Инвазивные травы и пожары угрожают исчезновению икон пустыни — сагуаро в Аризоне

TUCSON – It’s hard to imagine a cactus without thinking of a saguaro. Adam Farrell-Wortman has spent more than a decade caring for saguaros at the Tucson Botanical Gardens, where he is the director of horticulture. “You can go anywhere around the world, (and if you tell) a random person to draw a cactus, they will draw a saguaro,” Farrell-Wortman said. “It is the icon of the Northern American desert.” But these towering cacti are vulnerable to other climate related stressors — like extended temperatures, invasive species and fire. “I’ve lived here for 65 years,” said Flint Swerd, a retired high school teacher living in Cave Creek. “I’ve never seen so many saguaros dying.” Swerd often hikes and mountain bikes and has noticed saguaros rapidly disappearing as wildfires increase. “The desert ecology isn’t evolved with fire,” Farrell-Wortman said. Burns Saguaros’ strong interior could make them appear tough against fires. Kim Franklin, a conservation research scientist at the Arizona-Sonora Desert Museum, said the cacti are less resilient than they appear. If saguaros are burned at their base, they have a better chance at survival than barrel cacti or baby saguaros, Franklin explained, which are low to the ground. But they still catch fire easily, with fire rapidly traveling from the bottom to the top. Once a saguaro is ignited, fire can burn its soft tissue. If enough of the epidermis, or inner skin, is burned, the saguaro dies completely, she said. If it survives, it’s never the same again; its epidermis can no longer act as a protective barrier against pathogens. “Think about if your legs were burned from the knees down pretty significantly,” Franklin said. “That would be pretty hard on you.” Surviving saguaros are left with permanent burn scars that appear as charred patches on the lower trunk and arms of the cactus. When saguaros die completely, they are left with their ribs – the woody structures that once supported its weight. Native species Saguaro damage isn’t just cosmetic– it threatens coexisting wildlife, too. Birds like the Gila Woodpecker and the White-winged Dove dig out holes in the saguaro to nest in, making cavities. When a fire kills a saguaro, the birds become displaced. The saguaro is also a food source for many forms of wildlife, and fires put that at risk. “They’re incredibly important to all sorts of pollinators … so many different species, insects, birds, bats, depend on saguaros, for their nectar, for the pollen and for their fruit,” Franklin said. Animals like bats are less threatened by saguaro fires because they can fly away, Franklin explained. But if a slower animal like a desert tortoise is nearby during a fire, the immediate impact could be death. Invasive species Invasive species are a major fire risk factor for saguaros and the wildlife that coexist with them. On the Fourth of July in 2017, fireworks were set off around Sentinel Peak in Tucson. It led to a fire that burned hundreds of saguaros. Part of this, Franklin explained, was related to buffelgrass (Cenchrus ciliaris)– an invasive species living on the mountain that catches fire easily. Buffelgrass has thin green stalks with fluffy lavender spikes like cleaning dusters sprouting from it. You can pull on it and spread the soft bristles through the air like a dandelion. It’s also one of the biggest threats to saguaros. It can fuel intense fires, which burns the epidermis, or skin, of the saguaro. If enough of the saguaro is damaged, it doesn’t only damage the skin and pathogens — it can completely kill the saguaro. Where the saguaros were burned on Sentinel Peak, the buffelgrass returned, lush and thick. It replaced the hundreds of saguaros that used to stand tall. “There’s hardly any saguaros left there,” Franklin explained. The fires also destroyed other plants that used to thrive alongside saguaros. “But there’s also nothing else either,” she continued. “There’s no palo verdes… there’s no creosote, there’s no other plants either. It’s just buffelgrass.” Another invasive species that contributes to saguaros’ fire risk is stinknet (oncosiphon pilulifer), which is also starting to take off across Southern Arizona. In Phoenix, it’s already rampant. The invasive species appears like bright bunches of yellow flowers, but, like buffelgrass, it increases wildfire risk, she said. They form dense, flammable mats throughout the desert and pose a risk to surrounding saguaros. Buffelgrass and stinknet are replacing saguaros, not just threatening them. “People are really bad at longterm thinking, or maybe people don’t care because they’re going to get to see saguaros during their lifetime,” Franklin said. “But (their) grandkids are not going to get to see them. It’s just going to be a grassland.” The future Hope persists, thanks in part to the people working to preserve Arizona’s deserts. Tucson has a strong sense of place, Franklin explained, and the community cares deeply about biodiversity. “There’s hundreds, if not thousands, of people that go out every year to volunteer just to dig up buffelgrass or pull up stinknet,” Franklin said. Farrell-Wortman said the community usually steps up to help during environmental disasters. But they need to keep putting in the effort, he said. “We have to continue doing the things we are doing, like trying to pull out and remove invasive species,” Farrell-Wortman said. “We have to do things like replant … maybe putting even more effort, more resources … care more about the need to replant affected wild spaces so that they can recover from human activity.” But the most important thing we can do is at a societal level, Farrell-Wortman explained. “We can no longer pretend that our actions aren’t having a major effect on the natural world around us,” Farrell-Wortman said. “We have to accept that climate change is happening, is occurring, and that we need to do things to mitigate the destructiveness of that.”