Death Valley is a tectonic depression located primarily in Inyo County, southeastern California. Also a National Park, it is known to be the lowest, driest, and hottest area in North America, with its lowest point, Badwater Basin, at 86 meters below sea level. What is unique about the valley is that its geographical features, especially the surrounding mountains, cause air to circulate in a way that maintains its characteristic scorching-hot temperature. Rocks and sand at the bottom of the valley radiate large amounts of heat, which rises along the valley’s walls and falls back down. This air is then heated again by the air pressure of the low-elevation areas, forming an endless heat-trapping cycle. Moreover, the winds that blow through Death Valley contribute to the harsh environment. Occurring due to Pacific fronts, downslope winds dry rapidly on the leeward mountain sides, bringing strong and arid Foehn winds to the area.
Additionally, Death Valley is located east of the Sierra Nevada, a snow-capped mountain range that spans from the Mojave Desert to the Cascade Range. These mountains cause what is called the rain shadow effect: moisture from the Pacific Ocean is pulled upward into snow on the Sierra Nevada, leaving the air dry. As this air descends into Death Valley, it warms, engendering an intense heating effect.
Interestingly, this deadly environment triggers dramatic seasonal biodiversity. Life in Death Valley synchronizes its behavior to the seasonal cycle.
Desert Gold and Wildflowers
Despite Death Valley’s startling name and intense lack of rainfall and moisture, some organisms specialized to the sweltering climate manage to survive. One example of these resilient organisms is wildflowers. Desert Gold is a flower species commonly found in this area. Its scientific name is Geraea canescens, and it is usually one of the most common and first flower species to bloom in the spring, followed by other flower species across the bottom of the valley. Of course, these flowers are merely ephemeral, leaving seeds behind quickly after a short bloom before the heat of summer settles in. The seeds left by these flowers remain in the ground for years, even decades, waiting for a brief period of rainfall in the winter. Wildflowers in Death Valley have adapted to produce seeds with thick and waxy protective coatings, which contain natural germination inhibitors, allowing them to withstand the blistering temperatures for years until the proper conditions arrive.
Floods and Rainfall
Usually occurring during the summer monsoon season of July through August, or during rare storms, sudden surges of water can cause great damage. Death Valley’s soil exhibits a property called soil hydrophobicity, meaning it cannot absorb water from floods at once. Flash floods can send enormous debris down narrow canyons to the valley floor, displace seeds, and leave large deposits of sediment, causing vulnerable plant and animal communities to suffer immediate damage. On the other hand, these floods are accompanied by heavy rain. If the seeds are fortunately not washed away by the flash floods, the deep moisture saturation from this rainfall may cause dormant seeds to bloom during the following spring.
Spring Superblooms
Death Valley is well-known for its superblooms, which begin to occur around spring, when many species of flowers bloom simultaneously. A superbloom is not technically defined but generally refers to a situation where the flowers bloom in massive, continuous patches rather than individually. The flowers will fill out the lower valley until March, and the higher valley comes into bloom in April and continues until June.
While these flowers do exist every spring in Death Valley, superblooms are rare, as they only occur under very specific weather conditions that create the ideal environment for thousands of wildflowers to bloom. Thus, superblooms occur about once a decade, often following the year after heavy rain induced by an El Niño event. Furthermore, the blooming of these flowers in the spring also gives rise to animal communities that consume the small flowers, creating a fleeting food chain. An unusual phenomenon arises: butterflies, bees, moths, and hummingbirds appear in multitudes to eat and pollinate the flowers. In turn, they attract rodents, birds, lizards, snakes, and foxes. Flower species like Desert Gold contribute directly as the primary producers in this short-lived trophic chain, a crucial role of Spring biodiversity in Death Valley.
Summer
Summer is the most difficult season for organisms in Death Valley due to extreme heat and dryness. Most wildflowers have already wilted, leaving seeds behind that will remain dormant until the weather becomes milder. To withstand Summer conditions, local plants and animals display various adaptations to the climate. Plants such as cacti prevent water loss during the day by employing crassulacean acid metabolism (CAM): they open their stomata at night when the temperature is lower rather than during the day. Animals, on the other hand, have a number of behavioral adaptations that are advantageous to their survival. For instance, the desert tortoise spends the majority of its life underground and only comes out onto the land when the temperatures are cooler, as do a number of other animals.
