Winkler Cactus

Pediocactus winkleri

Description

Winkler's cactus, Pediocactus winkleri is a small globose (globular) cactus with stems 1 to 2.5 in (2.5 to 6.2 cm) tall and up to 2 in (5 cm) in diameter. It has clusters of 9 to 11 small radial spines with dense fine woolly hairs at their base; erect central spines are lacking. The flowers of this taxon are urn shaped, 0.7 to 1 in (1.7 to 2.5 cm) long and 0.7 to 1.5 in (1.7 to 3.7 cm) diameter, and have a peach-to-pink color. The fruit is barrel shaped, 0.3 to 0.4 in (7.5 mm to 1 cm) high and 0.31 to 0.43 in (7.7 mm to 1.7 cm) wide, dehiscing (process of opening) by a vertical slit along the ovary wall. The seeds are shiny black, 0.12 in (3 mm) long and 0.08 in (2 mm) wide.

Pediocactus winkleri was discovered in the early 1960s and described in the scientific literature in 1979. The plant genus Pediocactus contains eight species, of which seven are rare endemics of the Colorado Plateau region of Utah, Colorado, New Mexico, and Arizona.

Habitat

Individual P. winkleri plants are usually situated on the tops and sides of rocky hills or benches in Atriplex (saltbush)-dominated desert shrub communities. The species grows in alkaline silty loam or clay loam soils derived primarily from the Dakota formation, the Brushy Basin member of the Morrison formation, and the Emery sandstone member of the Mancos formation.

Distribution

P. winkleri is endemic to lower elevations of the Colorado Plateau in south-central Utah. Three of the four populations of this taxon form a narrow arc extending from near Notom in central Wayne County to the vicinity of Last Chance Creek in southwestern Emery County, Utah. The fourth is a disjunct population occurring near Ferron, Utah, in western Emery County. Most of these populations occur in widely scattered patches 2.4-48 acres (1-19.2 hectares) in size in a range about 36 mi (58 km) long and about (0.76 mi) 480 m wide. About two thirds of the population occurs on lands managed by the Bureau of Land Management east and north of the Capitol Reef National Park boundary. The remainder of the plants are found within the Park.

Based on extrapolations from direct surveys of the four extant populations conducted in the late 1990s, the U.S. Fish and Wildlife Service (FWS) has estimated that Pediocactus winkleri numbers about 20,000 plants. This estimate is substantially higher than the one provided in the October 1993 proposal to list P. winkleri as endangered; a total of 3,500 plants in six populations was given then, based on a 1984 status report. More intensive and accurate recent surveys have prompted this upward revision Surveys through 1998 have documented about 5,800 individual P. winkleri plants, and analysis of survey data collected in 1994, 1996, 1997, and 1998 indicates that the total population for this taxon, based on these numbers and the amount of available habitat, could be reasonably estimated at the 20,000 figure given above.

Other recent developments tend to support this new population estimate.

Since the proposed rule to list the species was published, a survey conducted by the Bureau of Land Management (BLM) discovered an additional population near the town of Ferron in southwest Emery County, Utah. Joint FWS and BLM surveys conducted throughout the entire potential habitat range of P. winkleri —silty soils derived from the Dakota, Mancos, and Morrison geologic formations—discovered additional sites within existing population areas. The Park Service reported larger numbers of this cactus within Capitol Reef National Park, as did the BLM from the Last Chance Desert population. FWS biologists visited these sites, reviewed the status of all extant populations of this cactus, and then consolidated the five P. winkleri populations in Wayne County into the Notom and Hartnet groups, in an effort to be consistent with the more recently discovered Last Chance and Ferron populations in Emery County. This increased total populaton estimate for Winkler cactus is not so much evidence of reduced threats to the species as it is a function of the increased effort put forth to locate individual plants. Older surveys were conducted by one or two individuals with limited resources, while more recent BLM surveys were conducted by four or more individuals over a period of several weeks.

