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California barrel cactus, Ferocactus cylindraceus. |
Barrel cacti are kind of as their names imply, barrels full of water.
The problem is, the water isn't just hanging out in the cactus like a
big glass of water. The water is stored inside of the cells that fill
the interior of the cactus. The best way to get this water is to eat
the tissue, though it won't taste very good and probably will make you
sick. The thick layer of hooked spines will also deter any person or
animal from easily accessing this water though. In drought however, the
barrel cacti is one of the best sources of water for desert animals
there is, that is, if they can get through the spines. Small animals
like rats, chipmunks, or mice can avoid spines by burrowing underground
slightly to where there are no spines and then eating up into the
cactus. I have actually found a few barrel cacti that have been
entirely hollowed out by rodents, yet have there skin and spines fully
intact. Larger animals such as deer have no such luck though accessing
moisture from a standing barrel cactus though. The spines become just
too big of a deterrent.
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Red spines of the barrel cactus show up after being wet by rain. |
Fortunately, for larger mammals the barrel cactus has a fatal flaw. As a
barrel cactus grows it generally leans towards the southwest, which is
the direction from which the most intense sun comes from. Nearly all
barrels lean to the southwest, just as a compass always points north,
thus the common name compass barrel. It might seem that leaning in the
direction of the brightest sunlight might mean the cactus is trying to
gather as much sunlight as possible. This is however the exact opposite
of what it is doing. With the top of the cactus pointing directly at
the most intense sun, spines at the top actually shade out much of this
light and all sides of the cactus actually avoid this direct sunlight.
The sides however gather the most sunlight from the sides, as the sun
comes up or goes down, when the sun rays are less intense and therefore
less damaging to the cactus. Pointing tops towards the most intense
sunlight is therefore actually a protection mechanism, rather than a
gathering mechanism, against intense sunlight.
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A barrel cactus that fell over due to leaning towards the southwest. Even though this cactus fell over, it continues to grow. |
Leaning is an important adaptive strategy of the cactus, but is this
strength also lays a huge weakness. As the barrel cacti grows and leans
it becomes very off balance. Older, large cacti will often simply fall
over. Oddly, even when the cactus falls over it will continue to live
and grow as it lives laying on the ground. Once the barrel cactus falls
over, the underside of the cactus is exposed which is unprotected by
spines. Large mammals will often start eating the barrel from this
unprotected portion during drought.
I like it, interesting
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