A study of Sonoran Plant Species Densities and Relation to Elevation

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A Study of Sonoran Plant Species Densities and Relation to Elevation


  • The densities of four selected plants characteristic of the region are hypothesized to peak within the elevation region that is most beneficial to the plant species for its survival.

Sky Islands

  • 27 mtn ranges in SW

  • Relatively isolated since glaciation

  • Include Catalinas

  • Unique ecosystems

  • 3,000 ft to 9,157 ft on Mt. Lemmon

  • Includes more than 2,000 plant species


  • Fonquieria splendens

  • be found from southeastern Californian deserts to west Texas and south into Mexico

  • grow mainly in open, stony, well-drained desert slopes below 5,000 feet

  • plant blooms annually, with red blossoms, leafless most of the year

Spoon Agave

  • Dasylirion wheeleri

  • Western Texas, southern Arizona, south and central New Mexico

  • Grows at the elevation of 3000-5000 ft

  • Short, thick, central stem with long, thin bluish-green leaves

  • Flowering stalk grows from the center

Mexican Manzanita

  • Arctostphylos pungens

  • Grows from 4000 to 7000 feet

  • Found throughout Mexico and in California, Nevada, Utah, Arizona, New Mexico and parts of Texas

  • Distinct green, pointed leaf with mix of smooth brown and rough grey bark

Ponderosa Pine

  • Pinus Ponderosa

  • Found at elevations of 6000 to 8000 feet

  • Largely concentrated in Colorado Plateau

  • Reach heights of 30 to 50 meters

  • Egg-shaped, red-brown cones

  • Provides habitat for many forest animals

Materials & Methods

  • 200 ft of rope and 4 stakes

  • Map of Catalina highway

  • Choose and research four plant species

  • Measure out 50’ x 50” squares in desert

  • Count number of individual species

  • Repeat for different area at similar elevation

  • Go through entire process for varying elevations, at increments of 1000 feet


Species Density according to Elevation


  • results were supported given hypothesis

  • For all plants studied densities were highest in the elevation category that corresponded to their optimal environments

  • results obtained by analysis of observed data support the theory that plant densities will be highest at elevations with microclimates that are best suited to each particular plant species


  • revised due to physiological and temporal constraints

  • original plan to randomly select plots at specific elevation intervals not possible with the means that the group had

  • Results still significant despite having to compromise in order to accommodate Catalina Mountains and the highway


  • exemplify the unique ecological diversity of the “sky islands” of Southern Arizona

  • Future preservation of the particular plant species demands that elevation constraints be considered when planting or modifying a geographic area

  • Urbanization must be restricted when it takes over the space at certain elevations needed for specific plant species to grow and flourish

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