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Sustainable Landscape Construction
A Guide to Green Building Outdoors
By J. William Thompson, Kim Sorvig
ISLAND PRESSCopyright © 2008 J. William Thompson and Kim Sorvig
All rights reserved.
Keep Healthy Sites Healthy
The first rule of the tinkerer is to keep all the pieces.
—Aldo Leopold, quoted by E. O. Wilson, Biophilia
Every site resembles a living organism, and like organisms, sites vary in health. This chapter discusses what "site health" means, and methods for preserving it during construction. Like human health, site health is not easy to define in a simple formula. Prevention is usually more successful—and less expensive—than cure.
Protection of sites—particularly those with mature vegetation and healthy soils—is of increasingly critical importance because deforestation links to global climate change (see p. 14). Site protection can make local, cumulative differences.
Landscape construction that accidentally or deliberately damages a healthy site is doubly wasteful. While restoration methods can repair many site injuries, there is a point of no return, beyond which restoration is neither cost-effective nor ecologically sufficient. Mature trees needlessly destroyed in construction are not effectively "restored" by planting saplings, for example. Thus, the first principle of sustainable landscape construction is self-evident yet easily overlooked: avoid harm to healthy sites.
Protecting a healthy site requires care throughout the design and construction process, from initial reconnaissance through final cleanup. Sustainable design anticipates and integrates appropriate construction methods, influencing choices about siting, structures, and materials. The quality and coordination of such choices can make the difference between irreparable damage and minimal impact.
What Is a Healthy Site?
"Health" is one of those conditions everyone knows when they see it, but which remains impossible to define completely. Despite this difficulty, it is important for both ecological and economic reasons to develop at least an operational definition of what "site health" means.
It is fairly easy to say when a site is unhealthy: stripped of topsoil by natural erosion or human carelessness, polluted by chemicals, supporting only a small percentage of the richness of plant and animal life found in the region, or overrun with invasive species, sick sites are often obvious eyesores.
Some site "illnesses" are brief ones, with quick recovery. A site drowned in sediment by a flood, or burned by a forest fire, may look unhealthy, but usually retains vitality and soon begins regrowth. In fact, many plant communities and soil types depend on such events for long-term health. A site that is healthy and has plentiful resources (water, soil fertility, sunlight) can recover from minor construction damage, too.
More serious ill health results when toxic chemicals are involved, or when soil is removed, massively eroded, compacted, or paved. Some plant and animal species invade the site in much the way that parasites, microbes, or even cancers invade the human body.
The cumulative effect of small, normal stresses also affects site health. Individual factors like wind, temporary drought, or increased ultraviolet radiation can add up over time to weaken plant life that holds a site together. Human use of a site produces new stresses. A site that had limited resources to start with may be unable to adapt to added stress.
Like healthy humans, healthy sites are productive, have vitality enough to keep growing despite some stress, and generally have a satisfying "look" and "feel." The appearance of a site can tell much about its health. Some healthy sites, however, go through messy-looking phases, and some landscapes conventionally viewed as stylish conceal serious ill health. Conventional landscape aesthetics are not a reliable guide to site health. (See Figure 1.1 and Figure 1.2.)
Healthy ecosystems provide what have been called "environmental services," keeping air and water clean, improving local climate, and creating food—services on which human life depends. Healthy sites also provide many amenities. Compared to landscapes cleared and flattened for convenience in construction, healthy sites have significantly higher property values (by at least 5–20 percent).
Healthy sites are recognizable by several characteristics:
They support diversity of plant and animal life adapted to the region and linked to one another in a web of interdependence.
They are seldom dominated exclusively by one species, and especially not by species imported there by humans. (Criteria for agricultural sites are different, but crop monocultures are also unhealthy.)
Their communities or ecosystems (soil, plants, and animals) are essentially self-maintaining, not dependent on outside resources supplied by people.
Their living species are self-reproducing.
The geological portion of the site is not changing too rapidly to support the living community, nor poisoned or infertile.
The site has sufficient vitality to overcome a variety of stresses.
The community changes with age through a process called succession.
