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5-YEAR REVIEW 

Mancos milkvetch/Astragalus humillimus

1.0 GENERAL INFORMATION 

1.1 Reviewers 

Lead Regional Office: Southwest Regional Office, Region 2 

Susan Jacobsen, Chief, Threatened and Endangered Species, 505-248-6641 

Wendy Brown, Endangered Species Recovery Coordinator, 505-248-6664 

Maggie Dwire, Recovery Biologist, 505-248-6663 

Julie McIntyre, Recovery Biologist, 505-248-6507 

Lead Field Office: New Mexico Ecological Services Field Office 

Eric Hein, Terrestrial Branch Chief, 505-761-4735 

Thetis Gamberg, Fish and Wildlife Biologist, 505-599-6348 

Laura Hudson, Vegetation Ecologist, 505-761-4762 

1.2 Purpose of 5-Year Reviews: 

The U.S. Fish and Wildlife Service (Service or USFWS) is required by section 4(c)(2) of the 

Endangered Species Act (Act) to conduct a status review of each listed species at least once 

every 5 years. The purpose of a 5-year review is to evaluate whether or not the species’ status 

has changed since it was listed (or since the most recent 5-year review). Based on the 5-year 

review, we recommend whether the species should be removed from the list of endangered and 

threatened species, be changed in status from endangered to threatened, or be changed in status 

from threatened to endangered. Our original listing as endangered or threatened is based on the 

species’ status considering the five threat factors described in section 4(a)(1) of the Act. These 

same five factors are considered in any subsequent reclassification or delisting decisions. In the 

5-year review, we consider the best available scientific and commercial data on the species, and 

focus on new information available since the species was listed or last reviewed. If we 

recommend a change in listing status based on the results of the 5-year review, we must propose 

to do so through a separate rule-making process including public review and comment. 

1.3 Methodology used to complete the review 

The U.S. Fish and Wildlife Service (Service) conducts status reviews of species on the List of 

Endangered and Threatened Wildlife and Plants (50 CFR 17.12) as required by section 

4(c)(2)(A) of the Endangered Species Act, as amended (Act) (16 U.S.C. 1531 et seq.). Public 

notice for this status review was published in the Federal Register on April 23, 2007 (72 FR 

20134), requesting information on the status of Astragalus humillimus (Mancos milkvetch). 

Written comments were received from the Navajo Nation Department of Fish and Wildlife 

(2009), and a long-term demographic study report was received from the State of New Mexico 

Forestry Division (2008). 
3

This review was a collaborative effort comprised of biologists from the Service’s Region 2 

Regional Office and New Mexico Ecological Services Field Office, the Region 6 Western 

Colorado Field Office, and the State of New Mexico Forestry Division. Several botanical and 

species experts in Colorado and New Mexico were contacted in spring of 2010 for updated 

information. Robert Sivinski, Botanist for the State of New Mexico Forestry Division, was 

contracted through a section 6 grant to gather relevant information and prepare a draft of this 

review. The final review and recommended classification were prepared by the New Mexico 

Ecological Services Field Office. 

1.4 Background 

The purpose of this 5-year review is to ensure that Astragalus humillimus has the appropriate 

level of protection under the Act. The review documents a determination by the Service of 

whether the status of the species has changed since the time of its listing. The review also 

provides updated information on the current threats, ongoing conservation efforts, and the 

priority needs for future conservation actions. 

1.4.1 FR Notice citation announcing initiation of this review: 

72 FR 20134: April 23, 2007

1.4.2 Listing History: 

 

Original Listing 

FR notice: 50 FR 26568 

Date listed: June 27, 1985

Entity listed: Species, Astragalus humillimus

Classification: Endangered, without critical habitat 

1.4.3 Associated rulemakings: None.

1.4.4 Review History: A 5-year review was initiated on November 6, 1991, (56 FR 

56882) for all species listed before 1991, but no document was prepared for this species. 

1.4.5 Species Recovery Priority Number at start of 5-year review: 2. 

The recovery priority number is 2, indicating a high degree of threat, a high recovery 

potential, and the listed entity is a species.

1.4.6 Recovery Plan or Outline

Name of plan or outline: Mancos Milkvetch (Astragalus humillimus) Recovery Plan 

 Date issued: December 20, 1989 

Dates of previous revisions: The recovery plan has not been revised. 
4

2.0 REVIEW ANALYSIS 

2.1 Application of the 1996 Distinct Population Segment (DPS) policy 

The Distinct Population Segment policy does not apply to Astragalus humillimus because it is 

not a vertebrate animal. 

2.2 Recovery Criteria 

 2.2.1 Does the species have a final, approved recovery plan? Yes. 

Although there is a final recovery plan, it does not reflect up-to-date information on the 

species’ biology, nor does it address all five listing factors that are relevant to the species. 

When the recovery plan was finalized in 1989, limited available data made it impossible 

to quantify habitat requirements with enough precision to establish further recovery 

criteria. Thus, while criteria for recovery, downlisting, and delisting were established, 

they are difficult to quantify and have not been met. 

2.2.1.1 Does the recovery plan contain objective, measurable criteria? No 

The recovery plan lists one main goal which is to remove Astragalus humillimus

from the Federal list of endangered and threatened species by managing the 

essential habitat to sustain natural populations in the wild. The delisting criteria 

within the recovery plan are meant to demonstrate (1) long-term stability of 

populations and habitat through at least 10 years of monitoring, and (2) continued 

assurances that threats have been alleviated for all presently known populations, 

and 75 percent of any plants and habitat has been discovered. 

The criteria given for downlisting A. humillimus to threatened are summarized 

below, including known details on their current status. 

 

1) Census and map all known populations. 

 Known populations were surveyed and mapped for Navajo Nation, Bureau of 

Land Management, and State of New Mexico lands during the 1980s; 

monitoring plots for these three agencies were last surveyed in 2008 (see 

Section 2.3.1.2). Colorado Natural Heritage Program has census and map 

data for this species on Ute Mountain Ute tribal lands, but no new information 

has been collected since the late 1980s. 

2) Use this data to develop formal documentation of long-term mineral, oil, gas, 

and energy development potential in the area. 

 Navajo Nation, Bureau of Land Management, and State of New Mexico lands 

are managed to protect and minimize impacts to federal, state, or agency listed 

species regarding any mineral or energy development (see #3 below on habitat 

management plans). Each of these three agencies will determine the need to 

consult with the Service based on whether the proposed project location 
5

overlaps with known populations previously surveyed and mapped. It is 

unknown if the Ute Mountain Ute tribe uses their census and map data (last 

prepared by Colorado Natural Heritage Program in the late 1980s) to manage 

for the protection of this species if and when mineral or energy development 

is proposed. 

3) Develop a habitat management plan to administer mineral development in the 

area and to provide for this species’ welfare. 

