Creating Landscapes in Water-Scarce Environments: A Case Study of Tucson, Arizona
An Essay on a public lecture presented by Margaret Livingston at Darat al-Funun, Amman on May 30, 2001
Prepared by Mohammad Al-Asad and Majd Musa in association with Margaret Livingston, 2001
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Support for the publication of this essay has been made possible by a grant from the Prince Claus Fund for Culture and Development.
Additional support has been provided by Darat al-Funun - The Abdul Hameed Shoman Foundation.
Table of Contents:
Margaret Livingston (1) presented in this public lecture a number of ideas on landscaping for water-scarce environments in Tucson, Arizona. She began by stating that since her audience does not primarily consist of landscape architects and related professionals, it would be best to present a broad overview of the subject. Livingston also emphasized the relationship between Tucson and Amman. She mentioned that in spite of the numerous differences between Tucson and Amman there also are many similarities between both cities in terms of environments as well as the social, economic, and cultural factors that influence those environments. Such similarities make an exposure to the experience of Tucson useful and of importance to specialists as well as the public in Amman. In fact, Livingston made numerous comparisons between the two locations during the course of her lecture.
Livingston's lecture was divided into three major sections. The first section provides an introduction to Tucson. It deals with Tucson's natural environment and native plants and animals, and watercourses occurring throughout the city, and the human influences affecting them. These range from cultural influences to historical and current land-uses. The second section deals with the issue of water conservation and discusses how Tucson has addressed this issue. The third section presents different landscape solutions that have been utilized in Tucson.
The city of Tucson is located in southern Arizona, one of the states of the southwestern United States. It is located in the Sonoran Desert, which in turn is embraced by two other deserts, the Mojave (also called Mohave) Desert to the west, and the Chihuahuan Desert to the east. The Chihuahuan Desert, on average, receives more rainfall (and occurs at higher elevations) than the Sonoran Desert, and the Mojave Desert gets less rainfall. Consequently, the vegetation in the Chihuahuan Desert is sometimes perceived as having a lusher look than the Sonoran Desert, and that of the Mojave Desert as being very sparse in comparison to the Sonoran Desert. (2) In addition to those three deserts, there is the Great Basin Desert that is located in northwestern Arizona and parts of three other states. This last desert is classified as a cold desert, and presents environmental and climatic considerations that greatly differ from those affecting Tucson.
Tucson is located in a valley and is surrounded by three tree-covered mountain ranges, reaching elevations as high as 2900 meters. Figure 1 shows the landscape of Tucson as seen from the ridges of the surrounding mountains. To the right of this figure appears the saguaro (Carnegiea gigantea), a very unique plant (cactus) that has become a symbol of the state of Arizona. The saguaro plant is commonly found in foothill areas around Tucson. It can reach a height of over fifteen meters, and is by far the tallest feature of the natural vegetation in that area, most of which is less than three meters tall. The majority of the remaining plant community in the area has a rather scrubby appearance and is referred to as “desert scrub.”
Livingston noted that the soils of Tucson are of relatively low fertility, which is one of the major differences between the environments of Amman and Tucson. Plants in Tucson have had to become very "opportunistic" in terms of adapting to low fertility and especially very low water availability. For example, the saguaro has two root systems: a deep root system aimed at extended rainfall patterns and a shallow one aimed at short rainfall patterns. It therefore uses two ways to collect water. Another manner of adaptation found in Tucson's vegetation is that numerous plants use other plants as "nurses." Such plants establish themselves under taller (nurse) plants, which provide them with protection as they mature. Here, Livingston stressed the importance of looking at the different "nurse plants" and micro-sites available in Tucson's arid environment and at how they provide shady spots (almost oases) for other plants. Livingston added that one should learn from the natural environment and try to apply the information one gets from it in the design of created landscapes.
