A few summers ago, I took a walk one evening to find a California redwood 5,600 miles from home. Sequoia sempervirens, the sign said, Latin for ever green or everlasting, which is to say such trees are both non-deciduous and among the oldest living things on Earth. Located in the Jardin des Prébendes, a few blocks from the French city center of Tours, this particular sequoia was a mere 150 years old, but had I seen it towering somewhere north along my own Pacific coast, it couldn't have been more wondrous.
I had the good fortune to spend three days in the field, last week, with a wildlife biologist and her field crew, in their study area in the Southern Canadian Rockies, observing and helping the team “pull transects,” inventory tree growth, and track for wolf and other predator sign. They were compiling data for evidence of “trophic cascades,” in the ecosystems at the mountain-prairie interface. Trophic cascades are the energy that ripples out from the presence of a top predator, or a “keystone species,” in an ecosystem—not necessarily through direct predation so much as through an “ecology of fear,” which keeps herbivores vigilant and on the move, balancing browsing with scanning for predators. Removal of the predator can result in a collapse of the number and complexity of the energy cascades; presence of a predator amplifies and expands the energy ripples. Through such “cascade” effects, we ultimately might establish links between, say, wolf presence and songbird diversity. (For some ecosystems, a “mesopredator” like the coyote fulfills the function of the wolf.) Or so the theory goes.
Theoretical or not, I like to call it the wolf-songbird complex.