Even the plants of the Sonoran Desert aren’t immune to climate change

In the hotter, drier deserts of North America, climate change is declining plants once thought to be near-immortal and replacing them with shorter shrubs that can benefit from sporadic rainfall and warmer temperatures.

Numerous studies have documented how a hotter, drier world is causing a redistribution of vegetation in temperate mountain regions. A new study at the University of California at Riverside documents the unexpected ways plants do in a portion of the Sonoran Desert.

“Plants are changing, but in strange ways,” said Tessa Madsen Heap, first author of the study and UCR doctoral candidate in Ecology and Evolution. “We thought most would move to higher elevations with cooler temperatures. But while some of the lower-elevation trees are retreating and shifting higher, we’re also seeing some other species moving downward, toward the hotter parts of the desert.”

Furthermore, the researchers believe that the trends they observed are likely to continue despite the extreme precipitation events of the past few months. “It is really high temperatures that cause the most stress to these species, and a year’s worth of rain will not mitigate the long-term course of the drought,” said Madsen Heap.

Published in the journal functional ecologyNot only search documents How do some plant species move downward in height but examines the physical characteristics of those plants to explain why this shift occurs.

To make their observations, the research team visited the Boyd Deep Canyon Desert Research Center, just south of Palm Desert, in 2019. The research area stretches 8,000 feet from the desert to the summit of the mountain, where they traveled through top-down sampling vegetation. This same region had previously been examined by ecologists in both 1977 and 2008, providing a basis for comparison with more recent findings.

“Species that we normally think of as highly stress-tolerant, such as the California juniper and pine pine, are declining or moving upwards. And even though they’re evolving, they don’t seem to thrive in their new locations,” Madsen-Heap said. “Transitioning to their former low-elevation sites are plant species with shallow root systems, such as the brittle shrub, the burrowing shrub, and the ottolo.”

In addition to root systems that don’t rely so much on deep soil water, which gets scarce, these shorter plants are also able to grow faster and invest fewer resources in their leaves.

“These are weeds. They have ‘cheaper’ leaves in terms of carbon cost to produce, and they shed from drying out,” said Marko Spasoewicz, senior author and assistant professor in the Department of Evolution, Ecology and Biology at UCLA.

In other words, they can drop leaves when conditions get too stressful and wait for the drought to end.

Plants that keep their leaves year-round tend to invest in thicker leaves with a higher carbon content. They are at a disadvantage compared to plants that are easier to get rid of. When plants drop their leaves, the atmosphere can no longer draw water from them, which reduces the demand on the roots to supply the lost water.

“The old slow living strategy that used to work for plants in this environment just doesn’t work very well anymore. Increased climatic stress in an already harsh environment pushes them to their physiological thresholds,” said Madison Heap. . “Once these plants reach their limit, there’s no way they can be fixed,” she said. “There’s not much we can do to bring them back.”

The team also found that unlike more temperate ecosystems, lower desert elevations warm faster than higher elevations. Bushes and jungles are not necessarily coming from the highest points in the desert. They are also low-growing plants that have generally expanded their range.

At about 29 meters per decade, the upward range shifts are on par with the higher end of global rates of plant movement in response to a warming climate. On average, vegetation in temperate regions showed band shift rates of 5–30 m per decade.

“We often think of the tundra as the driver of climate change. The Arctic and Alpine ecosystems are very sensitive. We see here that this ecosystem is just as sensitive, if not more so,” Spazojewicz said. “And we already know the answer to decompressing it. It’s very simple. Cut fossil fuel emissions.”