The range of Winkler cactus converges upon populations of the listed endangered cactus P. despainii (San Rafael cactus). P. despainii and P. winkleri are described as separate species in all taxonomic treatments involving those species in regional floras and in monographs of the genus. Cytotaxonomic research demonstrates that typical P. winkleri from the Notom population is genetically different from typical P. despainii from the San Rafael Swell. However, the two species are phylogenetically related, and it was suggested by Lass in 1990 that they be treated as varietal subspecies of P. winkleri, the earlier of the two species to be described. Occasional plants within the northern portion of the Last Chance population bear characteristics intermediate between P. winkleri and P. despainii. The two species are, however, morphologically distinct and geographically separated. Winkler cactus has uniformly smaller seeds than P. despainii.

P. winkleri areoles—the basal structure at the tip of stem tubercles which forms the base from which the spines arise—are wooly with dense villous hairs, while P. despainii areoles are naked except for its spines. These facts, established through recent cytotaxonomic research strongly suggest the current taxonomic distinction between the species is accurate. If they later become recognized as subspecies, their designations as threatened and endangered species will still remain valid.

Threats

The small, restricted populations of Winkler cactus make the species highly vulnerable to human-caused habitat disturbances. Off-road vehicular (ORV) activity, mineral development, road and utility corridor development, and livestock trampling have adversely affected this species. P. winkleri is especially vulnerable during the spring flowering period, when seasonally moist soils make it susceptible to damage and mortality from surface disturbance of its habitat. The taxon is easily dislodged by domestic livestock and ORV actvity during periods when the soil is wet. ORV use and livestock grazing are most intense during the mild spring season when the species is most vulnerable to habitat disturbance. During periods of drought, these cacti do not protrude above ground level, thus rendering them less susceptible to livestock trampling and damage by ORV activity. However, the species forms flower buds in the autumn that persist over winter. These flowering buds at the ground surface level are very vulnerable to surface disturbance.

A considerable portion of the habitat of this species, as well as individual plants, are being damaged by ORV activity. Occupied Winkler cactus habitat, located at the northern and southern limits of its range on sparsely vegetated slopes in readily accessible areas, is adjacent to heavily used ORV recreational areas, and is being harmed by this activity. Except for habitat within Capitol Reef National Park and the Last Chance population on BLM lands, the remaining habitat of P. winkleri is experiencing similar but lesser damaging impacts from ORV activity. Hard-tired ORVs such as motorcycles, four-wheel drive trucks, and other heavy highway vehicles are most damaging to the species. These hard-tired vehicles can cause damage and mortality even when the plant is dormant. Increased erosion as a consequence of ORV damage to the natural desert pavement and cryptogamic crust potentially increases P. winkleri exposure to losses from extreme weather events which occur in the area.

Livestock trampling has affected every population of this cactus including those in Capitol Reef National Park (the Park is not closed to livestock grazing). This species is poorly adapted to the impacts of large, sharp-hoofed ungulates, and plants are easily dislodged and killed by domestic livestock herds moving through its habitat. This trampling impact is most damaging during periods when the soil surface is wet. These conditions occur most commonly during mild winter and early spring days when livestock grazing is most intense in the desert range habitat of P. winkleri. According to the BLM, livestock use in Winkler cactus habitat has decreased in recent years, but trampling continues to damage some populations. Most of the reduction in livestock grazing within Capitol Reef National Park occurred in its southern portions, out of the range of this cactus. Grazing and trampling impacts are believed to be mostly low-level chronic threats rather than high-level acute threats, affecting no more than one percent of the P. wink-leri population every year. Individuals lost due to livestock trampling probably could be replaced by natural recruitment from the populations' seed bank. However, cumulative impacts from collecting, localized ORV destruction, and natural losses from disease and parasitism are at sufficient levels in the Notom and Ferron populations that their viability is impaired.