A habitat management plan with conservation recommendations was 

completed by the Nature Conservancy for Navajo Nation lands in 1992, but 

enactment of the provisions within the plan is unknown. Navajo Nation 

classifies this species as Group 2, which is defined as a species or subspecies 

whose prospects of survival or recruitment is in jeopardy. Bureau of Land 

Management classifies this plant as a sensitive species (SS) found in the 

Hogback Area of Critical Environmental Concern (ACEC). State of New 

Mexico and Ute Mountain Ute lands do not have management plans, even 

though the State of New Mexico considers this species to be “endangered” 

and Colorado State classifies this species as “rare.”

4) Establish permanent long-term monitoring plots at population sites. 

 All systematic plot monitoring ended in 2008 on State of New Mexico and 

Bureau of Land Management lands; only observational visits continue to be 

performed. The Navajo Nation established two permanent plots in 1991 

located on the Hogback geologic formation; however, only one of these plots 

was relocated, remapped, and surveyed in 1991. The status of all known 

populations and known potential habitat on Navajo Nation lands was 

summarized in a 2009 letter to the Service. We are not aware of any longterm monitoring plots on Ute Mountain Ute tribal lands. 

The recovery plan also contains an implementation table of prioritized actions to 

recover A. humillimus. These actions address the stated recovery goal, but cannot 

be quantified. Of the 13 actions recommended, 3 have been implemented or are 

ongoing, including: 

1) enforcement of existing laws; 

2) research into the species ecological requirements; and 

3) research regarding seed biology. 

Although the downlisting criteria and prioritized actions provide guidance for 

recovery, they do not offer benchmarks for measuring progress towards recovery 

or specifically address current threats. Even though the original listing factors 

remain relevant to this species, climate change (specifically severe drought) and 

off-road vehicle use are now recognized as additional threats to this species’ 

recovery. 
6

2.3 Updated Information and Current Species Status 

2.3.1 Biology and Habitat 

2.3.1.1 New information on the species’ biology and life history

Morphology, reproductive biology, and phenology 

Astragalus humillimus is a diminutive, tufted perennial growing in clumps up to 

30 centimeters (cm) (12 inches [in]) across with a dense crown of persistent spiny 

leaf stalks; no other mat-forming Astragalus species has persistent, subspinescent 

petioles (Barneby 1964). Stems are up to 1 cm (0.4 in) long and are crowded with 

leaves up to 4 cm (1.6 in) long (Barneby 1964). Flower branches support 1 to 3 

lavender/purplish flowers with a conspicuous lighter-colored spot in the throat of 

the corolla tube (Service 1989). Astragalus humillimus flowers in late April and 

early May (Service 1989). Root systems proliferate about 7 cm (3 in) below the 

surface (Service 1989). Larger plants may produce over 100 flowers in a growing 

season and fruits mature by mid-June (Service 1989). The fruit is egg-shaped and 

laterally compressed measuring about 4.5 millimeters (mm) (0.2 in) long and 2 

mm (0.1 in) in diameter (Barneby 1964), and each produces 4 to 9 seeds (Service 

1989). In New Mexico, monitoring results revealed that it takes two growing 

seasons for seedlings to mature with flowering into the third or fourth year as 

compared to other species of Astragalus, which typically take one growing season 

to bloom (New Mexico State Forestry Division 2008). 

Pollination biology 

Astragalus humillimus plants produce viable fruit by outcrossing and selfpollination (Tepedino 2002). Flowers of rare plants, including A. humillimus, 

often require pollination by native bees to produce seeds (Tepedino 2002). 

Possible pollinators of A. humillimus were studied in 1989 by the Bee Biology 

and Systematics Laboratory for the Navajo Nation; a full list is provided in the 

Habitat Management Plan for Navajo Nation (House and Engelking 1992). They 

found the most common visitors were two members of the bee family 

Megachilidae: Osmia titusi and O. sculleni. Honey bees and butterflies, 

including the painted lady butterfly (Vanessa cardui), were also noted as potential 

pollinators (Service 1989). Fruit set is generally good and no pollinator 

limitations were detected (Tepedino 2002). 

Habitat, geology, and plant community 

This species occurs on sandstone substrate ledges and mesa tops in cracks or 

shallow bowl-like depressions (tinajas) that accumulate sandy soils and rainfall 

(Service 1989; New Mexico State Forestry Division 2008). Populations are found 

along the Colorado Plateau subdivision of the Great Basin Desert of northwestern 

New Mexico and southwestern Colorado within pinyon-juniper woodland and 

desert scrub communities (Dick-Peddie 1993). Potential habitat corresponds to 

rimrock outcrops of the Point Lookout and Cliffhouse members of the Mesa 

Verde sandstone series with flat or gently sloping surfaces at an average elevation 
7

of 1,854 meters (m) (5,650 feet [ft]) (Service 1989). This species is confined to 

large sheets of exfoliating whitish-tan colored sandstone (New Mexico State 

Forestry Division 2008) alongside Fraxinus anomala (single leaf ash), Brickellia 

microphyla var. scabra (scabrous bricklebush), Cercocarpus intricatus (small leaf 

mohagany), and Ipomopsis roseata (rosy ipomopsis) (Service 1989). Overall 

cover is very low (less than five percent), and resource competition for all of these 

species is minimal (Service 1989). At a broader landscape scale, dominant plant 

associates are Achnatherum hymenoides (Indian ricegrass), Gutierrezia sarothrae 

(broom snakeweed), Yucca angustissima (narrow leaf yucca), and Artemisia 

tridentata (big sagebrush) (Service 1985). 

Fecundity and genetic variability 

At the time of listing, a limited amount of information was available about the 

species’ life history and habitat requirements. While the 1989 Recovery Plan 

identified specific information needs, few studies have been conducted to increase 

our knowledge. Many Federal permits have been issued for collection and study 

of this species since the early 1980s, but only a few of these research projects 

have been completed. One final report involved research on several populations 

of Astragalus from Arizona and New Mexico, including A. humillimus, which 

were assessed for morphological, reproductive, genetic, and ecological 

differences (Allphin et al. 2005). Results suggest that two endangered taxa, A. 

humillimus and the closely related A. cremnophylax var. cremnophylax (sentry 

milkvetch), appear to have low fecundity (fertility). The authors suggest that 

environmental fluctuations would not likely be a contributing factor to their small 

population size; instead, low fecundity and reduced genetic variability is more 

likely due to inbreeding depression (Allphin et al. 2005). Reduced fitness is 

commonly found within the Astragalus genus where many species persist in 

small, highly restricted populations and are endemic to particular geologic 

formations (Karron 1989). 

