About seven years ago, Cascade Business News published an article talking about the need to modify our approach to urban landscapes in response to a rapidly changing climate: The Future of Landscape Design: Water, Climate Change and Public Perception. I wrote that article to increase awareness of the environmental changes that would affect our ability to retain conventional landscapes in central Oregon — things like lawns, high water-use ornamental plants and unsustainable maintenance practices. Now, nearly a decade later, the State and municipalities are implementing changes in the allocation of water rights, construction standards and irrigation restrictions as methods to address the resource limitations and climatic conditions we’re experiencing from a continually changing climate. Cities, homeowners, developers and the “green industry” are now being required to change their landscaping practices.
For the past year or so the City of Bend has been busy revising the Tree and Planter Strip Landscaping Code. Those revisions go into effect on August 16, 2024. They require developers to utilize native or low-water (xeric) plants in landscapes between streets and sidewalks, install water-efficient drip or low-flow irrigation systems and refer to a much broader palette of trees from which to choose for planter strips. Landscape professionals will need to become familiar with native and xeric plants and low-water irrigation techniques in order to meet the updated standards and remain viable as these standards are undoubtedly expanded to all future landscaping in central Oregon.
While the need for these code modifications has been discussed for decades, they are currently being implemented in part because of changes in how the Oregon Water Resources Department (OWRD) is reassessing the allocation of water rights and may be restricting access to additional water resources across the state; including municipalities. According to the OWRD, “The current groundwater availability review process does not adequately address the cumulative and long-term impacts to existing users and the groundwater and surface water systems over time. The current process evaluates one-year short-term acute impacts to surface water bodies within one mile of the proposed location in the application. Under the current rules, permits are generally granted until the basin has more water allocated than may be available at the specific location.”
In Bend, where approximately 60 percent of residential water use is for landscaping, the need to conserve water as an essential resource has become critical. We must get serious about conserving water in our semi-arid environment, but also need to increase our understanding of the importance of a biodiverse urban environment to the health and well-being of ourselves and our community.
But how can we maintain the aesthetic values inherent in urban landscapes while conserving water and other resources? The answer is in designing and creating landscapes and gardens with plants that are adapted to our climate and soils, preserving as much of the native landscape as possible, and understanding that some of the characteristics that make it possible for plants to survive in our sometimes extreme environment are different than characteristics of some more common landscape species.
For example, some of our native shrubs such as wax currant or sagebrush enter into a summer dormancy in response to drought and heat. Wax currant will often shed its leaves in the summer as a strategy to reduce transpiration and save water. Understanding that these types of adaptations are natural and necessary parts of surviving in our climate helps us appreciate the strategic nature of central Oregon vegetation and reduces the need for irrigation in landscapes that utilize these species. And awareness of the importance of these adaptations becomes even more important with climate change.
Heat domes have now become an annual event. The first half of July this year experienced temperatures significantly higher than historic averages, humidity levels significantly lower than historic averages, and no precipitation. Soil moisture levels in unirrigated locations dropped well below 15 percent — generally considered the “permanent wilting point” for plants. Our climate is changing, becoming hotter and drier and increasing drought stress on our urban landscapes. Maintaining the health and vigor of urban plantings becomes increasingly difficult without increasing irrigation and using more water than may be available in our region, especially when the state is reassessing the allocation of water rights and recommending (not yet a requirement) a statewide reduction in water use.
An increase in temperatures and a decrease in humidity levels affects the transpiration rate of plants; the loss of water from plants through small openings called stomates. Transpiration is one-half of “evapotranspiration” or the combination of transpiration and evaporation (the transfer of water from the ground to the air). Most landscape irrigation schedules are based on evapotranspiration. The conditions we experience during heat domes (high temps and low humidity) are not only hard on us but may be even more stressful on plants in our landscapes.
Generally, maintenance practices strive to minimize water stress in landscapes. There is often more water available to the plants than they need. Water-wise landscaping tries to balance the water requirements of plants with the irrigation schedule so there is a minimum of excess water available for plants. The supply balances with the demand.
Heat domes increase the water requirement of landscapes through increasing transpiration rates of individual plants and increasing evaporation rates from soil. Typically, we respond by irrigating more often or for longer durations, primarily to maintain the aesthetic value of the landscape. We want it to look good even through periods of extreme stress.
And there’s the issue. As discussed back in 2017, we need to alter our views of landscapes. With continued climate change and the subsequent and inevitable revision of landscape code and water use restrictions, we can no longer justify the design, construction and maintenance of conventional landscapes. We need to increase our understanding and awareness of the environmental impacts of our landscaping practices and be proactive in addressing the very real effects of a continually changing climate. Plant choices, planting techniques, maintenance practices and embracing the biology that supports communities of plants must be incorporated into our planning and design if we want to continue creating environments that support ourselves and all the other life with which we share this planet.
Rick Martinson is the founder and director of the High Desert Horticultural Center and co-owner of WinterCreek Nursery in Bend. He worked as a landscape contractor in Bend for over 25 years, served on the Oregon Landscape Contractors Board and holds a Ph.D. in horticulture from Oregon State University.
highdeserthorticulturalcenter.org
The above article was prepared by the author in his/her own personal capacity. The opinions expressed in the article are the author’s own and do not necessarily reflect the views of Cascade Business News or of Cascade Publications Inc.
