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Federal Register / Vol. 86, No. 246 / Tuesday, December 28, 2021 / Proposed Rules
within each DPS having either a medium or high relative risk of decline.
Chapter 9 of the SSA report Service 2021, pp. 167193 discusses the potential change in magnitude and extent of threats and the species response to those threats into the future.
We have determined that the effects of climate change and its impact on increasing temperatures, changes to precipitation and hydrology, and influence on wildfire and drought, as well as the continued regulated flows from managed streams, will drive threats on the species and affect its status into the future. The timeframe of our analysis for these threats is approximately 40 years. This period represents our best understanding of the projected future environmental conditions related to threats associated with climate change that would impact the species increasing temperatures, greater proportion of precipitation falling as rain instead of snow, earlier snowmelt influencing streamflow, and increased frequency, duration, and severity of extreme events such as droughts, heat waves, wildfires, and floods. The 40-year timeframe was also used in our PVA as part of its analysis on determining risk for the species into the future Rose et al. 2020, entire.
Although we possess climate and habitat change projections that go out beyond 40 years, there is greater uncertainty between these model projections in the latter half of the 21st century and how the effects of the modeled changes will affect the species response when projected past 40 years.
Accordingly, we determined that the foreseeable future extends only 40 years for the purpose of this analysis and we rely upon projections out to approximately 2060 for predicting changes in the species conditions. This timeframe allows us to be more confident in assessing the impact of climate and habitat changes on the species. Therefore, based on the available climate and modeling projections and information we have on the species, we have determined 2060 as the foreseeable future timeframe for the foothill yellow-legged frog.
Our assessment of future condition interprets the effects that the future changes to threats would potentially have on foothill yellow-legged frog resiliency, representation, and redundancy. In order to accomplish our review, three plausible future scenarios
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were considered and each DPSs future resiliency, redundancy, and representation under each scenario was assessed. As discussed above, we used information from a PVA Rose et al.
2020, pp. 2227 to assist us in determining the potential condition of foothill yellow-frog populations into the future. Although there are an infinite number of possible future scenarios, the chosen scenarios i.e., lower change scenario, mean change scenario, and higher change scenario reflect a range of reasonable scenarios based on the current understanding of climate change models, threats, and foothill yellowlegged frog ecology. The environmental conditions in each future scenario are plausible in that they are not meant to represent the lowest and highest projections of what is possible. Rather, the lower change and higher change scenarios are at the lower and upper ends of confidence intervals from climate change projections, land cover models, and stream temperature models Rose et al. 2020, pp. 2223.
Environmental conditions for the three future scenarios are based on published studies that used ensembles of global climate models Isaak et al. 2017, p.
9188; Swain et al. 2018, p. 427; Sleeter et al. 2019, p. 3336. For the projections of spatially explicit covariates i.e., land cover and stream temperature, downscaled regional climate model data were used Isaak et al. 2017, p. 9186;
Sleeter et al. 2019, p. 3339. The information from these studies reflects the best scientific and commercial information available for projections of land cover Sleeter et al. 2019; Sleeter and Kreitler 2020, unpublished data, stream temperature Isaak et al. 2017, and climate variability Swain et al.
2018 within the range of the foothill yellow-legged frog.
Descriptions of each scenario and the anticipated effects of each scenario on resiliency, representation, and redundancy for each foothill yellowlegged frog DPS is in the SSA report Service 2021, Table 17, sections 9.3
9.5, pp. 171, 174193 and is summarized below.
Resiliency Resiliency is having sufficiently robust populations for the species to withstand stochastic events i.e., events arising from random factors. For the foothill yellow-legged frog, we determined that resiliency is a function
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of metapopulation health and the distribution and connectivity among metapopulations and subpopulations.
To determine if foothill yellow-legged frog populations were resilient, we first assessed spatial and temporal trends in occupancy and abundance. We then assessed structural and functional connectivity among occupied areas. We also evaluated results from a study that modeled the risk of 50 percent decline in occupied stream segments using demographic and environmental information. Finally, we related our results to information from scientific literature, reports, and species experts.
Table 2 below summarizes the current condition and future conditions of resiliency for each of the foothill yellow-legged frog DPSs. In the SSA
report and the table below, we split the North Coast DPS into a California and an Oregon analysis unit. These two analysis units are later combined for determination of the status of this DPS
as a whole. The current condition column reflects the current resiliency of the analysis unit. The current resiliency of each DPS was characterized as having an intact, reduced, substantially reduced, or extensively reduced condition. Under each future scenario, we assessed how the following resiliency measures would change from current condition: 1 Occupancy and abundance, 2 connectivity, 3
modeled risk of population decline, and 4 status of threats. Because changes to environmental conditions under the future scenarios were reflected by environmental covariates in the PVA
see Service 2021, section 9.2
Scenarios; Table 17, we were able to forecast the magnitudes of changes in resiliency by comparing the modeled risk of decline Rose et al. 2020, entire under current conditions to modeled risk under the three future scenarios.
The lower, mean, and higher change scenario columns represent any changes from each DPSs current resiliency. For this analysis, functional extirpation is defined as such extensive reduction in condition that extirpation of the entire unit is likely to eventually occur as remnant populations experience normal environmental and demographic fluctuations. For additional detail on current and future conditions of the DPSs, see the SSA report Service 2021, chapters 8 and 9, pp. 122193.

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