A Journey to the Desert's Edge, Part Three

Note: this is the third in a series of occasionally appearing entries focusing on deserts in general and the drylands of West Texas in particular

The nature of a place is seen in what the soil nourishes when there is little or no human interference...

Such was the philosophy guiding Forrest Shreve.  An ecologist before the term became fashionable, Shreve became familiar with plant life, first in his native Maryland and then later on the island of Jamaica, before taking a job with the Carnegie Institution's Desert Botanical Laboratory in Tucson.  His great gift to those of us enamored of North America's drylands was a 1942 article and map dividing the continent's arid regions into four distinct ecosystems based on the plant life in each region:  the Great Basin, the Mojave, the Sonoran, the Chihuahuan...

Forrest Shreve's Desert Country, 1942

Shreve's proposal represented a semi-major shift in scientific thinking about the deserts of the Lower 48.  A few years after Wladimir Koeppen divided dry regions into arid and semi-arid places, a 1906 New York Times article touting work at the Carnegie lab noted "two great desert areas"-- a Sonora-Nevadan and a Chihuahuan-- had been delineated in North America by geographers, botanists, and meteorologists... 

As Shreve rambled across the dusty Southwest and northern Mexico, he noticed some species grew almost everywhere he traveled but others sprouted only in certain areas.  (The reason for such localized growth, we now know has much to do with adaptations to varying soils types, rainfall patterns, and seasonal temperature fluctuations.)  Creosote bush pops up from sun baked west Texas to bone dry California but the desert traveler finds saguaro cactus towering over gravelly hillsides in northern and central Arizona and parts of California.  Tarbush fails to thrive where that magnificent giant flourishes.  Its home appears to be only in southwest Texas, southern New Mexico, and a tiny corner of southeastern Arizona...       

Forrest Shreve, circa 1940

Approximately 1500 years ago, native people abandoned their settlements on the upper elevations of Tumamoc Hill about a hundred miles from the last Arizona tarbush stands.  Exactly why they left a place their ancestors had lived for a thousand years is unknown but archaeologists tell us they began using the mesa as a place of ritual, ceremony, and religious pilgrimage.  The base of Tumamoc Hill later served the Hohokam who came after these people.  It became a farming area and agave plantation centuries before Columbus visited the New World.  By the late 19th century, Tumamoc was a grazing site for the cattle and goats of white settlers, site of a basalt quarry, and home to a hospital directed by Sisters of St Joseph of Carondelet...

Tumamoc enters our story about desert plants thanks to questions Frederick V Coville asked himself in 1891 while he explored Death Valley, hundreds of miles away from a barren corner of southeastern Arizona.  How could plants survive the heat and aridity of such a hellish place and how could there possibly be such a variety of things growing in an area so desolate?  He pondered these mysteries for more than a decade...

Tumamoc Hill

In 1902, a gift to the nation from its richest immigrant, a man considered second only to John D Rockefeller of Standard Oil Company fame in terms of personal wealth, helped Coville begin searching for answers... 

Andrew Carnegie came to the United States as a boy.  Born into a family of weavers, the young Scotsman found work in 1848 at age 13 as a cotton mill bobbin boy.  He considered himself lucky to change large spools for twelve hours a day for six days a week for less than two cents for an hour.  Young Andrew was ambitious.  He left the mill to become a messenger for a telegraph company, paying attention to every detail of his work and the financial transactions conducted by wire.  His job offered free passes to a local theater troupe's performances of Shakespeare's plays.  Carnegie took advantage of this as well as a chance to improve his education when a well-to-do Colonel James Anderson opened his personal library of 400 volumes to poor lads hoping to better their station... 

Bold yet wise in his investment strategy, Carnegie rose rapidly in the business world and ultimately became the prime organizer of the United States Steel Corporation, a man whose fortune was estimated at around thirty million dollars when he died in 1919.  It would have been larger but he'd already given $350,000,000, possibly a bit more, to charitable causes.  Carnegie, who limited personal expenses to no more than $50,000 yearly, viewed himself as a trustee of wealth meant to better mankind, most especially the working poor who toiled long and hard and saw but very little for their labor...   

Andrew Carnegie with canine companion

Encouraged by President Theodore Roosevelt, Carnegie funded an Institution whose mission was to increase educational opportunities and spread scientific knowledge.  Frederick Coville who had asked himself questions about plants in Death Valley was now chief Botanist for the United States Department of Agriculture.  He applied to the Institution for a grant to learn how plants survive hot, dry environments.  The Carnegie approved $8000 for this laudable endeavor, directing Daniel T MacDougal to assist Coville in finding a suitable location for the necessary laboratory.  The pair jostled through the southwest and Mexico until they chanced upon Tumamoc Hill near the bustling city of Tucson...