Succession is a regionally characteristic series of changes. Healthy meadow or bog may be superseded by healthy forest. Unlike invasion by imported species, succession is healthy. It is like the changes in a healthy human from infancy through adolescence, maturity, decline, and death—and in the case of plant communities, includes rebirth. Accelerating or holding back succession without weakening the site's health is one of the most sophisticated methods of site management. Excessively slow or fast succession, like unusual aging in people, can indicate ill health.
It is seldom up to a single construction or design professional to decide precisely how healthy a site is. However, if developers, designers, and contractors learn to recognize relatively healthy sites, such sites will be valued and protected more often. Recognition and protection of site health is increasingly required of landscape professionals.
Take a Role in "Pre-construction"
Prior to what is conventionally considered the beginning of either design or construction work, a great deal can happen to the site. The pre-construction actors are likely to be realtors, surveyors, developers, utility companies, and government agencies. Increasingly, projects stand or fall on the input of neighborhood groups as well.
Landscape professionals can influence most of these groups toward sustainable practice—but only if they form strong channels of communication and give input at the right time. Failing this, these same groups will act on the site, often by default, before landscape professionals are involved. Some standard practices—including hiring a landscape consultant only at the last moment to "shrub up" an already completed design—attempt to disguise unsightly or unhealthy results. Although not easy, winning influence over land-use planning is critically important to sustainability. The teamwork required among landscape architect, contractor, architect (or other consultants), and client/user is a good place to start forging community connections.
One very specific pre-construction practice is increasingly unacceptable in light of the clear links between vegetation loss and global warming (see p. 14). This is the practice of "pre-clearance"—bulldozing a site flat and removing all vegetation and much of the topsoil before putting up a For Sale sign. Although realtors clearly believe flattened sites are attractive to commercial buyers, pre-clearance is truly destructive. Convenient, perhaps, for a big box or parking lot, but what if a corporation wanted to create a model green headquarters? Much of the incentive, and many "environmental services," are now destroyed. We suspect that pre-clearance is an end run around development permit processes—if the site is cleared before the regulatory process begins, there is nothing left to regulate.
Sometimes pre-cleared sites lie naked and vacant for years, waiting for sale, planning, design, and construction. During that time, for absolutely no reason, all the air and water benefits of healthy plants and soils are lost. Site clearance should not only be kept to a minimum, but should not be done any longer in advance than truly necessary. Responsible, sustainability oriented developers will not pre-clear. Unfortunately, some conventional realtors and developers have to be threatened with legal penalties before they consider anything beyond their own interests. No site should ever be cleared until a specific master plan or design has been approved.
Do Your Homework First: Knowledge as Sustainability
Those who think that site analysis before design or construction is expensive need to consider the costs of ignorance, which are always far greater.
There are two kinds of "homework" involved in protecting a healthy site. The information gained from each applies to every subsequent step of sustainable landscape work, from design through maintenance. The first involves attitude; the second, facts.
It is impossible to protect what you don't respect. Even with a strong love of nature, working on a site involves carefully setting priorities, and in many cases, reeducating clients and coworkers. Attitudes about preserving natural conditions have a strong influence on design and construction priorities. Is the desire for home soccer practice worth flattening the backyard? Is impressing the neighbors justification for using extra resources or replacing native plants with lawn? Choices like these are never easy and involve basic attitudes about human relationships to landscapes. This book's introduction includes thoughts about cultivating sustainable attitudes, as does the conclusion.
Between attitude and facts are concepts and models used to understand and organize complicated subject matter. Landscape ecology is one important concept whose influence continues to grow. Around 1994–95, at least five federal agencies developed land-management principles based on landscape ecological concepts. These policies treat landscapes and ecosystems as nested systems at several scales, with fuzzy boundaries, interacting with other units to form the whole. A related conceptual system that is useful for understanding landscapes in a dynamic way is called complexity science, which studies and digitally models systems made up of many independent "agents."
Even with respectful attitudes, protecting what you do not thoroughly understand is difficult. Information gathering is critical to sustainable work, from the earliest preliminary feasibility studies, through design and construction, and into maintenance. Data gathering, both informal site reconnaissance and technical surveying, benefits from a team effort, clear communication, and information sharing.
