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Federal Register / Vol. 86, No. 166 / Tuesday, August 31, 2021 / Rules and Regulations We reviewed the potential risk factors i.e., threats or stressors that are affecting Bartrams stonecrop now and into the future. While there are multiple stressors affecting Bartrams stonecrop, the best available information indicates that these threats are not immediately impacting Bartrams stonecrop such that the species meets the definition of an endangered species under the Act.
Section 4a3 of the Act requires the Secretary of the Interior Secretary to designate critical habitat concurrent with listing to the maximum extent prudent and determinable. The designation of critical habitat may not be prudent if the species is threatened by taking or other human activity and identification of critical habitat can be expected to increase the degree of such threat to the species. Bartrams stonecrop is an attractive and small plant that can be easily collected by gardeners and succulent enthusiasts.
This stressor was first noted in 1982, and observed in 19971998. Three researchers described the potential for collection of Bartrams stonecrop and factors that may make collection more likely. The lifespan of Bartrams stonecrop plants has been estimated at 510 years, allowing sufficient time for discovery and collection. As noted in the August 8, 2012, 90-day finding for this species 77 FR 47352, small populations may not be able to recover from collection, especially if the mature, reproductive plants are removed. The removal of mature plants reduces the overall reproductive effort of the population, thereby reducing the overall resilience of the population. While documented instances of collection are limited, the impacts from collection can be profound for small populations. In this case, we have found that the designation of critical habitat for Bartrams stonecrop is not prudent at this time as it would be likely to put the species at higher risk of collection.
24 Comment: The commenters state that there is no evidence that illegal collection of Bartrams stonecrop individuals is a significant threat and that illegal collection is unlikely due to the short lifespan of the species and difficulty growing it horticulturally.
Response: The illegal collection of succulents is known to occur, and is often difficult to detect. Illegal collection of Bartrams stonecrop individuals has been reported, and the threat from it is more pronounced in small populations such as those in which the species occurs. More than half 58 percent of Bartrams stonecrop populations contain fewer than 50
individuals. The lifespan of Bartrams stonecrop plants has been estimated at
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510 years, allowing sufficient time for discovery and collection.
Bartrams stonecrop is an attractive and small plant not available from nurseries that can be easily collected by gardeners and succulent enthusiasts.
This stressor was first noted in 1982, when exact localities were excluded from a summary report due to the possibility of illegal collection. Tagged individuals were uprooted and taken from two sites in the Santa Rita Mountains in 19971998. Plants in close proximity to trails have higher discovery potential and are therefore more likely to be collected. Collectors advertise in internet forums seeking Bartrams stonecrop seedlings or rooted cuttings. The similar southern Arizona species, Graptopetalum rusbyi San Francisco leatherpetal, is cultivated and legally available for sale from cactus nurseries. However, Bartrams stonecrop is more difficult to propagate and maintain in captivity and is therefore vulnerable to collection from the wild because collectors cannot find them for purchase in nurseries. Small populations may not be able to recover from collection, especially if the mature, reproductive plants are removed. The removal of mature plants reduces the overall reproductive effort of the population, thereby reducing the overall resilience of the population. While documented instances of collection are limited, the impacts from collection can be profound for small populations.
25 Comment: The commenters state that there is no evidence that trampling is a significant threat to Bartrams stonecrop.
Response: As Bartrams stonecrop is typically found in shady canyons, the possibility of individuals being lost to trampling remains. Trampling of individuals direct mortality or damage due to crushing related to recreation activities has been observed historically.
Human traffic within Bartrams stonecrop populations can cause soil erosion and plant loss, including damage from researchers. Individual Bartrams stonecrop were trampled in a group of plants that bordered a campsite Shohet 1999, p. 60. Westland Resources 2013, p. 19 noted that the potential placement of a trail through Bartrams stonecrop populations may impact individual plants. A Bartrams stonecrop plant in a group located within 10 meters 32.8 feet of a frequently used hiking trail was covered by rock fall Ferguson 2016a, pp. 14
15. Threats to individuals can be particularly important to small populations.
26 Comment: Some commenters state that altered precipitation, drought,
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and flooding regimes pose an uncertain threat to Bartrams stonecrop, and that freezing is not detrimental unless severe.
Response: The southwestern United States is warming and experiencing severe droughts of extended duration, decreased stream flows, changes in amount and timing of snow melt, and changes in timing and severity of precipitation and flooding CLIMAS
2014, entire. The seasonality and general precipitation requirements for Bartrams stonecrop are described in detail in the SSA report chapter 2, p.
26. Bartrams stonecrop occurs in habitats and microhabitats with a higher soil moisture, humidity, and vegetative community indicative of more mesic conditions than other succulents.
Drying of habitats and more arid conditions have been associated with population extirpation. Bartrams stonecrop and its habitat are very susceptible to drought, loss of humidity, increases in temperature, and increased intensity of storms and flooding NPS
2015, p. 4.
Bartrams stonecrop occurs in Madrean woodlands characterized by warm, wet summers and mild winters.
Precipitation within the sky island mountain ranges is bimodal, with winter snow and rain, and summer monsoon rain. Mean annual precipitation in these habitats is 1017
inches, with more than 50 percent occurring in summer. The winter snow and rain coincide with Bartrams stonecrop seed germination and growth.
Winter precipitation is needed for Bartrams stonecrop germination although some germination likely occurs following summer rains, and both summer July and August and fall captured partially in the October and November winter data precipitation is needed for Bartrams stonecrop flower production.
The current and projected future trends in precipitation in the range of Bartrams stonecrop are discussed in the SSA reports sections 2.6 and 4.5
Service 2020a, pp. 26, 5468. The region has experienced serious drought a prolonged period of abnormally low rainfall in recent decades Bowers 2005, p. 421; Garfin et al. 2013, p. 3;
CLIMAS 2014, entire. Winter precipitation, in particular, has decreased over the past century, as recorded by weather stations within sky island mountain ranges containing Bartrams stonecrop see SSA report, figures 2.6ah Service 2020a, pp. 27
30. Winter precipitation is projected to decrease in the southwestern United States IPCC 2013, p. 1080.

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