Plant Ecology (Desert Institute)


11-13 April 2008





Stefanie Ritter, M.S.,


“was awarded a M.S. degree from the Technical University in Braunschweig, Germany, specializing in zoology, botany, and genetics. She has taught Biology at Copper Mountain College and presently holds the position of Museum Coordinator for the Hi-Desert Nature Museum where she is responsible for all educational programs. Stefanie has also taught geography, ecology, and botany for the National University at the Twenty-nine Palms Campus.”


Mark Wheeler, M.S.,


“M.S. in Education and a journeyman’s degree in natural history, has spent thirty years hiking and studying the mountain and desert landscapes of the west coast. Mark has worked extensively with wilderness-adventure programming groups, such as Outward Bound, training both students and instructors in wilderness travel skills and group dynamics. A working writer, he has focused on subjects about the natural world and is nearing completion of a book on traveling alone in the wilderness for extended periods.”





John Richardson Jr.




I.                     Introduction

a.      6K species, or 25% of the NA flora occur in California; isolated by mountains on east and ocean on west

b.      Desert

                                                              i.      Defined as precipitation of less than 10” per year

                                                           ii.      Mechanism, rain shadow

                                                         iii.      Transpiration (desert looses more water than rainfall)

1.      Cottonwood (native) versus Tamarisk (invasive)

a.      Mesquite uses less than cottonwood (UA Renewal Resources, 1997)

b.      T may use 13.5 gallons/day (up to claims of 200 gallons/day according to NPS)

                                                         iv.      Solar radiation

1.      One megawatt photovoltaic solar power generating system needs nine acres at present

c.       Distribution and interactions in hierarchical order:

                                                              i.      Biosphere, the earth or another planet

                                                           ii.      Region, (e.g., California Floristic Province) “medium-scale area” or highest scale short of biosphere

1.      Great Basin Desert

2.      Chihuahuan Desert

3.      Sonoran Desert

4.      Colorado (combination of 3 and 5; JTNP falls between)

5.      Mojave Desert

                                                         iii.      Landscape, arrays of ecosystems within a region

                                                         iv.      Ecosystem, biotic and abiotic components of environment

1.      Biotic

a.      Producers

b.      Consumers (herbivores, average size: kangaroo rat) or (carnivores, average size: owls, bobcats, and mountain lions)

c.       Decomposers (beetles, fungus, bacteria, termites, ants; fire, carbon into ground)

2.      Abiotic

a.      Minerals in the soil

                                                            v.      Community (aka vegetation type), different species within an environment (influences)

                                                         vi.      Interactions (allocations; flows of energy between —conformers and regulators) such as pollinators (since plants are rooted and can’t get around otherwise):

1.      Energy Flows in primary production (for relationships)

a.      Standing Plant biomass (above ground plants)

                                                                                                                                      i.      Tropical, 1000-3500 grams/square meter

1.      28 grams = 1 ounce; 4 calories per gram

2.      4K-14K calories

                                                                                                                                   ii.      Deciduous, 600-2500 grams/square meter

1.      2.4K-10K calories

                                                                                                                                 iii.      Grassland, 250-1500 grams/square meter

1.      1K-6K calories

                                                                                                                                 iv.      Desert, 0-250 grams/square meter

1.      0-1K calories per square meter

2.      Types of Inter-species relationships

a.      Neither profits, no relationship (neutralism)

b.      One profits, one doesn’t care (commensalism)

                                                                                                                                      i.      Birds nesting in a tree

                                                                                                                                   ii.      Cattle egret in Costa Rica

c.       Both profit (mutualism)

                                                                                                                                      i.      Yucca moth/yucca (total co-dependency)

d.     One profits, other doesn’t (parasitism)

                                                                                                                                      i.      Mistletoe

e.      One profits, killing the other (predatorism)

                                                                                                                                      i.      Venus fly trap

3.      Examples of Relationships

a.      Moths/caterpillars

                                                                                                                                      i.      White/pale color flowers (night-time)

                                                                                                                                   ii.      Strong smells

                                                                                                                                 iii.      Long narrow tubes with nectar

b.      Butterflies

                                                                                                                                      i.      Bright (pastels/bright red)

