Desert Trees and Sustainability
Sustainability, like many other ecological/environmental terms, presents a relatively simple word to illustrate a vastly more complex biological construct. Natural systems sustain themselves, or come to some state of “equilibrium,” after thousands or millions of years of trial and error. The balance achieved is unique to a specific locale and is the result of a matrix of physical, environmental, genetic and climate interactions.
When we extend the desire for sustainability to the designed landscape, the variables change a bit but are still highly dependent of the physical location of the landscape (in our case arid regions), local environmental conditions, aesthetics and, surprisingly, economics. The challenge, with regard to sustainable landscape designs, is to create attractive environments while including as many complimentary horticultural characteristics that will amplify and extend the positive environmental qualities to the greater community. As with all biological systems there are trade-offs or, put in economic terms, costs and benefits. The maximum benefit would be generated by those landscape elements that would address multiple positive environmental objectives.
The deserts of the southwest are a harsh genetic crucible where the combination of alkaline soils, high temperatures, low humidity and relentless sunlight have fostered the evolution of tree species well adapted to challenging conditions. When these trees are incorporated into designed landscapes, their hard won horticultural qualities make them the ideal choice for genuinely sustainable designs.
Roots of desert legume trees species, like Mesquites, Palo Verdes, Acacias, and Ironwoods, are not only amazingly well adapted to grow, colonize and stabilize poor desert soils, their genetic ability to fix atmospheric (gaseous) nitrogen and convert it into plant useable nitrate, has the potential of eliminating the need for supplemental fertilizing of maturing trees. These qualities increase soil stability, reduce potential erosion while eliminating the need for application of nitrogen based fertilizers that can contaminate none target water sources and sewers.
Tree leaf canopies benefit the environment by reducing atmospheric CO2, capturing particulates suspended in the air, releasing oxygen, mitigating heat islands and buffering sound, all while providing physically cooling shade and a visually attractive landscape. Shade is always a valued commodity in the desert. With the possible exception of mature thornless mesquites, most desert species do not generate the same level of summer shade when compared with more ornamental species, but the benefits listed above are delivered to the landscape and surrounding community with a minimal application of precious water. Couple these advantages in combination with promoting a sense of place in the desert and their ability to be partially or entirely naturalized (in certain locations and soil types) to survive on native rainfall and the benefits are even more compelling.
People have been drawn to the American deserts since the railroad opened up the West in the 19th century. The desert’s matchless beauty and quiet grace offered an undisturbed natural landscape found nowhere else on earth. As we move into the 21st century, the horticultural qualities of these unique trees, combined with imaginative landscape design and professional maintenance, hold the promise of achieving sustainability while celebrating and complimenting the beauty of our surrounding desert.