MacDougall and Coville established their facility in October 1903.  Devoted strictly to desert vegetation studies, it attracted Professor Volney Spalding who had taught the world's first true course in forestry at the University of Michigan more than twenty years earlier.  Spalding brought more to the Desert Botanical Laboratory than his personal expertise.  He brought his wife Effie.  Academically qualified in her own right, she published Tumamoc's first research paper in 1905 on the topic of how saguaro cactus stems expand to hold water made available by rain and contract as the succulent uses moisture...

Forrest Shreve found his way to the Desert Botanical Laboratory in 1910.  The Sonoran landscape he trekked more than a century ago no longer exists just as the western Concho Valley of Texas which Vernon Bailey and Harry Oberholser traveled in 1899 and 1901 remains only in photographs taken during their expeditions...

Western Tom Green County, Texas, near Twin Buttes, 1901

Desertification is a phenomenon puzzling to those of us who don't fret over the condition of the drylands.  It is the reason Shreve would no longer feel entirely at home in the empty land outside Tucson and why John Chisum-- known to many of us courtesy of John Wayne's movie about him--- might refuse to believe he'd grazed cattle in the Concho Valley on his way to building a ranching empire in Lincoln County, New Mexico.  How can an arid or semi-arid environment, desert by definition, become a wasteland less capable of sustaining life?  Climatic changes (severe drought or a long term increase in aridity, for instance) plays a role but not as significantly as a person might think.  Desert plants, after all, adapt not only to dryness but erratic rainfalls in the hard country...

Western Tom Green County, Texas, near Twin Buttes, 2011

Human activity usually works hand-in-hand with long dry spells to make arid lands even more desert like.  When I feel the personal need for a tirade, I rant about overgrazing rangeland and farming areas with poor soils and erratic rainfalls.  Mining operations also take their toll.  Desert environments are the product of tens of thousands of years that have a created a delicate ballet of plant and animal life on a stage of surprisingly fragile soils.  Even the simplest human activity can disrupt Mother Nature's dance.  Towards the end of the 19th century, settlers decided to help desert streams and rivers keep their banks safe from erosion.  They planted salt cedar...

Roads to ecological hell can be paved with good intentions, the grandchildren of these settlers learned after salt cedar established itself along desert waterways.  The genus Tamarix is native to the drier regions of Eurasia and Africa.  It is rarely damaged by the occasional wildfires sweeping across southwestern Texas.  Extremely long taproots and adventitious roots that form in unusual places of the plant guarantee its ability to drain both nearby streams and underground water sources dry.  Making our non-native salt cedar an even more ideal candidate for environmental disaster comes with its ability to take salt from deep groundwater, distribute it throughout its leaves, and then deposit it on the soil surface surrounding the plant without causing damage to itself.  Good for salt cedar, not so good for native vegetation...

Salt cedar, O C Fisher Reservoir, San Angelo, Texas.  A single
plant can lose 200 gallons daily through evapotranspiration, a
charateristic that is not useful in the semi-arid West Texas desert

How has this non-native plant and the proliferation of H2O guzzling native mesquites brought on by overgrazing affected my part of Southwest Texas?  The Concho River proper actually begins in the city of San Angelo at the junction of three smaller streams imaginatively named the North Concho, the Middle Concho, and the South Concho.  In the 1850s, all three were perennial streams-- each one of them deep, fast running, and somewhat dangerous...

 

About 50 years ago, the North and Middle Concho began showing fairly serious signs of distress after a seven year dry spell compounded by farming and damaged rangeland.  Today, the South Concho still flows but is akin to Uncle Joe from the old television show Petticoat Junction-- movin' kind of slow.  According to the United States Geological Survey, the Middle Concho gave up its last measurable discharge in June, 2009.  I personally have not seen water in the North Concho except for short-lived puddles after rains for more than year now...

Salt cedar (Tamarix spp) has wreaked havoc on the Concho,
Pecos, and Rio Grande riparian habitats of southwestern Texas

Forrest Shreve's Sonoran Desert has seen its own changes.  Human activity promoted the spread of buffalo grass, more at home in semi-arid desert grasslands than in arid deserts.  Areas that were once bare soil are now carpets of short, dried grasses waiting for lightning strikes or a tossed cigarette to create a raging inferno on land that once had no fear of fire...

North Concho River, 2011

Note: All images located through Google Images without source information except as follows: Forrest Shreve circa 1940 and North American Deserts According to Shreve (1942) from The Encyclopedia of Earth (eo.org); Tumamoc Hill from the University of Arizona News; Twin Buttes Area circa 1901 from Texas Natural History: A Century of Change by David J Schmidley (Texas Tech University Press, 2002); Salt Cedar Invasion Map from southwestclimatechange.org; Twin Buttes Area circa 2011 and North Concho River by San Angelo State Park and Salt Cedar at O C Fisher Reservoir by Louis R Nugent.