                                                                                                                                   ii.      Flowers which hang down

c.       Beetles

                                                                                                                                      i.      Large bowl shaped flowers

                                                                                                                                   ii.      Strong smells

                                                                                                                                 iii.      No nectar

                                                                                                                                 iv.      Beetles eat pollen or aphids on flower

d.     Bees (native European, not the honeybee which live in hives)

                                                                                                                                      i.      Yellow

                                                                                                                                   ii.      Patterns/lines to nectar

                                                                                                                                 iii.      Places to land

                                                                                                                                 iv.      Sweet smells

e.      Hummingbirds

                                                                                                                                      i.      Bright colors

                                                                                                                                   ii.      Flowers that dangle

                                                                                                                                 iii.      No place to land

                                                                                                                                 iv.      Deep tubes, lots of nectar

f.        Wasps

                                                                                                                                      i.      Orchids (look like a female wasp)

g.      Bats

                                                                                                                                      i.      Pale colors/white

                                                                                                                                   ii.      Flower open at night

                                                                                                                                 iii.      Large flowers

                                                                                                                                 iv.      Fragrant smells

                                                                                                                                    v.      Lots of nectar

h.      Other interactions

                                                                                                                                      i.      Eating (caterpillars)

                                                                                                                                   ii.      Sleeping (bees in aster)

                                                       vii.      Populations of Plants (six largest families):

1.      sunflower, composite flowers in disk-like heads

2.      grass,

3.      pea, Banner, wings and keel

4.      figwort,

5.      mustard, 4 petals and 6 stamens--4 tall and 2 short

6.      sedge


Aster or Sunflower


flowers with parts in threes; sepals and petals usually identical


5 separate petals and a column of stamens


Square stalks and opposite leaves; often aromatic



Compound umbels; usually hollow flower stalks



                                                    viii.      Individual, organismal (higher, vascular plants, technically, tracheophytes; and lower, mosses for example)

1.      Desert Mallow (Sphaeralcea rusbyi)

2.      California Buckwheat (Eriogonum fasciculatum)

a.      Leaves restricted largely to base of plant

b.      Flowers very small

c.       White, pink, or yellow (Jaeger, p. ***)

3.      Desert Mistletoe (Phoradendron californicum)

a.      Survives on another plant (cat’s claw, Acacia Greggii)

b.      Brack-like leaves, less water loss

c.       Small leaves, less transpiration

d.     Minute, non-showy berries

e.      Waxy coating on stem

4.      Juniper

a.      Low to ground, less evaporation

b.      Small needle like leaves

c.       Dead branches is not due to fire; self-pruning due to drought conditions

d.     Waxy (scrape with knife or may be sticky)

5.      Creosote bush (Larrea divaricata or tridentata)

a.      “widespread, conspicuous, and successful” Jaeger

b.      Tall and rangy, wind evaporates moisture

c.       Tiny leaves, prevent loss of water

d.     Coated to keep in moisture

                                                                                                                                      i.      Rain washes it off, improves photosynthesis

e.      Chemical smell,

f.        Spaced out; doesn’t grow in colonies, due to chemical in roots (neighbors keep their distance)

g.      Drought enduring plant (60-70% of its moisture?)

                                                                                                                                      i.      Old part dies and new clones grow surrounding it so plant lives very long time

h.      Rain

d.     Concepts

                                                              i.      niche (versus habitat or environment) theory = multidimensional space, fundamental versus realized niche; width (see Hutchinson, 1957, for examples).  Fitness or yield

                                                           ii.      competition for light (duration, slope direction and shade), moisture (rainfall and relative humidity), necessary nutrients (n=16?), substrates (pH ranges from zero to 14—acid or alkaline, oceans are 8.1 and desert plants can thrive up to 8.0 or perhaps higher, but using sulfur or lime can be sweetened; texture (sandy—about 1 millimeter--to granules to pebbles to cobbles to boulders—over ten inches, and depth), temperature (proper), plus periodic disturbances (range of tolerance; habitable zone)

