With the rapid expansion of the city, the degradation of the natural environment has gradually aroused widespread concern in society. In recent years, the saguaro cactus (Carnegiea gigantea), one of the most iconic plants in the Sonoran Desert, has attracted the attention of ecologists because of its declining population and wildfires. They began to think that understanding how people living in urban areas, at the forefront of species change, observe and interpret ecological changes could provide important insights into environmental change and climate adaptation, because people tend to understand climate change through discrete, landscape-specific events that produce environmental changes. Examples include prolonged droughts, changes in average temperatures, and changes in the distribution of plant species. Sometimes, these historical preservation observations build up local ecological knowledge of the species over time, leading to a new understanding of the environment around people who have lived and worked in a given range for a long time.
The saguaro cactus, which is used by more than 100 species of animals for survival in the Sonoran Desert, is shaped like giant tree-shaped columnar cacti with protective spines. Under the right growing conditions, some saguaros can live for 150 to 200 years and reach a maximum height of 18 meters. Typically as they age, they form branches that often curve upward and whose wooden ribs can be used to build roofs, fences, and furniture parts. Currently, the saguaro is found only in the Sonoran Desert. The most important factors for its growth are water and temperature. If grown at too high an altitude, the cold weather will kill the saguaro. The Sonoran Desert is one of the largest and hottest deserts in North America, and has a large number of saguaro growing around Tucson, Arizona. They generally experience winter and summer rains here, but people widely believe that saguaros get most of their water during the summer rainy season.
In the 1930s, Arizona was considered to have some of the best saguaro cactus forests in the United States. To conserve this population, the National Park Service created a national monument there to protect the forest. However, a large number of cactus deaths shocked the staff in 1939. Researchers speculated that the deaths may have been due to bacterial infections, extreme freezing events, and a lack of analysis of the age structure of the cactus. Before this, due to large-scale human logging activities, land pressure and urban expansion, there were far fewer young saguaros than mature saguaros. The immature saguaros’ age structure caused the species to lack the ability to withstand risks, resulting in a dramatic decline in the population. In addition, due to the existence of desert ecology in Arizona, the probability of wildfires is also increased. A lightning strike started a wildfire (known as the Bighorn Fire) in the Santa Catalina Mountains north of Tucson on June 5, 2020 and was extinguished on July 23, 2020. Except for rugged mountain roads, drought and delayed summer rains have also led to fuel drying and increased fire activity. Reduced water availability and continued high temperatures have decreased the viability of the saguaros to some extent.
Today, Tucson, AZ still retains a large number of saguaros, as a symbol standing in every corner of the community. Its powerful water storage capacity for the ecological significance of the entire desert is extraordinary. As the Sonoran Desert keystone species, any change in its population structure can have a multi-directional impact on the region’s related species and community combinations. Current data, however, suggest that their numbers are at a crossroads.
Due to past human activity, young saguaros’ “Nurse plants,” the Velvet mesquite (Prosopis velutina) and Foothill paloverde (Parkinsonia microphylla) have gradually disappeared from the landscape. They are critical to the survival of young saguaros in non-rocky habitats because they protect the saguaro from crushing and predation by herbivores, creating an environment that regulates maximum soil temperatures in summer and minimum temperatures in winter. Throughout the 20th century, ecologists worked to pass laws banning logging and grazing to regenerate and rehabilitate these nurse plants and return them to their normal functions. Their efforts have paid off, after the wake of the Bighorn Fire, many respondents living in and near the affected areas expressed concern about the social and ecological impact, which was closely linked to the promotion of public science, and respondents began to think about the natural threats that low desert areas are facing and to build new risk perceptions.
Featured photo: © Shizhe Li
Leave a Reply