Reconnaissance should identify and evaluate site features before design begins. (In fact, this knowledge should inform selection of properties to develop, but rarely does.) Much reconnaissance is visual, observing and noting conditions without technical equipment. Published sources, such as soil and topography maps or land-use records, are also important in effective reconnaissance. Contractors usually carry out a separate reconnaissance just before bidding a contract. Ideally, their insights should be part of the design process, though this is rare.
Surveying with technical instruments is too often used only to establish ownership boundaries, general contours, and a few construction control points. GPS and GIS (see below) leave little excuse for not locating all major site features prior to starting design. Assuming that "design" means remaking the site without reference to anything existing is often at the root of inadequate surveying.
Whether done with survey instruments or camera and sketchbook, detailed site-specific mapping is a critical part of building sustainably. Homework left too late may be of poor quality or may be overridden by assumptions made before good information is gathered. Much conventional construction is undertaken from site plans that are nearly blank. Given clearer site data, designers can work with existing topography or trees, while contractors can prioritize site-protection zones and avoid hazards to construction.
Site-specific data has long been considered prohibitively expensive to gather using conventional survey methods. In this book's first edition, we noted the then-recent arrival of Global Positioning Systems (GPS) and Geographic Information Systems (GIS). GPS, for gathering ecologically important site information affordably with less site impact, and GIS, to store, analyze, and selectively map site data, have become standard tools. They have generated more, better, and cheaper site-specific information. Despite a few attempts to monopolize this information for profit, the overall result is better public access to site data.
Increasingly, online information sources are helpful site reconnaissance tools. (They should seldom become substitutes, however, for field observation.) Extremely valuable site information formerly only available in print—the US Soil Survey, climate data, geological diagrams, native and invasive plant lists—is available via the Internet. A wide variety of maps and air photos is also online, some updated almost in real time. For example, the University of New Mexico's Center for Rapid Environmental Assessment and Terrain Evaluation has redeployed military technology to turn satellite data into maps instantly. One projected use is mapping forest fires as they happen. Studies of vegetation change, flooding, and other quickly occurring processes are also in the works.
Software for organizing and visualizing Earth data is improving rapidly. Google Earth provides views of most locations on the planet. It is beginning to be used as a central repository for links to other site-specific information. In theory, by clicking on a place on the Google Earth map, one can access site photos, as-built drawings, regional soil or climate data, or local history. The software has been used to expose "mountaintop removal" by coal companies in Appalachia; it could as easily be used to link any site to full ecological data. While no systematic effort has yet been made, readily accessible "site-indexed" background information could be a quantum leap toward making sustainable design the norm rather than the exception. Microsoft's Virtual Earth, released in 2006, will probably spur competitive developments of online geographic information.
CommunityViz is a software add-in for GIS that produces 3D visualizations of "what- if" land-use scenarios. For example, specific house types can be drawn, and the "look" of new development using a mix of those house types at different densities can be portrayed. This promising program has two major landscape-related blind spots. Houses "plopped" on topographic surfaces do not reflect actual grading; and air photos draped over 3D contour maps show vegetation and site features two dimensionally, as if steamrolled onto the slopes. Not dealing realistically with two issues that so frequently make development ugly and unsound, CommunityViz's current version can actually mislead citizens trying to visualize acceptable growth. Until those defects are fixed, it remains a potentially green tool that leaves landscapes out.
"Agent-based modeling" (ABM) programs simple rules of interaction into large numbers of individual "agents" and produces remarkable simulations of complex systems. This is perhaps the most promising trend in realistically envisioning ecological and social processes. Easy-to-learn but robust software for ABM is "Netlogo," downloadable free; for understanding any process where many small forces over time produce large results, Netlogo is a powerful tool that few landscape professionals yet use.
Use Flexible, Accurate Visualization Tools
Having good survey data doesn't help much if it can't become visible in the design process. Although design graphics are well outside the scope of this book, it is worth noting that some are better suited than others to visualizing irregular existing site features like rock outcroppings or specimen trees. The choice of the right tool can directly affect the ability to transform sustainable intentions into on-the-ground success.
Excerpted from Sustainable Landscape Construction by J. William Thompson, Kim Sorvig. Copyright © 2008 J. William Thompson and Kim Sorvig. Excerpted by permission of ISLAND PRESS.
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