1.      when niches are too similar; no overlap, no competition

2.      adaptation (due to environmental pressure)

a.      Chemical weapons

                                                                                                                                      i.      Strong taste/smell (flowers or leaves)

                                                                                                                                   ii.      Desert lavender

                                                                                                                                 iii.      White sage

b.      Small leaves

                                                                                                                                      i.      Loss of water (overheating)

                                                                                                                                   ii.      Antelope bush

                                                                                                                                 iii.      Desert almond

c.       Protective leaf coating

                                                                                                                                      i.      Creosote bush

d.     Hairy leaves

                                                                                                                                      i.      Little hairs reflect solar radiation

                                                                                                                                   ii.      Light color reflects

e.      Folded leaves

                                                                                                                                      i.      California fan palm

                                                                                                                                   ii.      Shaded

                                                                                                                                 iii.      Evaporation

                                                                                                                                 iv.      Needs water (large)

f.        Deep tap root and shallow root system

                                                                                                                                      i.      Honey mesquite (168 foot tap root)

                                                                                                                                   ii.      Creosote bush (25 meters down)

                                                                                                                                 iii.      Constant water supply

g.      Dormancy

                                                                                                                                      i.      Prevents water loss

                                                                                                                                   ii.      Black bush

h.      Upper/lower plants

i.        Escape

                                                                                                                                      i.      Annuals (winter and summer)

                                                                                                                                   ii.      Life cycle is short

                                                         iii.      Germination

1.      Monocots, one leaf, parallel veins

a.      Yucca, grasses, onion, blue dick

2.      Dicots, two leaves branching out, all cactus

                                                         iv.      succession, dynamics of geographical cycles (predictability, convergence, and equilibrium, see Clements, 1904 and 1916)

1.      Six stages:

a.      Nudation, bare area

b.      Migration, arrival on open site

c.       Ecesis, establishment of species

d.     Competition, interaction (“pests”)

e.      Reaction, modification

f.        Stabilization (as a result of five prior stages) or homeostasis

                                                            v.      Botanizing or botanizer

                                                         vi.      Native species (remnants or relics such as fan palms or rare, (paleo)endemism, and extirpated) or

                                                       vii.      Non-native (immigrants from the 18th to 20th centuries, invasive or dangerous such as the Russian thistle or tumbleweed from 1873 or 1877 from the Urals and unknowingly imported by Ukrainian/Russian farmers in SD; arrived in Antelope Valley in railroad cars carrying cattle in 1895)

1.      Fire systems

                                                    viii.      Physiology,

                                                          ix.      anatomy, gross structure

                                                            x.      morphology, structure

                                                          xi.      systematics includes phylogeny (natural relationships) and taxonomy (classifying) and nomenclature (identifying)

II.                Field Work

a.      Dichotomous keying

                                                              i.      Erect/mat

                                                           ii.      Stem = round or square

                                                         iii.      Leaves = ovate or thread-like

                                                         iv.      Veins = 1 to 5

                                                            v.      Inflorescence = see key, fig 4 of Dole and Rose

                                                         vi.      Entire = no teeth, even

                                                       vii.      Glabrous  = hairy or not

b.      Saturday, 12 April 2008, Twin Tanks Parking Area on Pinto Basin Road

                                                              i.      Started little after 8AM from Visitor’s Center

                                                           ii.      Arrived at 9AM light breeze, 78 degrees

                                                         iii.      10:30AM, 83 degrees in gravel

                                                         iv.      Aster with bee

                                                            v.      Mormon tea

                                                         vi.      Onion (lily family)

                                                       vii.      Gilia or desert calico

                                                    viii.      Indian Paint Brush

                                                          ix.      Flies eating aphids

                                                            x.      Mojave mound cactus

                                                          xi.      Claret cup of mound cactus

                                                       xii.      Wallace (rosate) asteroid

                                                     xiii.      Spiny lizard (on rock)

c.       Second Stop on Saturday, 12 April 2008, O’Dell Parking Lot; Light breeze at 11:30AM