Mycorrhizal associations 

The Arboretum at Flagstaff, an ongoing Federal permittee, is conducting studies 

on A. humillimus seed biology and ecological requirements (Service 2010). Seed 

germination trials from the Arboretum’s early work show that this species is 

difficult to keep in cultivation and is sensitive to over or under-watering; no seeds 

germinated in the first trial with seeds collected from 1993 (Center for Plant 

Conservation 2010). Other preliminary results found that soils collected from the 

Hogback ridge sandstone were low in arbuscular mycorrhizal fungi inoculum 

potential; these soils were just slightly higher in inoculant capacity than sterile 

potting soil (Haskins and Murray 2009). Mycorrhizal fungi are found in root 

tissues and increase the efficacy with which plants harvest soil minerals necessary 

for plant growth (Graham et al. 2006). Because Astragalus species are generally 

mycorrhizal dependent, this lack of mychorrhizae could be detrimental to the 

long-term persistence of A. humillimus (Haskins and Murray 2009). Another 

listed species in the same study, the sentry milkvetch (A. cremnophylax var.

cremnophylax), which is genetically related to A. humillimus and found in nearby 
8

Grand Canyon National Park, had much higher mychorrhizal inoculant capacity 

in occupied soils (Haskins and Murray 2009). More studies are underway to 

better understand the implications of this fungi-soil relationship. 

2.3.1.2 Abundance, population trends, demographic features, or 

demographic trends 

Astragalus humillimus is a narrow endemic known only from the Four Corners 

region of New Mexico, San Juan County, and adjacent Montezuma County, 

Colorado. Species distribution closely follows a narrow band of Mesozoic (Point 

Lookout and Cliff House) sandstone along a 10-mile section of the Hogback 

geologic formation (Service 1989). Prior to 1989, there were a total of 13 known 

populations with 3 of these located on Ute Mountain Ute tribal lands in Colorado 

(Service 1989). Since the completion of the recovery plan in 1989, the Colorado 

populations have not been monitored. New plots were installed for Bureau of 

Land Management (BLM) and State of New Mexico lands starting in 1990. Only 

Navajo Nation found their 13 previously known populations, along with one new 

population, allowing for some long-term comparisons to past population numbers. 

SPECIFIC STUDY AREA STATUS AND TRENDS 

COLORADO 

Ute Mountain Ute: In 1987, there were four populations of A. humillimus in 

Colorado on Ute Mountain Ute tribal lands; surveys were done by employees of 

the Colorado Natural Heritage Program (Colorado Natural Heritage Program 

2010). In 1987, the total estimated sum of individuals from the four populations 

was 4,421 with total occupied habitat about 43 hectares (ha) (106 acres [ac]); 

approximately 0.2 ha (0.5 ac) per population (Colorado Natural Heritage Program 

2010). Since 1987, access has been restricted, and no new information about 

these populations has been provided to the Service. 

NEW MEXICO 

Bureau of Land Management: In 1990, five plots were installed on a rim of 

sandstone at Slickrock Flats on the northwest BLM boundary with Navajo Nation 

(New Mexico State Forestry Division 2008). These plots were read annually until 

1999, then in 2002 and 2008 with an informal site visit in 2010. Plots were 

located on specific habitat (a single tinaja or crack segment) over 3.1 ha (7.6 ac). 

Initially, density (total plant counts), mortality, and recruitment were recorded. 

However by 1993, it became apparent that single plants were coalescing into 

single larger masses. Thus, new measurements were developed to determine at a 

minimum “population vigor” (total plant cover) while still counting new seedling 

density. 
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11

Navajo Nation: The Navajo Natural Heritage Program has 13 historical 

population records for A. humillimus. In 2007 and 2008, the Program Botanist, 

Daniela Roth, resurveyed known populations as well as potential habitat in the 

Hogback and Palmer Mesa areas. When surveys were conducted in 2007 and 

2008, 13 populations were found. However, plants at one of these 13 locations 

appeared to be extirpated, and one population was newly discovered, but 

contained only a single individual. Total plant counts in known populations 

clearly indicate a precipitous decline (Table 1). 

Table 1. Historical records and recent survey results summarized for Astragalus 

humillimus (Navajo Natural Heritage Program 2008a). 

Site 1980s 

(approximate) 

counts 

2007 or 2008 

counts 

Notes 

1 500 35 

2 200 115 All age classes 

3 500 28 90% juveniles 

4 200 14 

5 4,200 11 

6 1,700-2,000 100 Oil & gas activity 

7 ++ ++ *BLM ACEC 

8 50 8 

9 a few 12 

10 - - Cannot relocate 

11 100s 35 

12 17 7 

13 30 20 

14 1 Newly found. 

TOTAL: ~7,500 TOTAL: 386

*Bureau of Land Management Area of Critical Ecological Concern 

++ Monitoring data in New Mexico State Forestry Division 2008 final report. 

Historical records indicated that during the 1980s, total known population size 

was approximately 7,600 individual plants on Navajo Nation lands. By 2008, less 

than 400 plants were found in 12 populations and only 2 of the 12 populations (17 

percent) had more than 50 live plants (Navajo Natural Heritage Program 2008a; 

Navajo Nation Department of Fish and Wildlife 2009). Other 2008 results found 

the majority of plants remaining were small to medium in size; dead plants were 

observed in almost all locations; plants were widely scattered and only a very 

small fraction of the habitat was occupied; and 82 percent of the plants were 

ranked as fair to poor based on low plant numbers, plant condition, and landscape 

context (Navajo Natural Heritage Program 2008a; Navajo Nation Department of 

Fish and Wildlife 2009). 
12

Other Astragalus humillimus surveys: In 2006, presence/absence data was 

collected for this species along a 25.8 kilometer (km) (16 mile [mi]) right-of-way 

for the Segment A, Shiprock Substation, Navajo Transmission Project which 

included a small section of BLM land; no A. humillimus were found (Ecosphere 

Environmental Services 2006). 

In 2007, Western Area Power Administration contracted a botanical survey for 

the existing Lost Canyon-Shiprock and Kayenta-Shiprock Transmission Lines, 

approximately 45 km (28 mi) across Navajo Nation, New Mexico State, and 

Bureau of Land Management lands; 71 A. humillimus were found (56 live and 15 

dead) all on BLM land (Ecosystems Environmental Services 2007). 

In 2008, Ecosphere Environmental Services performed A. humillimus

presence/absence surveys on five oil and gas wells (Navajo #5, Navajo B #2, 

Navajo C #5, Mesa Gallup Unit #15, and Navajo G #222). All wells are located 

on Navajo Nation lands along the Point Lookout Sandstone mesa, and only the 

Navajo B #2 well location and associated pipeline had plants onsite. Two main 

populations were recorded with a total count of 109 plants (Ecosphere 

Environmental Services 2008b). As of 2011, BLM stated that most of the wells 

have been plugged and abandoned, and because the work required a biological 

monitor on site, the plants should have been protected (Kendall 2011). 