Interestingly enough, Amman and Tucson have very similar levels of precipitation, which amounts to approximately 300mm per year. The pattern of rainfall in each of the two locations, however, is different. Figure 2 shows a bar chart that illustrates the 20-year mean precipitation for both Amman and Tucson by month. The chart shows that Tucson has a bimodal rainfall pattern. Therefore, half of the rainfall occurs during the summer season, in July, August, and September, while the remainder occurs during the winter season, in December, January, and February. In contrast, the bar chart shows that Amman has a unimodal rainfall pattern that mainly occurs during the winter season, from December through March. Of course, one should keep in mind that there is considerable variation in the amounts of rainfall in the different areas of Amman because of the city's mountainous topography. The situation is different for the city of Tucson, which is located in a very flat area, and therefore does not have the fluctuations in the amounts of rainfall typical for Amman.
As a result of the bimodal rainfall pattern in Tucson, there are plants that are adapted to using winter rainfall, predominantly trees and shrubs, and those primarily expand their root systems during the winter when there is enough water. Other plants, such as native grasses and other herbaceous plants, take advantage of the summer rainfall to grow. In addition, numerous Mediterranean species are found in Tucson landscapes. Those species are adapted to dry summers, and therefore find an extra source of water in Tucson's summer rainfall. Some Mediterranean species have adapted to the wet summer in Tucson, while other species do not tolerate this pattern of rainfall, and therefore do not do well in Tucson.
The summer rainfall in Tucson is associated with strong sudden storms, and these storms provide a major problem affecting soils in Tucson. The soils cannot absorb the water fast enough during the violent storms, and therefore erosion results. In fact, the issue of preserving soils from erosion is a main environmental challenge faced in Tucson.
Tucson is surrounded by desert scrub, which can be divided into two plant communities. Those are the Arizona Upland, which appears in figure 1, and the lower Colorado River Valley. The dominant species in these communities are the saguaro (which was discussed earlier in this essay) and other cacti such as Opuntia species, palo verdes (Cercidium microphyllum and C. floridum), velvet mesquite (Prosopis velutina) (found in the Arizona Upland and lower Colorado River Valley), and creosote bush (Larrea tridentata) (found in the lower Colorado River Valley). The green bark of the palo verde works as a "food machine," in the sense that it can photosynthesize even without the need for leaves. Before building development took place, the basin area of Tucson was almost entirely covered with a creosote bush community (figure 3). The creosote bush serves as a nurse plant for certain grass species, such as the bush muhly (Muhlenbergia porteri). The transition from the lower Colorado River Valley into the Arizona Upland generally occurs at the base of the foothills, where one can find plants from both communities.
Ephemeral watercourses are a very valuable resource in Tucson. (3) These watercourses are seasonal, and most of them do not have constant water flow, but support shallow water tables under the surface. Occasionally, especially during the summer and winter rainfalls, water runs in these courses. One can view these watercourses as natural "corridors" running through Tucson. In some cases, parks have been developed along those watercourses allowing people to promenade and enjoy the plants and the wildlife that exist in those areas, without disturbing the natural wildlife. Watercourses are extremely important for the wildlife in Tucson in that many animal species live in these watercourses and the areas that surround them. Also, these watercourses serve as "highways" for the area's transient wildlife because they allow various animal species to move among the basin, upland, and mountain areas, thereby passing through the city.
Ephemeral watercourses in Tucson generally are classified into two types, Xeroriparian and Mesoriparian. Xeroriparian watercourses are small washes or streams. They are distinguished from the adjacent plant communities of the Colorado River Valley or Arizona Upland areas in that they have a higher density of plants and more foliage, though they often have similar species. Mesquite is a very common plant in that region. Mesoriparian watercourses are large washes that receive greater water flows than Xeroriparian watercourses. Their vegetation is more significant in structure than that of Xeroriparian watercourses, and includes a wide variety of species, thus allowing for significant biodiversity. Fremont cottonwood (Populus fremontii) is a common plant in Mesoriparian watercourses and provides an important haven in which large birds can nest and also provides habitat for other wildlife.
Human influences on Tucson's landscape
Tucson is a very multicultural city and its demographic structure is composed of a number of groups of people. One group consists of the immigrants who moved to Tucson from other states in the United States seeking warmer climates. A second group includes immigrants from neighboring Mexico, and who have had a significant impact on Tucson's demography and culture. A third group consists of immigrants coming to Tucson from other nations. The fourth group, representing the first settlers of this area, consists of the native Americans who also have had a great impact on the landscapes through their own culture and patterns of activities.
