Credit: Flickr user spaceamoeba
When I look within a plant species, I see variation. Some individuals are taller than others, some have tastier leaves, and some bloom at different times, all within the same species. Two things control such variation: the plant’s underlying genetic makeup and the environment it grows in. Two genetically identical plants can look very different if one grows in arid heat and the other in cold damp. This sort of variation can have cascading consequences for animals, such as insects, that rely on a given plant for food or shelter.
To study how animals respond to genetic variation within a plant species, I collect representative specimens of the plant species and grow them all in one place so as to minimize confounding environmental effects. This is called a “common garden” experiment, and after collecting specimens it becomes more a matter of farming than grappling with any “big” science questions.
My first common garden, at the University of Tennessee in Knoxville, was an enormous undertaking. I was studying goldenrod (Solidago altissima), a perennial herb that hosts lots of insect species and blankets roadsides along the eastern seaboard in autumn. In an old, abandoned agricultural field along the Clinch River of east Tennessee, I spent exhausting weeks tending hundreds of plants, often on my knees hand-weeding each plot in intense heat and humidity. Aided by a little free undergraduate labor, I built an irrigation system, and fences to keep deer out.
Eventually the common garden took on a life of its own. Plants bolted upward, insects arrived and colonized, and I began collecting data. From empty dirt emerged an ecological pattern. In that Tennessee garden, I found that the more diversity within a plot’s lone plant species, the more insect diversity there was. Time and again, the pattern holds: Plant diversity begets animal diversity.
Now I’m a post-doctoral candidate at the University of California in Berkeley, and planting common gardens has become a sort of obsession. I’ve spent months digging coyote bushes (Baccharis pilularis) from a forgotten garden in the coastal sand dunes north of San Francisco. On the shores of Humboldt Bay in California, I have two large fields of newly planted and rapidly growing willows. Each garden changes throughout the season. Plants flower, disperse seeds on the wind, and finally brown and wilt. When the first frost comes, my labor is at an end.
In the middle of the Mojave Desert, where most people only stop for gas on their way to Las Vegas, I’ve planted my most ambitious garden yet. There, resin-rich creosote bushes (Larrea tridentate) fill the dry air with their smoky, spicy aroma after a rain. Creosote is difficult to germinate, and grows slowly; it might take a decade to get the garden up and running, but I am still young. With any luck, before I retire a spring will come when desert bees arrive to drink nectar from the yellow-petaled creosote flowers, pollinating the plants and beginning the cycle of life anew.
Gregory Crutsinger is a community ecologist and a Miller Research Fellow at the University of California, Berkeley.
Originally published July 20, 2010