There are major individual site differences with regard to A. humillimus seedling 

density and mature plant cover. Despite these differences, it appears that 

maximum population development and density occur on larger, relatively flat 

surfaces with numerous cracks and tinajas that accumulate soil and rainfall (New 

Mexico State Forestry Division 2008). This observation is supported by distinct 

site differences found between the BLM and State of New Mexico plots. The 

BLM plots are all within a larger sandstone surface containing many sizable 

tinajas; whereas, the State of New Mexico plots are smaller sandstone islands 

with fewer depressions for soil and moisture deposition (New Mexico State 

Forestry Division 2008). 

Astragalus humillimus germination and initial seeding survival appear to be 

positively related to the death of older plants and subsequent moisture availability 

(New Mexico State Forestry Division 2008). This availability may be due to 

increased precipitation events aboveground in conjunction with moisture/nutrient 

releases belowground from the loss of adult root biomass. Seedling establishment 

and adult cohort mortality cycles may also be related to shade limitations (foliar 

canopy is reduced) and space limitations (sites become available for germination). 

Mortality of older plants (five to seven years of age) appeared to increase during 

and possibly after drought years, but dry conditions were also often associated 

with spider mite infestations, which could hasten mortality (New Mexico State 

Forestry Division 2008). 

 
13

2.3.1.3 Genetics, genetic variation, or trends in genetic variation 

Even though specific genetic studies are needed, inferences can be made from 

research on several rare Astragalus species in Arizona and New Mexico. Results 

from Allphin et al. (2005) suggest that two endangered taxa, A. humillimus and 

the closely related A. cremnophylax var. cremnophylax, appear to have low 

fecundity (fertility) and environmental fluctuation is not likely a contributing 

factor to small population size (Allphin et al. 2005). Moreover, one of two 

populations of A. cremnophylax var. cremnophylax (North and South Rim of 

Grand Canyon, AZ) was found to be genetically depauperate (lacking genetic 

diversity) indicating a bottleneck caused by historic trampling on the South Rim, 

and was less related genetically to the North Rim population than other taxa 

within this species complex (Allphin et al. 2005). These results suggest that 

inherent low fecundity and potential bottlenecks due to isolation could negatively 

affect A. humillimus populations through loss of genetic variation as reported for 

the closely related species A. cremnophylax var. cremnophylax. 

2.3.1.4 Taxonomic classification or changes in nomenclature

Taxonomic classification of A. humillimus has not changed since the recovery 

plan was finalized in 1989.

2.3.1.5 Spatial distribution, trends in spatial distribution or historic range 

The distributional range of A. humillimus has not changed since the recovery plan 

was finalized in 1989. Although there is suitable habitat within Ute Mountain Ute 

tribal lands, we are not sure if any new surveys have been done due to lack of 

communications from the tribe. 

2.3.1.6 Habitat or ecosystem conditions 

Climate 

Astragalus humillimus is a narrow endemic with very specific habitat needs in 

shallow tinajas, and appears to be sensitive to ecosystem conditions affected by 

changes in climate, particularly precipitation. The recent drought (2002-2003) 

spanning southwestern North America was anomalously dry, but is different from 

the 1950s drought in having unusually high temperatures (higher annual 

maximum and minimum temperatures as well as higher average summer 

temperatures) (Breshears et al. 2005). The IPCC (2007) predicts the average 

annual temperature in the southwest region of the United States could rise by 

about 2.5 to 3.9 o C (4.5 to 7 o F) during this century. This increasing rate of 0.56 

o C (1.0 o F) every 14 years has already been surpassed in Arizona since the 

1970s, and New Mexico is just slightly below this rising temperature rate (Lenart 

et al. 2007). 
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15

limited distribution, we would predict a substantial population reduction 

associated with a long-term warming trend. 

At the microsite level, A. humillimus is found in small depressions on sandstone 

substrates where cracks and fissures accumulate sands and form small soil 

pockets that support root systems that can extend 3 to 8 cm (1.1 to 3.1 in) below 

the surface (Service 1989, New Mexico State Forestry Division 2008). These 

distinct sites are affected by the slightest change in precipitation and temperature, 

and A. humillimus appears to respond quickly to the change. Study results 

indicated that this plant fared better in habitats consisting of deep cracks in the 

bedrock where depth provides shade and lower temperatures, increasing the 

amount and length of time when moisture is available to plants, particularly 

during drought years (New Mexico State Forestry Division 2008). 

Increases in herbivorous insects, both native and nonnative, are also predicted 

with changes in climate, and will adversely affect many species (Enquist and Gori 

2008). This herbivory was documented since the 1980s for A. humillimus during 

many of the drier years. During the drought of 2002 and 2003, an infestation of 

spider mites entirely covering many mature plant clumps often contributing to 

mortality of already stressed plants (Service 1989, Sivinski and Knight 2001, New 

Mexico State Forestry Division 2008). Spider mites feed on the leaf surface and 

these injured leaves are shed more quickly, and eventually the whole plant may 

die. Even a minor spider mite infestation can have a significant impact on a 

plant's health. 

Since the documented decline of A. humillimus is concurrent with drier years and 

the severe drought of the early 2000s, we would expect that if a change in climate 

led to increased severity or frequency of drought, it would have a negative impact 

on the species. Narrow endemics, like A. humillimus, often have very specific 

habitat requirements. Because plants are unable to move, a change in climate that 

causes mortality that exceeds reproduction and recruitment, could lead to the 

extirpation of A. humillimus. We believe the 2008 low population numbers are 

likely caused by cumulative losses since the 1980s due to several notable drought 

periods for this region. Continued long-term effects on their population numbers 

may not be entirely evident until drought conditions cease to exist. Some 

recovery, particularly for new seedlings, has occurred but appears to be triggered 

by both adult plant mortality and increased moisture events. 

2.3.2 Five-Factor Analysis

2.3.2.1 Present or threatened destruction, modification, or curtailment of its 

habitat or range – Factor A: 

Major threats to A. humillimus continue to be from surface disturbance activities 

associated with energy exploration and development, and transmission line 

construction and maintenance (Service 1989; House and Engelking 1992; Bureau 
16

of Land Management 2007; Navajo Nation Natural Heritage Program 2007, 

2008a, and 2008b; Navajo Nation Department of Fish and Wildlife 2009). 

Threats to habitat or range summarized below include: 

(1) energy exploration and development; 

(2) transmission lines; and 

(3) off-road vehicles. 