                                                              i.      Noon, 103 degrees in gravel; 112 degrees in sand

                                                           ii.      3:20PM, 80 degrees on rock

                                                         iii.      Popcorn, or forget me not (purple sap) (Plagiobothrys)

                                                         iv.      Hole in the sand

d.     Sunday, 13 April 2008, 9AM Pinto Basin Ecosystem, No Wind

                                                              i.      9AM, 88 degrees in gravel

                                                           ii.      10:30AM, 111 degrees in gravel; 122 degrees in sand

                                                         iii.      Pinto mountains ahead

                                                         iv.      Coxcomb to right

                                                            v.      Eagle Mountain Mine (to 1 PM)

                                                         vi.      Hexy Mountains (behind)

                                                       vii.      Good drainage; pinto well, 8-10K year old culture



III.             Useful WWW Sites

a.      “Unit 2: Communities of Life” from “Principles of Biology” at (accessed 8 April 2008)

b.      “Introduction to Ecology and the Biosphere” at (accessed 8 April 2008)

c.       “What is Integrated Pest Management?” at

(accessed 8 April 2008)

d.     “International Code of Botanical Nomenclature (aka St. Louis Code)” at (accessed 10 April 2008).

e.      The Student Conservation Association at (accessed 14 April 2008)—job opportunities

f.        “A Study of The Root Systems of Certain Sand Dune Plants in New Mexico” at (accessed 14 April 2008)

g.       “UC JEPS: Jepson Online” at (accessed 14 April 2008) searchable by Latin binominals or common names plus links to photos

h.      Rebecca Snell’s MS Thesis on Yucca, Ants’ Aphids, and Moths” at (accessed 12 April 2008).


IV.             Useful Books

a.      Marcia Bjornerud, Reading the Rocks: The Autobiography Of The Earth Westview Press, 2005.  --(Lawrence University, Appleton, WI, professor and chair of geology and Fulbright scholar in 2000/2001)





Normal Photosynthesis: Or, How to Make

“Nutritive organic molecules from inorganic sources”

By John V. Richardson Jr.



Let’s start with the simplified biochemistry formula for the normal metabolic pathway (i.e., the series of chemical reactions which produce sugar, or stored energy, from sunlight, etc.) within plant cells:


CO2 + H2O + E = CH2O + O2


On the left hand side (LHS) of the equation, the earth’s atmosphere, which is composed primarily of nitrogen and oxygen, provides the primary source of CO2 (but only about .038% of the atmosphere) and H2O (as rainfall or water vapor or humidity, up to 4% of the atmosphere) while the sun provides the solar radiation or radiant energy (E) which reaches the earth’s surface.  On the right hand side (RHS) of the equation, the reactions produces CH2O, the hydrates of carbon (aka sugar) and O2, which is important in cellular respiration (the opposite of photosynthesis, but more on that latter).

At the first level of our southwest desert ecology pyramid, the primary producers are land-based plants (which can be said to be autotrophic because they are self-sustaining or self-nourishing from inorganic materials, which is a good thing since they are rooted in their habitat and can’t go to McDonald’s at will). Their stomata (or pores in the leaves and stems) take in the CO2 and their roots take in H2O.  This intake is carried out by chlorophyll, which is embedded in the light-gathering cells called chloroplasts, inside the plant, which processes the LHS of the equation, storing glucose and releasing O2.  The specific type of photosynthesis (literally, “gathering of light”) may be characterized as C3, C4, or CAM, depending upon their particular adaptation or water use efficiency (WUE).

The first type is called C3 because the CO2 is taken into a three-carbon compound using an enzyme[1] named ribulose-1,5-biphosphate carboxylase/oxygenase (or, RuBisCO, for short) which is found in the plant’s leaves and is usually active only during the day.  In a C3 plant, the stomata are open during the day and photosynthesis takes place in the plant’s leaves.  The C3 photosynthesis is advantageous in a more temperate climate.  However, one disadvantage of this process is that trapped oxygen (due to closed stomata) is more attractive to the RuBisCO enzyme than CO2 and, thus, photo respiration can occur instead of sugar building.  As a result, the desert plant stops growing, especially if not enough water is available during long, hot, bright sunny conditions.

