I just love to look at relationships in living ecosystems. Zion is a great place to study them, because the canyons provide micro climates and the whole thing sits on the ecological transition zone between the Mojave Desert and Colorado Plateau. Some of the rocks “weep” as water from above filters down. They keep the otherwise dry area perpetually moist.
Cottonwood ecosystems are among my favorites. Cottonwoods are just tough and resilient. They sink their roots into the moist river bank soil and grow up into the deserts. Cottonwoods do not live long, by tree standards. If you plant one for your newborn child, there is a good chance the kid will outlive the tree. They grow easily from cuttings, and many spring from sticks that just get stuck in the mud and set down roots. Subsequently, they often spread by vegetative means, i.e. not seed. This means that the trees in a grove may be genetically identical and about the same age. That is why they sometimes all die about the same time.
My pictures show cottonwoods at various places in Zion. The sign says that they are Fremont cottonwoods. I really cannot identify cottonwood sub-species, so I take their word for it. Notice the ecological importance of the cottonwood. In the top picture, the protection provides shelter for other plants. In my other picture you see how cottonwoods are sometimes half dead, but they just do not die off. I also included a picture of some mountain goats. I do not know enough about them to write a whole post, but I wanted to include them.