Energy Exploration and Development: The majority of known occupied and 

potential A. humillimus habitat is located on the Navajo Nation lands. Most of 

this habitat is located on Palmer Mesa and the Hogback areas covering 

approximately 16,187 ha (40,000 ac) on Navajo Nation lands. These areas 

contain active and plugged oil and gas wells, including numerous roads associated 

with these activities. Navajo Nation and BLM lands contain significant deposits 

of oil and natural gas, and the development of these energy resources in the Four 

Corners Basin continues to increase (Energy, Minerals, and Natural Resources 

Department 2008). Nearly all known and potential A. humillimus habitat may be 

affected by natural gas or oil exploration and development. Most damage occurs 

after vehicles and heavy equipment drive over and crush individual plants as well 

as break apart sandstone areas that contain tinajas, which are required for A. 

humillimus seedling establishment (Navajo Nation Department of Fish and 

Wildlife 2009). 

Since listing, several reports documented negative effects to A. humillimus

populations. In 2007, the Navajo B Well #2 well plug and abandonment 

operation either crushed (11 plants) or killed (6 plants) all of the plant population 

within the disturbed area on west Palmer Mesa; damage was caused by industry 

vehicles driving off the designated well pad and existing road (Navajo Natural 

Heritage Program 2007; Bureau of Land Management 2007). The vehicles and 

heavy equipment also fractured sandstone, compacted soils, and created a new 

spur road that bisected part of this A. humillimus population (Navajo Natural 

Heritage Program 2007). In addition to this disturbance, but unrelated to the well 

activities, a pipe and electrical line were found nearby above ground with no 

history of installation; one plant appeared to have died from the line with eight 

live plants remained next to or under the line (Bureau of Land Management 

2007). 

In 2008, a separate incident occurred in the same general vicinity of Navajo B 

Well #2 where heavy equipment drove over several A. humillimus plants (they 

survived), but the surrounding habitat was extensively damaged (Navajo Natural 

Heritage Program 2008b). Several days later, two backhoes were found parked 

two miles away still encrusted in heavy mud. The impacts started nearby the well 

site, but also occurred alongside several access roads and involved tracks to other 

well sites within a two-mile radius. Significant scraping of the soil surface 

occurred, and the construction of an earthen berm and trenching for a pipeline was 

also recorded by Navajo Nation and BLM law enforcement (Navajo Natural 

Heritage Program 2008b). Due to the wet conditions at the time, severe backhoe 
17

damage occurred over two miles of sandstone and tinaja habitat essential to A. 

humillimus populations (Navajo Natural Heritage Program 2008b). 

 

 As of 2011, BLM has no new oil and gas development in the Hogback ACEC 

since 2008, only maintenance for existing wells (Kendall 2011). Presently, there 

are 7-8 active oil wells (one gas well) in the entire ACEC with over 30 plugged 

and abandoned wells, thus oil and gas development is nonexistent at this time 

(Kendall 2011). 

 The Desert Rock Energy Project (DREP) has been proposed by the Bureau of 

Indian Affairs (BIA) and is within the range of this species. The biological 

assessment for the project found that A. humillimus will be exposed to and 

adversely impacted by the deposition of contaminants from two other existing 

power plants as well as DREP (Ecosphere Environmental Services 2008a). The 

significance of these impacts to A. humillimus is unknown at this time because the 

DREP consultation has not been completed. 

Astragalus humillimus populations and their habitat have been negatively 

impacted by crushing from vehicles and equipment, direct removal and 

destruction from energy-related activities, and indirect effects of unauthorized 

traffic using roads constructed by oil and gas companies. Oil and gas well 

construction has resulted in a variety of unauthorized roads, multiple pipelines, 

and small but enduring piles of waste, all of which further degrade A. humillimus

habitat over the larger landscape. Also, some habitat damage has been reported 

by Navajo Nation from vandalism associated with theft of copper cables running 

between oil wells (Navajo Natural Heritage Program 2008b). Thus, we believe 

oil and gas development remains a severe threat to the species and will likely 

increase in the foreseeable future. 

Transmission Lines: Transmission lines have likely impacted A. humillimus

populations because potential habitat and recently surveyed plants have been 

found along several major transmission line corridors (Ecosphere Environmental 

Services 2007). A large population of approximately 1,000 plants was bisected 

by two major transmission lines, the Glen Canyon-Shiprock and the CurecantiShiprock transmission lines, which were constructed in 1962 and 1963 prior to the 

National Environmental Policy Act taking effect (50 FR 26570). Immediate 

impacts were complete scraping of topsoil and vegetation directly underneath the 

power line, thus it is unknown how many plants may have been destroyed. Since 

that time, any plants underneath and nearby the power line have been driven over 

by either maintenance vehicles or off-road recreation vehicles. At the time of 

listing in 1985, no repopulation had occurred, but the most recent survey done by 

Western Area Power Administration found 71 plants over approximately 45 km 

(28 mi) of Navajo Nation, State of New Mexico, and BLM lands; total area 

surveyed was 138 ha (342 ac) (Ecosphere Environmental Services 2007). 
18

The 1992 Habitat Management Plan (HMP) for A. humillimus describes the 

extensive transportation system within and surrounding Navajo Nation lands. 

This system, consisting of roads and corridors, is being developed by BIA, 

Navajo Nation, private corporations, and individuals, with little coordination 

between these entities on the protection of rare and endangered species’ habitat 

(House and Engelking 1992). The HMP also mentions the increased demand for 

utilities, which has led to disturbance of A. humillimus habitat. For example, in 

the early 1980s a powerline and tower were constructed within the Hogback 

population of A. humillimus destroying the northern part of this population 

(Service 1989). Similarly, the southern part of this population was also extirpated 

during the same period from a rock quarry operation (Service 1989). No new 

plants have ever been found in this area (Navajo Natural Heritage Program 

2008a). 

Impacts are generally associated with maintaining transmission line roads and the 

associated vehicles that crush plants. Conservation measures recommended in the 

recovery plan (Service 1989) and the HMP for Navajo Nation lands (House and 

Engelking 1992), such as avoidance and transplanting, could minimize impacts 

within the construction footprint of these types of projects. We do not know if 

these conservation measures were enacted on past projects, and whether they are 

being implemented currently. Thus, we believe that the ongoing impacts 

associated with transmission lines could be severe if they involve A. humillimus

habitat, but could be easily mitigated by implementing recommended 

conservations measures along these proposed corridors. 

Off-Highway Vehicles: Off-highway vehicles (OHVs) were not a threat until 

recently, but their impacts are now being considered. The recreational use of 

OHVs has increased dramatically since the plant was listed. This increase is most 

likely due to the recent expansion of oil and gas extraction and the resultant 

population growth within San Juan County. From 1980 to 2006, the human 

population of San Juan county increased by 55 percent 

(http://wrdc.usu.edu/htm/publications/). OHV-related damage to A. humillimus

and its habitat has increased, especially around oil and gas well pads and 

transmission line corridor roads (Service 1989; House and Engelking 1992; 

Bureau of Land Management 2007; Navajo Nation Natural Heritage Program 

2007, 2008, and 2008b; Navajo Nation Department of Fish and Wildlife 2009). 

