Abstract Detail

Conservation Biology

Revisiting the Tumamoc Globeberry.

Tumamoca macdougalii Rose (Cucurbitaceae) is a rare vine of the Sonoran Desert. The species was listed federally endangered in 1986, but subsequently delisted in 1993 when further research found it to be widely distributed in western Sonora, Mexico. Delisting included a requirement to monitor select populations until 1995. These monitoring studies did not reveal any particular vulnerability. The author and numerous volunteer ecologists have conducted monitoring studies of selected T. macdougalii populations for the past eleven consecutive years (2007-2021) in addition to surveying selected areas for new populations. The results of these new monitoring studies indicate a precipitous decline in populations believed to be stable in the mid-1990’s that occurred sometime between 1996 and 2007. Some that have been monitored very carefully since 2007 are in danger of local extinction (including the type locality for genus and species at Tumamoc Hill). Although population declines are very concerning it is important to note that the populations that have declined represent a very small fraction of known populations. The current status of the bulk of the species, which is mostly in Sonora, Mexico, is currently being investigated under a separate U.S. Fish & Wildlife Service/Arizona Department of Agriculture, Section 6 research grant.
Only one T. macdougalii population was consistently monitored from 1984-1995: a 0.21 ha population at the mouth of Sabino Canyon, Coronado National Forest. Here, every individual plant was marked with aluminum tags attached to heavy gauge aluminum wire which was pushed into the soil next to the stem. Monitoring involved one or two visits to the site every year from 1984-1991, and then 1993, and 1995. At no other site were plants permanently tagged and followed from year-to-year. The work to monitor the Sabino Canyon T. macdougalii site began in 1984 and continued, sometimes on a volunteer basis, sometimes funded by various agencies, mostly annually, but with a large gap from 1996-2006, and is ongoing today.
Many other sites in the Tucson-Avra Valley area were visited and thoroughly documented from 1984-1989. A few of these, including the site on the north side of Tumamoc Hill, were visited and re-surveyed in 1993 and 1995 as part of the mandated de-listing monitoring.
Goals and objectives of monitoring changed over time and the specific procedures and methods changed as well. Understanding the results and analyses reported here will be greatly facilitated with an understanding of the history of T. macdougalii monitoring.
The declines observed in monitored T. macdougalii populations correlate with Palmer Drought Severity Index (PDSI) calculated for the localities. Populations were stable or increasing from the beginning of monitoring in 1984 through 1995 under favorable climatic conditions indicated by PDSI values mostly >0. Drought in a warming climate (PDSI, mostly <0) that began in the late 1990s, immediately after monitoring ceased, resulted in mortality of established individuals and greatly reduced recruitment. From 2015-2016 PDSI increased, leading to modest recruitment.

1 - University Of Arizona, Desert Laboratory On Tumamoca Hill, 8657 E. CLYDESDALE TR., SCOTTSDALE, AZ, 85258, United States

Keywords:
Cucurbitaceae
Tumamoca macdougalii
rare plants
population biology
population decline
Sonoran Desert
monitoring study
species conservation
drought
endangered species
threatened species.

Presentation Type: Oral Paper
Number: CB3004
Abstract ID:23
Candidate for Awards:None