Most desert plants are C3; examples, nonetheless, include most of the winter annuals (which bloom in the “cool, wet season, and when water is available and conservation is not required” (Sowell, p. 35) and the creosote bush (Larrea tridentata; formerly Larrea Divaricata) which has been described as “the most widespread, conspicuous, and successful” according to Jaeger (1941, #294).  Finally, C3 plants are more efficient than C4 and CAM plants “under cool and moist conditions and under normal light” like the desert’s winter (Fiero, 2006).

The second type is called C4 because the CO2 is taken into a four-carbon compound first for carbon fixation.  Like C3 plants, their stomata are also open during the day, but the photosynthesis takes place in their inner cells.  This time the uptake of CO2 is handled by the phosphoenolpyruvate carboxylase (or just PEP carboxylase for short) enzyme rather than RuBisCO as in C3 plants for photosynthesis, so that photorespiration is less likely to occur.  The primary advantage of C4 is that it works well in intense light conditions and higher temperatures during the desert summers.  Although this C4 process is less efficient, it is also better than the risk of cellular respiration in an unusually hot desert ecosystem. The best examples of C4 desert plants are most of the summer annuals and many native grasses.

The third and final type is called CAM, which is short for crassulacean acid metabolism (and is named after the succulent plant family in which the process was discovered).  Unlike C3 and C4 plants, these open their stomata at night when there is no sunlight, the temperature is lower, and there are slower or no winds.  CO2 is stored as an acid.  The stored acid from overnight is released during the day to the RuBisCO enzyme for photosynthesis; interestingly, though, if water is abundant, then these desert plants can open their stomata during the daytime as well and process the CO2 just like a C3 plant does (a situation which is known as being facultative, able to adapt to different conditions; the C3 and C4 plants are obligate).  The primary adaptive advantage is better water storage and WUE than the C3 desert plants.  Notably, such plants can also “idle” their processing by closing their stomata during the day and nighttime and thus survive under extremely harsh arid conditions.  Examples of such xerophytic CAM plants include many succulents such as the cactus family[2] and agaves, plus the famous resurrection plant which can recover literally within hours after rainfall.

In summary, and risking over simplification, if you see a desert plant in the winter months, it is likely to be C3; during the summer, it is more likely to be a C4 plant; but, if you see a cactus (CAM process) plant, then you know its habitat is likely to be extremely harsh.




  1. Janice E. Bowers, Shrubs and Trees of the Southwest Deserts.  Tucson, AZ: Southwest Parks and Monuments Association, 1993.


  1. Joe M. Cornelius, Paul R. Kemp, John A. Ludwig and Gary L. Cunningham, “The Distribution of Vascular Plant Species and Guilds in Space and Time along a Desert Gradient,” Journal of Vegetation Science 2 (no. 1, February 1991): 59-72.


3.      Brad Fiero, “Types of Photosynthesis,” Pima Community College (Arizona) (1 November 2006; original 2001) at (accessed 14 April 2008).


4.      Fort Hays State University (Kansas), Department of Biological Sciences, “Desert Plants” at (accessed 15 April 2008).


5.      Edmund C. Jaeger, Desert Wild Flowers (Palo Alto:  Stanford University Press, 1941).


  1. Jay W. Sharp, “The Desert Food Chain: How Green Plants Manufacture Their Food,” at (accessed 17 April 2008).


7.      John Sowell, Desert Ecology: An Introduction to Life in the Arid Southwest (2001).


  1. S. R. J. Woodell, H. A. Mooney and A. J. Hill, “The Behaviour of Larrea Divaricata (Creosote Bush) in Response to Rainfall in California,” The Journal of Ecology 57 (no. 1, March 1969): 37-44.




[1] Usually a protein, serving as a “catalyst,” which speeds up a chemical process; as an aside, the term catalyst was coined by the Swedish chemist Jons Jakob Berzelius (1779-1848).

[2] The Opuntia bigelovii, aka Teddy bear cholla, can survive ambient temperatures up to 138 degrees, according to Bowers, 1993, p. 5.