Desert Survival Tactics: Trees

Years ago when I first visited Tucson I thought I could never live here because I would miss trees too much. I love the trees surrounding our home in Kansas in every season ­– leaf fall, bare branches silhouetted against a flaming winter sunset, the first hints of green as the earth awakens from its rest, and the shady fullness in high summer. I love it all and I hope to learn to love the desert trees, too.

Now, after living here for three months, I’m just beginning to get acquainted with the Sonoran trees as well as some alien trees in the city itself, such as eucalyptus and the cursed African sumac.

The aliens aside, I’ve found something to admire about the native trees, namely their strategies for survival in an arid environment. The strategy that jumps out at me is their leaves, which are tiny. For example, the native mesquite, which currently is shedding its leaflets in preparation for new growth, has the tiniest leaflets I’ve ever seen.

I’ve never seen the leaves of Arizona’s state tree, the palo verde, but in photos I’ve seen their leaves are equally tiny. This tree is too smart to depend on leaves for its food. The bark and twigs perform most of the palo verde’s photosynthesis, as is clearly evident in their green color.

The tree that has carried this strategy to the limit is Canotia holacanthe, whose leaves are merely tiny scales along its stems, making it virtually a leafless tree. Its smaller branches conduct all of its photosynthesis. We can see why the tree is also called “Crown of Thorns,” even though it isn’t thorny.

The strategy of tiny leaves makes perfect sense for a tree that must conserve water to the utmost. The surface to volume ratio of leaves is high, so that more moisture is lost through large leaves than through tiny ones.  But how did these trees figure that out?

I like to think that trees have intelligence and that they share information with one another. This notion is supported by a German forester, Peter Wholleben, the author of “The Hidden Life of Trees” What They Feel, How They Communicate – Discoveries From a Secret World.” According to a New York Times article about his book, “They can count, learn and remember; nurse sick neighbors; warn each other of danger by sending electrical signals across a fungal network known as the ‘Wood Wide Web’…”*

Who’s to say that the Sonoran trees didn’t hold a think tank and decide to grow little tiny leaves?

*German Forest Ranger Finds That Trees Have Social Networks, Too,” The New York Times, January 29, 2016.

Copyright 2016 by Shirley Domer