The agreement that parceled the Colorado River’s water among seven southwestern states nearly a century ago mistakenly used a period of abnormally high precipitation as the baseline average flow of the river, helping ensure today’s huge imbalance between supply and demand. At the same time, influenced perhaps by the same abnormally wet period that fooled the water planners between 1905 and 1922, a tree native to the Mediterranean was being introduced to Arizona by early pioneers. Reaching heights of up to 80 feet, Aleppo pines became popular sources of shade, thriving in the hot and dry conditions in the lower Sonoran deserts. Until recently.
Earlier this year, local media and neighborhood associations sounded the alarm over a spreading infestation of pine bark beetles now decimating Aleppo and other pine trees in older Tucson neighborhoods. Arizona’s long dry spell has begun seriously stressing desert-friendly but non-native trees like the Aleppo, inviting pestilence to take hold. One remedy is to water the tree deeply to combat growing heat stress. But as rain becomes less reliable and irrigation costs rise, deep watering becomes less of an option for many. The standing dead Aleppo pines might be the signal we need to begin adjusting our strategies and expectations as to residential landscaping in an era of less water and warmer temperatures.
Warning also comes from our neighbor to the west, where just outside Sequoia National Park native oak trees are dead or dying in record numbers in just year four of the California drought. If native oak trees are succumbing to dryness in California, it should not be a surprise that introduced varieties even from a Mediterranean climate have become vulnerable to pestilence in Arizona’s own era of less water.
The Arizona Department of Water Resources tells us that outdoor water use counts for nearly 60 percent of residential water use in the state. While much of this is due to overwatering and leaks, in many places we are still trying to grow thirsty vegetation that is incompatible with an era of less water. Long-time Arizonans know that our beloved mesquite trees are rarely “watered” at all, except perhaps upon planting and by our episodic rains. As native trees continue to thrive and introduced pines become dying sentinels of change, the desert is telling us to reconsider our selection of landscaping plants and trees.
One spot where southern Arizonans are finding what will survive in our drier world is Desert Survivors Native Plant Nursery, a unique organization that combines a highly diverse native plant source with an employment program for adults with developmental disabilities. Desert Survivors grows more than 650 species of local and bioregional plants, native to within an approximate 500-mile range of Tucson. Its plants are native to the region’s three great deserts and adjacent mountain ranges.
While improved irrigation techniques can help reduce landscape water inefficiencies, the smarter choice of trees and plants offered at spots like Desert Survivors will be much easier to keep alive and healthy. If we are able to irrigate with harvested rainwater in lieu of increasingly hard, mineral-laden municipal water, we will have even happier trees. Finally, the abundance of southwestern heritage food trees like fig, quince, pomegranate, lime, plum, guava, date, orange and others available at Desert Survivors means we can truly have our shade and eat it too.
We can’t do anything about the errors of a century ago that promised more water than is available. However, in our quest for a new way of landscaping, one that works with rather than fights against a changing atmosphere and diminishing water resources, there is hope that we can not only survive in the desert, but also thrive in the desert.