Cooperative Agreement for affiliated Partner with the Desert Southwest Cooperative Ecosystem Studies Unit (CESU)

The USGS Southwest Biological Science Center (SBSC) seeks to provide financial assistance for research investigating the vulnerability of saguaros to aridification in Saguaro National Park (hereafter SAGU), and how to make populations more resilient. The southwest U.S is experiencing a severe, long-term drought that is threatening regional water sources, human health, and plant and wildlife communities. Temperatures at SAGU increased 1.2°C since 1895 and are expected to climb in future decades. Managers at SAGU are observing changes in the vegetation communities, fire regimes, and water resources that are related to long-term drought and exacerbated by higher temperatures leading to long-term aridification. The Park’s namesake species, the saguaro cactus (Carnegiea gigantea), is a drought-adapted, long-lived keystone species that directly supports at least 100+ other plant and animal species. The park’s saguaro population began rebounding in the 1960s after decades of decline, most likely due to management practices that protected nurse trees, which young saguaros require for shelter from environmental stress. Many of these plants are now reaching reproductive age. However, since the mid-1990s scientists have documented declines in saguaro seedling survival. In the park’s Cactus Forest, recruitment since 1995 is <10% of what it was in prior decades, and similar results are observed throughout all habitats in the park. While recent studies provide insight into how saguaros are responding to changing environmental factors, they do not address causal effects or provide direct answers to questions related to long-term survival of saguaros in the park; key information needed by managers to decide how to protect this species soon. are essential to achieving the park’s mission. These questions are especially relevant today given the current poor recruitment in the plant’s drier western range including Organ Pipe Cactus National Monument and in the urban heat island of Phoenix, Arizona, where there is anecdotal evidence that otherwise healthy saguaros may be dying due to extreme night-time temperatures. Challenges to conserving an iconic, keystone species are not unique to SAGU and knowledge and management actions can be applied to other public lands on which saguaro’s and potentially other iconic cactus occur.