Monday, April 30, 2012

Life of a Cactus Part 1: A Cactus Home

A saguaro cactus in the Sonoran Desert.
So I got a bit carried away with writing about cacti, I think I have at least an eight part series ready to post.  I may be able to add more to that even.  Hopefully its not too boring for anyone because I personally find the existence of the desert cactus quite interesting.  Being the series will be so long I will not post each part in succession, there will be breaks where we have posts of differing subjects.  Hopefully this extended series will spark your interest in cacti!

The Cactus Home

Ask just about anyone why cacti are common desert plants and of course they will tell you it’s because they store water in their stem.  And of course this is true, but it’s only the tip of the iceberg.  Beyond water storage, every part of a cactus is highly adapted to moderately dry desert conditions.  I say moderately dry conditions because extremely dry deserts with say four or fewer inches of rain a year generally do not have many cacti.  Everything needs water, and cacti need slightly more than next to nothing.  Extremely dry deserts are generally barren of nearly all plants, including cacti, except for a few scraggly shrubs.  But even in extremely dry deserts cacti can be found in dry washes, owed simply to the slightly higher concentration of water in these areas after rare flash floods.  Even slightly more than four inches of rain annually, or even double or triple that, is still very dry.  Under these conditions everything seems to work against water storage for the cactus.  Even so, this is where the cactus works best. 
Hedgehog cactus growing in the Sonoran Desert.
Not only are deserts excruciatingly dry due to lack of rain, but many are also excruciatingly hot.  While not all deserts are hot, most cacti find their home in the hot deserts of North and South America.  Dryness only contributes to this heat.  Moisture and humidity work to stabilize temperatures, and therefore prevent extreme highs.  So called desert dry-heat is often oven like due to lack of humidity.  But even in the shade this extreme temperature can be tolerable.  Unfortunately, there is not a lot of shade to spare in the desert.  In more humid environments atmospheric moisture filters large amounts of sun from ever reaching the ground, thus shielding from harsh sun rays and extreme temperatures.  Dry desert atmospheres result in a sun intensity that can be as much as three times greater than humid temperate regions.  So from the simple lack of rain, temperature increases more, robbing even more moisture from everything in the environment.  The resulting low humidity also aids scorching sunlight which again contributes to higher temperatures and lost moisture.  Simply put, dry conditions make it even hotter, which makes it even dryer.  Cacti can thrive under these conditions when most other plants either go dormant or die.

The next part of this series will cover how cacti roots are adapted to the dry desert.

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