[Federal Register Volume 69, Number 108 (Friday, June 4, 2004)]
[Rules and Regulations]
[Pages 31523-31531]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-12659]


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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17


Endangered and Threatened Wildlife and Plants; 12-Month Finding 
for a Petition to Delist Astragalus magdalenae var. peirsonii 
(Peirson's Milk-vetch)

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Notice of 12-month petition finding.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service) announce a 
12-month finding for a petition to delist Astragalus magdalenae var. 
peirsonii (Peirson's milk-vetch) under the Endangered Species Act (Act) 
of 1973, as amended, (16 U.S.C. 1531 et seq.). After reviewing the best 
scientific and commercial information available, we find that the 
petitioned action is not warranted. We ask the public to submit to us 
any new information that becomes available concerning the status of, or 
threats to, the species. This information will help us monitor and 
encourage the conservation of this species.

DATES: The finding announced in this document was made on May 28, 2004. 
Although no further action will result from this finding, we request 
that you submit new information concerning the status of, or threats 
to, this species, whenever it becomes available.

ADDRESSES: The complete file for this finding is available for 
inspection, by appointment, during normal business hours, at Carlsbad 
Fish and Wildlife Office, U.S. Fish and Wildlife Service, 6010 Hidden 
Valley Road, Carlsbad, California 92009. Submit new information, 
materials, comments, or questions concerning this plant to us at the 
above address.

FOR FURTHER INFORMATION CONTACT: Jim Bartel, Field Supervisor, Carlsbad 
Fish

[[Page 31524]]

and Wildlife Office; telephone (760-431-9440).

SUPPLEMENTARY INFORMATION:

Background

    Section 4(b)(3)(B) of the Act requires that within 12 months after 
receiving a petition to revise the List of Threatened and Endangered 
Species that contains substantial information indicating that the 
petitioned action may be warranted, the Secretary shall make one of the 
following findings: (a) The petitioned action is not warranted, (b) the 
petitioned action is warranted, or (c) the petitioned action is 
warranted but precluded by pending proposals. Such 12-month findings 
are to be published promptly in the Federal Register.
    The Peirson's milk-vetch was listed as threatened on October 6, 
1998 (63 FR 53596). At the time of listing, the primary threat to the 
milk-vetch was the destruction of individuals and dune habitat from 
off-highway vehicle (OHV) use and the recreational development 
associated with it. On October 25, 2001, we received a petition to 
delist Astragalus magdalenae var. peirsonii dated October 24, 2001, 
from David P. Hubbard, Ted J. Griswold, and Philip J. Giacinti, Jr. of 
Procopio, Cory, Hargreaves & Savitch, LLP, that was prepared for the 
American Sand Association (ASA), the San Diego Off-Road Coalition, and 
the Off-Road Business Association (ASA et al. 2001). On September 5, 
2003, we announced an initial petition finding in the Federal Register 
that the petition presented substantial information to indicate the 
petitioned action may be warranted (68 FR 52782). In accordance with 
section 4(b)(3)(A) of the Act, we have now completed a status review of 
the best available scientific and commercial information on the 
species, and have reached a determination regarding the petitioned 
action. This determination meets deadline requirements established by a 
court-approved settlement agreement (ASA et. al. v. USFWS and Gale 
Norton, Stipulated Settlement Agreement, Civ. No. 03-315L LAB).

Species Description

    Astragalus magdalenae var. peirsonii is an erect to spreading, 
herbaceous, short-lived perennial in the Fabaceae (Pea family) (Barneby 
1959, 1964). Plants may reach 8 to 27 inches (20 to 70 centimeters) in 
height and develop taproots (Barneby 1964) that penetrate to the 
deeper, moister sand. According to Phillips and Kennedy (2003), plants 
largely die back to a root crown in the summer. The stems and leaves 
are covered with fine, silky appressed hairs. Young seedlings often 
retain their cotyledons (Phillips and Kennedy 2003). The leaflets, 
which may fall off in response to drought, are small and widely spaced, 
giving the plants a brushy appearance. This taxon is unusual in that 
the terminal leaflet is continuous with the rachis rather than 
articulated with it. The purple flowers are arranged in 10- to 17-
flowered axillary racemes. Romspert and Burk (1979) found 
inflorescences present from December through at least April. Astragalus 
lentiginosus var. borreganus, easily distinguished by its conspicuously 
broad leaflets, and Astragalus insularis var. harwoodii, easily 
distinguished by its smaller stature and shorter banner petals, are the 
only other Astragalus taxa found nearby.

