Educational Bulletin #16-1 A Reprint of the Desert Protective Council Ed Bulletin #1981-1

Have you ever wondered about sand dunes and why they

are called “living” dunes?

A quick look at the diagram below will give you a clue.

You will find an abundance of life, both inside and on the

outside of sand dunes.

The vast, and sandy open space favors sun-loving annual

plants. These desert wildflowers set seed. For years, and

miles, the wind both gathers and carries the seeds.

The same winds blow the loose sand, forming and

reforming the dunes, their ridges and valleys and ripples.

Dunes may cease to “move” if winds are obstructed or

the loose sands are compacted.

Within the dunes and along their outer edges live many

plants and animals. They depend upon each other for

survival; they depend upon the “living” dunes for survival.

The dune is a wind machine. “Bernoulli’s jet” drops both

sand and seed over the crest no matter which way the wind

blows. Thus the wind-gathered food (seed) is concentrated

daily on the dunes and a gathering of pocket rodents

concentrates nightly on the dunes to feed.

The Sand Dune Community of Life by Roland Ross, Ph.D., professor emeritus California State University, Los Angeles

Photo by Jim Morehouse.

Inner Dune LifeHidden Reptiles

Our Colorado Desert dunes have the usual food pyramid – a broad base of microbial life (bacteria, fungi), eaters of detritus and seeds (crickets), fewer lizards and snakes. Even smaller sand dunes and sand hills have insects, reptiles and plants.

The optimum temperature of desert reptiles (sand contact) is 98-100°F. More than two degrees higher leads to sudden death.4 To be unearthed with day-time sand temperatures much over 100° is to be killed outright – in seconds.

To avoid high ground temperatures, reptiles hide in burrows or holes. Hence people will say: “nothing’s there.” But dunes, small sand hills and stabilized brush-covered dunes are rich in animal life. In Coachella Valley (Edom) Cowles followed the mesquite dune-leveling tractor and collected large numbers of upturned reptiles of 14 species.8

Lower Insect Level“Swimming” down through the humid vadose zone, the

fringe footed lizard detects crickets by pressure sensing, and lives mostly internally in the dune, but rests near the top. “Sandtreading” characterizes various crickets – bristles and pads on the feet enable them to move through the dunes.

Arthropods of the Kelso Dunes include the camel cricket, the sand cricket and two kinds of cockroaches.1 Coachella Valley Dunes also harbor sandtreading crickets and camel crickets.⁵

Outer Dune LifeMost North American dunes have at least one kangaroo

rat. Kelso Dunes have two;1 Mojave and Colorado desert dunes 1-2. But these same deserts have ecologically richer dunes with more pocket rats and mice – up to six species plus a carnivorous mouse.

These six seedeaters vary in weight from 7-100 gm and live together in the dunes without competition (no elimination) since each selects seeds of a size suitable. Researchers check (empty) the cheek pouches of every capture, live or dead, to obtain these size preferences. In the same sand dune no two rats or mice are of the same size, i.e., no two species are equal-sized. This shows a co-existence pattern of long

standing; a remarkable aspect of the dune community.2The dune is a regular and positive (biological) territory

for kangaroo rats and mice. If displaced by dune buggies (to an open desert) each one would be de-tailed (bitten off) by proper territory owners. This loss of their balancing organ is fatal; the evasive leap with right-about turn is impossible; predators snap-up tailless rats and mice promptly.

Gathering Of Predators The seed-gatherers work at night among the dunes – it is

cooler, less windy and safer. Any dune can have five sizes of kangaroo rats in Southern California. Nocturnal predators stalk them, take them each to his own size – kit fox, skunks, snakes, and owls; even the desert coyote runs the dune edge. Badgers also formerly searched dunes for prey.

Dune shrubs and ephemeral dune flowers are a part of the established community. Some, like the creosote bush are many hundreds of years old. Some have been burried by blowing sands. Others are dependent upon specific insects for pollenization. Many species are rare or endangered. Some contribute to medical research.

The Dune CommunityVisible or invisible, each species is an integral member

of the dune community. The inner and outer zones are susceptible to changes, be they natural or man-made.

Never A Drop To DrinkThese kangaroo rats and pocket mice break the rules

– live without drinking water. From the splitting of the seed carbohydrates they manufacture their own water – metabolic water. The first knowledge of non-drinking mammals came from kangaroo rats gathered at the Algadones Dunes (1928-29). (Marine mammals have no fresh water.) The pocket rodents and the dunes go together, and they perish together. Actually these immigrants discovered the California dunes ice-ages ago.

