With “Principles of Ecological Landscape Design,” landscape architect Travis Beck gives professionals and students a book to translate the science of ecology into landscape design practice. This groundbreaking work explains key ecological concepts and their application to the design and management of sustainable landscapes. Beck makes these concepts more accessible with numerous photos and figures, as well as by drawing out guiding principles as section headings.
“Principles of Ecological Landscape Design” covers topics including biogeography, building plant communities, avoiding invasive species, integrating animals, and dealing with climate change. Beck draws on real world cases where professionals have put ecological principles to use in the built landscape, highlighting particularly effective examples throughout the text.
For our focus on designing drought-tolerant and water-wise landscapes, Beck provided the following excerpts from “Principles of Ecological Landscape Design.”
Choose plants that are adapted to the local environment
Because plants exhibit such a wide range of natural adaptations, we need not struggle — expending both limited resources and our collective energy—against the environment we find ourselves in to make it a better home for ill-suited plants. Using biogeography as our guide, we can always identify plants ready-made for the conditions at hand.
Gardeners, nursery owners, and landscape designers have long recognized that plants ill-suited to the temperature extremes of the place where they are planted are unlikely to survive their first year in the ground. The US Department of Agriculture has codified this knowledge in a map of hardiness zones, which was updated in 2012 (fig. 1.3). Hardiness zones represent the average annual minimum temperature, that is, the coldest temperature a plant in that zone could expect to experience. There are 13 hardiness zones, ranging from zone 1 in the interior of Alaska (experiencing staggering winter minimums of below –50°F) to zone 13 on Puerto Rico (experiencing winter minimums of barely 60°F). Plants are rated as to the lowest zone in which they can survive. Balsam fir (Abies balsamea), for instance, is hardy to zone three. The hardiest species of Bougainvillea are hardy only to zone nine. Plants are sometimes given a range (e.g., zones 3 to 6). Strictly speaking, hardiness refers only to ability to survive minimum temperatures, but the practice of indicating a range serves as shorthand for the overall temperatures in which a plant will grow. The American Horticultural Society (2012) has also prepared a map of heat zones for the United States, indicating the number of days above 86°F that a region experiences on average per year. Catalog descriptions of landscape plants may include reference to these heat zones and to the more common hardiness zones.
Given the wide acceptance of hardiness zones, it is somewhat surprising that similar thinking applied to water requirements for plants has developed only within the past few decades. Perhaps this is because of the ease of meeting the needs of some plants for more water with irrigation. Or perhaps it is because of the deep influence of English gardening traditions in the United States and expectations of what a cultivated landscape should look like. Regardless of local conditions, our nationwide default residential landscape is water-hungry lawns and summer-flowering borders. Many regions of North America are in fact too dry, or receive precipitation too unevenly, to support this kind of designed landscape without major inputs of water. In San Diego, for example, more than half of all residential water is used to irrigate lawns and landscapes (Generoso 2002). Using water this way can deplete aquifers, damage habitat in areas from which water is drawn, decrease local agricultural production, and leave our landscapes vulnerable to desiccation when water restrictions go into effect.
The negative consequences of landscape irrigation and the countervailing benefits of water conservation motivated Denver Water (the water department in Denver, Colorado) to introduce xeriscaping in 1981. Xeriscaping, from the Greek word xeros, for “dry,” emphasizes grouping plants in the landscape according to their water needs (Weinstein 1999). Not surprisingly, many xeriscapes feature xerophytes, plants with low water needs.
Denver exists in a semiarid environment, getting on average around 14 inches of precipitation a year, as compared to about 35 to 40 inches a year in most areas east of the Mississippi. Kentucky bluegrass (Poa pratensis) lawns, shade trees, and most common garden plants need additional water to survive. At their former home, Panayoti and Gwen Kelaidis ambitiously replaced their entire front lawn with plants well adapted to Denver’s semiaridity. These include sulfur-flower buckwheat (Eriogonum umbellatum), soapweed (Yucca glauca), and partridge feather (Tanacetum densum ssp. amani). Today, 20 years later, these plants are still thriving with no supplemental irrigation (see fig. 1.4 at top).
Selecting plants that are adapted to the temperatures and available water of the environment in which they will be placed is a fundamental step in creating an ecological landscape.
Fig 1.3.jpg: The 2012 USDA Plant Hardiness Zone Map. Note the fairly regular progression of zones from north to south in the center of the continent and the irregular zone boundaries related to mountain ranges and the moderating effects of large bodies of water (including the Great Lakes) in the west and east.
Image provided by the US Department of Agriculture.
Built landscapes also have physical and biological components: crudely, in industry terms, hardscape and softscape. Too often, these components are far from integrated. The hardscape is set in response to programmatic needs, and plants are tucked into the remaining spaces. If the physical environment is not right for the biological components, then it is altered, by providing irrigation, for instance.
Consider a typical landscape pond. An estate owner might pay a contractor to clear an area, excavate a hole, line it, fill it full of water from a well, and trim the whole setup neatly with rocks or lawn and perhaps a few aquatic plants on a planting shelf. As water evaporates from the unshaded pond, the well pump kicks in and tops off the pond. Even suburban homeowners want their own ponds and waterfalls, full of municipal water and lined with dwarf conifers or Japanese iris (Iris ensata) sitting like rocky puzzle pieces on their lawns. These systems are fully artificial, rely on supplemental water, and often require filtration or even sterilization to remain aesthetically acceptable. Physical and biological elements are divorced from each other and from their surroundings.
