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Federal Register / Vol. 86, No. 166 / Tuesday, August 31, 2021 / Rules and Regulations
areas, and are largely absent from hot deserts and arid lowlands. Therefore, it is not possible to predict a plants habitat based solely on knowing that it performs CAM.
Bartrams stonecrop exhibits morphological features characteristic of other Crasulaceae including a waxy covering of the leaves, a shallow root system, and the arrangement of the leaves in a rosette. These features are also found in succulents that occur in drier habitats and may act to promote water conservation, but do not alter the habitat requirements of Bartrams stonecrop.
11 Comment: A commenter noted that hundreds of plants and animals are at the northern fringe of their range in southern Arizona and are common and safe in Mexico.
Response: Historical distributions of Bartrams stonecrop populations are focused in southern Arizona, with some disjunct populations in northern Mexico. There have been surveys for this species in Mexico, and numerous biologists from Mexico have been consulted regarding its presence in the country. Habitat has been altered extensively in Mexico, and limited populations of Bartrams stonecrop have been located there; therefore, we do not find it reasonable to conclude that the species is common or safe in Mexico.
12 Comment: A commenter claimed that surveys by Sanchez-Escalante in Mexico were rushed, and occurred in the wrong habitat and at the wrong time of year.
Response: The researcher SanchezEscalante spent 35 days exploring 55
sites in Sonora and Chihuahua, and covered 6,900 kilometers with a team of trained botanists with the specific aim of locating populations of six identified rare plant species in appropriate habitats. Two new Bartrams stonecrop populations were located and two historical Bartrams stonecrop populations were confirmed out of 11
suitable habitat locations surveyed.
These surveys were conducted during the flowering season in late September when the plants are most visible.
Therefore, we concluded the SanchezEscalante surveys were conducted using appropriate methods. Thus, we base our current understanding of the Bartrams stonecrop occurrences in Sonora and Chihuahua on the best available scientific information.
13 Comment: A commenter mentioned that regular visitation is necessary to attain information on bloom period, seed production, reproduction method, pollinators, precipitation and growth relationships, and genetic diversity.

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Response: We are aware of limited information regarding the life history and species characteristics the commenter mentioned. The current knowledge of Bartrams stonecrop phenology and reproduction is described in the SSA report Service 2020a, p. 20. The inflorescence stalks of Bartrams stonecrop individuals grow for 3040 days in July and August before coming to their full height, with flowers opening primarily between September and November Kearney and Peebles 1951, p. 361; Phillips et al.
1982, pp. 2, 7; Shohet 1999, p. 25.
Flowering is triggered by fall rains and does not occur during periods of water stress Shohet 1999 pp. 22, 25, 36, 39.
Seed dispersal occurs from November to December.
Bartrams stonecrop requires pollinators for reproduction. The major pollinators of Bartrams stonecrop are true flies and house flies, although honey bees may also play a role in pollination. Other species that have been noted on Bartrams stonecrop include wasps, butterflies, and bee flies Shohet 1999, p. 41; Ferguson 2014, p.
26; Ferguson 2017b, p. 13. Fertilization success is greatest in earliest opening flowers, possibly due to more pollinators being available earlier in the season, although having a long period of flowering increases overall chance of pollination Shohet 1999, p. 57.
The full relationship between precipitation and plant growth in each life stage has not been fully elucidated.
However, winter precipitation is needed for germination, although some germination likely occurs following summer rains. Summer July and August and fall October and November precipitation is needed for flower production. We are supporting current research into the specific microhabitat requirements for Bartrams stonecrop including site characteristics of overstory vegetation, associated plant species, substrate characteristics, litter depth and character, local insolation and shade, soil temperature and soil moisture, and distance to perennial water. These studies will provide information on temperature and humidity parameters throughout the flowering, germination, and early seedling growth of the plants. Further studies will inform conservation and recovery efforts for the species.
14 Comment: A commenter claimed the Service did not do due diligence to list threats or make determinations, but used the petitioners list of threats.
Three commenters also opined that the Services analysis of stressors and classification of the current condition is speculative and not based on hard data.

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Response: The Services determination to list the species is based on a thorough, scientific analysis that was subject to appropriate peer review.
Although there are threats noted in common between the Bartrams stonecrop SSA report and the petition to list the species CBD 2010, there are also differences. The petition calls out mining, livestock grazing, and recreation as the primary threats to Bartrams stonecrop. The SSA analysis determined the following primary influences on viability: Loss of water availability; erosion, sedimentation, and burial; altered fire regime; and loss of shade. We based our analyses on the best available information, which included recent studies of and surveys for Bartrams stonecrop by the National Park Service, U.S. Forest Service, the Service, and private researchers.
15 Comment: A commenter claimed the Service lacks basic knowledge about the biology and habitat requirements of Bartrams stonecrop and is not following the mandate to base listing decisions on the best scientific and commercial data available.
Response: We based this final listing determination on the best available scientific and commercial information, and the commenter did not provide any new information for us to consider. The best available information on Bartrams stonecrop indicates the species occurs near water sources springs, seeps, or intermittent streams, which may provide humidity and create suitable microclimate conditions. The deep, narrow canyons and associated overstory species provide shade during a portion of the day and create a cooler temperature, and the vegetation litter promotes retention of soil moisture and contributes to the humid microenvironment. Additional Bartrams stonecrop biology and habitat research is ongoing, and results will inform future Service actions. In assessing the viability of Bartrams stonecrop, the best available scientific and commercial data provide information about some aspects of species biology and habitat requirements, but may not represent a full and complete knowledge of the species. We drew reasonable conclusions about other aspects of the species biology and requirements based on similar species, similar habitats, and best available information.
16 Comment: A commenter indicated that managed livestock and wild ungulate grazing reduce fuels for fires and requested all language relating to domestic livestock threatening Bartrams stonecrop be removed from the SSA report and the rule.

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