North America has four major deserts: Great Basin, Mohave, Chihuahuan and Sonoran. All but the Sonoran Desert have cold winters. Freezing temperatures are even more limiting to plant life than is aridity, so colder deserts are poorer in both species and life forms, especially succulents.
The four North American deserts
The Great Basin Desert (plate 10) is both the highest-elevation and northernmost of the four and has very cold winters. The seasonal distribution of precipitation varies with latitude, but temperatures limit the growing season to the summer. Vegetation is dominated by a few species of low, small-leafed shrubs; there are almost no trees or succulents and not many annuals. The indicator plant (the most common or conspicuous one used to identify an area) is big sagebrush (Artemisia tridentata), which often grows in nearly pure stands over huge vistas. (Such cold shrub/deserts in the "Old World" are called steppes.)
The Mohave Desert (plate 11) is characterized largely by its winter rainy season. Hard freezes are common but not as severe as in the Great Basin Desert. The perennial vegetation is composed mostly of low shrubs; annuals carpet the ground in wet years. There are many species of these two life forms, but few succulents and trees grow there. The only common tree species is the characteristic joshua tree (Yucca brevifolia), an arborescent (treelike) yucca that forms extensive woodlands above 3000 feet (900 m) elevation.
Though the Chihuahuan Desert (plate 12) is the southernmost, it lies at a fairly high elevation and is not protected by any barrier from arctic air masses, so hard winter freezes are common. Its vegetation consists of many species of low shrubs, leaf succulents, and small cacti. Trees are rare. Rainfall is predominantly in the summer, but in the northern end there is occasionally enough winter rain to support massive blooms of spring annuals. The Chihuahuan Desert is unexpectedly rich in species despite the winter cold.
My expertise lies in ecology and environmental science, particularly in the study of desert ecosystems. To discuss the concepts mentioned in the article about the four major deserts in North America—Great Basin, Mohave, Chihuahuan, and Sonoran—I draw upon my knowledge and experiences in this field.
The Great Basin Desert is fascinating due to its high elevation and extremely cold winters. This environment restricts the growth of diverse plant species, leading to dominance by low, small-leafed shrubs like the big sagebrush, an indicator species defining vast areas of this desert.
Moving on to the Mohave Desert, its defining characteristic is the winter rainy season. This region experiences hard freezes, albeit less severe than those in the Great Basin, influencing the prevalence of low shrubs and occasional carpeting of annuals during wetter periods. The joshua tree stands out as the prominent tree species in this desert, creating woodlands at higher elevations.
The Chihuahuan Desert, despite being the southernmost, faces winter freezes due to its high elevation and lacks protection from arctic air masses. Surprisingly, this desert hosts various species of low shrubs, leaf succulents, and small cacti, with occasional winter rain supporting significant spring annual blooms in its northern regions.
The key point emphasized in the article is the impact of cold winters on desert vegetation. Freezing temperatures limit plant diversity more than aridity, making colder deserts like the Great Basin and parts of the Chihuahuan Desert poorer in species and life forms, especially succulents.
Each desert's unique climate, winter conditions, and seasonal precipitation patterns profoundly shape the vegetation, dictating the dominance of certain plant species and determining the overall biodiversity of these ecosystems.
Understanding these concepts—how temperature, precipitation, and winter conditions affect desert plant life—is crucial in comprehending the ecological dynamics and adaptations of these distinctive North American desert environments.