By contrast, a pond that is conceived of as an ecosystem fuses physical and biological elements into a whole that integrates with, rather than sits apart from, the processes of the surrounding environment. Landscape architects Andropogon Associates created such a pond on a property in Greenwich, Connecticut. Naturally, throughout New England’s forests, in the spring small depressions in the landscape fill with water, which infiltrates as groundwater levels drop in the summer. These vernal pools provide important habitat for amphibians such as salamanders and frogs. On this property such a depression existed, set against a granitic outcrop, only it had long been filled with branches, leaves, and other green waste by generations of gardeners. When Colin Franklin, founding principal at Andropogon, discovered the rocky dell and the small spring at its base, he saw an opportunity. Andropogon Associates’ design philosophy has long been to build “dynamic, holistic systems,” that is, ecosystems.
Franklin’s approach was to line the center of the depression in order to maintain a minimum water level but leave the edges unlined. Water from the spring is collected in a sump beneath the pond and pumped via a slender waterfall off the rock outcrop and into the pond. In spring the pond overflows, recharging groundwater in the area. The margins are planted with trees and other plants that are adapted to this seasonal flooding. Between the open water, the planted wetland at the pond’s edge, and the seasonal wetland beyond, the design provides diverse habitat. When water levels drop to the level of the liner, the wetted margins dry, mimicking the cycle of vernal pools. If water levels drop further, the sump pump and waterfall can make up the difference from the recharged groundwater. Because the pond is in the forest, however, evaporation and the need for makeup water are minimal.
This forested pond is now a hub of life and the center of the entire landscape. Rather than create a sterile water feature of dissociated elements, Andropogon created an ecosystem, with natural physical cycles and plants and animals adapted to them.
Meet plant water needs through contouring and drainage
Water is not merely something to be slowed, cleansed, and sent on its way. It is a resource that keeps alive every living thing on the planet. That is why we love fountains and pools in our landscapes. And it is why nearly every garden includes a source of water, if not an entire computer-controlled irrigation system. Water can also be a destructive force. It can erode hillsides, dig gullies, undermine paving and foundations, push over trees, and deposit mud, rocks, and debris in alarming places. Every designed landscape walks a balance between having too little water and too much.
If we have matched our plants to our climate, then what we grow should be able to survive on natural precipitation alone. But within each biome live many different communities of plants, some in drier sites, others in wetter. Manipulating the flow of water with contouring and rainwater harvesting techniques can move water away from where it is a problem to where it is a resource, dissipate its destructive power, and create a range of conditions suitable to growing a variety of plants.
Where we do not want water, such as around the foundations of buildings, we can use grading and drainage channels to direct the water away. These areas then become places to plant more drought-tolerant plants, and the water directed away becomes a resource for other areas of the landscape. Just as Wenk Associates did at Menomonee Valley Community Park, slowing the water, spreading it out, and getting it to infiltrate recharges groundwater and keeps it available for local ecosystems. When this practice is carried out fully, dry springs can resume their flow, and once-ephemeral streams can become perennial. Although the best place to store water is in the ground, rain barrels and cisterns can also be used to capture seasonal surplus water that would otherwise leave a site and make it available during later dry spells.
Water drained from other areas of a landscape can help certain plants grow in regions where the annual precipitation figures make it seem as if they should not. Say, like Brad Lancaster of Tucson, Arizona, you wanted to grow a tree in the Sonoran Desert, the home of saguaro ([ital>Carnegiea giganteanProsopis velutina<ITAL]). w:st="on" Mesquite grows naturally on seasonally flooded terraces next to rivers and streams and along washes that concentrate rainwater from the surrounding area.
Lancaster (2008, 2012) took advantage of similarly concentrated flows of water on the impervious street beside his house. With all the appropriate permissions, Lancaster cut a series of openings in the curb that separated that street from the barren public right-of-way that ran along his and his brother’s property. Behind each curb cut they dug a sunken infiltration basin and used the dirt from their excavations to build a meandering raised path through the right-of-way. Now when it rains, each basin fills with water, then overflows back into the street, sending water along to the next curb cut and basin. Lancaster also placed layers of organic mulch in each basin to keep the water that has infiltrated from evaporating away.
Thanks to these simple techniques, the previously sun-baked right-of-way is now shaded by maturing trees, without the need for extensive watering. Starting in 2010, the City of Tucson now requires all new commercial landscapes to provide 50 percent of their landscape water needs through rainwater harvesting, primarily passive techniques such as those demonstrated by Lancaster (City of Tucson 2009). Curb cuts and infiltration basins planted with trees have also been used in cities such as Portland, Oregon; these features are not for arid regions only.
A properly graded landscape will preserve built structures, create dry routes for access and circulation, and infiltrate rainwater in areas where it can recharge groundwater and nourish plants with higher relative water needs. The microtopography thus created opens opportunities to grow communities of plants with different water needs across a site.
Principles of Ecological Landscape Design
By Travis Beck
© Island Press (December 2012)
Island Press Paperback and E-Book
296 pages | Price: $ 40.00
ISBN: 978-1-59726-702-1 (P)