Life History

    Astragalus magdalenae var. peirsonii has variously been considered 
an annual or perennial (Munz 1932, 1974; Barneby 1959, 1964; 
Spellenberg 1993; Willoughby 2001). Willoughby (2001) states that A. m. 
var. peirsonii apparently is a short-lived perennial, and as such its 
response to rainfall was predictable. Documented persistence of 
individuals also attests to the perennial nature of A. m. var. 
peirsonii (Phillips and Kennedy 2002, 2003). The onset of germination 
may occur anytime between the beginning of January and the end of 
February (Porter in litt. 2003b). Plants are reportedly in flower from 
as early as mid-November through May (Barneby 1965; Porter in litt. 
2003b; Phillips and Kennedy 2002).
    As part of his studies of the natural history and pollination 
biology of Astragalus magdalenae var. peirsonii, Porter (in litt. 
2002a) has identified a white-faced, medium-sized, solitary bee as the 
only effective pollinator. His preliminary experiments in the field and 
under greenhouse conditions indicate that A. m. var. peirsonii plants 
are not capable of self-pollination in the absence of pollinators. This 
is a significant consideration for population structure and function. 
Large populations of standing individuals are likely necessary to 
provide adequate numbers of individuals for cross pollination and to 
ensure adequate seed set.
    Based on current understanding of the species' life history, 
sufficient rain in conjunction with wetter-than-average fall weather 
appears to trigger germination events. Seedlings may be generally 
present in suitable habitat throughout the dunes, especially during 
above-normal precipitation years. In intervening drier years, plant 
numbers decrease as individuals die and are not replaced by new 
seedlings. The species likely depends on the production of seeds in the 
wetter years, and the persistence of the seed banks from all years, to 
persist until appropriate conditions for production and germination 
occur. Further research and modeling are necessary to better understand 
the dynamics of this system and how the species may be responding to 
natural and man-made disturbances within its range. As one of the peer 
reviewers noted, this species has a complex life history, and while it 
can act as a perennial, it is more apt to behave as an annual (McCue, 
2003).
    The relative contribution of first-year plants of Peirson's milk-
vetch to the seed bank and survival of the taxon is not fully 
understood. The available data suggest that older age classes may 
produce substantially more seeds than first-year plants and that, 
therefore, the older persisting plants may be more important for 
reproductive success (Phillips and Kennedy 2002, Romspert and Burk 
1979). Phillips and Kennedy (2002) reported that the older plants 
produced a mean of 171 fruits per plant, compared to an estimated 5 
fruits per each younger plant in the earlier spring survey. Romspert 
and Burk (1979) state that Peirson's milk-vetch plants that become 
reproductive the first season do not contribute a great deal to the 
seed bank, but that mature plants produced copious amounts of seeds.
    In desert plants, the majority of seedlings may die off at the 
onset of the dryer season as noted by previous reports. Pavlik and 
Barbour (1988) studied the establishment and survivorship pattern of 
Astragalus lentiginosus var. micans, another dune endemic plant, and 
recorded a complete crash of the 1984-1985 seedling cohort. These 
authors also reported that 54 percent of the 1985-1986 cohort of 
seedlings survived. However, none of these plants reached reproductive 
maturity within the year. Thus, a large or very large number of 
seedlings of Peirson's milk-vetch may succumb prior to producing and 
dispersing seeds. Peirson's milk-vetch populations must then rely on 
the cumulative seed bank, not the seed production of a single year even 
if germination was high. This demonstrates the need for long-term 
analysis of the population dynamics of this plant to adequately assess 
adaptive management concerns and recovery actions.

Seed Biology

    The fruits of Peirson's milk-vetch are 0.8 to 1.4 in (2 to 3.5 cm) 
long, one chambered, hollow, and inflated.

