Climate change threatens the survival of iconic saguaro cactus in the Southwest

The saguaro cactus is being threatened by drought conditions and rising temperatures. Scientists surveying Saguaro National Park in Arizona say the situation is increasing the mortality rate of young saguaros. Stephanie Sy has more on what those trends mean for ecosystems in the Sonoran desert.

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  • Amna Nawaz:

    An icon of the desert, the saguaro cactus, is being threatened by drought conditions and rising temperatures.

    Our reporter Stephanie Sy ventured into the Sonoran Desert to see what those trends mean for ecosystems across the Southwest.

  • Stephanie Sy:

    On the edge of Saguaro National Park in Tucson, Arizona, Maria Francisco And Tanisha Tucker uphold a sacred tradition of the Tohono O'odham Tribe, harvesting fruit from the majestic saguaro, the largest cactus in the U.S.

    Using an old saguaro rib as a gathering tool, they have only a few weeks each summer to do the picking before Southern Arizona's monsoon season spoils the fruit.

  • Tanisha Tucker, Tohono O’odham Member:

    The fruit that we cook and turn into syrup becomes wine. And that wine is then used for rain ceremonies.

  • Stephanie Sy:

    The sacred tradition has remained the same, but the saguaros themselves are changing.

    For Francisco, the first sign of this is the late ripening of the fruit.

  • Maria Francisco, Tohono O’odham Member:

    When I used to come out here with my aunt Stella, I would be out here like mid-May, and she'd be out here mid-May. Now it's like mid-June.

  • Don Swann, Biologist, Saguaro National Park:

    What we're concerned about is that we're seeing far fewer very small saguaros.

  • Stephanie Sy:

    In Saguaro National Park, which is brimming with the plants, biologist Don Swann says prolonged drought conditions and higher temperatures are increasing the mortality rate of young saguaros.

  • Don Swann:

    The older they are, the more resilient they become to deeper and deeper droughts, right?

    So they're very resilient when they're 60 years old, but they're not very resilient when they're 5 years old.

  • Stephanie Sy:

    A 2018 National Park report showed that, of the 10,000 saguaros studied within the park, just 70 were less than 15 years old.

  • Don Swann:

    We're trying to understand how changes in temperature and precipitation in the future might affect the reproductive potential of saguaros, everything from how old they are when they start reproducing to how many flowers do they produce.

  • Stephanie Sy:

    To do this, they fix a GoPro camera to what amounts to a very tall selfie stick. In spring and summer, they regularly take pictures of the flowers that bloom on the tops of saguaro arms.

    When compared over time, the pictures document changes to the saguaro life cycle. The plants' flowers, which when pollinated produce the fruit, can give scientists key information about long-term impacts of climate change.

    But, to Swann, the saguaros are about more than science.

  • Don Swann:

    For me, what's so wonderful about saguaros is really kind of the way that they move people.

    And a lot of people who live here will tell you that one of the reasons they live here is because of this plant.

  • Stephanie Sy:

    Rising temperatures and drought aren't the only threats to the saguaros. Invasive grass species like this compete for water and also increase fire risk.

  • Ben Wilder, Ecologist:

    We have this increase of non-native grasses, the grassification of the Western United States and in many of the deserts. And that drives a fire regime and introduces a fire regime to the desert that's pretty novel.

    And you can see the burn marks on that one.

  • Stephanie Sy:

    Ben Wilder is an ecologist, studying the long-term impact of fire damage on the Sonoran Desert ecosystem.

    Remnants of the 2020 Bighorn Fire can still be found in the Santa Catalina Mountains on Tucson's perimeter. Thousands of saguaros were killed in the blaze.

  • Ben Wilder:

    It's eye opening in terms of, what is the desert capacity for resilience in the face of fire? And that's truly an open question right now.

  • Stephanie Sy:

    The saguaro is not the only Western species under threat from the wildfires being fueled by climate change. Within the Mojave National Preserve in California, an estimated 1.3 million Joshua tree were killed in a 2020 wildfire.

    That same year, wildfires killed approximately 10 percent of the world's giant sequoia trees. Last year, another 5 percent were lost to additional wildfires in the state.

  • Ben Wilder:

    Coming to grips with the massive loss that is happening is part of the ecological change that were all within.

  • Stephanie Sy:

    To counter the loss, the Tucson Audubon Society is planting young saguaros, positioning them near so-called nurse plants, which act as shade and shields.

    Jonathan Horst says saguaros are a keystone species.

    Jonathan Horst, Director of Conservation and Research, Tucson Audubon Society: We have got 14 species of birds, multiple species of bats, hundreds of species of insects, rodents, javelina, foxes. Everything is chowing down on the fruits when they drop.

    Without saguaros, in a lot of ways, giant pieces of the Sonoran Desert ecosystem just implode.

  • Stephanie Sy:

    Soon, thousands of these saguaros will be planted in Southern Arizona's Santa Catalina Mountains as part of a larger restoration effort.

  • Jonathan Horst:

    Those first two years, that's the most critical establishment phase. Then, the survival rate significantly increases.

  • Stephanie Sy:

    These imposing desert plants armored with spikes suddenly seem vulnerable. And to Tanisha Tucker and Maria Francisco, it is like watching a relative suffer.

  • Tanisha Tucker:

    We have a relationship with them. So, in our creation stories, we mention them, and we talk about them as being people and elders.

  • Stephanie Sy:

    But they also talk about them as nature's survivors, whom they revere. After scraping the fruit out and savoring its sweetness, the empty pods are solemnly returned to the giver.

  • Maria Francisco:

    As a Native American, we're very resilient people. We always bounce back. And that's how I see these saguaros. They're going to adjust to climate change.

  • Stephanie Sy:

    Who and what can adjust is the biggest question facing not only the Sonoran Desert, but the whole planet.

    For the "PBS NewsHour," I'm Stephanie Sy in Tucson, Arizona.

  • Amna Nawaz:

    On the "NewsHour" online, a growing number of people who aren't scientists by trade are helping advance federal research and our understanding of the world more broadly.

    Learn more about citizen science and how you can participate on our Web site. That's PBS.org/NewsHour.

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