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.