Livingston gave the example of the Tumacacori National Historic Park as an existing illustration of the influences of other nations and cultures on the landscape of Tucson. In this park, one finds numerous Mediterranean plants such as olives (Olea europaea) beside native plants such as mesquites. Livingston added that when the Spanish and French missionaries came into Mexico and then migrated towards the north, these Mediterranean plants moved with them. This is why a number of traditional Mediterranean gardens had been established in America as early as the seventeenth century. The Mexican influence on the landscapes of Tucson is prominently emphasized in the use of color throughout created landscapes. This is expressed in the use of colorful plants such as the bougainvillea (Bougainvillea sp.), as well as in the use of color for walls, shades, and outdoor furniture. Livingston adds that those landscapes usually "embrace the sense of outdoor rooms," and often give those wandering through them the feel of walking through an oasis (figure 4).
Another demographic effect on the landscapes of Tucson is the city's very rapidly growing population. Tucson has a population of about 800,000 people, and has the unique position of being one of the largest cities in the United States for which the majority (90%) of its water is obtained from ground water. This is why Tucsonans have reached a point where they need to seriously think about the city's rapidly growing population, and about protecting what remains of the city's natural vegetation and underground water supplies.
Livingston reviewed some activities that have influenced the landscapes of Tucson. Historical land uses traditionally concentrated on agriculture, mining, and livestock grazing. The latter was of special significance, particularly during the nineteenth and early twentieth centuries, when the land was subjected to extensive over-grazing. Figure 5 shows an area outside Tucson in the 1950s. What appears in the figure is different from what traditionally was found in the Tucson area: semi-desert grassland that has a healthy Savana-like appearance. Unfortunately, that area was over-grazed to the point that the land became bare and the native grasses disappeared. The situation was very serious, and even when livestock grazing activities were greatly reduced, the native grasses were unable to significantly grow back. Figure 6 shows the same area in the year 2000. Livingston stated that when looking at the high density of grasses that have been re-established, one might think that the area has become environmentally healthy. The situation, however, is more complicated than first impressions might lead one to think. The land had been so degraded that it needed the introduction of a new grass species, which was introduced from South Africa. The newly introduced species adapted exceptionally well to the environment in which it was introduced, and continued to spread into other plant communities such as the Arizona Upland. Unfortunately, it was not intended for these areas. Fires are associated with semi-desert grasslands in part due to high amounts of fuel provided by extensive grass cover, whereas the Arizona Uplands are not adapted to fire. Therefore, the spread of fires into these other communities has resulted in considerable harm, thus threatening to extensively change the area's ecosystem.
Agriculture also used to be a very important activity in areas surrounding Tucson, but now is being greatly reduced as the economy is becoming more service oriented and urban areas are expanding. This has resulted in large areas of abandoned farmland, leading to loss of vegetation and soil and extensive dust storms that affect nearby urban centers. Consequently, specialists have started to educate the public about the threats caused by bare lands and have been working on re-vegetating and rehabilitating those lands, especially in areas where water for irrigation is still available.
Obviously, land-use patterns in and around Tucson have changed dramatically. Urban development is spreading rapidly, and is emerging as a main threat to the landscape. Considering the extremely rapid growth of Tucson, it is incredibly difficult to develop a current comprehensive plan for the city (figure 7), and existing zoning regulations are frequently re-evaluated. This has resulted in considerable damage to the environment and the area's natural resources. For example, riparian areas in the Southwest are decreasing as a result of the fragmentation of watercourses that has resulted from the process of continuous development. Those areas constitute a major natural resource in Tucson and their continuous loss negatively affects riparian vegetation communities as well as the wildlife associated with them.
Livingston believes that such urban sprawl and associated land use practices that are prevalent in Tucson need to be more closely regulated. Planners and decision makers should deal with clearly defining areas for development, areas that should be protected, and the kind of relationship that needs to exist between Tucson's green and urban spaces. They will have to act quickly to come up with a plan that will direct growth while protecting the valuable landscapes of the city along with the biodiversity that those landscapes support before such landscapes are permanently lost.
