Plants alter and create the spaces that surround them; different species respond to the ground in different ways. This work reconsiders the role of tree roots in the landscape and the way urban spaces are designed. As landscape architects, the ground is our medium. Recently, we’ve begun to understand the ground as something that is alive, something with depth and a certain quality of being. This research will serves as a practical guide to what is happening below ground, but also as a catalyst for rethinking the dynamic nature of the ground. By considering the planting of a tree not as a neutral act, but as an act of optimism, trees can be understood as dynamic mediators between the depths of the ground and the spaces that we inhabit above the ground.
As landscape architects, the ground is our medium. Recently, we’ve begun to understand the ground as something that is alive, something with depth and a certain quality of being. As we being to pay attention to the soil, we attune ourselves to its chemistry, composition, and ecology of microorganisms. But in this interest in soil, we forget to consider another element of the ground: the root. Roots support and nourish the tree and in the process, nourish the soil with organic matter. They assist in organizing the soil into horizons, regulate water, and support diverse ecologies through the chemical compounds that they exude. Roots are the ground. Roots are also plant brains. According to Darwin “It is hardly an exaggeration to say that the tip of the radicle acts like the brain.” The tip of the root senses its environment and reacts to it.
“Designers are typically focused on the aesthetic and spatial characteristics of a plant―those that can be seen, smelled, or otherwise experienced in space, above the ground level. But the hidden, underground roots deserve just as much attention[.]” Turner 2011
Trees are often one of the most influential elements of the landscapes that we design with almost two-thirds of their total mass below ground. This research considers the morphology of tree roots; it considers how roots interact with soil, and how roots interact with other roots. Information about the roots of grasses and herbaceous plants is accessible, but little has been published about trees.
This research began with an intense investigation of 100 years of tree root research. I developed a process of considering the form of tree roots in the built environment based on tropisms. I tested this concept through discussion with botanists and foresters. Drawings and the excavation of seedlings also severed to test my predictions of root growth. The research lead to design provocations about how root research might affect design, and how design might affect root research; it became a conversation between disciplines.
“Root systems of trees seldom receive the attention given crowns and stems partly because they are concealed in the soil and partly because the interrelationships of roots seem hopelessly complicated” Lyford and Wilson, 1964
A root has a set of tropisms or ways of reacting to the ground. By knowing these tropisms and species specific morphologies, we can think like a root. By interpreting the ground as a root we can predict the resulting root system architecture. Instead of three root typologies (taproot, heart root, lateral root), there becomes an almost infinite matrix of possibilities as roots adapt to different conditions with different tendencies and morphologies.
The general depth of a root system can be approximated by understanding the soil. While different species have different thresholds of adaptation to soil conditions, it can be assumed that roots will penetrate deeper on loose well drained soils, and root systems will be quite shallow on heavy soils with less drainage.
In addition to the interactions between tree roots and the ground, this research describes the interactions between the roots of one tree to the roots of another tree. Plants are thought to communicate chemically through the ground. Root systems are “aware” of the presence of other root systems; some species will react differently to a nearby root system of its own species then it will react to the nearby root system of a different species. This signaling between plants affects their growth. It is concepts such as these that can be applied practically to a site design, but also serve to reintroduce elements of wonder to the landscape.
Roots are often drawn incorrectly in sectional representations of the landscape (and are absent from tradition plan drawings). By providing a visual resource that depicts the shifting morphologies of roots, a logic of the ground can begin to define a logic for the design of the site. This research includes a compendium of drawings and characteristics of the root systems of over thirty species. Each species reacts slightly differently to the ground, with different ‘personalities’ in their general form and different adaptation strategies to site conditions.
This research resulted in four lectures and printed compendiums of collected research and provocations. It is a call for further research into ways of describing the dynamic nature of ecologies below ground and a call to change the way landscape architects design with (and draw) tree roots.
Scientific research of the dynamics of tree roots in the built environment is severely lacking. As designers of these spaces, we ought to encourage and be a part of this research. We might design management plans for urban forests that build soil through the seasonal growth and decay of fine tree roots. We might design streets and sidewalks that reflect the aliveness of the ground below them. We might design patterned forests by planting one clonal tree and designing a ground that gives directionality to the colony that it produces. We might design for the planting of tree seeds in the built environment so that their roots are never transplanted. We might slowly bury or slowly excavate a tree and witness their ability to form roots from shoots and shoots from roots. What does it mean to design for roots? What does it mean to design the ground?
“The ability to connect to a larger world is a direct consequence of the ability to effectively engage the ground and bring this within human comprehension and action. Ground is where human artifice and natural process commingle for the benefit of both.” Dripps, 2004
Roots exist in a space that until recently we could not occupy or observe without disturbance and destruction. They have remained separate from our realm; an ignored “other.” When roots are discussed, they are often considered a problem; roots damage things. If 80 percent of all landscape tree problems start below ground, then an informed understanding of subsurface conditions is imperative to prevent the expense of tree loss. This research will serve as a practical guide to visualizing possible adaptations of root systems to ground conditions, but it will also serve as a reminder of the beauty in the complexity of the ecologies below ground. Roots will not be treated as a problem that need to be fixed, but as an opportunity to reconsider relationships between the designer, the soil, and the plant.
Associate Professor and Chair of Landscape Architecture, University of Virginia
Albemarle County Garden Club
Dr. Peter del Tredici
Senior Research Scientist, Arnold Arboretum of Harvard University
Dr. Francis Hallé
Professor Emeritus of the University of Montpellier