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Federal Register / Vol. 86, No. 155 / Monday, August 16, 2021 / Rules and Regulations
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soil disturbance or trampling, effects of nearby timber harvests, or the two combined have been moderate to high.
Continuing to monitor sites where Cumberland sandwort is or could be exposed to potential threats that were previously determined to place the species at risk of extinction will provide an opportunity to work with land managers to avoid or minimize adverse effects should the threats increase in severity or extent.
In our analysis of Cumberland sandworts resiliency, discussed above in Recovery Criteria, we incorporated available data regarding threats that could potentially modify habitat or curtail the species range. We determined that 42 occurrences currently meet the criterion of being protected and self-sustaining. These occurrences have been known to exist for an average of 21 years, with a range of 7 to 44 years from the first to the most recent observations recorded for the species in these sites. In addition to these 42 occurrences, 9 occurrences are protected in the Obey River watershed and 2 in the South Fork Cumberland watershed in Tennessee for which sufficient monitoring data for evaluating trends in abundance or threats is lacking. However, seven of these occurrences in the Obey River drainage have no evidence of substrate or forest disturbance and are located in PCNA, where TDEC no date, pp. 1011
surveys potential trail routes to prevent new trail construction that would expose occurrences to threats from recreational uses. No other potential threats to the habitats at PCNA have been documented. The two occurrences in the South Fork Cumberland drainage are located in BSF and are not affected by any known threats because they are remotely located from trail access and protected from timber harvest.
Thus, available data indicate that Cumberland sandwort is resilient to the factors discussed above that were determined at the time of listing to constitute a threat of habitat modification or curtailment of the species range. Additionally, management actions have been effective at reducing potential adverse effects of disturbance associated with recreational activities at sites where those activities are most prevalent.
Limited Distribution and Small Population Sizes The listing rule for Cumberland sandwort 53 FR 23745; June 23, 1988
identified the species restricted distribution, limited to a small portion of the Cumberland Plateau in northern Tennessee and southern Kentucky, and
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the small size of many populations, as factors increasing the risks of population loss and potential extinction of the species. The species is still restricted to a small portion of the Cumberland Plateau, but the number of known occurrences has increased from 11 at the time of listing Wofford and Smith 1980, pp. 918; 53 FR 23745, June 23, 1988 to 71 currently TNHID
2018. Three projects have been funded to support searches for new Cumberland sandwort occurrences Kentucky State Nature Preserves Commission KSNPC
1991, entire; TDEC 2000, entire; TDEC
2008, entire. The single search effort that occurred in Kentucky, only in McCreary County, did not expand the known range of Cumberland sandwort, but confirmed the known occurrence located in Big Spring Hollow and documented that thousands of plants were present at two sites mapped at the occurrence KSNPC 1991, entire.
Searches conducted in Tennessee in 2000 TDEC 2000, entire and 2006
2007 TDEC 2008, entire produced records for 30 new occurrences on conservation lands in Fentress, Pickett, and Scott Counties, Tennessee. In addition to these three Cumberland sandwort survey projects, surveys at PCNA for prospective trail routes have produced records for six additional occurrences on conservation lands in Fentress County TNHID 2018. These survey efforts, funded in part by the Service via the Acts section 6 grants to State agencies for endangered species recovery, contributed greatly to increasing the species distribution to the 71 extant occurrences known today.
Fourteen protected and self-sustaining occurrences are located outside of Pickett County, satisfying the recovery criterion concerning geographic distribution. Also, 12 of the 71
occurrences are located in the Obey River watershed in Tennessee, increasing the species distribution beyond the South Fork Cumberland watershed, to which the species was thought to be restricted at the time of listing.
The 1988 listing rule discussed small population size as a threat to many occurrences, but did not include information on population sizes known at the time or specify the number of individuals or the size of habitat area occupied that would be necessary to buffer against extinction risk. As discussed above in Recovery Criteria, we used available data to evaluate the species abundance at known occurrences. We consider populations consisting of fewer than 100 individuals or occupying less than 1 m2 of habitat to be at heightened risk of 1 losing
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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.
However, we note that the risk of inbreeding depression due to unavailability of incompatible mates might be low for Cumberland sandwort, as self-compatibility apparently evolved twice in geographically distant populations of the closely related congener Mononeuria =Arenaria glabra at the edges of that species range Wyatt 1984, p. 815. Based on available data, 12 populations consist of fewer than 100 individuals or occupy less than 1 m2 of habitat. Six of these 12
have been known to persist as small populations for lengths of time ranging from 24 to 41 years, indicating that even small populations are likely to persist when threats are minimized TNHID
2018. The remaining six were discovered in 2000 or later. In contrast, 27 occurrences contain 1001,000
individuals or occupy 1 to 5 m2 of habitat, and 30 occurrences contain more than 1,000 individuals or occupy greater than 5 m2 of habitat. Estimates of abundance available for 24 of the largest occurrences indicate that they collectively hold at least 67,000
Cumberland sandwort individuals.
These data demonstrate that risks associated with small population size are a potential threat likely affecting less than 20 percent of the 71 extant Cumberland sandwort occurrences.
Despite the potential risks associated with small population sizes, available data demonstrate long-term persistence of Cumberland sandwort at all sites where abundance is low and stable or increasing trends at more than 60
percent of the small populations for which trend data are available. Thus, available data support the conclusion that small population size is neither a widespread threat to Cumberland sandwort nor has it been demonstrated to place populations at high risk of decline or extirpation.
Techniques for micropropagating, cryopreserving, and outplanting Cumberland sandwort have been developed and successfully applied to establish an introduced population at DBNF Pence et al. 2011, entire, which is not counted among the 71 extant occurrences discussed above. This introduced population has grown from an initial outplanting of 63 individuals to 255 individuals, representing multiple life stages, as of 2017 Taylor
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