Wednesday, January 7, 2015

Christmas in El Paso 1

 The part of the city that wraps around the southern end of the Franklin Mountains.

I remember the first time I laid eyes on the green-spotted tan brown of west Texas from the air, and called it a "substrate-dominated landscape."  Today, many visits later, this northern end of the Chihuahaun Desert has become pretty familiar, though not nearly so much as my native northeast.  Familiar, too, is my packing list, which must include the variety of clothing that can insure comfort outdoors in any weather, my field guides, camera and notebook, a bag for specimens, and a good hat.

Our family has flown to be with my wife's family every Christmas of the twenty-five years we've been married.  Most of these visits have been to New Orleans, where my wife's parents and one brother are.  But as they get older, more and more of them are to my wife's sister's family in El Paso, where she is a librarian, and her husband a UTEP professor. 

Christmas weather in El Paso can range from short-sleeves to warm coat, and sunny to raining or--occasionally--snowing.  (This Christmas was colder there than in eastern Massachusetts.)  But it's the landscape and natural history that really stand out to me. 

Being familiar with another environment is a lot like being familiar with another language: it gives you some objectivity, a place to stand and look back, a standard for comparison.  This is the El Paso landscape's chief value to me.  

 Fairly regular spacing of plants is a feature of this desert.  Another is rocks 
whitened with a coating of calcium carbonate (lime).

The differences must begin with the large scale landscape.  The city of El Paso wraps around the southern end of a small mountain range called the Franklins.  Though my sister-in-law's family now live in a suburban house, their first apartment was on a street that snuggled up to the mountains themselves; it was no big surprise to find tarantulas wandering the parking lot, and scorpions in your shoes.  (A certain small vacuum cleaner was the designated "scorpion sucker.")  As mountains go, the Franklin Mountains have a certain domestic air, since each is topped with an array of communications towers.  Mountains farther off, particularly those in nearby Mexico, are wilder-looking, at least from a distance, and some are so steep in places as to have sheer cliffs.  Eastern Massachusetts, by contrast, is flat or gently rolling; if I want a climb, I drive twenty minutes to Great Blue Hill, which is pretty and a little wild, but seldom at all scary and not a challenge to climb.

The soil is the next surprise--beginning with the fact you can see it.  Most of the underlying rock is limestone, the remains of ancient coral reefs and sea life.  This makes for a brown- or tan- ranging to almost cream-colored soil. 

The Chihuahuan Desert (some would say "semi-desert") gets most of its little rainfall in the summer months, but it can get a little precip in winter, as well.  Because the limestone in the soil dissolves slightly in water, a solution of calcium carbonate sinks deeper into the ground; but since there is usually too little rain to wash it more than perhaps a foot or so, evaporation leaves that lower soil cemented by solid calcium carbonate.  This concrete-like layer (called caliche) makes it even more of a challenge for plant roots.  The topsoil, such as it is, is light in color, but caliche exposed by erosion can be lighter still. 

The plants often stand arms-length apart, giving the appearance of wanting their personal space; in reality, they are mainly staking out area adequate to collect enough rainfall to sustain life.  This regular spacing with mostly bare soil between is what so struck me when I viewed it from the air.

 Arroyo Park (visible in the above image as a flat-looking ne-sw slash just below center
 and extending from the mountain) is a convenient place to encounter nature in relative comfort.  There are places there you could pretend you were not in a large city
--until you are surprised by a jogger or off-road cyclist.

Looking down arroyo southwest.

Looking up arroyo northeast.
Looking across arroyo. 
Fog over the foothills north of arroyo.
Down in the arroyo.
Down in the arroyo. 
 Mountains south of arroyo park, in Mexico.

The iconic plant of the Chihuahuan desert is creosote bush (Larrea tridentata).  Creosote bush is one of the few plants to have leaves and to keep those leaves year-round.  This shrub is able to survive such severe desiccation that its cells are left shriveled but barely alive inside their waxen leaves, but then rehydrate and leap into life when the rains come again.  This gives creosote bush a leg up on cacti--which have no leaves but must photosynthesize with their stems, and plants such as ocotillo, which grow new leaves with every significant rain.

Creosote Bush (Larrea tridentata) survives drought with chemicals
that allows it cells to to dessicate to a significant degree without dying.

Creosote bush has tiny, hard, waxy leaves and gray-furred fruits.

Lechugilla (Agave lechugilla) is the low thick-leaved plant in the foreground,
with creosote bush and the gray-stemmed ocotillo further back.

Though creosote bush is the most visible representative of the desert flora, the indicator plant--the plant that says, "you are now in the Chihuahuan (not Sonoran, not Mojave) desert," is lechugilla (Agave lechugilla).  This spiny, sprawling succulent spreads in colonies of genetically identical individuals.  Each of these grows for years saving up resources, then blowing the whole bank account on one towering flower stalk, and then dying.  

 Some of the neighbors live in houses that cling to the hillsides.

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