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Federal Register / Vol. 86, No. 166 / Tuesday, August 31, 2021 / Rules and Regulations 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 plant 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 mature, reproductive Bartrams stonecrop individuals 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.
Small Populations
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Small population size affects Bartrams stonecrop population resiliency, as all stressors are exacerbated in populations with only a small number of individuals fewer than 50. Small populations are less able to recover from losses caused by random environmental changes Shaffer and Stein 2000, pp. 308310, such as fluctuations in reproduction demographic stochasticity, variations in rainfall environmental stochasticity, or changes in the frequency or severity of disturbances, such as wildfires.
Twenty-nine of the 50 extant Bartrams stonecrop populations in the United States contain fewer than 50
individuals. Losses due to mining, erosion, trampling, collection, herbivory, fire, severe frost, or other stressors mentioned above are exacerbated in small populations and have the potential to seriously damage or completely remove these small populations.
In summary, the stressors that pose the largest risk to future species viability are primarily related to habitat changes:

Groundwater extraction from mining, long-term drought, and alteration in wildfire regime. These stressors may reduce nearby water levels, shade, and humidity within Bartrams stonecrop habitat and may directly impact individuals. Other important stressors include erosion or trampling from livestock, wildlife, or human activities;
illegal collection; herbivory of Bartrams stonecrop individuals or their shade trees by wildlife and insects; abnormal freezing or flooding events; or other stressors that have the potential to seriously damage or completely remove small populations. Synergistic interactions among altered precipitation, nonnative grasses, drought, and increased temperatures cumulatively and cyclically impact Bartrams stonecrop, and all stressors are exacerbated in small populations.
Population Resiliency of Bartrams Stonecrop To determine current condition, we assessed each population in terms of its resiliency. Our analysis of the past, current, and future stressors on the resources that Bartrams stonecrop needs for long-term viability revealed a number of stressors influencing this species. Four Bartrams stonecrop populations contain nonnative grasses, and nonnative grasses are present upslope from several additional populations. Further, altered fire regimes have the potential to affect all Bartrams stonecrop populations. This altered fire regime enhances the spread of nonnatives. Consequently, all Bartrams stonecrop populations will be further impacted by nonnative grasses in the future. Altered precipitation, increased temperatures, increased evapotranspiration, decreased soil moisture, and decreased winter and spring precipitation are current and ongoing environmental conditions impacting all populations of Bartrams stonecrop and exacerbating an altered fire regime.
Many currently undeveloped areas of locatable mineral deposits may be explored or mined in the future. We do not know the full extent of future mine activity within Bartrams stonecrops range; however, 12 mining projects are currently ongoing or proposed within 8

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kilometers 5 miles of Bartrams stonecrop populations in Arizona. The range of current and projected mining activities varies from 1 to 10 per mountain range with Bartrams stonecrop occurrences USFS 2012, entire. One population, Sycamore Canyon 115 adult individuals in 2016, would be affected by groundwater drawdown due to the Rosemont Mine.
Sycamore Canyon currently exhibits high resiliency. Further, this species is illegally collected and sold. Synergistic interactions among wildfire, nonnative grasses, decreased precipitation, and increased temperatures cumulatively and cyclically impact Bartrams stonecrop, and all stressors are exacerbated in small populations. In addition, over half of extant Bartrams stonecrop populations are small;
therefore, loss due to erosion, trampling, collection, herbivory, fire, severe frost, or other stressors have the potential to seriously damage or completely remove these small populations.
Resiliency categories of low, moderate, and high are characterized by relative levels of abundance, number of subpopulations and the spatial distribution of groups, seed production, recruitment, and extent of suitable habitat. The categories of conditions used to determine population resiliency are further described in the SSA report Service 2020a, table 5.12 and the proposed listing rule 84 FR 67060, December 6, 2019, p. 84 FR 67069. Of the 50 extant populations, 2 populations 4 percent exhibit high resiliency also described as high condition, 40
populations 80 percent are in moderate condition, and 8 populations 16 percent are in low condition. Many small populations exhibit moderate resiliency due to other demographic and habitat factors considered in the analysis of resiliency including number of subpopulations, recruitment, riparian elements, precipitation, and shade.
Thus, the resiliency analysis of a population with a low abundance score and high scores in several or all the other categories of resiliency factors may result in an averaged score in the moderate resiliency category. The current resiliency of the known Bartrams stonecrop populations is shown in table 1.

TABLE 1BARTRAMS STONECROP CURRENT POPULATION RESILIENCY
Number of individuals
Sky island
Population
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Brown Canyon
Sabino Wash
Thomas Canyon
Echo Canyon

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Current resiliency Moderate.
Low.
Moderate.
Moderate.