Lessons from Travels: Desert Plants

by Carl Strang

Last week’s focus was on some commonalities between plants of the Alaskan tundra and those of Illinois. Today it’s about contrast. There is not much that seems familiar in the dominant plants of the continent’s southwestern deserts. It’s worth the trip just to see some of the iconic species:

Joshua trees. Note the cumulus cloud that has formed above the mountain, where convection is carrying the paltry bit of humidity up to where it meets air cool enough for condensation.

Joshua trees. Note the cumulus cloud that has formed above the mountain, where convection is carrying the paltry bit of humidity up to where it meets air cool enough for condensation.

Saguaro, hundreds of years old.

Saguaro, hundreds of years old.

And my favorite, the ocotillo.

And my favorite, the ocotillo.

Here’s a closer look at ocotillo in leaf:

During the relatively brief time when the ocotillo is not just bare branches, its stems become covered with tiny leaves.

During the relatively brief time when the ocotillo is not just bare branches, its stems become covered with tiny leaves.

These little leaves photosynthesize like mad in the desert sun, taking advantage of a brief period when there’s enough soil moisture to support them. Surviving on low rainfall is the theme in desert plant ecology, and various plants accomplish this in different ways. Cacti photosynthesize in thick, wax coated stems rather than moisture-draining leaves.

Cactus in bloom, a Mammillaria, I think. The leaves are in the form of protective needles.

Cactus in bloom, a Mammillaria, I think. The leaves are in the form of protective needles.

Animals can take advantage of those needles’ protection.

Cactus wren nest in a walking stick cholla cactus.

Cactus wren nest in a walking stick cholla cactus.

Another dramatic sign of moisture limitation is the plants’ spacing.

Note the bare soil areas between these evenly spaced plants.

Note the bare soil areas between these evenly spaced plants.

Their roots have staked out territories as surely as a great horned owl’s hooting. This moisture’s mine!

Photos can only partly convey the beauty of these places, and the value of their quiet. Photos cannot begin to express the sensations of heat, of sun, of the dry air. Also there’s some history missing. Many of these desert places were grasslands, the grasses growing when they got moisture, then allowing their tops to senesce in dry times like the ocotillo. Cattle grazing converted many desert grasslands to desert shrublands, as Aldo Leopold and other early ecologists pointed out (I believe this is true in particular of the last photo above, dominated by creosote bush, which not only has small waxy leaves but is distasteful to cattle).

The deserts are worth exploring and experiencing, if only to help us understand our own home landscape better.

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