Unauthorized roads, trails, and recreational OHV use on sandstone cliffs and 

outcrops have been observed on and near known populations of A. humillimus

(Bureau of Land Management 2006). For example, surveys undertaken in 2006 

on BLM plots found scattered glass and OHV tire marks where 24 plants were 

found alive and 11 dead; cause of mortality was unknown, but this site is a 

popular recreational parking area with unrestricted access (Bureau of Land 

Management 2006). Not only did several plants appear damaged from being 

crushed, but their micro-habitat (small depressions or tinajas) has been fractured 

leaving a dearth of required habitat for future seedling establishment. Although 
19

most OHV activity is restricted to the southern part of the ACEC (outside of 

known milkvetch habitat), the potential for impacts still exists (Kendall 2011). 

Lack of law enforcement continues to be problematic for both BLM and Navajo 

Nation. We believe that use of OHVs is presently a moderate threat to this 

species and will likely increase in the foreseeable future. 

 

2.3.2.2 Overutilization for commercial, recreational, scientific, or educational 

purposes – Factor B: 

Overutilization for commercial, recreational, scientific, or educational purposes 

has not been documented for A. humillimus. The species has no known 

commercial use and illegal collection does not appear to be a threat currently or in 

the foreseeable future. 

2.3.2.3 Disease or predation – Factor C: 

No diseases have been observed on this species. Herbivory by wildlife and 

livestock has not been reported although no formal studies have been conducted. 

Livestock grazing is not considered a current threat, or a threat for the foreseeable 

future. Some insect herbivory by seed weevils and Lepidoptera larvae has been 

reported (NatureServe 2010), but appears to occur at insignificant levels during 

favorable rainfall years (New Mexico State Forestry Division 2008). Spider mite 

infestations have been recorded and appear to kill plants particularly during 

drought periods when the plant is already stressed (Siviniski and Knight 2001). 

The mites pierce the epidermis to ingest the sap which results in leaf discoloration 

and death, weakening the plant even further and causing mortality (Sivinski and 

Knight 2001). Insect infestations appear to be relatively rare, but could increase if 

drought continues into the foreseeable future. Thus, insect predation is 

considered a minor threat at this time. 

2.3.2.4 Inadequacy of existing regulatory mechanisms – Factor D: 

Astragalus humillimus was listed as threatened without critical habitat in June 

1985 (50 FR 26568). The Act is the primary Federal law providing protection for 

the species. Beyond the listing of the species, these protections are afforded 

particularly through sections 7 and 9 of the Act. Section 7 of the Act requires 

Federal agencies to ensure that any action authorized, funded, or implemented by 

them is not likely to jeopardize the continued existence of listed species or modify 

their critical habitat, if critical habitat has been designated. Section 7 also 

encourages Federal agencies to use their authorities to carry out programs for the 

conservation of listed species. Section 9 of the Act prohibits the removal, 

damage, or destruction of listed plants on Federal lands and on other areas in 

knowing violation of any State law or regulation or State criminal trespass law. 

The National Environmental Policy Act (NEPA) may provide some protection for 

A. humillimus for projects with a Federal nexus (i.e., funding, authorization, or 
20

permitting). NEPA requires that the planning process for Federal actions be 

analyzed to ensure that effects on the environment are considered. The NEPA 

process is intended to help public officials make better decisions based on an 

understanding of the environmental consequences of their actions and to take 

actions to protect, restore, and enhance the environment (40 CFR 1500.1). 

Carrying out the NEPA process ensures that agency decision makers have 

information about the environmental effects of Federal actions and information on 

a range of alternatives that will accomplish the project purpose and need. 

Federally listed plants occurring on private lands have very limited protection 

under the Act unless they are also protected by State laws. Astragalus humillimus

is listed as endangered by the State of New Mexico under the New Mexico 

Endangered Plant Species Act, Section 75-6-1 NMSA 1978, which protects it 

from unauthorized collection, transport, and sale, but provides no protection from 

land use impacts. There are no regulatory protections for federally listed 

threatened and endangered plant species from surface disturbing land uses on 

private or state owned lands in New Mexico, unless they are authorized, funded, 

or carried out by a Federal agency and subject to section 7 consultation of the Act. 

Prohibitions for this species under State law would not be sufficient for its 

conservation if A. humillimus was delisted. 

The Lacey Act, as amended in 1981, prevents the import, export, sale, acquisition, 

purchase, or interstate or foreign commerce of any plant and/or animal taken, 

possessed, or sold in violation of any law, treaty, or regulation of the United 

States, any Indian tribal law, or any regulation of any State. If transported or 

exchanged for currency, the plant could be protected under the Lacey Act. 

Bureau of Land Management Manual 6840 establishes Special Status Species 

(SSS) policy for plant and animal species and the habitat on which they depend 

(Bureau of Land Management 2008). This SSS policy refers not only to species 

protected under the Act, but also to those designated by the BLM State Director 

as Sensitive. The BLM maintains A. humillimus as a SSS. The intent of the 

sensitive species designation is to ensure actions on BLM administered lands 

consider the welfare of these species and do not contribute to the need to list any 

SSS under the provisions of the Act. As written, the BLM management 

prescriptions allow several avenues of protection for this plant including, but not 

limited to, managing existing oil and gas leases under Controlled Surface Use 

constraint and discretionary closure on new leases. These protective measures 

should be sufficient to the conservation of this species, yet negative impacts 

continue to occur particularly on Navajo Nation lands with lease oversight by 

BLM. At this time, BLM’s SSS policy has not been sufficient for the 

conservation of this species. 

The Hogback Area of Critical Environmental Concern (ACEC), located on BLM 

administered lands, was established after A. humillimus was listed in 1987. This 

ACEC designation is intended to ensure that proposed projects in this area receive 
21

the highest environmental scrutiny before being implemented. Projects are not 

prevented from occurring in the ACEC, but recommendations may be made to 

modify them to protect certain critical resources including A. humillimus habitat. 

Despite these additional protections for listed species, recreational OHV use and 

energy maintenance activities continue to have the potential to impact known 

populations throughout the Hogback ACEC, thus this BLM designation has not 

been sufficient in the conservation of this species. 

