After six years of living in Arizona, I had never visited the Grand Canyon. That finally changed this year. It was a marvelous ecological experience. The descent into the canyon is a journey back in time that ultimately reaches basement rocks that are nearly two billion years old. And it is also a journey through climate space, from the cold forests of the rim to the warm deserts of the river.
The top is covered by conifer forests – pictured here is the Colorado piñon (Pinus edulis).
Five thousand feet of elevation change covers a temperature differential of at least ten centigrade degrees. Looking down from the top, it is hard to imagine such a radical climate change could be tucked into the narrow bottoms of the rock layers.
But things change – here, about halfway down, western redbud (Cercis canadensis, blooming magnificently in purple) and other less hardy species begin to appear.
Further down the narrow side canyons begin to transport surface water. Dry ridges host warm desert-adapted species like Agave utahensis, but the wetter areas are able to support riparian species like cottonwood (Populus fremontii).
And then, magically, the river appears – the hidden architect of the canyon, the gathering place of water from these narrow side-canyons and also for hundreds of miles in every direction.
Walking alongside the river from its banks, I was impressed by its force as an ecological actor – to provide life and take it from such a wide portion of the continent, to cut down five thousand feet of rock in a few scarce million years, to so provide habitats for such diverse species, and to serve as a dispersal barrier for the many animals and plants (and people) stranded on either side of the rim.
Visiting the canyon after six years of thinking about ecology was undoubtedly a richer experience than if I had gone on the first day I moved to this part of the world. It is a marvelous teacher, and one that I am sure will continue to teach me.