The habitat of Winkler cactus contains oil and gas, bentonite clay, and some uranium ore deposits. The development of these natural resources and the surface disturbances caused by annual mineral assessment work have directly affected the species. Oil and gas field development activities are currently harming the Ferron population. This activity has destroyed individual plants and occupied habitat. Over 80% of the area occupied by the Ferron population is leased for oil and gas, and mining claims cover almost the entire Last Chance Desert population, a portion of which has already been lost to a gas well. A portion of the Hartnet population is also in an oil and gas lease area. The transfer of mining claim patents from the Public domain to private ownership is not affected by the ESA. The recent development of a mine for high quality, cosmetic grade bentonite clay is damaging the Last Chance population by destroying individual plants and occupied habitat.

Winkler cactus is an attractive small cactus, especially when it is in flower. This rare plant, difficult to cultivate in most horticultural settings, has become highly desired in cactus collections and gardens; so much so that both hobby and commercial cactus collectors seek it out. The fact that this species is difficult to maintain in garden settings stimulates a continual demand for replacement plants as cultivated garden and greenhouse plants die. Cactus collectors are active in the Colorado Plateau, going from the habitat of one species of Pediocactus to the next to collect a complete set of the genus. A portion of the Notom population of P. winkleri has been severely reduced, primarily from losses to plant collectors. Overall the population in the immediate vicinity of monitoring transect periodically inspected by the the FWS declined from 387 individuals in 1994 to 221 in 1997. In addition to the Notom population, the Hartnet and Ferron populations are highly vulnerable to specimen collecting because of their ease of access and their being known to cactus collectors.

There are several other factors and conditions that pose lesser current or potential threats to this taxon. Because of its small size and the shortness of its spines, this species of cactus is less protected from animals than more spiny species. The effects of livestock grazing on desert vegetation may produce indirect impacts on Winkler cactus populations. The desert range of this cactus had very sparse use by large, wild ungulates prior to the introduction of domestic livestock. Livestock grazing has caused changes in the floristic composition of theP. winkleri desert ecosystem with the introduction of weeds. These introduced weeds have the potential to outcompete native plants like P. winkleri over the long term, eventually reducing or displacing them. This taxon is also susceptible to natural infestations of beetle larvae, an insect known to kill an individual plant within two years of initial infestation. Unauthorized utility and road development in the Notom population area caused individual plant mortality and habitat degradation in 1995; further activities of this kind remain a potential threat to the species. Winkler cactus is restricted to a small geographic area with scattered, isolated occurrences and relatively low population numbers per occurrence, which render this cactus vulnerable to any random natural events.

Prior to federal listing, the inadequacy of existing regulatory mechanisms was itself a threat to this species. Without direct federal protection for P. winkleri, the National Park Service and the BLM found it hard to control overcollection of this taxon, one of the activities most deleterious to its long-term prospects for survival. Collection of desirable and small cacti that are widely scattered over remote country is an action very difficult to detect and control, even in Capitol Reef National Park. Federal listing provides greater statutory protection and more stringent penalities for take.

Conservation and Recovery

Winkler cactus occurs on federal lands managed by the Bureau of Land Management and the National Park Service (NPS). Both of these federal agencies are responsible for insuring that all activities and actions on lands that they manage are not likely to jeopardize the continued existence ofP. winkleri.

Both the BLM and NPS are aware of the threats facing Winkler cactus and are actively involved in the management and monitoring of this listed taxon. BLM has drafted a Conservation Agreement and Strategy with the assistance of the NPS and other partners aimed at reducing and eliminating identified threats to P. winkleri. In an effort to eliminate soil compaction and plant destruction, the BLM Draft will restrict ORV use to existing roads and trails through the preparation of a managment plan.

Contact

U.S. Fish and Wildlife Service
Utah Ecological Services Field Office
145 East 1300 South, Suite 404
Salt Lake City, Utah 84115-6110
Telephone: (801) 524-5009
Fax: (801) 524-5021

Reference

U.S. Fish and Wildlife Service. 20 August 1998. "Final Rule To Determine the Plant Pediocactus winkleri (Winkler cactus) To Be a Threatened Species." Federal Register 63 (161): 44587-44595.