[[Page 31525]]

Peirson's milk-vetch fruits contain 11 to 16 large, flattened black 
seeds. The seeds, among the largest seeds of any Astragalus in North 
America (Barneby 1964), average less than 0.1 ounces (oz) (15 
milligrams (mg)) each in weight and are up to 0.2 in (4.7 millimeters 
(mm)) in length (Bowers 1996). Seeds are either dispersed locally by 
falling out of partly opened fruits on the parent plant, salt-shaker 
style, or by their release from fruits blown across the sand after 
falling from the parent plant. Seeds require no pre-germination 
treatment to induce germination, but show increased germination success 
when scarified (outer cover is broken). Porter (in litt. 2002a) 
reported about 98 percent of scarified seeds germinated while only 21 
percent of unscarified seeds germinated. In germination trials 
conducted by Romspert and Burk (1979), 92 percent or more seeds 
germinated within 29 days at temperatures of 77 [deg]F (25 [deg]C) or 
less, and no seeds germinated at temperatures of 86 [deg]F (30 [deg]C) 
or higher. This indicates that seeds on the dunes may likely germinate 
in the cooler months of the year. Porter (in litt. 2002a) reported 
that, under greenhouse conditions, seed germinated within 5 days of 
sowing. In the same report, Porter identified the primary dormancy 
mechanism in Peirson's milk-vetch is the impermeability of the seed 
coat to water. He demonstrated little loss of viability in seeds stored 
for three years, consistent with species having a seed bank (Given 
1994). Dispersed seeds that do not germinate during the subsequent 
growing season become part of the seed bank (Given 1994). Romspert and 
Burk (1979) noted that older plants were the primary seed producers, 
and plants that become reproductive in the first season do not make 
significant contributions to the seedbank. Considering statements by 
Phillips and Kennedy (2002) that plants in early 2001 were estimated to 
produce 5 fruits per plant compared to 171 counted in a small sample of 
older plants that year, it is likely that older plants are important 
contributors to the seed bank and survival of Peirson's milk-vetch.
    In a given year, an annual or short-lived species can fluctuate 
between large numbers of plants to few or even no plants. Many species, 
and Peirson's milk-vetch may be one of them, have periodic ``rescue'' 
episodes from the seed bank where large flushes appear when germination 
conditions are suitable (Elzinga et al. 1998). To the extent that 
plants are precluded from adding seeds to the seed bank by being 
eliminated by summer drought, herbivory, and OHV impacts, these 
individuals cannot be expected to contribute to the reproductive 
success of Peirson's milk-vetch. Development of a seed bank and 
associated dormancy allows plant species to grow, flower, and set seed 
in years with most favorable conditions (Given 1994). When measuring 
seed bank dynamics, to determine the viability and productivity of a 
seed bank, it is considered necessary to estimate the rate of seed 
mortality and aging, the amount of seed removed by predators, and the 
variability in germination events are among the factors considered 
necessary (Elzinga et al. 1998).

