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Federal Register / Vol. 86, No. 41 / Thursday, March 4, 2021 / Proposed Rules
sufficiently moist for successful seedling recruitment, particularly in the hottest/driest time of the year normally May/June. If soils become too dry, other more drought-tolerant species are likely to encroach and outcompete the Arizona eryngo Simms 2019, p. 6; Li 2019, p. 1, or if or if it becomes very dry such that the roots are not in moist soil, the plant is likely to die. If the soil is inundated with water such that there is standing water on the surface for too long, other species that grow more aggressively in mesic conditions are likely to outcompete the Arizona eryngo Li 2020, p. 2.
Sunlight Highly resilient Arizona eryngo populations require full sun. Under canopy cover, the species grows less densely, and flowering is reduced. Tall native and nonnative vegetation appears to outcompete and suppress growth of the Arizona eryngo. While these species may compete for sunlight, water, and nutrients, lack of sunlight may be a primary factor driving the absence or decreased abundance of the Arizona eryngo.

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Risk Factors for the Arizona Eryngo We reviewed the potential risk factors i.e., threats, stressors that could be affecting the Arizona eryngo now and in the future. In this proposed rule, we will discuss only those factors in detail that could meaningfully impact the status of the species. Those risks that are not known to have effects on Arizona eryngo populations, such as overutilization for commercial and scientific purposes and disease, are not discussed here but are evaluated in the SSA report. The primary risk factors affecting the status of the Arizona eryngo are: 1 Physical alteration of cienegas Factor A, 2 water loss Factor A, and 3 changes in cooccurring vegetation Factor A. These factors are exacerbated by the ongoing and expected effects of climate change.
Direct harm or mortality due to herbivory or trampling Factor C may also affect individuals and the seedbank, but not at levels likely to affect species viability.
Physical Loss and Alteration of Cienega Habitat Historically, cienegas were more common and larger than they are today.
Greater than 95 percent of the historical area of cienegas in the southwestern United States and northwestern Mexico is now dry Cole and Cole 2015, p. 36.
Functional cienegas were much more common prior to the late 1800s, as evidenced by pollen and fire records,
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General Land Office survey notes, and early trapper and settler diaries Hendrickson and Minckley 1985, p.
131; Fonseca 1998, p. 111; Cole and Cole 2015, p. 36; Brunelle et al. 2018, p. 2. Estimates of cienega abundance in the International Four Corners Region of the Southwest Arizona, Sonora, New Mexico, and Chihuahua vary from hundreds to thousands Cole and Cole 2015, p. 36; Sivinski 2018, entire. Of the 155 cienegas that Cole and Cole 2015, p. 36 identified in the International Four Corners Region, 87
56 percent are either dead or so severely compromised that there is no prospect for their restoration. In addition to the reduced abundance of cienegas in the International Four Corners Region, the remaining cienegas are greatly reduced in size, and due to many being severely incised, they are more similar to creeks than marshes Cole and Cole 2015, p. 36.
A number of complex factors, many of which are interrelated, led to the historical loss and degradation of cienegas and continue to contribute to this loss today. The primary factors include intensive grazing of domestic livestock, the removal of beavers Castor canadensis from regional streams and rivers, and agricultural recontouring Minckley et al. 2013a, p. 214; Cole and Cole 2015, p. 32. Intensive overgrazing by sheep and cattle from the late 1500s to the late 1800s led to barren soil, erosion, headcutting erosional feature in a stream that contributes to lowering the water table of the surrounding system, and increased frequency of or intensity of destructive floods, all leading to the alteration or complete destruction complete loss of ecological function of cienegas Minckley et al.
2013a, p. 214; Cole and Cole 2015, p.
32. Beaver dams, once numerous within the range of the Arizona eryngo, slowed water and created pools and wetlands along water courses, and enhanced groundwater recharge;
however, high levels of beaver trapping in the 1800s resulted in increased erosion and channel cutting of these once complex, shallow wetlands Gibson and Olden 2014, p. 395; Cole and Cole 2015, p. 32. Additionally, early settlers recontoured e.g., diverted, dammed, channelized cienegas for agricultural, mining, disease control, and other purposes; this resulted in further channelization and concentrated flow, greatly reducing the size of cienegas and further lowering the water table Cole and Cole 2015, p. 32;
Minckley et al. 2013b, p. 78.
We expect that Arizona eryngo populations were more widespread and occurred at historical cienegas that have
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lost their ecological function due to physical alteration, such that populations were more abundant, occurred closer to one another, and were more connected through pollination and seed dispersal than they are currently. As a result of these lost cienegas, the four extant Arizona eryngo populations are now disjunct.
Although grazing was one cause of the loss of historical cienega habitat, grazing and trampling by livestock occur only occasionally at Arizona eryngo populations. No grazing is authorized at Lewis Springs, and we are not aware of any grazing occurring at La Cebadilla and Ojo Vareleno. Trespass livestock could enter Lewis Springs and affect habitat in the cienega; although there was no evidence of cattle in 2018 or 2019, there was evidence i.e., scat and light trailing of a trespass horse in the area when Service biologists visited the site in 2019. Cattle are present at Rancho Agua Caliente, Sonora, and the habitat is somewhat disturbed by cattle Sanchez Escalante et al. 2019, p. 16.
Livestock e.g., livestock trailing and gathering can trample vegetation and expose and compact soil, resulting in habitat erosion and altered hydrological function, but the effects of livestock are dependent on many factors such as the intensity, duration, and timing of grazing. In the absence of other forms of disturbance e.g., fire, it is possible that selective, well-managed livestock grazing in the winter or spring could create habitat disturbance and open sun conditions favoring Arizona eryngo seedling establishment.
Other physical alterations that occurred in the past likely continue to affect extant populations of Arizona eryngo through changes in the natural hydrology of cienegas supporting the species. For example, a berm that has been present at La Cebadilla since at least 1941, as well as various houses and roads adjacent and near the cienega, all affect the natural hydrology of the site. Similarly, the railroad that runs parallel to Lewis Springs likely affects the hydrology of the cienega. Unlike the historical physical alterations that severely degraded cienegas, these alterations berm, railroad, houses, etc.
have not destroyed cienega function.
Water Loss Water loss in cienegas poses a significant threat to the Arizona eryngo.
Causes of water loss are complex, but the primary causes at cienegas historically or currently supporting Arizona eryngo are: 1 Groundwater pumping/withdrawal, 2 spring modification, 3 water diversion, and 4 drought. These stressors are all
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