Autumn and Winter
With the arrival of Autumn, there is a gradual decline in Death Valley’s temperature. Animals that avoided activity during daytime become increasingly diurnal. Nocturnal predators such as the desert kit fox and the sidewinder rattlesnake forage longer, while migratory birds begin their southbound journey along the Pacific Flyway in late September. Night temperatures also begin to drop during Winter.
Winter is when temperatures are finally mild, and birds have finished most of their migrations. Reptiles and amphibians, such as the chuckwallas and desert iguanas, perform brumation, which is a state of slowed metabolism and movement in response to colder temperatures. In contrast, large mammals such as desert bighorn sheep and coyotes are still visible. This is also the season when dormant seeds prepare for the arrival of spring, as cooler temperatures and consistent winter rains create an ideal environment for germination. If there is an additional lack of harsh winds, it becomes the perfect setting for a superbloom.
Micro-Habitat Biodiversity
In the past, freshwater lakes provided a suitable habitat for aquatic species. During pluvial periods, a time of significantly increased rainfall and humidity, large bodies of water like Lake Manly covered Death Valley’s floor, allowing ancestral pupfish populations to flourish. However, as the climate became increasingly arid, severe evaporation reduced open water surfaces and degraded aquatic populations, leading to the current landscape of Death Valley.
As many lakes dried up, aquatic organisms became isolated in small, separate bodies of water, such as spring-fed oases and seeps. A primary example of this is Devils Hole, a deep cavern filled with water, which serves as the only natural habitat for the Devils Hole pupfish population. This endangered pupfish has been isolated for 10,000 to 20,000 years and has evolved as a distinct species.
The flora and the fauna of the valley have all adapted to the hyper-arid conditions, as shown by the cacti and wildflower food web. These adaptations, along with seasonal variation in biodiversity, are most apparent in spring when dormant seeds sprout, and the insects, reptiles, mammals, and birds all appear in their own habitats.
There are a number of micro-habitats within Death Valley: sand dunes, springs and seeps, salt flats, and dry lake beds. The sand dunes, such as the Mesquite Flat Dunes provide a stable habitat for a variety of life forms. The springs and seeps provide a home for aquatic organisms and support large mammals that require water. Meanwhile, the salt flats in Badwater Basin and the Racetrack Playa are both extremely harsh environments with low macroorganism diversity, housing only certain bacteria and invertebrates.
The Future and Global Warming
Death Valley ecosystems are not an exception to the effects of global warming. Climate change poses a major threat to the valley’s fragile biodiversity by altering the natural seasons and damaging habitable areas.
Increased temperatures in the region pose the most significant threat to Death Valley ecosystems, as temperatures are already extremely high. Heightened evaporation from water bodies threatens the water supply, the very source of life for organisms. This means that moisture in the soil will evaporate as well, leaving seeds stripped of the chance to sprout. Additionally, animal and plant populations struggle to survive, as the high temperatures rise beyond their physical limits. These organisms will shift upward in elevation to cooler areas to avoid extinction; for species that already inhabit high-elevation regions of the valley, they have nowhere to escape to, causing declines in their communities.
At the same time, global warming negatively affects the valley’s aquatic species. As the water warms, the dissolved oxygen will leave the water bodies; therefore, the water bodies will become hypoxic, making it challenging for organisms in the water to survive and reproduce. In the micro-habitats, such as the Devils Hole and the small springs, increased water temperatures are severe stressors for aquatic populations.
Lastly, warming temperatures in winter and shifting rainfall timing cause phenological mismatches, meaning wildflower species will bloom out of sync with the appearance of other organisms that feed on them, disrupting the ecosystem’s original seasonal flow and ultimately affecting biodiversity.
Conclusion
Every year, Death Valley goes through its four seasons with drastic changes in the landscape, the temperatures, and the organisms. Although it is a climate that seems to be unsuited for life, the plants and animals that inhabit it prove that life can persist. Recently, climate change and global warming have been negatively impacting the fragile ecology of the valley; preserving biodiversity in Death Valley requires a profound understanding of the delicate interactions between the environment and the organisms.
By: Seoyoon Lee
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