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Federal Register / Vol. 86, No. 155 / Monday, August 16, 2021 / Rules and Regulations
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recovery criteria to indicate when threats to the species have been adequately addressed and prescribed actions that were thought to be necessary for achieving those criteria.
Below we discuss our analysis of available data and our determination as to whether recovery criteria for Cumberland sandwort have been achieved.
Recovery Criteria The objective of the recovery plan is to delist the Cumberland sandwort.
Recovery criteria in the plan state that Arenaria cumberlandensis Cumberland sandwort will be considered for reclassification from endangered to threatened status when 30
geographically distinct, self-sustaining occurrences are protected in four counties in Tennessee and Kentucky and have maintained stable or increasing numbers for 5 consecutive years. The species will be considered for delisting when 40 geographically distinct, self-sustaining occurrences are protected and have maintained statistically stable or increasing numbers for 5 consecutive years. At least 12 of these occurrences must be in counties other than Pickett County, Tennessee.
Methods were chosen for monitoring that minimize trampling of Cumberland sandwort and disturbance of the sandy soil substrate the species occupies. The tradeoff of using this method to minimize disturbance is the inability to statistically analyze trends for individual occurrences or Cumberland sandwort as a species. To address this limitation, we developed a framework for using available distribution and monitoring data, aerial photography, and qualitative assessment of trends for each occurrence to evaluate whether recovery criteria for Cumberland sandwort have been achieved.
Using this framework, we assessed the species viability based on the three conservation biology principles of resiliency, representation, and redundancy Shaffer and Stein 2000, entire. Resiliency is the ability to sustain populations in the face of environmental variation and transient perturbations. To be resilient, a species must have healthy populations that are able to sustain themselves through the range of possible environmental conditions. The greater the number of healthier populations, the more resiliency a species possesses.
Representation is the range of variation or adaptive diversity found in a species, and is the source of a species ability to adapt to nearand long-term changes in the environment. Maintaining adaptive
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diversity requires conserving both ecological and genetic diversity, which enable a species to be more responsive and adaptive to change and, therefore, more viable. Finally, redundancy protects species against the unpredictable and highly consequential events for which adaptation is unlikely, allowing them to withstand catastrophic events. Redundancy spreads risk and is best achieved by having multiple populations widely distributed across a species range.
We characterized the resiliency of 69
of the 71 extant Cumberland sandwort occurrences using available data on three factors complete data were not available for two of the extant occurrences: Occurrence size expressed as estimated abundance or areal coverage, recorded observations of threats causing disturbance to plants or the substrates in which they were rooted, and assessment of general forest conditions from recorded observations or evaluation of aerial photography, for the reasons that follow. Occurrence size influences resiliency because smaller populations are at greater risk of 1
losing genetic variation due to drift change in the frequency of alleles in a population due to random, stochastic events, and 2 inbreeding, which decreases the likelihood that an individual will receive pollen from a compatible mate and produce viable offspring Allendorf and Luikart 2007, pp. 122123. Small populations also may face higher risks of extinction due to diminished resilience to demographic and environmental stochasticity Munzbergova 2006, p. 143.
Demographic stochasticity is the variation in vital rates i.e., probabilities of survival and reproduction among individuals of a given age or life-cycle stage, at a given point in time, while environmental stochasticity is variation in vital rates over time, affecting all individuals of a given age or stage similarly Lande 1988, p. 1457.
Incorporating available data regarding disturbance to Cumberland sandwort plants or the substrates where they occur into the resiliency assessment serves as a proxy indicating whether physical conditions are appropriate to support multiple life stages.
Undisturbed substrates contribute to Cumberland sandwort resiliency by providing suitable sites for germination, growth, and reproduction to occur.
Similarly, evaluating forest condition in the vicinity of Cumberland sandwort occurrences is a proxy indicating whether ecological conditions are likely to support resilience to environmental variation. The presence of contiguous
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forest vegetation in the vicinity of Cumberland sandwort occurrences helps to maintain suitable hydrology and microclimate, potentially buffering severity of stress resulting from environmental perturbations, such as drought. We evaluated representation by considering the distribution of resilient occurrences among the counties and watersheds from which the species is known. Finally, we evaluated redundancy based on the overall number of resilient occurrences distributed throughout its range.
In evaluating resiliency, we used estimates of abundance, where available, combined with estimates of areal coverage to provide a basis for categorizing occurrences into groups of low, medium, or high abundance.
Occurrences with fewer than 100
individuals Heschel and Page 1995, pp.
128131; Munzbergova 2006, p. 148 or with areal coverage less than 1 square meter m2 were ranked low;
occurrences with 1001,000 individuals or with areal coverage ranging from 1 to 5 m2 were ranked medium; and occurrences with more than 1,000
individuals or areal coverage greater than 5 m2 were ranked high. We ranked substrate conditions at each occurrence based on recorded observations of threats TDEC 2011b, pp. 3744. Substrate conditions were ranked high for sites with no record of disturbance; medium for sites with moderate risk of exposure to the threat based on limited historical evidence of digging for archeological artifacts i.e., relic digging or trampling by humans or wildlife in limited areas within available habitat; and low for sites with high risk of exposure as indicated by recent evidence of relic digging or trampling throughout available habitat.
We used aerial imagery available through Google Earth ProTM to determine whether forests in the general vicinity of Cumberland sandwort occurrences exhibited signs of timber harvest, as indicated by substantially reduced tree densities; presence of logging equipment trails; or conversion to nonnative, evergreen forest types. We used available data on global forest loss to provide an objective basis for confirming our determination of locations where timber harvest was suspected to have taken place Hansen et al. 2013, entire. Forest conditions were ranked high in locations where late seral forest was present upslope and downslope of occupied sites and in adjacent areas; medium in locations where risk of exposure to the threat was moderate based on evidence of logging having occurred within the prior 15

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