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Foothills of Sonora KIRK ANDERSON, GARDENS COLLECTION MANAGER


A botanically rich but seldom visited portion of T e Living Desert’s gardens will soon be the center of attention. Tucked amid the dappled sunlight and secluding canopy of the Foothills of Sonora Garden, T e Monarch of the Desert jaguar exhibit funded by the William Fries II Foundation is set to open April 1.


Foothills of Sonora was originally defi ned as one of the seven subdivisions of the Sonoran Desert by preeminent desert ecologist Forrest Shreeve. It has since been reclassifi ed as thornscrub or Sinaloan thornscrub and is no longer considered a desert biome. Sinaloan thornscrub serves as the transitional vegetation between the Sonoran Desert proper on the Plains of Sonora to the west and Arizona Upland in northern Sonora, Madrean oak woodlands to the east and the most northern reaches of tropical deciduous forest on the slopes of the Sierra Madre in southeastern Sonora. T ornscrub is said to be the mother of the Sonoran Desert and the tropical deciduous forest its grandmother.


T e Sonoran Desert is a tropical desert with half of its fl ora having ancestry based in the tropics. Insuffi cient rainfall and decreasing minimum temperatures halt the spread of many of the tropically derived species along the increasingly arid western plain and amongst the cooler northern latitudes. T e south to north cooling and west to east drying gradients induce changes in the stature and composition of the vegetation. T e profi le becomes shorter as conditions become colder and drier and the more tender plants are replaced by more drought and cold tolerant species.


Jaguars in the desert? T e region of Sonora, Mexico, represented in this garden is known by some as the Arborescent Desert. T e density of plants in the Foothills region leaves no shortage of cover for these secretive cats and the line between where desert fl ora begins and tropical ends can be decidedly blurred.


T e state of Sonora Mexico contains an amazingly rich heritage of biodiversity attributable to a coincidence of geographical factors. T ese include its latitudinal positioning uniting tropical and temperate climate zones and the convergence of maritime (Gulf of California) and continental (Sierra Madre Occidental) infl uences that set the stage for a multitude of diverse biomes: Sonoran desert, including the subdivisions Plains of Sonora, Central Gulf Coast and Arizona Upland; Sinaloan thornscrub, Sinaloan deciduous forest, Madrean oak woodlands and pine forests. Within each biome there are a variety of geological substrates and topographical features that create niche habitats for further specialization including beaches, coastal plains, mesas, arroyo margins, streams, canyon bottoms, canyon and mountain slopes, cliff s, mountain tops and ridges and swamps.


Sinaloan thornscrub is distinguished from desert by (1) the increased density of plant cover, 20 to 90 percent, in the form of shrubs and short, small-leaved (microphyllous) trees (2) the heavy presence of plants not represented in desertscrub such as boat-thorn acacia (Acacia cochliacantha) and (3) the absence of key Sonoran species such as creosote (Larrea tridentata) and jojoba (Simmondsia chinensis). Small woody and herbaceous shrubs, perennial forbs and grasses make up a larger component of the fl ora and ephemeral annuals less, especially in comparison with our local desert where over 50 percent of the plant species are annuals. T e stature of the irregular canopy varies in height from six to over twenty feet. Some plants typical of Sinaloan thornscrub that make it into the U.S. and reach their northern limit in southern Arizona include feather bush (Lysiloma watsonii, syn. L. thornberi, L. microphylla v. thornberi), yellow bells (Tecoma stans) Sonoran kidneywood (Eysenhardtia orthocarpa) and coral bean (Erythrina fl abelliformis).


T e tropical deciduous forest barely reaches into the Southwest region but in doing so provides the conduit for an exotic array of tropical species. In southeastern Sonora the Sinaloan deciduous forest is relegated to the steep slopes and canyons of the Sierra Madre Occidental where propitious positioning secures increased precipitation and relief from winter cold. T e tropical infl uence is notable due to the presence


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