Ironwood Trees!

I finally saw some ironwood trees. I tagged along on a field trip with a class from Pima Community College. It has been so hot since I've been here that being outside has just not been pleasant. Last week, though, was glorious. As is this week. But anyway, we were west of Tucson in a state park full of classic Sonoran desert plants. Lots of saguaro, palo verde, acacia, barrel cactus, three kinds of cholla, lots of opuntia, mesquite... I even saw lots of little mammilaria plants. I've never seen them in the wild before. One of the students called them "Target plants," because it is one of those classic plants they put in little cactus bowls, which they always have out at Target.

As excited as I was about all the plants, I wanted to write a little about ironwood trees. These trees can get pretty huge for something in the desert. And they can live for hundreds of years (I read 1,500 years in one book!). You can imagine how important such a large tree could be in the desert- it would serve as a great apartment building for birds and would change the micro climate around it, to allow other plants and animals to thrive: an oasis of shade. Here's a picture of one of the biggest trees in the Tucson area, which was right where we were:
For scale, that picnic table could easily seat more than 12 people. I wonder how old this tree is? The trunk was really neat up close: all twisted and craggy and beautiful. Apparently this area got practically no rain this year, so the canopy is much more sparse than usual. Not that these trees have huge leaves anyway. When you grow up in a nice moist place, like I did, you can get the idea that tree leaves tend to be on the big size- like the many species of oaks, magnolias, dogwoods, and maples that I used to press into my childhood leaf collections. But most desert plants have tiny leaves. So the picture at the top is of ironwood tree leaves. They are rather small!

So why the small leaves? It has to do with water loss. Smaller leaves lose less water. This has to do with surface area: that part of the leaf that is exposed to the air around it. Getting rid of leaves altogether is hard, since of course you need leaves for photosynthesis, which is how plants make the energy they need (me, I like to cook a nice pasta with a good roasted tomato sauce). Some desert trees even nearly avoid the leaf requirement altogether: they can photosynthesize in their branches and trunk. These are the palo verde trees. They're easy to recognize because, like Kermit the Frog, they are green all over. I have two of them in my yard, one of which I am constantly doing battle with. As cool as they are to look at, some of them are covered with spines (like the one growing into the gate into my backyard). To the right is a nice close-up I took of a little leaf palo verde.... it is nearly "leaves optional"... What a cool tree!


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