Navajo Tribal Code 17 Section 500(8) defines and protects species in three 

Groups based on a species’ conservation status. Group 1 pertains to species or 

subspecies that are no longer found on the Navajo Nation. Group 2 applies to 

species or subspecies whose prospects of survival or recruitment are in jeopardy, 

and Group 3 incorporates species or subspecies whose prospects of survival or 

recruitment are in jeopardy in the foreseeable future. Astragalus humillimus is 

listed as a Group 2 Endangered species on the Navajo Nation lands, which means 

that the species prospects of survival or recruitment are or are likely to be in 

jeopardy. Tribal laws protect species in Group 2. Title 17 § 507 of the Navajo 

Tribal Code makes it unlawful for any person to “take, possess, transport, export, 

process, sell or offer for sale or ship any species or subspecies” on the Navajo 

Endangered Species List. Despite these regulatory mechanisms, continued habitat 

destruction through oil and gas development has occurred, and none of the 

recovery actions identified in the 1985 recovery plan have been initiated on 

Navajo Nation lands (Navajo Nation Department of Fish and Wildlife 2009). 

 

Existing regulatory mechanisms, secured through the Act, have reduced some 

threats on Federal lands. In the absence of the Act’s protective regulatory 

mechanism, we believe the situation would be considerably worse. After 

considering the regulations other than the Act designed to protect this plant, and 

due to continued negative impacts to this species, we believe other Federal, 

Tribal, and State legal protections provided for this species have not been 

sufficient for its conservation in the foreseeable future. 

2.3.2.5 Other natural or manmade factors affecting its continued existence – 

Factor E: 

Pesticide Use: Pesticides are considered a potential threat because they could 

directly harm a plant, but also could indirectly kill pollinators of A. humillimus or 

their host plants (Service 1989). Herbicides are commonly used for noxious weed 

control, but no documentation has been provided on whether any A. humillimus

populations have been directly or indirectly affected. In the Navajo Nation 

Habitat Management Plan for A. humillimus from 1992, agricultural use of 

pesticides is mentioned in regard to the Navajo Indian Irrigation Project and local 

Navajo farmers along the San Juan River (House and Engelking 1992). 

 Pesticides, particularly insecticides, are linked to bee declines (Kearns et al. 1998, 

Kremen et al. 2002, National Academy of Sciences 2007), with the abundance 
22

and diversity of wild bee communities negatively correlated with increasingly 

intensive chemical applications of pesticides (Tuell and Isaacs 2010). Although 

the toxicity of pesticides to pollinators is challenging to quantify in a field setting 

and varies depending on the chemistry, quantity applied, degree of contact, area 

treated, and seasonal timing (Mineau et al. 2008, Tuell and Isaacs 2010), some 

pesticides cause immediate mortality to bees if applied upon crops while bees are 

actively foraging (Johansen 1977). Both wild and honey bee (Apis mellifera) 

declines have been found in areas adjacent to sprayed fields, suggesting a wider 

spatial impact to the pollinator community than just a targeted area (Kevan 1975, 

Kevan et al. 1990). Furthermore, depending on the seasonal timing of pesticide 

application, effects to pollinator communities may be chronic and cumulative, yet 

difficult to assess due to the different phenologies and nesting situations of 

pollinator species (Desneaux et al. 2007, Tuell and Isaacs 2010). 

 Pesticide application, particularly aerial spraying, occurs in the local agricultural 

areas to control crop pests in Farmington, New Mexico. Most of the A. 

humillimus populations are miles away, but could be affected by drift if aerial 

spraying were to occur on Navajo Nation lands, particularly the Navajo Indian 

Irrigation Project or local Navajo farmers (House and Engelking 1992). There is 

no information on pesticide use and subsequent monitoring on Navajo lands and 

local farmers are not monitored. Due to the lack of information, we are uncertain 

whether pesticides directly or indirectly affect the survival of A. humillimus. 

Thus, we do not consider pesticides to be a threat to this species currently or in 

the foreseeable future. 

 Natural Processes: Natural processes such as erosion could account for some 

mortality, yet they also are responsible for soil deposition in the bedrock 

depressions that are essential habitat for this species. Since this species is 

restricted to small and widely dispersed segments of sandstone, the resulting 

populations are disjunct and scattered. This fragmented distribution impedes gene 

flow among subpopulations. Without the maintenance of genetic diversity to 

buffer against stochastic events, the species becomes increasingly vulnerable to 

external threats. Genetic limitations (low fecundity) and ecological isolation 

(disjunct and small populations) increase the risk of extinction when considering 

additional pressure from human impacts as well as stochastic events such as 

severe drought.

Climate Change: Based on the unequivocal evidence of warming of the earth’s 

climate from observations of increases in average global air and ocean 

temperatures, widespread melting of glaciers and polar ice caps, and rising sea 

levels recorded in the Intergovernmental Panel on Climate Change Report (IPCC 

2007), climate change is now a consideration for Federal agency analysis (GAO 

2007). The earth’s surface has warmed by an average of 0.74 o C (1.3 o F) during 

the 20th century (IPCC 2007) and, since 1960, the annual average temperature 

across the United States has increased by more than 2 F (1.1C) (Global Climate 

Change Impacts in the United States [GCCIUS] 2009). The IPCC (2007) projects 
23

that there will very likely be an increase in the frequency of hot extremes, heat 

waves, and heavy precipitation events as a result of climate change. The IPCC 

projects there will be an increase in the frequency of extreme weather events that 

are temporally and spatially more variable as a result of climate change (IPCC 

2007). 

The most recent drought (2002-2003) spanning southwestern North America, 

prior to the current drought (winter 2010-summer 2011), was anomalously dry 

with unusually high temperatures (Breshears et al. 2005). In Shiprock, NM, 

within A. humillimus habitat, no precipitation was recorded in 2002, whereas in 

2004 only 33 mm (1.3 in) was recorded, the third lowest level measured since 

1926 (Western Regional Climate Center 2010). Mean annual precipitation since 

the drought (2003-2007) has been 97 mm (3.8 in), well below the long-term 

average (Western Regional Climate Center 2010; see Figure 3). 

Climate change also involves an increase in atmospheric carbon dioxide which is 

commonly associated with increased temperatures and the greenhouse gas effect. 

Since 2000, the observed emissions of greenhouse gases, which are a key 

influence on climate change, have been occurring at the mid- to higher levels of 

the various emissions scenarios developed in the late 1990s and used by the IPPC 

for making projections (e.g., Raupach et al. 2007, Pielke et al. 2008, Manning et 

al. 2010). This increased carbon dioxide directly affects plant photosynthesis 

(Huxman and Scott 2007). At the plant level, adapting to drought involves the 

ability to balance carbon sequestration (the uptake and storage of carbon), carbon 

respiration (efflux back into the atmosphere), and maintain sustainable 

evapotranspiration rates (Huxman and Scott 2007). Adaptation would also 

require a plant to change its phenology (timing of life cycle events) to coincide 

successfully with extreme shifts in temperature, precipitation, and soil moisture 

(Walther et al. 2002) which are all part of the evapotranspiration equation. The 

potential for rapid climate change, which is predicted for the future, could pose 

significant challenges for plants because they may not be able to adjust their 

phenology or photosynthetic mechanisms quickly enough. 