A few landscape protection measures have been taken in Tucson such as those being applied to protect Mesoriparian watercourses. The inhabitants of the city enjoy visiting those watercourses because of their lush vegetation and beauty, especially when water runs through them. In some cases, however, people abuse such fragile watercourses in a manner that causes their erosion and disturbs their wildlife habitat and the vegetation around them. Here, Livingston stressed that everything in the ecosystem is very fragile and all parts of the ecosystem are connected. She added that the ecosystem is a very large circle, and once one piece in this circle is disturbed, the whole system is disrupted. As a protection measure for the Mesoriparian areas, some areas are now being monitored, and visitors need to obtain permits for access. Also, educational handouts are being given to visitors, and these explain what a visitor to those protected areas is allowed and not allowed to do.
Livingston stressed that the issue of water conservation needs to address three areas. The first is the need for community support, which is not an easy goal to achieve in Tucson. This is because the city's population is growing rapidly and also is very transient. The majority of the Tucson's inhabitants move in and out of the city within three to five years, which often is not enough time to develop a sense of belonging to the city. Moreover, new residents of Tucson are often attracted to its warm weather but do not necessarily like the desert as their landscape. Consequently, they strive to recreate the lush water-consuming environments of the other areas of the United States from which they moved, which primarily are the East Coast and the Midwest.
The second issue is the use of education to raise awareness concerning water conservation. Figure 8 shows a public landscape in Phoenix, Arizona, which conserves water and is a type of landscape solution that the public needs to know more about. People with little exposure to the concepts of arid landscaping usually like to introduce turf areas into their landscapes. However, after they learn about arid landscapes, about the aesthetic potentials they provide, and the significant diversity they allow, many of them become very excited about arid landscaping solutions such as the one shown from Phoenix.
The third area is that of public regulation and enforcement, where monitoring needs to be put in place to make sure that regulations regarding water-conserving landscape practices are followed. Livingston added that considering the complexities involved in getting a piece of legislation drafted and passed, and setting up the administrative mechanisms required for its implementation, this third goal usually is the hardest to achieve.
Public education and the concept of xeriscape
Public education about arid landscaping includes teaching water conservation principles, where the concept of "xeriscape" is stressed. The term "xeriscape" is a result of combining the Greek word "xeros," which means "dry," and the suffix "scape," and was coined by the Denver Water Department in 1981 as an educational concept. Xeriscape stresses water conservation in combination with creative landscape designs. In some cases, people will have negative connotations when presented with a concept such as xeriscape since they think it is all about using cacti and rocks for landscape designs, even though the concept allows for considerably diverse solutions. Consequently, it is important to educate the public about the concept of xeriscape and the diversity of landscaping solutions it provides.
Livingston mentioned the seven principles of xeriscape, which were organized into two groups. The first group included water-wise planning, using low-water consuming plants, and limiting turf areas. With those principles in mind, one starts by zoning one's landscape. For example, areas such as front yards that are close to entryways can be designed as low water-use landscapes. On the other hand, high activity areas such as backyards can be treated more as oasis-like areas, and one can use a mixture of drought-tolerant and lush plants such as palm trees for these areas. One also can emphasize the oasis effect by incorporating a shaded patio with lush-looking plants around it (figure 9). In such a case, the use of water is minimized, and the turf - which generally requires considerable water and maintenance - is reduced to limited areas.
Actually, many wonderful compositions can be created with low water use plants. For example, one can create a "layering effect" with those plants. In such a case, one would start with "upper story" species such as the palo verde with its remarkable green bark. Then, one would introduce a lower layer of native accent plants, and complete the composition with "lower story" plants such as ground covers in the foreground. Livingston emphasized that creating examples of creative compositions of landscapes that are accessible to the public can effectively convey the message that people do not have to be very sparse in their planting; they just have to be conscientious of the kind of layers they are creating.
