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Federal Register / Vol. 86, No. 166 / Tuesday, August 31, 2021 / Rules and Regulations Response: Livestock grazing is not noted in the SSA report or the rule as a major threat to Bartrams stonecrop.
Rather, the Bartrams stonecrop SSA
report concluded that because Bartrams stonecrop typically occurs on steep terrain, the plants are largely protected from grazing. However, trampling may occur when cattle graze in areas where Bartrams stonecrop occurs. Mortality may be caused by direct trampling by livestock Searle and Meyer 2020, p. 6, and dislodging of soils by the hard edges of hooves may lead to increased erosion or burial of nearby plants, affecting Bartrams stonecrop individuals in areas with livestock grazing pressure. Therefore, while grazing is not a major threat to the species, trampling and direct mortality act as stressors to Bartrams stonecrop in some circumstances, and the effect of livestock is analyzed in the SSA report.
17 Comment: A commenter suggested using past climate data at a local level rather than modelling projections when discussing climate as a threat.
Response: In the Bartrams stonecrop SSA report, figures 4.11ac show both the past and projected mean daily maximum temperatures in Cochise, Pima, and Santa Cruz Counties, Arizona Service 2020a, pp. 6367. The data for past mean daily maximum temperatures also indicate increases in temperature in all three counties. Modelling projections based on the Intergovernmental Panel on Climate Change Fifth Assessment report IPCC 2014, entire and future climate projections from the National Climate Explorer Tool USGS 2017a, entire downscaled to county level were used to discuss climate change and the effects of current and future changes on Bartrams stonecrop. Section 4.3 of the SSA USFWS 2020, pp. 3751
describes these modelling projections in greater detail.
18 Comment: A commenter stated that demographic and environmental stochasticity are naturally occurring phenomena for which Bartrams stonecrop plants are very well adapted.
Response: Demographic and environmental stochasticity are naturally occurring phenomena Shaffer 1981, p. 131. However, Bartrams stonecrop populations adapted to naturally occurring phenomena now experience the additional stressors related to a changing fire regime, nonnative species, and the effects of a changing climate beyond the scope of normal occurrence. For example, effects due to a changing climate, coupled with other stressors, can have a cumulative impact resulting in greater than anticipated decline in rare species
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Souther and McGraw 2014, pp. 1471
1472. In addition, populations that experience variability in abundance must maintain a minimum viable population to be able to repopulate after a demographic or environmental stochastic event or catastrophe Holsinger and Falk 1991, p. 45.
Following a stochastic event that extirpates a population, suitable habitat for Bartrams stonecrop must be present, including humidity and shade, to provide conditions for potential recolonization or regrowth. Rangewide including Mexico, 29 of the 50
Bartrams stonecrop populations 58
percent are small fewer than 50
individuals. When the effect of small population size exacerbates other stressors beyond those naturally occurring phenomena that Bartrams stonecrop has adapted to, population abundance may be reduced to the extent that repopulation does not occur.
19 Comment: Three commenters stated the analysis of mining as a threat is cursory, unsupported, and overstates the likelihood of mining projects occurring within the range of the species. They noted that no mining projects outside of Rosemont are specifically identified and that the Service used an outdated 2012
document/map for this discussion. The commenters also stated that there is no evidence that loss of water from mining operations is a significant threat to Bartrams stonecrop and noted that the shade trees associated with Bartrams stonecrop habitat do not rely on groundwater. Therefore, the proposed rule overstated water drawdown from mining as a threat.
Response: Mining is expected to affect Bartrams stonecrop individuals and populations in several ways. The direct removal of Bartrams stonecrop individuals due to erosion or burial from mineral extraction sites, test pits, and debris piles is expected to impact small populations. Fragmentation of Bartrams stonecrop populations due to placement of mining operations and associated activities can interfere with pollination and reproduction Rathcke and Jules 1993, p. 276. Due to uncertainty regarding the effect of fugitive dust or heavy metal pollution generated by mining operations on Bartrams stonecrops growth and vigor, these potential stressors were not analyzed. The primary threat to Bartrams stonecrop analyzed with regard to mining was the loss of overstory shade trees due to dewatering of nearby streams and groundwater drawdown.
Bartrams stonecrop-associated shade trees include the following riparian
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obligate species: Salix sp. willow, Populus sp. cottonwood, and Platanus sp. sycamore. Within the following Bartrams stonecrop locations, the associated overstory includes riparian trees that provide between 50 and 80
percent shade to the sites: 1 Penasco Canyon: Willow; 2 Stronghold East:
Ash; 3 Cave Canyon: Sycamore; 4
Josephine Canyon: Cottonwood and willow; 5 Santa Rita Sycamore Canyon: Ash; 6 Madera Canyon:
Sycamore; 7 Jordan Canyon:
Cottonwood, ash, and willow; 8
Warsaw/Old Glory Canyons: Willow; 9
Sawmill Canyon: Sycamore; and 10
Death Trap Canyon: Ash. Our response to Comment 6, above, describes the importance of riparian shade trees in maintaining the microhabitat needed by Bartrams stonecrop.
Dewatering of streams in the vicinity of mining operations may lead to overstory canopy changes and loss of shade, as well as reduction in spring and stream flow and humidity in nearby Bartrams stonecrop populations. One mine has been proposed in the Santa Rita Mountains. Bartrams stonecrop individuals and populations in the analysis area could experience indirect impacts from groundwater drawdown USFS 2013a, p. 676. According to the Rosemont Final Environmental Impact Statement USFS 2013a, p. 339, the proposed mine pit would create a permanent drawdown of the water table, and groundwater flowing toward the pit would be lost to evaporation. The water would be perpetually replenished in part by groundwater from the regional aquifer, and the pit would act as a hydraulic sink. The Bartrams stonecrop plants growing just southwest of the proposed Rosemont Mine were analyzed in the Rosemont Final Environmental Impact Statement USFS 2013a, pp.
346350. The predicted groundwater drawdown in the affected population at the end of active mining is 0.15 feet, depending on the site assessed and the model used. At 20 years from the mine closure, the predicted drawdown increases to a maximum of 1520 feet.
In our analysis, we describe a range of potential mining scenarios that may affect Bartrams stonecrop: 1 Ongoing mining activity, 2 one to three new mining activities across the range of the species, and 3 greater than three new mining activities across the range of the species, to represent future levels of stressors to Bartrams stonecrop from mining. We used the information from Coronado National Forest Mining Activity USFS 2012 to develop these plausible ranges of potential activities.
We are not aware of any other sources regarding potential mining activities;

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