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Federal Register / Vol. 86, No. 166 / Tuesday, August 31, 2021 / Rules and Regulations expected to continue to increase Westerling et al. 2006, p. 943, given historical land management actions, an increase in fire starts from cross-border human activity and recreationists e.g., from campfires, cigarettes, target shooting, nonnative plant invasion, and continuing drought conditions Westerling et al. 2006, p. 940;
FireScape 2016, entire; Fire Management Information System 2016, p. 2. Direct impacts of fire include burning of Bartrams stonecrop individuals, resulting in injury, reduction in reproductive structures, or plant mortality. Indirect impacts of fire on Bartrams stonecrop may include increased runoff of floodwaters, postfire flooding, deposition of debris and sediment originating in the burned area, erosion, changes in vegetation community composition and structure, increased presence of nonnative plants, alterations in the hydrologic and nutrient cycles, and loss of overstory canopy shade essential to maintaining Bartrams stonecrop microhabitat Griffis et al. 2000, p. 243; Crawford et al. 2001, p. 265; Hart et al. 2005, p. 167;
Smithwick et al. 2005, p. 165; Stephens et al. 2014, p. 42; Ferguson 2014, p. 43;
Ferguson 2016a, p. 26. Fire primarily alters hydrology and erosion processes by consumption of the protective canopy, ground cover, and organic matter. When plants and litter are removed by fire, ground surface protection is decreased, less rainfall is intercepted, and less infiltration occurs Pierson et al. 2011, p. 443. The exposed bare soil becomes susceptible to increased runoff generation and sediment detachment and transport Pierson et al. 2011, p. 444. Amplified runoff post-fire carries sediment Pierson et al. 2011, p. 443, causing erosion or burial of Bartrams stonecrop plants.
We are aware of 11 wildfires that occurred in known Bartrams stonecrop sites from 20072017, killing some Bartrams stonecrop individuals and removing shade in some sites Ferguson 2014, pp. 910, 15, 2829; Ferguson 2016a, p. 13; Ferguson 2016b, entire;
Ferguson 2017b, p. 32; Ferguson 2017c, p. 2. Although we do not have pre-fire population counts in any population, two of the largest Bartrams stonecrop populations occur in sky island mountain ranges that have had the fewest acres burned from 20102017, which indicates these populations may have experienced less of the detrimental effects of fire than smaller populations.
Wildfires have burned in all nine sky island mountain ranges of southern Arizona with known Bartrams
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stonecrop occurrences within the last decade. Wildfire could potentially cause extirpation of small Bartrams stonecrop populations throughout the range of the species and have negative impacts on larger populations. Bartrams stonecrop seeds are very tiny, reside at or near the soil surface Shohet 1999, p. 48, and show no characteristics that would promote survival in a wildfire.
The nonnative plants in the uplands surrounding and within Bartrams stonecrop populations include nonnative grass species such as Lehmanns lovegrass and rose natal, both of which have numerous advantages over native grasses.
Lehmanns lovegrass resprouts from roots and tiller nodes not killed by hot fire, is not hampered by the reduction in mycorrhizae associated with fire and erosion, responds to winter precipitation when natives grasses are dormant, produces copious seed earlier than native grasses, maintains larger seedbanks than native grasses, and has higher seedling survival and establishment than native grasses during periods of drought Service 2020a, p.
50. Rose natal is capable of growing in low moisture situations, has prolific seed production, and has stems that root from the nodes Stokes et al. 2011, p.
527. Both species outcompete native plants, reduce structural and spatial diversity of habitats, and increase biomass and fuel loads, increasing the fire frequency. Nonnative grasses have been reported with Bartrams stonecrop individuals in four instances, at Sycamore Canyon, French Joe Canyon, Shaw Canyon, and Juniper Flat populations, and upslope of several populations of Bartrams stonecrop in the Dragoon Mountains, increasing the likelihood of fire occurrence and subsequent impacts to these populations Heritage Database Management System, E.O. ID 55; Simpson 2017, pers. comm..
Nonnative plant species increase the frequency and severity of wildfires;
such wildfires can directly and indirectly impact individuals and populations.
Altered Precipitation, Drought, Flooding, and Freezing Regimes The southwestern United States is warming and experiencing severe droughts of extended duration, changes in amount of snowpack and timing of snowmelt, and changes in timing and severity of precipitation and flooding Garfin et al. 2014, entire. The effects of a changing climate are important considerations in the analysis of the stressors to Bartrams stonecrop, including increased nonnative competition described above and
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altered fire regimes during times of altered precipitation and drought. To analyze the effects of a changing climate to Bartrams stonecrop, we relied on the Intergovernmental Panel on Climate Changes IPCC Fifth Assessment IPCC
2014, entire and IPCC Climate Change 2013The Physical Science Basis IPCC
2013, entire. Four emission scenarios, referred to as Representative Concentration Pathways RCPs, were developed for the IPCC report IPCC
2014, p. 57. We evaluated the effects of climate change on Bartrams stonecrop using RCP 4.5 and RCP 8.5 to bracket the range of environmental variability.
The IPCC report 2014 expresses confidence that emissions will fall within the RCP 4.58.5 range.
Precipitation is bimodal within the mountain ranges where Bartrams stonecrop occurs, with winter snow and rain, and summer monsoon rain. Fall and winter October through March precipitation is needed for Bartrams stonecrop germination, and both summer July and August and fall October and November precipitation is needed for Bartrams stonecrop flower production. Flowering is triggered by fall rains and does not occur during periods of water stress Shohet 1999, pp.
22, 25, 36, 39. Altered precipitation timing and form i.e., snow versus rain, as well as reduced precipitation in the winter and spring and prolonged drought, are important stressors influencing the viability of Bartrams stonecrop due to impacts on moisture availability for germination, growth, and flowering. In addition, due to increased nonnative competition during times of reduced precipitation and drought, impacts from these stressors to Bartrams stonecrop populations would be exacerbated.
Altered precipitation timing and form snow versus rain, as well as reduced winter and spring precipitation and prolonged drought, are currently occurring and projected to increase or be altered from normal in the Southwest Garfin et al. 2014, entire. Recently, there has been a decrease in the amount of snowpack, earlier snowmelt, and increased drought severity in the Southwest Garfin et al. 2013, entire;
Garfin 2013b, p. 465. Further, more wintertime precipitation is falling as rain rather than snow in the western United States IPCC 2013, p. 204; Garfin 2013b p. 465. This means that the amount of runoff in the spring when snow melts is reduced, as is soil moisture. Late winter-spring mountain snowpack in the Southwest is predicted to continue to decline over the 21st century under RCP 4.5 and 8.5 because of increased temperature Garfin et al.

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