July in the Sonoran Desert

It is this time of year that the desert waits for the violent monsoon rains.  So far the storms have been hit or miss and much of the desert has not received any significant rainfall.  As is typical, higher elevations are more likely to receive rain than the lower and hotter elevations.  And eastern portions of the Sonoran Desert, such as around Tucson, are far more likely to receive rain than western portions, such as around Yuma. The end of June through mid-July are unbearably hot, highs over 110 degrees are quite common.  Rain has been absent from the desert for months on end, and the desert life hides from the relentless heat and sun.  Life simply dries up or congregates around waterholes this time of year.  Everything becomes sluggish except for the Saguaro fruit ripening which livens things up for a few weeks.  But as Saguaro harvest wains so does activity of nearly all desert life.  The desert simply waits and longs for cooling life giving rain.

An Anvil Cloud that often proceeds a Monsoonal thunderstorm.  An Anvil Cloud is a type of cumulus cloud.

Even though the rains have not come that does not mean the violence of these storms has not come to the desert.  As is typical of the desert, the rain comes with a lot of hype.  Often these monsoonal storms are proceeded by humidity, gigantic anvil clouds, dark stormy clouds, wind, clouds that are raining but rain never hitting the ground, dust storms, and sometimes if we're lucky rain.  This whole process can be quite disappointing to desert dwellers to say the least.  Too often these storms simply end in just a lot of dust, wind, and no rain.  This disappointing end does provide some relief however.  Even in the absence of rain clouds shade some of the suns scorching rays and the rain that never hits the ground still cools the air considerably in some cases.  Humidity that proceeds monsoons can also drop the temperatures five to ten degrees for weeks ahead of the first rains.  In the Sonoran Desert if its not the 110 degree dry heat, its the 105 degree humid heat, you decide what is worse...

Haboob dust storm in Phoenix, Arizona.  Picture from Wikipedia.

Dust storms in the Sonoran Desert are quite the interesting phenomena.  These are not sand storms like in the Sahara Desert, they are actually clay particles picked up and blown around by the wind.  The reason for this is that clay is the smallest dust particle and is easiest to be picked up off a dry landscape and blown around.  The technical name for these "clay storms" are haboobs.  Yes, this is an awkward weird word but it is Arabic, so of course it won't seem normal to English speakers.

Haboobs are very important soil formation events.  All of the dust and clay within these dust storms has to fall on soil somewhere.  Dusts from these storms is deposited on soils and enriches them with magnesium, calcium, iron, and of course clay.  After these things are deposited on soil surfaces, rain water will carry them deeper into the soil.  After thousands of years of this happening iron stains the soil red, magnesium stains rocks on the surface black, calcium forms a rock-like layer called caliche about 2-3 feet deep, and clay forms a dense clay-rich horizon just above the caliche called an argillic (Click here for more info from an prior blog entry).  Caliche and argillic soils are extremely important in determining what types of plants live in a particular locations.  Some plants prefer soils with caliche or argillics while others do not.  More on that another time though.

The rains should come to nearly the whole Sonoran Desert within the next few weeks or so.  That is, at least the eastern portion.  Normally Tucson receives about six inches of rain, Phoenix three, and Yuma less than one during Monsoon season.  But actually amounts vary from year to year.  In Phoenix I have seen years with only a half inch or so, and other years with nine inches.  It has been a few years since we have had a really good amount of rain during Monsoons season, maybe that means this will be a good one!

Eastern deciduous forest dry uplands

A late successional mature dry Eastern Deciduous Forest composed primarily of White Oaks.

The third type of Eastern Deciduous Forest is the dry, or xeric, forest.  These forests are often on hills adjacent to rivers and have sandy dry soils.  Standing on one of these hills, which can be quite large, you might be surprised to know that millenniums ago the hill was actually in the river!  That is, the sandy sediments in and along the river were blown on shore forming sand dunes.  These sandy wind deposited soils, called loess, stabilized when vegetation was established and eventually formed prairies or forests similar to what we see today in the Midwest.  So many millenniums ago the sandy hills that line rivers simply wouldn't have been there.  They would have instead been sandy sediments along the riverbed awaiting winds to blow them away and deposit them as dunes that would eventually turn into hills.  This is not always the case for xeric woodlands but is very often the case.

A loess hill Tall Grass Prairie, Oak Savanna near Cedar Rapids.  This Loess hill is adjacent to the Cedar River floodplain.  It has extremely sandy soil which once resided in the Cedar River until it was blown away and deposited as this hill.  The Red and Bur Oak trees in this savanna are adapted to prairie fires, the dry soil conditions, and are therefore important early successional trees in this type of environment.  A savannah, in the absence of fire, is a type of early successional forest.

One way you can identify loess deposits is to look for sandy soils, especially on hills, that are adjacent to rivers.  The sandy soils are course or gritty feeling and typically light in color, indicating low organic content.  Also, the absence of rocks and bedrock may indicate loess.  These sandy soils drain water rapidly and are warmer, therefore making them dry.  All plants that colonize these areas therefore must be well adapted to dry Midwestern conditions.  While nothing compared to desert conditions, some desert species such as yuccas and prickly pear cacti can on occasion be found here.  And being grasses generally favor drier conditions than trees, prairies often favor these sandy sites.  Red, Bur, and White Oak trees are also well adapted to these dry conditions and will often colonize these areas forming savannas, which is an early successional stage of xeric forests.  These oak species are well adapted to prairie fires, therefore allowing them to survive surrounded by prairie.  Sumac and Red Cedar are also important colonizing or early succession forest species, but these can only grow in the absence of fire.  Oaks and Cedars are very long lived and tough trees.  Cedars have the remarkable ability to grow just about anywhere including out of cracks in rocks.  Typically early successional trees do not survive into later more mature forests but both Oaks and Cedars can survive hundreds of years, seeing a forest from first establishment all the way through late successional maturity.

Oak, Hickory, and Ironwood xeric forest near Cedar Rapids, Iowa.

Typically, once Oaks are established more shade tolerant trees will start to colonize the area.  Hickory trees are one of the more common large trees that come along later in xeric forests.  Ironwood are a common understory tree with dogwoods as a common shrub layer.  With all the acorns and Hickory nuts within these forests they are popular places for squirrels, deer, and turkey.  There are also a lot of fruits present in the dry forests.  Wild Black Cherries seem to have a preference for these sandy soils.  Tree diversity is less in xeric forests when compared to mesic forests and as a result there is less bird diversity, but birds and other animals are abundant none-the-less.  As for bird watching though I typically stick to more mesic forests, but for admiring majestic Oaks and Hickory trees that are hundreds of years old I'll go for the xeric forests.

Old mature White, Red, and Bur Oaks growing in a dry deciduous forest.

Albuquerque Rio Grande Botanical Garden and Aquarium

I recently made a quick trip through Albuquerque and was privileged enough to stop by the Albuquerque New Mexico Rio Grande Botanical Garden and Aquarium (click here for website).  The Aquarium is on the smaller size but has a number of great tanks.  The shark tank was quite impressive and I enjoyed their native fish displays.  I also enjoyed botanical garden, especially the Rio Grande Heritage Farm with their livestock, large gardens, flowers, and orchard.  The orchard was especially impressive to me.  Anyway here are some pictures of the aquarium and garden, well worth a visit is you live in the area or are passing through.  This is an absolutely wonderful place to learn all kinds of things about plants, animals, fish, and farming. 

Prickly Pear Cactus flower

Apache Trout

Purple Cone Flower

Coryopsis

Butterfly garden

Lily pad

Rio Grande Heritage Farm

Rio Grande Heritage Farm