BY CAROL E. BECKER
The oak is our national tree for a reason. Oaks are endemic to our native landscapes in all regions of the United States, easily identified by their leaf shape and gnarly branches. The size of the mature white oak (Quercus alba), spreading up to 120 feet, is one reason we associate oaks with strength, along with the density of the wood and an oak fire’s burning hot and long in the woodstove. Native oaks fall into two taxonomic groups, white and red, and their landscape uses vary depending on soil moisture. But most important today, as Douglas Tallamy, a professor of entomology and wildlife ecology at the University of Delaware, points out, oaks are the “quintessential wildlife plants.” They provide food to more than 500 species of caterpillars and other insects. In this fact lies the oaks’ value to the entire food chain, from the birds that eat insects to the humans who rest in the trees’ shade.
We need more oaks in our landscapes, mostly for the food benefits they provide. But instead of being sought-after plants, oaks are underused, undermarketed, undercultivated, and therefore in short supply. Landscape architects don’t often use them, clients don’t ask for them, and thus growers don’t grow them. A reverse scenario also holds true. Few nurseries grow Quercus species, particularly Q. macrocarpa, Q. muehlenbergii, and Q. alba, because they are hard to grow and suffer significant transplant death. So clients don’t see them and don’t ask for them and, in turn, landscape architects don’t specify them. Whatever the reason and wherever you start, it’s a circle of mutually reinforcing supply and demand.
The oaks are but one example of the larger problem for design professionals working to create sustainable landscapes with hardy plants in a given region. The interest in doing so—the imperative of doing so—is unequaled by the supply of appropriate species. This shortage also helps perpetuate clients’ expectations of plant specimens they do in fact see at the retail level, plants that are well-shaped, blooming, varied, and maybe even a bit exotic. The landscape architecture profession has taught them to value this aesthetic at least since the mid-19th century, when Andrew Jackson Downing codified ornamental landscaping in A Treatise on the Theory and Practice of Landscape Gardening. Now, we find ourselves in a world where, in just the past 40 years, half the songbird species in the United States and more than 90 percent of the monarch butterflies have disappeared. Honeybees and bumblebees have fallen to a mysterious virus, a cataclysmic problem that threatens the entire food chain. We do know how to reverse these trends and preserve biodiversity in landscapes, but we can’t get it done because clients still want constantly blooming and well-shaped plants with no bugs.