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Federal Register / Vol. 86, No. 166 / Tuesday, August 31, 2021 / Rules and Regulations
Precipitation is projected to decrease in the future with climate change, although it is expected to be more intense when it does occur Seager et al.
2007, p. 1181; Karl et al. 2009, pp. 24, 33. Some projections suggest an overall similar amount of precipitation in the Southwest, but that it will be distributed differently in timing and intensity Zhang et al. 2012, p. 390. Most climate change scenarios predict that the American Southwest will also become warmer during the 21st century Overpeck et al. 2012, p. 5; Karl et al.
2009, p. 129, and the frequency of droughts is projected to increase by the end of the 21st century.
Continuing drought, increased temperatures, and increased evapotranspiration are expected to reduce vegetation cover and shade in Bartrams stonecrop habitat through overstory tree loss Ferguson 2014, p.
42. Such tree mortality has already been observed in Bartrams stonecrop populations, negatively impacting available microhabitat Ferguson 2016a, pp. 12, 17, 26. Drought or reduced water resources disproportionately affect seedlings, as this stage is particularly vulnerable to desiccation.
Bartrams stonecrop plants are almost always located near water sources springs, seeps, or intermittent streams, but above the floodline Phillips et al.
1982, p. 4; Shohet 1999, p. 22; NPS
2014, p. 2. Crevices above the floodline offer protection from typical flood events. Bartrams stonecrop needs crevices in solid bedrock or in shallow soil pockets on rock ledges and cliffs in deep, narrow canyons above normal flood levels to avoid seeds and plants being washed away during flood events.
An increase in the flood frequency or intensity could result in an increase in the number of plants dislodged.
Based on climate change projections, it is likely that the severity of storm events will increase, resulting in more runoff, more severe flooding events, and more erosion and sedimentation affecting populations, especially following wildfire events in the uplands. Rainfall events in the southwestern United States are projected to be less frequent but more intense, and larger flood events are expected to be more common in the future Karl et al. 2009, p. 24. Erosion and soil loss from such storm events may increase with higher peak stream flows. Flooding can remove Bartrams stonecrop individuals occurring near the streams edge and has the potential to remove entire small populations Phillips et al. 1982, p. 10; The Nature Conservancy 1987, p. 2; Ferguson 2014, p. 42; Ferguson 2016a, p. 26; NPS 2015,
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p. 4; Ferguson 2017b, p. 15. One group within a Bartrams stonecrop population was extirpated due to dislodging from a flooding event followed by drying of habitat The Nature Conservancy 1987, p. 2.
Bartrams stonecrop is susceptible to damage from freezing events Ferguson 2014, pp. 23, 40. An early season frost was reported in one Bartrams stonecrop population, and a hard frost is suspected of killing all plants in another population Indian Creek in 2011. Frost events are not projected to decrease in severity Kodra et al. 2011, p. 3.
Because continuing drought, more severe freezing events, and increased high intensity rainfall events all pose threats to Bartrams stonecrop across the range of the species, this stressor is considered in our analysis of future species viability. We conclude that abnormal freezing events can seriously damage or completely remove small populations.
27 Comment: Three commenters indicated that the Services conclusion that small and isolated populations are a threat to Bartrams stonecrop is incorrect.
Response: Small population size has the potential to decrease Bartrams stonecrop population resiliency, as all stressors are exacerbated in populations with only a small number of individuals. 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 wildfires.
Most known Bartrams stonecrop populations are small, with over half of known individuals of the species residing in five populations. Twentynine of the 50 extant known Bartrams stonecrop populations 58 percent rangewide contain fewer than 50
individuals, and 43 populations 86
percent contain fewer than 150
individuals. The effect of more minor threats such as erosion, trampling, and illegal collection are all increased when Bartrams stonecrop populations are already small.
Determination of Bartrams Stonecrops Status Section 4 of the Act 16 U.S.C. 1533
and its implementing regulations 50
CFR part 424 set forth the procedures for determining whether a species meets the definition of an endangered species or a threatened species. The Act defines endangered species as a species in danger of extinction throughout all or a
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significant portion of its range, and threatened species as a species likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range. The Act requires that we determine whether a species meets the definition of endangered species or threatened species because of any of the following factors: A The present or threatened destruction, modification, or curtailment of its habitat or range; B
overutilization for commercial, recreational, scientific, or educational purposes; C disease or predation; D
the inadequacy of existing regulatory mechanisms; or E other natural or manmade factors affecting its continued existence.
Status Throughout All of Its Range After evaluating threats to the species and assessing the cumulative effect of the threats under the section 4a1
factors, we summarize our findings below. We have carefully assessed the best scientific and commercial information available regarding the past, present, and future threats to Bartrams stonecrop.
Bartrams stonecrop has experienced population declines, and three populations have been lost entirely.
Currently, 50 extant Bartrams stonecrop populations contain 4,682 individuals in the United States and Mexico. Four Bartrams stonecrop populations contain nonnative grasses and several more are near nonnative grasses resulting in current habitat loss and continued loss in the future Factor A. Further, an altered fire regime Factors A and E
impacts all populations currently or in the near future and drives the spread of nonnatives Factor A, exacerbating the encroachment of nonnative grasses.
Consequently, all remaining populations of Bartrams stonecrop are impacted by nonnative grasses now or will be in the near future. Altered precipitation Factors A and E, increased temperatures Factors A and E, and decreased annual precipitation Factors A and E are current and ongoing regional conditions that are impacting all populations of Bartrams stonecrop. These environmental conditions exacerbate an altered fire regime, driving the spread of nonnative grasses with competitive advantages over native grasses during periods of drought. Many currently undeveloped areas of locatable mineral deposits may be explored or mined in the future Factors A and E. The range of current and projected mining activities varies from 1 to 10 per mountain range with Bartrams stonecrop occurrence USFS
2012, entire. One population, Sycamore
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