At the population level, A. humillimus is a spring flowering species (Service 

1989). Growing seasons are becoming longer and warmer in many regions 

(Parmesan 2007) including the southwest (Cayan et al. 2001; Easterling 2002; 

Lenart et al. 2007; Enquist and Gory 2008). A reduction in soil moisture and 

earlier soil moisture stress to the plant could decrease flowering and reproduction 

of the species. Because A. humillimus has a limited distribution, we would predict 

a substantial population reduction with a long-term warming trend. 

Astragalus humillimus is likely to have experienced and rebounded from periods 

of drought in the past. If climate change materializes with increased severity and 

frequency of drought, it would likely reduce the long-term survivorship of this 

species. Narrow endemics, like A. humillimus, often have very specific habitat 

requirements. This species has affinity for depressions in the sandstone, 
24

suggesting that water is critical for its germination and development, thus climate 

change could affect its continued existence. We believe the 2008 low population 

numbers are likely caused by cumulative losses since the 1980s due to several 

notable drought periods for this region, thus we believe that climate change is a 

severe threat to this species in the foreseeable future. 

 

 
25

2.4 Synthesis

Prior to anthropogenic threats and anomalous climate extremes, A. humillimus populations likely 

adapted to more cyclic disturbance regimes with high mortality balanced by successful 

regeneration and reproduction. Preliminary observations suggest that adult mortality is 

necessary for new seedling establishment, so there is a relatively short-term mortality cycle 

required for continued population establishment. However, cumulative mortality due to more 

frequent and extreme droughts from the 1980s to present may be affecting the baseline 

population size and the continued genetic integrity of this species. Although some recovery is 

evident, population numbers have not returned to the earliest field estimations (approximately 

10,000 on Navajo Nation lands as of 1989), and decreased dramatically after the 2002-2003 

drought (less than 400 on Navajo Nation lands as of 2008). The overall population trend appears 

to be declining in New Mexico; population size and status is unknown for Colorado. 

Since the development of the recovery plan in 1989, threats have increased rangewide. 

Populations have been directly impacted by human caused disturbance which not only has killed 

plants, but also has destroyed the unique micro-habitat required for new seedling establishment. 

Although some level of regulatory protection exists for all known populations, these protective 

measures have not been applied sufficiently to adequately protect the species. It appears that 

most of the negative impacts to this species occurred due to lack of on-the-ground enforcement 

of mitigation and conservation measures before, during, and after implementation of energy and 

transmission line projects. 

 

Although the recovery criteria have not been entirely met nor do we anticipate that they will be 

met in the foreseeable future, progress has been made by the ongoing census and mapping of 

known populations (Recovery Criterion 1); development of a draft habitat management plan by 

Navajo Nation (Recovery Criterion 3); and installation of long-term monitoring plots that were 

last read in 2008 (Recovery Criterion 4). As damage to plants may occur unintentionally, the 

construction of protective fencing around known populations to prevent inadvertent destruction 

of plants could protect the remaining individuals. Active, standardized surveying and monitoring 

to record the species’ status, and tracking of seed collection, germination, and survival would 

assist with the understanding and conservation of this plant. With the implementation and 

enforcement of conservation measures recommended in the draft habitat management plan for 

Navajo Nation, and as specified for the Hogback ACEC on BLM land, recovery of this plant 

would be further supported. 

Upon reviewing the combined significance of current threats, we recommend that the federally 

endangered status of A. humillimus remain unchanged at this time. We also recommend that the 

plant be closely monitored for future population trends, new population discoveries, and the level 

of cumulative threats. We note that serious threats continue such as: (1) energy exploration, 

development, and maintenance activities; (2) transmission line installation and maintenance; (3) 

increased off-road vehicle use; (4) inadequacy of implementing existing regulatory mechanisms;

(5) increased understanding of this species’ genetic limitations within the context of ecological 

isolation and restricted distribution; and (6) predicted increase in frequency and severity of 

drought. For these reasons, this species continues to have a tenuous existence. 
26

3.0 RESULTS 

3.1 Recommended Classification: No change; remain as endangered. 

____ Downlist to Threatened 

____ Uplist to Endangered 

____ Delist 

 ____ Extinction 

 ____ Recovery 

 ____ Original data for classification in error

 __X_ No change is needed 

3.2 New Recovery Priority Number: 5C

Brief Rationale: We recommend the recovery priority number be changed from 2 (high degree 

of threat and high recovery potential) to a 5C (high degree of threat and low recovery potential 

with some conflict). This change is justified based on recent genetic research that indicates this 

species has low fecundity, which would increase the potential for a genetic bottleneck in 

conjunction with its isolated and restricted distribution, and limited micro-habitat. As well, there 

has been no long-term propagation success despite numerous attempts. Our review also 

indicates that human-caused threats such as energy development, transmission lines, and OHV 

use are more numerous at present than at the time of the listing and are more immediate. In 

combination, these factors indicate a low recovery potential is more appropriate for this plant at 

this time, and support the change from a high to a low recovery potential. 

3.3 Listing and Reclassification Priority Number: Not applicable.

 
27

4.0 RECOMMENDATIONS FOR FUTURE ACTIONS 

 

 Revise recovery plan to incorporate new information on biology, ecology, threats, and 

conservation recommendations. 

 Recommend Federal plant permittees report on number of seeds collected over time and 

status of attempts to germinate (success/failures). Because native seed bank viability and 

longevity in the field is unknown, knowing how many cumulative seeds are being taken 

from this rare species could be important to its future regenerative capacity in the field, 

particularly during drought periods. 

 Provide viable A. humillimus seeds to a seed bank operating under the Center for Plant 

Conservation guidelines. 

 Continue research on species biology, ecology, reclamation, and transplantation. 

 Develop standardized survey and monitoring protocols for this species to be conducted 

annually by experienced personnel. 

 Develop a mitigation banking requirement (a system whereby proponents of projects that 

may cause harm to A. humillimus or its habitat pay for plants to be preserved in an area 

suitable for their preservation as mitigation for losses incurred during projects). 

 Develop an A. humillimus multi-agency working group to share and disseminate 

information regarding this listed species by promoting education, protection, and 

recovery actions. 

 Work with the BLM Farmington Field Office to develop and implement consistent 

conservation measures in the Resource Management Plan revision that will avoid and 

minimize impacts to A. humillimus and its habitat from livestock trampling, ORV 

activities, and energy development. Include protection for all occupied and suitable 

habitat in the conservation measures. 

 Work with the Ute Mountain Ute tribe to encourage and support surveys, monitoring and 

conservation measures for A. humillimus on their land, and development of their 

management plan to include this species. 
28

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