Arizona hedgehog cactus (Echinocereus triglochidiatus var. arizonicus)—A systematic data assessment in support of recovery

Abstract

The Arizona hedgehog cactus ( Echinocereus triglochidiatus var . arizonicus ) is endemic to central Arizona in Gila and Pinal Counties, and has been federally listed as endangered by the U.S. Fish and Wildlife Service (FWS) since 1979. Mining, mineral exploration, and highway development have resulted in habitat degradation and loss of individual plants. Therefore, decreases in the population of the cactus are expected to continue. In response to a request from FWS to compile, evaluate, and synthesize data for the cactus, we identified and evaluated existing survey and monitoring data for the cactus and conducted a demographic analysis with suitable data. Systematic surveys for the Arizona hedgehog cactus did not begin until the late 1970s. Early surveys generally were anecdotal descriptions of cactus populations and precisely georeferenced records of individual cactus occurrence did not occur until global positioning systems were widely used. Much of the georeferenced data have been collected by consultants for mining operations, the Arizona Department of Transportation, the U.S. Forest Service, and independent surveyors. Occurrence records have been compiled by the Arizona Game and Fish Department Heritage Data Management System, but submission of these data may be incomplete, and the attributes reported have varied among the contributing entities. The compilation and management of survey data is essential for field-based evidence of the size, distribution, and range extent of the cactus. In support of consistency in future survey data collection, this report makes several suggestions for future surveys. Monitoring for the Arizona hedgehog cactus, defined as repeat observations of the status of cactus individuals, has been done by consulting companies for three mines. Demographic monitoring further involves marking individual cacti in consistently defined plots and recording the fate of each cacti through time, including birth, growth, reproduction, and death. We were able to use demographic monitoring data provided by two consulting companies to calculate survival and population growth rates, using several statistical approaches. Resulting models indicate that larger cacti, as measured by their number of stems, have greater survival rates. Larger individuals also had higher probability of producing more flowers. Small cacti had the lowest survivorship, with potentially only 15–20 percent reaching large size. Most populations monitored by the two companies were stable to increasing. However, there were differences in the growth rates among plots and some plots had negative population growth rates. The demographic monitoring data we used represented relatively dense populations of undisturbed cacti. Hence, overall positive population growth rates were not influenced by any large-scale disturbances. Previous analyses with cacti and other species suggest that more than 10 years of data are necessary to accurately forecast long-term population trajectories. As the monitoring intervals we evaluated were shorter, they represent short-term dynamics only. Several suggestions are made in the report to improve collection of monitoring data to support evidence-based estimates of demographic characteristics of the Arizona hedgehog cactus.