Gina Crandell, one of this month’s guest bloggers, is visiting professor of landscape architecture and environmental planning at the University of California at Berkeley. She is also principal of Gina Crandell Landscape Architecture, a Boston practice working with campuses and land trusts.

Trees in Retiro Park, Madrid, Spain (Photograph by Gina Crandell)

Why do Americans think of trees as individuals, even when they’re part of a group?

For example, Americans will replace trees in an allée one by one, as each tree dies—or, more likely, they won’t replace the dead trees, and the architectural structure of the allée will slowly degrade. And why do colleges designate single trees as memorials, rather than whole groves? (Fund raising for a grove could bring in much more money.) Why are there so many tree huggers in the U.S.? (Some have been living in trees at the University of California at Berkeley for more than a year.)

Whatever the reasons—and they are complicated—it’s obvious that Americans think it is more natural not to replace a whole group of trees, and not to plant trees so that they have architectural purpose.

Frederick Law Olmsted—whose botanical architecture often established a “meadow and forest” structure, rather than a geometrical one—believed that “individual tree beauty is to be little regarded but all considerations [are] to be given to beauty and effectiveness of groups in passages and masses of foliage.” Let’s use the term “tree garden” for the planting of trees where the architectural structure matters more than the individual tree. Some of our fondest memories are likely of tree gardens—a densely planted courtyard of a campus quadrangle, an allée leading to an historic building, an orchard.

One striking quality of a tree garden is that it shows evidence of time. Aging stands are memorable and loved: Someone no longer living has deliberately planted trees to make a lasting impression for generations who follow. In today’s disposable world, the slow but dramatic growth of trees—whose lives are often longer than our own—is a rare experience of time. Trees age. Natural processes take over. Their trunks thicken. But if they have been planted to form spaces, the evidence that they are part of a human construction remains visible—and becomes even more striking as it contrasts with the trees’ aging forms.

At some point, though, aging will so degrade the architectural structure of a tree garden that a strategy will be needed to maintain it: It will need either partial or whole replacement. Many European tree gardens have been replaced again and again over many centuries. At some American colleges, tree gardens that once provided structure to the whole campus as well as to some of the most important public spaces—the quad, the oval, the main allée—have been degraded and lost. A few very old trees left standing like childless widows can be very beautiful, but they are neither a garden nor a future.

Tree gardens express human desire and are environmentally productive as well. Trees produce oxygen, absorb carbon dioxide, improve water quality, and mediate climate extremes to reduce energy consumption. They reduce noise levels and wind speed. They produce flowers, fruits, nuts, and wood. But what should matter most to a college administrator committed to making a memorable campus is that trees produce beloved human spaces. —Gina Crandell

You can read Gina Crandell’s previous posts here, here, and here.