Plants on the Run

Plant Response to Drought and Heat Stress

Article Provided by Cindy Odgers

Photo by David Sola on Unsplash

When the climate changes, so do the presence of plants in different areas worldwide. The fossil record has proven invaluable in tracking plants from one location to another in response to drought and heat stress, showing that plants are indeed mobile organisms. For plant species, migrating in response to changes in environment is a matter of survival.

One may think this migration occurs slowly over hundreds or thousands of years, impossible for humans to notice. But from 1970 to 2011, researchers at the University of Miami tracked plant communities consisting of 20,000 species and 20 million individual observations across the Americas. They found that warmth-loving plants were growing more common everywhere the researchers looked. Many North American plants have moved in the last several decades approximately 36 feet to higher elevations or 10.5 miles to higher latitudes every ten years. The Arctic tree line moves 131 to 164 feet northward towards the pole each year. Plant and vegetative zones shift in response as temperatures increase and soil moisture changes. Plants experiencing a shift in their range will affect the ecosystem (a biological community of interacting organisms and their physical environment) they are leaving and the ecosystem into which they are moving. Disruption in any part of an ecosystem affects the entire ecosystem.

To understand how plants may cope with environmental changes such as drought and heat stress, scientists at the University of Washington compiled geographic coordinate data for the locations of nearly 300 plant species within seven distinct regions (including Arizona) across western North America. Researchers compared these findings to changing environmental conditions, such as drought, temperature, rain, and snowfall. The expectation was that plants would move toward cooler temperatures, but the research indicated water was a more defining factor than temperature.

Drought is a distinctly different stressor than high temperatures on plants, and plants respond to each differently. “Some plant species are very tolerant of drought, some very intolerant, some in-between,” says Professor Alex Niemiera, School of Plant and Environmental Sciences at Virginia Technical University. “Soil type will also affect drought response. Plants growing in moisture-retentive soils fare much better than those in less retentive soils.” Extreme heat may eliminate plants that do not have the mechanisms to withstand even short episodes of high temperatures. To survive or go extinct, plants must shift their distribution, alter their annual vegetative and reproductive cycles, or acclimate or adapt to environmental changes.

The effect of drought and heat stressors on landscape plants will vary over a species distribution. Creosote in Phoenix, for example, may respond differently than creosote in Tucson. Increasing temperatures have brought about earlier plant bloom times, creating a potential timing mismatch between pollinators and plants.

Invasive species have a greater opportunity to thrive and, in extreme cases, take over landscapes when drought and higher temperatures occur. Buffelgrass, common Fountain Grass, and Stinknet top the list of invasive and noxious plants causing widespread problems in Arizona landscapes and threatening the unique Sonoran Desert ecosystem.

As the weather warms, more destructive insect and disease pests will survive the milder winters, have more reproductive success (more generations during a given season), and their growing populations will cause more damage to landscape plants. Rising temperatures are also driving some insects to invade new territories, sometimes devastatingly affecting the local plants.

One can implement several strategies to support the current landscape plant palette during stress. Appropriate irrigation practices, fertilizer and pesticide application reduction, and minimal pruning will prove beneficial. Surface mulches will reduce evaporation and lower soil temperatures. Planting times are more crucial during prolonged stress periods. Even though one can install landscape plants at any time during the calendar year in Arizona, preferred times such as mid-fall and early spring result in better establishment and, in turn, longer-lived plants, reducing costs and labor. Some plants may survive and perform well, while others may not. In all likelihood, the landscape plant palette will change.

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