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Federal Register / Vol. 86, No. 41 / Thursday, March 4, 2021 / Proposed Rules moist soils, and nonnative and woody plant species outcompete Arizona eryngo for sunlight, space, and water, thereby reducing the quantity and quality of habitat.

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Species Condition Here we discuss the current condition of the Arizona eryngo, taking into account the risks to those populations that are currently occurring. We consider climate change to be currently occurring and exacerbating effects of drought, warming, groundwater withdrawal, diversion, and invasion of nonnative and woody plant species. In the SSA report, for each population, we developed and assigned condition categories for three population factors and two habitat factors that are important for viability of the Arizona eryngo. The condition scores for each factor were then used to determine an overall condition of each population:
high, moderate, low, or functionally extirpated. These overall conditions translate to our presumed probability of persistence of each population, with populations in high condition having the highest presumed probability of persistence over 30 years greater than 90 percent, populations in moderate condition having a presumed probability of persistence that falls between 60 and 90 percent, and populations in low condition having the lowest probability of persistence between 10 and 60 percent.
Functionally extirpated populations are not expected to persist over 30 years or are already extirpated.
Overall, there are four remaining populations of Arizona eryngo, all restricted to small cienegas in the Sonoran and Chihuahuan Deserts in Arizona and Mexico. Historically, Arizona eryngo populations were likely connected to one another, but today they are small and isolated due to cienega loss throughout the region.
Repopulation of extirpated locations is extremely unlikely without human assistance. Two populations are currently in moderate condition and two are in low condition, and two have been extirpated.
La Cebadilla La Cebadilla contains the largest population of the Arizona eryngo, with a population estimate of over 30,000
individuals. However, this population occurs in a very small area; the occupied area is approximately 0.04
hectares 1.1 acres, and the population depends on stable groundwater to maintain springflow into the cienega.
The cienega has been altered by increased presence of trees, bank
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erosion, pasture grading, utility construction, and subdivision development Fonseca 2019, p. 3.
Historical images indicate that the cienega was more extensive in 1941, with fewer trees on some margins of the cienega and no forest on the southern margin of the cienega Fonseca 2019, p.
1. Due to the encroachment of woody vegetation, this site has varied sunlight conditions, with more shade currently than in the past.
The cienega has been shrinking, indicating the aquifer is being depleted Fonseca 2019, pers. comm.. The aquifer supporting the La Cebadilla springs supports numerous private wells including the Tanque Verde Guest Ranch Eastoe and Fonseca 2019, pers. comm.. In addition to groundwater use, aquifer depletion could also result from increased evapotranspiration of tree cover and stream channel adjustments.
La Cebadilla Estates and the Pima County Regional Flood Control District PCFCD are committed to the conservation of the unique ecological diversity of La Cebadilla cienega and are working to reduce woody vegetation.
The homeowners association of La Cebadilla Estates manages their portion of the cienega as common property for the common use and enjoyment of its members. PCFCD manages their portion of the cienega as natural open space, which has a restrictive covenant that limits development and protects natural resources on the property.
Because of the small extent of the population and the encroachment of woody vegetation, the Arizona eryngo population is currently in moderate condition and is at risk of extirpation from decreased springflow due to continuing loss of groundwater from the aquifer.
Lewis Springs The population of Arizona eryngo in Lewis Springs, estimated at 1,813
plants, occurs along a very narrow cienega parallel to a railroad, occupying about 0.04 hectares 0.1 acres Li 2020a, p. 1. In 2005, there were more than a dozen springs and seeps in the wetland complex; as of 2019, some of the wetland patches appear to be drying, with soil drier at several sites than it had been in 2005 Simms 2019, entire.
The water source of Lewis Springs Cienega is supplied by mountain front recharge westward flow from the Mule Mountains and eastward flow from the Huachuca Mountains Baillie et al.
2007, p. 7; Stromberg et al. 2019, p. 6.
Groundwater pumping up to several kilometers away may be affecting the regional groundwater flow to the
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wetlands along the San Pedro River, including Lewis Springs Stromberg et al. 2019, p. 9.
Nonnative Johnsongrass is aggressively invading Lewis Springs and appears to be suppressing Arizona eryngo, particularly in the drier areas of the cienega Simms 2019, p. 22; Li 2020a, p. 2. Similarly, baccharis has been invading and appears to be suppressing Arizona eryngo, as no Arizona eryngo plants were found growing in the understory of baccharis Simms 2019, p. 6; Li 2019, p. 1. In the wetter areas of the cienega where the soil is saturated and surface water is generally present, common spikerush Eleocharis palustris and bulrush appear to suppress Arizona eryngo Li 2020a, p. 2.
BLM has conducted some removal of Johnsongrass at Lewis Springs and is currently planning for additional removal of the species. BLM is also planning experimental removal of baccharis shrubs at Lewis Springs, and they are considering establishment of additional populations and/or subpopulations of Arizona eryngo at suitable sites within Lewis Springs and the SPRNCA. BLM is also collecting seeds for propagation and banking.
Because of the moderate population size, extremely small population extent, decreasing springflow and increased drying of soils, and plant species invasion, Lewis Springs is currently in moderate condition. The population is currently at risk of extirpation from drying due to drought, groundwater pumping, and invasion of nonnative Johnsongrass.
Rancho Agua Caliente, Mexico The Arizona eryngo population at Rancho Agua Caliente occupies about 1
hectare 2.5 acres. The population is estimated to be several hundred plants, including juveniles Sanchez Escalante et al. 2019, p. 16; Sanchez Escalante 2019, pers. comm.. This cienega is the only known population of Arizona eryngo in Sonora.
Rancho Agua Caliente is an active cattle ranch, and Arizona eryngo habitat is somewhat disturbed by cattle Sanchez Escalante et al. 2019, p. 16, which may help create open sun conditions for the species. We have no information on the groundwater source for the spring.
Because of the small numbers of individuals at Rancho Agua Caliente, the population is currently in low condition and is at risk of extirpation due to drought and drying of habitat.

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