This is the third in a series of posts on carbon fixation in Mohave desert plants. In this post we will focus on plants that use CAM carbon fixation which includes cactus, yucca and agave. The most important benefit of CAM to plants is the ability to leave most leaf stomata closed during the day. Plants employing CAM are most common in arid environments, where water comes at a premium. Being able to keep stomata closed during the hottest and driest part of the day reduces the loss of water through evaporation and transpiration, allowing such plants to grow in environments that would otherwise be far too dry. Plants using only C3 carbon fixation, for example, lose 97% of the water they take up through the roots to transpiration – a high cost avoided by plants able to employ CAM. The Mojave Desert is the northernmost “hot desert” in North America and essentially a transition land between the Great Basin and Sonoran. It’s the smallest of the Big Four, covering some 54,000 square miles of southeastern California, southern Nevada, and itty-bitty strips of southwestern Utah and northwestern Arizona. Roughly speaking, the Great Basin Desert yields to the Mojave at the northern range limit of creosote bush, the defining shrub of North America’s hot deserts; its distribution essentially outlines them. You can rightly think of it as the hot-desert equivalent of big sagebrush. But the trademark plant of the Mojave, the one whose geography basically maps out this desert, is the Joshua-Tree. This outsized yucca actually flourishes best on the Mojave margins, reaching peak development on middle slopes of foothills and bajadas. Interestingly, the Joshua-Tree uses C3 carbon fixation while most of the remaining yucca and agave use CAM carbon fixation, along with all of the cactus species.
Since we were in Santa Clarita for the past two weeks, caring for our grandson, we decided to visit the Angeles National Forest to see the wildflowers. The Angeles National Forest (ANF) of the U.S. Forest Service is located in the San Gabriel Mountains and Sierra Pelona Mountains, primarily within Los Angeles County in southern California. The ANF manages a majority of the San Gabriel Mountains National Monument. The San Gabriel Forest Reserve was established on December 20, 1892, the San Bernardino Forest Reserve on February 25, 1893, and the Santa Barbara Forest Reserve on December 22, 1903. They became National Forests on March 4, 1907, and they were combined on July 1, 1908, with all of the San Bernardino forest and portions of San Gabriel forest and Santa Barbara forest composing the new Angeles National Forest. On September 30, 1925, portions of the Angeles National Forest and the Cleveland National Forest were detached to re-establish the San Bernardino National Forest. Angeles National Forest is registered as California Historical Landmark, for being the first National Forest in the state.
Most people who do not live in a desert environment consider cactus to be an unattractive species. Nothing could be farther from the truth, cactus are a beautiful species, similar to euphorbia in Africa. Euphorbia can be found all over the world. The forms range from annual plants laying on the ground, to well developed tall trees. In deserts in Madagascar and southern Africa, convergent evolution has led to cactus-like forms where the plants occupy the same ecological niche as cacti do in deserts of North America and South America. The genus is primarily found in the tropical and subtropical regions of Africa and the Americas, but also in temperate zones worldwide. The 1,500 to 1,800 species of cacti mostly fall into one of two groups of “core cacti”: opuntias (subfamily Opuntioideae) and “cactoids” (subfamily Cactoideae). Most members of these two groups are easily recognizable as cacti. They have fleshy succulent stems that are major organs of photosynthesis. They have absent, small, or transient leaves. They have flowers with ovaries that lie below the sepals and petals, often deeply sunken into a fleshy receptacle (the part of the stem from which the flower parts grow). All cacti have areoles highly specialized short shoots with extremely short internodes that produce spines, normal shoots, and flowers. In Las Vegas we have one of the best cactus gardens in the world at the Ethel M Botanic Garden.