Sonoran Desert - Code: Ne2B

The Sonoran Desert is the lushest and most iconic of Nearctic desert landscapes. This botanically diverse desert is home to some of the strangest flora on the continent, including the emblematic Saguaro (Carnegiea gigantea) and colossal Mexican Giant Cardón (Pachycereus pringlei) cacti and the otherworldly Boojum Tree (Fouquieria columnaris). The spectacular flora and fauna here are best seen in April–May or in the monsoon period of late summer, when animals are active and the landscape is green. This habitat is open enough that it is easily walked through, though spiny plants and midday heat should be avoided.

The Sonoran Desert is the hottest of the Nearctic desert regions, with mild winters and scorching summers, when temperatures approach 120°F (49°C), especially along the lower Colorado River. There is some relief from the summer heat when monsoon rains in July and August cool things off by roughly 10°F (5°C). The monsoons drop about half of the region’s annual rain in intense and unpredictable late afternoon thunderstorms. The intense burst of plant growth following monsoons is accompanied by widespread herp movements and the re-nesting of many bird species. This period is often called the “Second Spring” and is the best time for wildlife observation. The rest of the region’s rain falls more consistently in December and January, for an annual total of 3–20 in. (75–500mm).

The most notable botanical feature here is the array of giant cacti, which are often the tallest plants. Saguaro grows to heights of 50 ft. (15m) and Organ Pipe Cactus reach 20 ft. (6m). These widely spaced cacti live for centuries and serve the same function as trees for cavity-nesting birds. Along with these giants, there is a large variety of common, smaller succulents, including agaves (Agave spp.), yuccas (Yucca spp.), barrel cacti (Echinocactus spp.), pricklypears (Opuntia spp.), and chollas (Cylindropuntia spp.). Apart from the succulents, the other common plants are thorny shrubs and small trees, which are the dominant vegetation by area, if not by mass. The most prominent of these shrubs is Creosote (Larrea tridentata), the most common plant in this and many other Nearctic desert shrublands. Paloverdes (Parkinsonia spp.), mesquites (Prosopis spp.), Catclaw Acacia (Senegalia greggii), Ocotillo (Fouquieria splendens) and Desert Ironwood (Olneya tesota) are also abundant. In areas with higher amounts of available water, mesquites can form impenetrable thickets. In the foothills and upper elevational limits, this habitat can form dense brushy patches that are structurally like chaparral and are prone to fire. Despite the structural difference, floral and faunal composition remains nearly identical.

The Vizcaíno-Baja California Desert subtype of the Sonoran Desert habitat covers most of the Baja Peninsula and are notably different in appearance.  Coastal areas are dominated by the massive Mexican Giant Cardón. This is the largest cactus on the planet and reaches 60 ft. (18m) in height. Other prominent features on the landscape include numerous Boojum trees and small stands of squat-gnarled Elephant-trees (Bursera spp.). This subtype is found in the driest sections of the Sonoran desert and typically lacks many of the low thorny shrubs found in the n.Sonoran Desert. This subtype has the most diverse array of small succulent plants and cacti in North America and is arguably the most spectacular and alien desert landscape on the continent. 

Near springs and areas of abundant water in the lower Colorado and Baja sectors Palm Oases occur. These tall isolated forests have a canopy strongly to completely dominated by California Fan Palm (Washingtonia filifera), with an understory of alkali sacaton (Sporobolus airoides) and wiregrass (Aristida spp.).