The second group of xeriscape principles that Livingston mentioned includes water harvesting, efficient irrigation, the use of mulch, and proper maintenance. Water harvesting emphasizes collecting rainwater and using it in different ways to serve the needs of people, plants, and animals. Water harvesting has been used historically in Tucson as well as in Amman. Rainwater falling on roads, patios, and roofs can be harvested. For example, an existing slope in a certain landscape can be used to direct water towards plants located at the lower level of that slope, instead of just losing the water to the streets. (4)
As for efficient irrigation, an underground drip irrigation system is recommended. It also is necessary to find out how much water the plants in a certain landscape require and to apply only that amount of water. Therefore, when designing an irrigation system, one should try to locate groups of trees, shrubs, ground covers, and turf areas on different control valves. Each of these groups of plants has different irrigation requirements, and one should be able to control the irrigation process for each of them separately. Also, the frequency of irrigation should be changed according to the changes in water requirements in the different seasons.
The use of mulch is another important principle in xeriscape. Mulches cover the soil and help reduce water evaporation, and consequently reduce water use. They also protect the soil and consequently improve root growth and limit the germination of weeds. In general, there are two kinds of mulches. The first is organic mulch such as bark chips, wood grindings, and the natural drop of leaves and flowers that when left on the ground are very good for the soil. The second kind is inorganic mulch, which is more commonly used in Tucson's landscapes. The most common kind of inorganic mulch used in Tucson is decomposed granite, which basically consists of small pieces of crushed granite. Usually, these pieces are obtained from leftover granite used for other construction. They come in different colors, and one may pick a mulch color that either contrasts or complements the adjacent architecture. Livingston mentioned that numerous inorganic mulches are available in Jordan such as "touf," which is a porous volcanic stone that can be found in different sizes and shades.
Livingston believes that appropriate garden maintenance is an essential component of creating successful xeriscapes. Created landscapes need maintenance such as pruning, weed removal, and maintenance of the irrigation system. In general, to create a successful landscape, one needs to provide a good design, to effectively implement that design, and to maintain it appropriately. If these three components are satisfied, xeriscapes not only save water but also time and money. (5)
Regulation of water conservation
Livingston discussed a number of the ordinances related to water conservation that are being implemented in Tucson. One of those is the Native Plant Preservation Ordinance. Here, when someone wants to develop a large-area, the existing native plants on that land need to be taken into consideration. The Native Plant Preservation Ordinance specifies four general methods for dealing with those plants. Developers can set aside 30% of the area of the site and keep it untouched. In case it is decided to develop the entire site, then the developer is required to replace certain plants at a ratio of three to one. For example, if there are five mesquites on the site and the whole site is to be developed, the developer would need to replace the existing mesquites with fifteen nursery-grown ones. A third method consists of a combination of the first two, and a fourth method is to salvage the existing plants. In this case, before construction takes place on the site, the affected plants would be moved to a retention area to then be replanted in the site after construction is completed. According to Livingston, salvaging practices are improving in a way that the number of plants being damaged as a result of the moving, storing, and replanting processes has decreased significantly.
Another ordinance Livingston mentioned is the Watercourse Ordinance, which is concerned with protecting the watercourses of Tucson and the biodiversity they support. This ordinance requires that watercourses be provided with minimally disturbed buffer areas around them. Also, one of the newest ordinances to be considered in Tucson is the Sonoran Desert Conservation Plan, which is concerned with preserving large open spaces such as rangelands, ranches, and abandoned farmlands surrounding the city.
Livingston presented examples of re-vegetation projects that have been carried out in Tucson. Some of the examples showed the re-vegetation of native grasses and wildflowers that live on irrigation during their first year and after that survive on natural rainfall. Ocotillo (Fouquieria splendens) is another native plant that appeared in the examples Livingston presented. It is a very drought adapted plant and often leafs out several times during the year, depending on how much water is available to it. It also produces red flowers that attract hummingbirds. Livingston also mentioned examples where the mixes of plants used to re-vegetate certain areas were very close to what occurs there naturally, making it difficult to distinguish the planted area in such developments from the natural preexisting vegetation around it.
Examples of Landscapes in Tucson
The last part of Livingston's lecture provided a visual sampling of landscaping solutions devised and implemented in Tucson. Livingston organized the examples she presented into two overlapping categories. The first includes "constructed elements," and the second includes "natural elements" in landscapes.
