Abstract Detail

Conservation Biology

Reichenbacher, Frank [1].

Multidecadal Calescent Drought, Lessons from a Delisted Species, and the Fates of Species Considered as Candidates for listing as Endangered and Threatened in the Southwest.

In 1980 Tumamoc globeberry (Tumamoca macdougalii, Cucurbitaceae) a rare vine of the Sonoran Desert, was added to the U.S. Fish and Wildlife Service (FWS) list of plant species considered to be candidates for listing as endangered or threatened under the Endangered Species Act of 1973 (ESA). In 1983 the then largest known population of T. macdougalii was discovered in the route of the Central Arizona Project in Eastern Pima County, Arizona. Due to the impacts of the proposed aqueduct and other considerations T. macdougalii was listed endangered by 1986. Subsequent research discovered many more populations in Arizona and Sonora and the species was delisted by 1993. Required post-delisting monitoring found largely stable populations. No organized monitoring of T. macdougalii populations occurred from 1996-2007. In 2007 I revisited populations of T. macdougalii that had been stable or increasing in the mid-1990s and found some populations had experienced a precipitous decline that occurred between 1996 and 2007. The population declines are clearly related if not directly caused by the two decades drought and high temperatures that have characterized the climate of most of Arizona since 1996. This same drought combined with high temperatures may have affected hundreds of species of rare plants that are much less well studied than the T. macdougalii. U.S. Fish and Wildlife Service procedures implementing the Endangered Species Act of 1973 included a process to identify plant species that may be determined to be endangered or threatened. In 1980 USFWS published its first “Candidate Notice of Review” (CNOR) providing a list of candidates as well as a list of species that had been evaluated but were dropped from further consideration. This process of reviewing, retaining, adding, and dropping species from further consideration continues today. From the 221 candidates for listing considered and dropped from 1980-2020, 15 were eventually listed as endangered or threatened under provisions of the ESA, one species, Wright’s thistle (Cirsium wrightii) is still under consideration. All but five species were dropped from consideration in the decade prior to the onset of drought and high temperatures that became prevalent in Arizona from 1996 on. The correlation, clearly coincidental and not causal in nature, is striking. The federal agencies implementing ESA, principally FWS with respect to plants, do have some resources available to re-review the candidates that were dropped from consideration and have not been actively monitored since then. For example, the ESA requires adequate review of citizen petitions advocating review and research grants are available through the ESA Section 6 provision. Nevertheless, the majority of the former candidate species have not been reviewed, resurveyed, or otherwise evaluated since they were dropped from consideration just before the onset of multi-decadal drought in Arizona.

1 - University Of Arizona, Desert Laboratory On Tumamoca Hill, 8657 E. Clydesdale Trail, Scottsdale, AZ, 85258, United States

rare plants
population decline
species conservation
Endangered Species Act
endangered species
threatened species
Tumamoc globeberry
Tumamoca macdougalii
monitoring study
multi-decadal drought

Presentation Type: Poster
Abstract ID:26
Candidate for Awards:None


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