The Iconic Saguaro Cactus Across its Landscape

Abstract

All photographs in this section are provided by authors of papers in our scientific journals and are used by permission. All copyrights reserved. The saguaro cactus (Carnegiea gigantea) is a long-lived columnar cactus that is among the most well-studied plants in the world. Long-term research indicates that saguaro establishment is generally episodic and strongly influenced by precipitation and temperature. Drought conditions can reduce survivorship of recently germinated saguaros up to 100%. Long-term drought will likely cause saguaro populations to decline as older or vulnerable saguaros die without new cohorts replacing them. However, the relative importance of local habitat variability and the coinciding drought impacts on establishing populations remain largely unexplored. We modeled saguaro establishment in response to drought in various habitat and soil types at Saguaro National Park. Recent, severe drought coincided with drastic declines in saguaro establishment that has seen few saguaros establishing in recent years. Overall, saguaro establishment was best explained by the interaction of drought and habitat type. The best model identified bajada and foothill plots as responding somewhat similarly to drought regardless of severity but foothill plots outperformed bajada plots regardless of drought severity. Furthermore, the predicted number of saguaros to establish in bajada or foothill plots dropped to near zero under the most severe drought but remained higher in slope plots, suggesting that the most suitable habitat type for establishing saguaros has shifted during the recent drought. These results reveal that saguaro establishment strongly correlates with drought but that the impact of drought varies with local habitats and their associated physical characteristics. Overall, our study shows that incorporating the range of local variability in how plants may respond to past climate conditions is important for predicting future response to climate change. The following image gallery is meant to illustrate the demographic complexity of saguaros and how the interactive dynamics of desert climate with landscape position influence population regeneration trends in Saguaro National Park. Photo by D. E. Winkler. Photo by D. E. Swann Photo by J. L. Conver. Photo by D. E. Winkler. Photo by D. E. Winkler. Photo by D. E. Swann. Photo by D. E. Winkler. Photo by D. E. Winkler. Photo by J. L. Conver. Photo by J. L. Conver. These photographs illustrate the article “The interaction of drought and habitat explain space–time patterns of establishment in saguaro (Carnegiea gigantea)” by Winkler et al., published in Ecology 99(3), https://doi.org/10.1002/ecy.2124