Constructed elements in landscapes
Constructed elements are those dealing with man-made elements in the landscape such as outdoor patios, walls, walkways, seatings, covered porches or "ramadas," water features, and sculptures. A variety of materials are used in these constructed elements. Brick is a very common surface material in Tucson's landscapes. It is a Mexican influenced surface, and is very effective, particularly in more formal landscape designs. Also, it blends very nicely with the colors of the Sonoran Desert, and with the colors of Aleppo pine (Pinus halepensis) and euphorbia (Euphorbia rigida), plants naturally found in Jordan.
Another surface that is commonly used in the landscapes of Tucson is flagstone. This can be set in the natural ground as a walkway. In such cases, it provides water-harvesting potentials for adjacent plants and also complements the natural look of the landscape. Another way of using flagstone is to set it in mortar. There are many skilled Mexican masons who work with flagstone and slate in Tucson. They are third and fourth generation masons, and can create beautiful, complex designs (figure 10).
Exposed aggregate also is very widespread in Tucson, and usually is used to give a rather "contemporary" look. In some examples, those surfaces are complemented with the use of native grasses such as a bunchgrass called deergrass (Muhlenbergia rigens). This bunchgrass is found at high elevations near Tucson and therefore cannot survive without irrigation. However, one of its advantages is its low invasiveness: it does not spread aggressively over a given site compared with other kinds of grasses. Another advantage of deergrass is its beautiful form and the shadow patterns it gives during the winter when the sun is at a low angle.
Concrete pavements also are being used in different combinations and provide very effective patterns. In addition, a combination of these various materials can be used. Figure 11 represents an example of combining different materials in the landscape, in this case stone for the walls, and flagstone and interlocking concrete pavement for the ground. Another common combination of materials is the use of sandstone for seats, and exposed aggregate for walkways. Both materials provide bold surfaces that complement the finely textured plants of Tucson. In this context, Livingston added that the native plants of Arizona are much more finely textured than those of Amman and surrounding areas. In Amman, one finds plants such as oleander (Nerium oleander) and carob (Ceratonia siliqua), which are medium to boldly textured plants. Livingston added that such plants offer greater potentials for the creation of oases in arid landscapes than native plants in Tucson because of their naturally more lush appearance.
Stucco is another material that is commonly used in landscaping solutions in Tucson. This material, which provides yet another example of Mexican influence, is made of sand and cement, and can be applied to surfaces either by trowelling or spraying. It can be used to give a smooth-finished (figure 12) or rough-finished surface (figure 13), and can be applied in different colors. Interestingly enough, Livingston noted that the colors used for buildings and landscapes in the historical site of Petra in Jordan and those used for building surfaces in Tucson are very similar.
Livingston stated that another connection between landscapes in Jordan and the Tucson area is the use of gabions. Gabions consist of large stones held together in a certain form through the use of large metal "cages." Figure 14 shows a gabion from Tucson used as a wall with a concrete form put on top of it. Similar gabions are found along the Dead Sea – Aqaba Road in Jordan. The "naturalistic" look of the wall in the Tucson gabion is combined with the native bunchgrass to give an "organic feel" to the site. Stone provides another similarity between the materials used in Amman and Tucson, and the wide variety of colors and textures it offers allows for the creation of very effective compositions.
Ramadas are another important element that is common in landscaping solutions in Tucson. Natural bamboo and wood are often used for ramadas in the Southwest to give an organic feel to the outdoor space (figure 15). However, wood needs frequent maintenance when used outdoors in a dry climate such as that of Tucson (and also Amman). It splinters very quickly because of the dryness of the climate, and therefore needs to be sealed often. Consequently, Livingston suggested the use of steel for ramadas because of its durability. Also, steel can easily be painted in different colors. In this context, Livingston presented an example of landscape architect Steve Martino's work in which steel beams and columns were used. A stucco finish was applied to the columns, and the roof consisted of perforated metal panels that often are used for security doors (figure 16). This rather transparent cover gives very effective shadow patterns, especially in the wintertime. As is the case with colored walls, colored ramadas provide a powerful contrast with the fine-textured plants of Tucson such as the honeysuckle (Anisacanthus thurberi), the blue palo verde (Cercidium floridum), and the Indian fig (Opuntia ficus-indica).
