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Federal Register / Vol. 86, No. 185 / Tuesday, September 28, 2021 / Proposed Rules provide a reasonable degree of confidence in the prediction. Thus, a prediction is reliable if it is reasonable to depend on it when making decisions.
It is not always possible or necessary to define foreseeable future as a particular number of years. Analysis of the foreseeable future uses the best scientific and commercial data available and should consider the timeframes applicable to the relevant threats and to the species likely responses to those threats in view of its life-history characteristics. Data that are typically relevant to assessing the species biological response include speciesspecific factors such as lifespan, reproductive rates or productivity, certain behaviors, and other demographic factors.
Analytical Framework The SSA report documents the results of our comprehensive biological status review for the species, including an assessment of the potential threats to the species. The SSA report does not represent a decision by the Service on whether the species should be proposed for listing as an endangered or threatened species under the Act. It does, however, provide the scientific basis that informs our regulatory decisions, which involve the further application of standards within the Act and its implementing regulations and policies. The following is a summary of the key results and conclusions from the SSA report; the full SSA report can be found on http www.regulations.gov under Docket FWSR2ES20200015.
To assess the viability of the South Llano Springs moss, we used the three conservation biology principles of resiliency, redundancy, and representation Shaffer and Stein 2000, pp. 306310. Briefly, resiliency supports the ability of the species to withstand environmental and demographic stochasticity for example, wet or dry, warm or cold years, redundancy supports the ability of the species to withstand catastrophic events for example, droughts, large pollution events, and representation supports the ability of the species to adapt over time to long-term changes in the environment for example, climate changes. In general, the more resilient and redundant a species is and the more representation it has, the more likely it is to sustain populations over time, even under changing environmental conditions. Using these principles, we identified the species ecological requirements for survival and reproduction at the individual, population, and species levels, and
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described the beneficial and risk factors influencing the species viability.
The SSA process can be categorized into three sequential stages. During the first stage, we evaluated individual species life-history needs. The next stage involved an assessment of the historical and current condition of the species demographics and habitat characteristics, including an explanation of how the species arrived at its current condition. The final stage of the SSA involved making predictions about the species responses to positive and negative environmental and anthropogenic influences. This process used the best available information to characterize viability as the ability of a species to sustain populations in the wild over time. We use this information to inform our regulatory decision.
Summary of Biological Status and Threats In this section, we review the biological condition of the species and its resources, and the threats that influence the species current and future condition, in order to assess the species overall viability and the risks to that viability.
Based on the conditions of the only known current and historical populations, the South Llano Springs moss requires a constant flow of mineral-rich spring water or spring-fed river water over shallow limestone rocks. Seven Hundred Springs and the areas thought to contain the Redfearn sites are supported by spring flows within the Edwards-Trinity aquifer and the South Llano River watershed Seven Hundred Springs and Big Paint Springs. These springs have never ceased flowing in recorded history.
Water from these springs emerges at a very consistent temperature and is rich in travertine minerals. Rocks and plants immersed in the upper South Llano River quickly become encrusted with travertineor tufa-like mineral deposits, to an unusual degree not seen in most springs in the Edwards-Trinity aquifer Service 2017, p. 2. Thus, it is possible that high mineral concentrations, or the precipitation of minerals from solution, could be requirements for the establishment and growth of South Llano Springs moss individuals.
The water temperature of Seven Hundred Springs was consistently 21.5
degrees Celsius C 70.7 degrees Fahrenheit F in June, and the pH
ranged from 7.0 to 7.2 Wyatt and Stoneburner 1980, p. 516. The species occurred in both shaded and exposed niches at Seven Hundred Springs Wyatt and Stoneburner 1980, p. 516.
Associated vascular plant species
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included maidenhair fern Adiantum capillus-veneris, southern shield fern Thelypteris kunthii, watercress Nasturtium officinale, and members of the mint family Lamiaceae and composite family Asteraceae Wyatt and Stoneburner 1980, p. 516.
Associated moss species included Hygroamblystegium tenax and Eucladium verticillatum Wyatt and Stoneburner 1980, p. 517.
Mosses closely related to the South Llano Springs moss reproduce both sexually and asexually. However, there is no evidence that sexual reproduction is occurring in the single remaining known site of occurrence, as no plants with female reproductive structures were observed in the wild population or during a 16-month propagation study in 1978 and 1979 Wyatt and Stoneburner 1980, p. 517. The plants cultivated in captivity produced only male reproductive structures. It is possible that the known population may be a clone of a single or a few male individuals and that sexual reproduction is no longer possible for the species.
In addition to the habitat requirements described above, resilient populations of South Llano Springs moss need to be large enough that local stochastic events do not eliminate all individuals, allowing the overall population to recover from any one event. The larger a population is, the greater the chances that a portion of the population will survive. The minimum viable population size is not known for this species. However, the geographic extent is provided from the observations of Wyatt and Stoneburner 1980, p. 516.
When last observed, the South Llano Springs moss grew in the spring outflow partially submerged in shaded areas within a 10 m 33 ft zone between the springs and the river below Wyatt and Stoneburner 1980, p. 516. We assume that the population could be as large as the spring flow and substrate allow in this zone. The area occupied by a moss population is a practical surrogate for abundance, provided that it is understood that this does not address the number of genetically unique individuals.
Recruitment is also needed for populations to be resilient. The colony at Seven Hundred Springs may be a clone of a single individual, or only male individuals, and is presumed incapable of sexual reproduction Wyatt and Stoneburner 1980, p. 520. Unless female individuals are present, the colony of South Llano Springs moss at Seven Hundred Springs can persist and grow only through vegetative budding or through the establishment of
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