Dietary WaterFemales of pocket rats and mice cannot carry a fetus,

and will not breed, without vitamins and extra water – they ignore pooled or standing water. They obtain dietary water for breeding from green foods.3 If autumn rains only occur, no breeding occurs; autumn and spring rains are needed.

If only spring rains come, then breeding is later in summer.When machines flatten out and compact the open desert

around the dune, there will be no dietary water, no seeds, no reproduction, no life. The visiual blight of mechanical destruction is purely superficial; what we do not see is the total loss, the extinction of the outer dune community.

Mechanical Impacts On Sand Dunes1) When sand dunes are compacted by wheels or

tractor treads:

– vegetation and some animals and insects are killed

indirectly,

– indirectly, plants, animals, insects and the food chain

are altered forever:• temperatures are too high for spring flowers

• perennials and shrubs on the dune fringes are elimi-

nated,

• burrows are mashed,

• moisture content is reduced,

• nearby flatlands are pulverized and blowing dust

increases, increasing the potential for lung disease

downwind,

• unique shrub islands (center of animal life) are oblit-

erated.– the bulk, water content and temperature of the

dunes change:

• bulk decreases, density increases,

• water penetration is reduced by a factor lineally re-

lated to the log of the number of passages, sometimes

approximating 100%

• thermal capacity is increased up to 30%

• at high sun, both soil and air temperatures increase. 6,7

2) Riding down dune shrubs desecrates plants, some de-

cades old, some older than the redwoods. Trees, buried in

dunes, attest to the antiquity of vegetation.

3) Riding down animals and reptiles may result in direct

death or death from stress, dehydration or dislocation.

4) Destruction of rare and endangered species is illegal.

Tender Loving Care Of Dunes CommunitiesSpecial race routes or play areas should be prepared with

instructions, guides and information flyers.Free vehicle use of any or all of a dune should be

carefully controlled.Developments should not impact or destroy dune systems.Listening, observing, walking through or visiting dunes,

by day or night, should be arranged by management. Visitors to dunes are “guests” of the Dune Community.

Visitors and managers should upgrade their thinking: they should label any natural dune “A Dune Community: A Living Sand Dune.”

Enjoy Your Next Visit To

“A Sand Dune Community Of Life”

Bibliography:

1Shelford, V. E. ‘64. The ecology of North America. U. Illinois Press, p. 389.

2Brown, J. H. & Lieberman, S. R. ‘73. Resource utilization and co-existence of seedeating desert rodents in sand dune habitat. ECOLOGY 54:788.

3Beatly, Janice C. ‘69. Dependence of dune rodents on winter annuals and precipitation. ECOLOGY 50 (4):721.

4Cowles, R. B. Nov.1, ‘39. Possible implications of reptile ther-nal tolerance. SCIENCE 90:405.

5Tinkham, E. R. ‘66. New genus and species of Stenopelmatus cricket. BIOL. ABSTRACTS 52:909; 52:113, ‘63. Same for Kelso Dunes. GREAT BASIN NATURALIST 25:63.

6Liddle & Morse. Dec. ‘74. The microclimate of sand dune tracks: the relative contribution of vegetation removal & soil com-pression. J. APPL. ECOL. 11 (3):1057.

7Liddle & Grieg-Smith ‘75. A survey of tracks and paths. J. APPL. ECOL. 12 (3):893.

At the Algodones Dunes

Tandesert sandis heaped in ancientwaves, breaking over androlling silent, instillness andsun.

We shuffle upThe slipface, we are seeking thereclusive endangered species and we are wanting.We walk in psammophillic wonder in -- we have botany, and taxonomic differentiation toworry about -- plus our cars, and bills waiting at home (where we get our mail butnot where we’re from). Desert plants have shallow roots: they extendmany meters, and their seeds can travel long distances onthe wind, but listen; we saw a four-foot tuft of grassrustle in the dry hot breezes, we know it hassoftly swayed in this very spot fora century or two yet wewalk, with yearningfor our ownHome.

Wewander over thedunes together, stem and rootand mind and compassion, we slip through thesands, you and I, and eventually the seed lands, we watchthe rain (the promise fulfilled) fall, we turn our palms up to the sky.The grains of the Algodones roll downwind, bury the roots,expose the new soft stems, and we are fragile too, likefresh spring leaves in the hot sun, we feardesiccation, boredom, indifference,predation; we are unsurethat once planted, wewill, assuredlybloom.

Glamis, California, Spring 2000

Jim Ricker