Water features often are used in landscapes of different scales in Tucson. People like landscapes that appeal to many of their senses, and water features help provide that effect. In one example of water features that Livingston presented, a pump from an old ranch was used, but the pump provided a strong contrast with the contemporary setting in which it was placed, and which consists of a very simple concrete basin with rocks at its base. Such a use of water provides a sense of an oasis to the landscape.
Livingston added that sculpture provides an effective way to celebrate the regional context of one's area as well as to communicate an educational message concerning the use of arid landscaping. Representing native plants in sculpture helps people to connect to and become enthusiastic about the type of plants they see in the Sonoran Desert. Sculptures that represent the wildlife of the Sonoran Desert also are being used in the landscapes of Tucson. Figure 17 shows a sculpture of a jackrabbit, a very popular animal in the Tucson area. Such a sculpture gets people excited about the wildlife of the area and supports efforts aimed at protecting it.
Livingston added that the wildlife of the Sonoran Desert is very rich. It is common for visitors to view the Sonoran Desert as a hostile place where dangerous creatures live, but this is not the case. It is the habitat of numerous reptiles and amphibians, and most of them are quite harmless. For example, horned lizards are very common small reptiles that live in Tucson. They are very "passive" animals and do not bite. However, when one holds a horned lizard too tightly, it sprays blood from the glands it has above its eyes. Gila monsters are venomous lizards that live in the Sonoran Desert. However, they move slowly and therefore one has to not be paying attention to be bitten by a Gila monster. There are not many dangerous insects in the Sonoran Desert, but there are scorpions, even though one rarely sees them. Many species of birds live in the Sonoran Desert environment such as hummingbirds, hawks, and Gambel's quail. (6) Livingston emphasized that it is best to stress the practice of appreciating but not disturbing the native creatures and their habitat.
Natural elements of landscapes
Livingston discussed the elements that occur naturally in the landscapes of Tucson. She presented a few design examples that take advantage of such elements or incorporate them into created landscapes. Such natural elements include landforms, boulders, natural ponds, watercourses, mulches, and plants. Boulders often are used in landscapes to stabilize banks. In other cases, planting pockets are created within those boulders to help visually soften the rough effect they give. Boulders also are used as design features in the landscapes that provide additional contrast within that landscape (figure 18). Organic mulches are not frequently available in Tucson, therefore inorganic mulches need to be used. Small stone or decomposed granite is commonly used for mulches and in pathways.
Livingston emphasized the use of plants that provide refuge for native birds. In this context, she presented the example of her own front yard where she grew plants such as the desert marigold (Baileya multiradiata) that attracts Inca doves and the purple prickly pear that is popular with Gambel's quails. Livingston also incorporated into her landscape mesquites in which doves nest and to which quails and woodpeckers also are attracted. She also introduced to her landscape the fairy duster (Calliandra eriophylla) to attract hummingbirds.
Another point Livingston illustrated is the use of bold-textured plants along with fine-textured plants. Here, she showed the example of the rough- textured palm trunk that serves as a background for a native fine-textured milkweed (Asclepias subulata). Livingston also suggested the use of plants in layers, which would give the illusion of a much denser landscapes, instead of just having a few sparse desert plants.
Livingston also showed how plants can protect one another. For example, overstory plants are protected from radiation reflected from the ground underneath by using understory plants that tolerate heat. Also, we can protect understory plants from sunburn and frost by providing cover with appropriate overstory plants. Livingston also suggested the use of hardier plants in pots. One can use, for example, an evergreen accent such as sago palm (Cycas revoluta), instead of water-loving annuals such as pansies.
Towards a More Sustainable Landscape
Livingston believes that more sustainable landscaping solutions should be sought in Tucson, and this can be achieved when input equals output: where not too much is being consumed in terms of natural resources. One can follow four guidelines to reach this goal. The first is to try to select and use plants from the existing native ecosystem. Many people get confused and think that because a certain plant is an Arizona native, they can use it in Tucson. However, one should be aware that the area near Tucson has various elevations, and therefore one cannot use a plant that grows naturally at an elevation of 2000 meters - such as native oaks (Quercus spp.) - in Tucson, where the elevation is 900 meters. This is the reason why it is necessary to educate the inhabitants of Tucson about the kind of plants that grow in and around the city. Also, whenever introducing exotic plants, one should always think about the effects that the introduction of such plants would have on the natural ecosystem. The aim always should be to enhance the existing ecosystem rather than to modify it.
