Plants and structures can be used together in an attractive and cost effective manner to construct living walls, sound barriers, and earth retention systems.

Winding country lanes lined with colorful hedgerows constitute one of the scenic delights of the countryside in southwest England, particularly in Cornwall. These hedgerows are an ecological system unto themselves that support a diverse collection of birds, animals, and plants. The Cornish hedgerow is basically a wall constructed with dry laid stones surrounding a central, earthen core. It is this earthen core which gives the Cornish wall its unusual properties and attributes. During construction, live cuttings of various plant materials are intentionally inserted between the openings in the rock into the earthen core. Eventually the cuttings root and leaf out. Miraculously the roots do not pry the wall apart, instead they flow and wiggle around the rocks binding the entire wall together in a monolithic, unitary mass. Some hedgerows ultimately support not only plants and shrubs but also large mature trees. The final appearance is spectacular and beautiful. The construction of Cornish walls is carried out by artisans who have been trained in this tradition...an art form or building skill that is now in danger of dying out.

The term "biotechnical construction" has been minted to describe the combined or integrated use of plants and inert structural materials. In this approach live wood cuttings of woody plant material are purposely arranged and embedded in the ground to strengthen and indurate a soil mass. The cuttings and plant material can also be introduced into the frontal openings or interstices of porous retaining structures or revetments; alternatively they can be established on the horizontal benches of tiered retaining structures. These plantings can greatly mute the stark appearance of a retaining wall and also provide a whole new range of opportunity for imaginative landscaping on near vertical surfaces. Would- be wall graffiti artists, on the other hand, are likely to be less enthusiastic.

Most engineers would probably shudder at the thought of purposely introducing plants into a structure. Engineers are trained to work with inert materials; concreted, wood, stone, steel. These materials have predictable properties and forms that do not change much with time, unlike biological materials that tend to grow and regenerate. Some structures are also stark and visually intrusive - a factor to be considered when proposed for use in natural parks or scenic areas. The facts are that vegetation can usually coexist quite happily adjacent to and within structures. Plant roots exhibit a property known as edaphoecotropism which means quite simply...stress avoidance. Roots are smarter than we give them credit for; they tend to grow away from obstacles and away from the front of retaining structures where they would be subject to moisture deficiency and light stress. There are exceptions of course; in some cases plant roots can disrupt structures. A case in point are poorly chosen street plantings, e.g., camphor trees with their elephantine root systems, that heave up sidewalk pavements.

The advantages and opportunities for incorporating vegetation into retaining structures and revetments are being realized more and more. Europe has led the way in developing vegetated or "living wall" systems. A number of different retaining walls that pointedly tout the benefits of this approach are now marketed in the USA. These range from open front cribwall systems like the Evergreen wall to articulated block wall systems like the Loffelstein wall. The same approach has been incorporated into sound barriers. A good example of this is the "Willow Wall" a lattice work of live willow stems and branches that are backfilled with earth. The central earthen core supports the growth of the surrounding willow stems which root into the soil. More importantly, the central earthen core provides the mass necessary for effective noise attenuation. Contrary to popular misconception, vegetation per se is not an effective noise attenuator. A willow wall provides a pleasant visual screen in addition to attenuating traffic noise.

Bank holdups should be executed with grace and elegance. They need no longer rely on stark, brute force. Retaining structures can now be designed and constructed that combine the use of inert structural elements and living, vegetation in a pleasing and functional manner. LASN