Invasive Species

In comparison to many other ecosystems, the extreme aridity of deserts can prevent the establishment of invasive plants. Unlike warm climates, only a few dozen species threaten California's desert systems. (11) However, these species are highly productive and can outcompete/replace native species. Often the introduction of one of these species leads to a reduction in native biodiversity. (12) Some examples of these invasives are listed below.

Livestock Production

Livestock production occurs in every desert system, including California. Introduced with the colonization of the Spanish in the 1700s, livestock significantly destabilized the fragile ecosystem. (3) Many of the desert plant species were not adapted to heavy grazing and the natural aridity of the landscape prevented rapid regrowth. (4) When accounting for this grazing combination with dewatering rivers for irrigated forage crops, killing of predators and “pest” species, forage competition between native and domestic animals, soil compaction and erosion, changes in fire regimes, spread of alien plant species, and loss of biodiversity, livestock grazing is the human caused action that causes the most significant impact on desert ecosystems. (4) Livestock grazing activity risks long-term ecosystem damage while often not generating enough revenue to provide for adequate management. (5)

Mining

Extractive mining has occurred in California deserts for over a hundred years. Industrial-level mining such as open pit gold mines, sand, gravel, salt and limestone extraction; as well as concentrated recreational “dry-washing” mining pursuits engaged in by prospector clubs directly destroy habitat and harm the desert ecosystem. (10) Mining also has several indirect effects such as wildlife potassium cyanide poisoning and runoff from mines which causes chemical, metal, and nutrient pollution in nearby waterways. (8) Even abandoned mines, of which there are many scattered through California’s deserts, can cause environmental damage through subsidence and collapse. (9)

Urbanization and Development

Climate Change

Climate models indicate that Southern California’s deserts that average annual temperatures could increase anywhere between 5.4 to 9 °F. (1) However, because this heating will not be evenly distributed over time, this projected rise in temperature will actually take the form of longer and more severe droughts/heat events. This could lead to three months of the year having highs of 114 °F or hotter. (1) Lizards, like the desert iguana or chuckwalla, have a maximum temperature tolerance of 112 °F. (2) This could lead to the displacement or extinction of these species. Chuckwalla populations are already being measured as less healthy (smaller in size) than previous years. (2) This movement has also already been tracked for plant species in the University of California’s Deep Canyon Desert Research Station in Palm Desert. (1) This rise in heat will also have an effect on the timing and abundance of precipitation. (1)