The second point Livingston made in the context of sustainable landscapes is the need to increase the use of water harvesting. The third point is to increase energy conservation. This point includes the conservation of energy used for mowers, weed-eaters, and leaf-blowers. Here, it should be kept in mind that low-maintenance plants use less energy. The last point that Livingston made concerning the issue of sustainable landscape is that of recycling local materials. She presented examples such as the use of broken concrete to provide a mosaic-like walking area, the use of the soil of the site to build a wall, and the use of rocks that originally were present on site in paving a driveway. Such examples help the public to understand, visualize, and sympathize with the concept of recycled materials.
Livingston ended her presentation by showing a small-scale recycling project that took place in her neighborhood in Tucson (figure 19). The project, which includes the construction of a traffic circle, was an example of active community involvement. Site preparation and concrete paving were made by a neighborhood resident who owns a construction business. A nursery donated native plants. Also, recycled bicycles were used to mount the reflectors that keep people from driving through the traffic circle. This example shows how everyone can have a part in producing a more sustainable landscape, even on a very small scale.
(1) Margaret Livingston is an assistant professor in the School of Landscape Architecture at the University of Arizona at Tucson. She teaches courses relating to plant taxonomy, plant materials, planting design, landscape ecology, and rangeland plant communities. Her research interests include habitat restoration and re-vegetation, analysis of arid land plant communities, and identification and management of endangered plant species. Her design work is predominantly residential in scale with an emphasis on xeriscaping, native plants, and habitats for urban wildlife.
(2) For additional information on the deserts of the United States, see the web site http://www.desertusa.com/desert.html. This web site includes information on the geology, plants, animals, and wildlife of these deserts.
(3) Concerning watercourses and riparian areas in Tucson, see Ervin Zube, "Sharing Rivers, Sharing Opinions - Perceptions of Riparian Areas: Values and Uses," and Susan McGinley, "Wildlife in the City: Conserving Natural Habitats in Tucson." Both articles are included under the 1996 research reports found in the web site of the College of Agriculture at the University of Arizona at http://ag.arizona.edu/pubs/general/.
(4) For additional information on water harvesting, see the water harvesting section in the Tucson Water web site.
(5) For additional information on the principles of xeriscape, see Xeriscape: Landscaping with Style in the Arizona Desert - A Step-by-Step Guide for Planning, Installing and Caring for your Landscape (Tucson: Arizona Department of Water Resources, 2000).
(6) Concerning the wildlife of the Sonoran Desert, see the web site http://www.desertusa.com/animal.html.
List of figures*
Figure 1: A typical view of the landscape surrounding Tucson.
Figure 2: A 20-year average rainfall chart for Amman and Tucson.
Figure 3: A creosote bush (Larrea tridentata) community in the Tucson area.
Figure 4: An example of the use of color in landscape designs.
Figure 5: An image from the 1950s showing an area outside Tucson where the plant community was destroyed as a result of over-grazing.
Figure 6: An image from the year 2000 showing the same area represented in Figure 5 after being re-vegetated with exotic grasses.
Figure 7: Urban sprawl in Tucson.
Figure 8: A low water consuming public landscape design in Phoenix, Arizona.
Figure 9: A landscape design featuring an oasis-like shaded area with a patio.
Figure 10: The use of slate surfaces in a landscape design.
Figure 11: The use of a combination of flagstone and concrete surfaces in a landscape design.
Figure 12: The use of smooth-finished stucco in a landscape design.
Figure 13: The use of rough-finished stucco in a landscape design.
Figure 14: The use of a gabion in a public landscape design.
Figure 15: The use of a wooden ramada as a shade-providing element in a landscape design.
Figure 16: The use of a steel ramada as a shade-providing element in a landscape design.
Figure 17: The use of a sculpture of a jackrabbit as a feature in a public landscape design.
Figure 18: The use of boulders in a landscape design.
Figure 19: A neighborhood traffic circle in Tucson constructed through the participation of the neighborhood inhabitants.
* All images are courtesy of Margaret Livingston.