides. These assessments are part of a long-term ecological research project on the limitations of seed source in restoration sites across the Mojave Desert. The results from this research further contribute to the development of seed transfer zones.
A suncup blossom (Chylismia brevipes), ready to be hand-pollinated!
A tray of desert plantain (Plantago ovata), some of which has been sacked in order to prevent seed escape!
And, since 40 hours a week of researching and working with native plants isn’t enough, I have also spent quite a few evenings and weekends botanizing in the amazing natural areas that surround Las Vegas. Lake Mead National Recreation Area, Red Rocks National Recreation Area, Death Valley National Park, and Ash Meadows National Wildlife Refuge are just a few of the places I have ventured into, armed with my hand lens and a borrowed copy of the Jepson Desert Manual. As I am not spending a substantial amount of time out in the field during my internship, this is a way for me to both enjoy desert natural areas and begin to learn the flora of the Mojave. A few of my favorite spring-flowering desert plants have been sand blazing star (Mentzelia involucrata), turpentine-broom (Thamnosma montanus), Mojave hedgehog cactus (Echinicereus triglochidiatus), ground cherry (Physalis crassifolia), and desert sandmat (Euphorbia albomarginata).
Ground cherry (Physalis crassifolia), a member of Solanaceae.
Sand blazingstar (Mentzelia involucrata), a member of Loaceae, a family that I’d never encountered before coming to the Mojave!
Whitemargin sandmat (Euphorbia albomarginata), a member of Euphorbiaceae and possibly my favorite desert wildflower.
To my knowledge, this is the first CLM internship of its kind. It’s been very exciting to be part of such groundbreaking work. After my work on the Mojave Desert is finished, I’ll be working on a similar document for the Sonoran Basin and Range – an ecosystem which, with its biannual blooms and distinct subdivisions, may prove to be even more challenging to understand than its northern counterpart.