A Study of Sonoran Plant Species Densities and Relation to Elevation

Hypothesis

• 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

Ocotillo

• 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

Data

site Ocotillo 1 Ocotillo 2 Spoon agave 1

Spoon agave 2

Mexican manzanita 1

Mexican manzanita 2

Ponderosa pine 1

Ponderosa pine 2

3500 ft 20 20 0 0 0 0 0 0

4500 ft 18 5 8 3 0 0 0 0

Thimble peak

0 0 10 8 29 15 0 0

Windy point

0 0 2 0 12 9 0 0

Aspen 0 0 0 0 0 0 25 20

Ski valley 0 0 0 0 0 0 29 46

Species Density according to Elevation

3500

5500

8000

Ocotillo Manzanita

0

10

20

30

40

50

60

70

80

Elevation (ft)

Plant

Count

Plant Densities and Elevation

Ocotillo

Agave

Manzanita

Pondorosa

Ocotillo

0

10

20

30

40

50

3500 4500 5500 6500 7500 8500

Elevation (ft)

Number of Plants

Ocotillo

OcotilloH0: X

2=3.84X2

Stop1 17.2Stop2 8.24Stop3 21.0Stop4 21.0Stop5 21.0Stop6 21.0

Agave

0

5

10

15

20

3500 4500 5500 6500 7500 8500

Elevation (ft)

Number of Plants

Agave

Desert Spoon AgaveH0: X

2=3.84X2

Stop1 10.4Stop2 2.44Stop3 5.94Stop4 7.17Stop5 10.4Stop6 10.4

Manzanita

0

10

20

30

40

50

3500 4500 5500 6500 7500 8500

Elevation (ft)

Number of Plants

Manzanita

Mexican ManzanitaH0: X

2=3.84X2

Stop1 21.6Stop2 21.6Stop3 32.3Stop4 0.43Stop5 21.6Stop6 21.6

Pondorosa

0

10

20

30

40

50

60

70

80

3500 4500 5500 6500 7500 8500

Elevation (ft)

Nuber of Plants

Pondorosa

Ponderosa PineH0: X

2=3.84X2

Stop1 400Stop2 400Stop3 400Stop4 400Stop5 1.25Stop6 37.85

Conclusions

• 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

Revisions

• 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

Implications

• 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