Distribution and Habitat

    Astragalus magdalenae var. peirsonii is reported from northeastern 
Baja California, Mexico (Barneby 1959, 1964; WESTEC 1977; Spellenberg 
1993), and has been verified in the Gran Desierto of Sonora, Mexico 
(Felger 2000). In the United States, this plant is restricted to about 
53,000 acres (21,500 hectares) in a narrow band of the central portion 
of the Algodones Dunes of eastern Imperial County, California, which 
are one of the largest dune fields in North America. The Algodones 
Dunes are often referred to as the Imperial Sand Dunes, a designation 
derived from their inclusion in the Imperial Sand Dunes Recreation Area 
(ISDRA) established by the Bureau of Land Management (BLM). Nearly all 
lands in the Algodones Dunes are managed by the BLM. However, the State 
of California and private parties own small inholdings in the dune 
area. Approximately 52,780 ac (21,359 ha) of the 185,000 acre ISDRA 
have been proposed as critical habitat for A. m. var. peirsonii (68 FR 
46143).
    The western boundary of the dunes is marked by a series of 
parallel, longitudinal southeast trending ridges. The northern third of 
the dunes is narrow, about 2 mi (3 km) wide, and increases in elevation 
from 200 to 300 feet (ft) (60-91 meters (m)) in the northern portion to 
300 to 400 ft (91 to 121 m) in the southern portion north of Highway 
78. Areas in the central portion of the dunes reach an elevation 500 ft 
(152 m) south of State Highway 78, but reach elevations of only 200 ft 
(60 m) for most areas just north of Interstate 8. The central portion 
of the dunes is wider, about 5 mi (8 km), and is characterized by deep 
bowls (hollows among the dunes) and slip faces (areas so steep that the 
loose sand naturally cascades downward) that run transverse to the 
primary ridge line (Norris and Norris 1961). The area south of 
Interstate 8 is generally characterized by a lower elevation, dunes 
less than 300 ft (91 m).
    The Algodones Dunes are one of the driest and hottest regions in 
the United States. Romspert and Burk (1979) reported average 
precipitation between 1941 and 1970 was 2.6 in (67.8 mm) per year. 
Rainfall amounts differ from place to place and from year to year with 
areas to the northwest being generally dryer than those to the 
southeast (Willoughby 2001). Habitat for this plant is found in a band 
that runs parallel to the active, linear dunes on the western edge of 
the dune field in a northwest to southeast direction. The band is 
between these active linear dunes on the west and transverse ridge 
dunes to the east. This includes the area within the central dunes 
between State Highway 78 and Interstate 8. The dunes in this band are 
composed of a series of transitional crescentic ridges (Muhs et al. 
1995). A. m. var. peirsonii occurs on the open, higher, more active 
dune areas with generally less than 20 degrees slope, in a vegetation 
community referred to as psammophytic (dune loving) scrub (Thorne 1982; 
Willoughby 2000).
    Psammophytic scrub in the dunes proper occurs on the relatively 
stable substrates on the leeward side of the dune ridge tops in areas 
gradually sloping up from the bowls at the bases of the steep leeward 
slip faces (Phillips and Kennedy 2002). Because of the tiered nature of 
the dune system, a system of alternating slopes and swales, areas 
suitable for development of psammophytic scrub and thus Peirson's milk-
vetch occur as scattered occurrences distributed among the dunes. These 
areas are protected from extreme deposition or removal of sand 
(Phillips and Kennedy 2002) and may shift in position over time. 
Therefore, the distribution and relative abundance of the plant varies 
from place to place and over time (WESTEC 1977, Willoughby 2000, 2001; 
Phillips and Kennedy 2003).

Abundance

    Peirson's milk-vetch exhibits temporal variability in plant numbers 
apparently associated with annual precipitation patterns. Based on 
current understanding of the plant's life history, sufficient rain in 
conjunction with cooler fall weather appears to trigger germination 
events. Seedlings may be generally present in suitable habitat 
throughout the dunes, especially during above-normal precipitation 
years. In intervening drier years, plant numbers decrease as 
individuals die and are not replaced by new seedlings. The species 
likely depends on the production of

[[Page 31526]]

seeds in the wetter years and the persistence of the seed bank.
    WESTEC (1977) was a study done under contract to BLM to determine, 
among other things, the distribution and abundance of seven sensitive 
plant taxa including the Peirson's milk-vetch. BLM surveyed 34 selected 
west-east transects in 1998 that were a subset of those used by WESTEC 
(Willoughby 2000). The document compares its findings to those of the 
earlier WESTEC study and concludes that all six of the plants taxa 
monitored in 1998 are at least as abundant and widespread in the entire 
dune system as they were in the 1977 WESTEC study. However, the BLM 
document cautions that the data are not directly comparable because the 
rainfall amounts were different for the two years and different 
methodologies were used in the two studies.
    The number and location of standing plants may vary considerably 
from year to year due to a number of factors including the amount, 
timing, and location of rainfall; temperature; soil conditions; and the 
extent and nature of the seed bank. BLM continued to monitor the 
Peirson's milk-vetch population along the 34 transects and reported 
that 942 plants were found in 1999 and only 86 plants in 2000, both low 
rainfall years compared to the wetter year 1998, when 5,064 plants were 
found (Willoughby 2001).
    In spring 2001, Thomas Olsen and Associates (TOA) conducted a 
survey of a portion of the Peirson's milk-vetch populations on 
approximately 35,000 acres of the dunes that were open to vehicle 
access. In the 13 days of ground surveys, approximately, 71,926 plants 
were reported (TOA 2001), but this single census does not provide any 
information on population trend. In addition, TOA (2001) states that 
``extrapolation of the census data to the entire dunes or to other 
specific areas was not warranted.'' Plant mortality over the short term 
may also be considerable (Phillips and Kennedy 2002).
    The count was reportedly the result of an explosive germination 
event in response to wet conditions during the winter of 2000 through 
2001 (TOA 2001). The record of steep decline of the cohort counted by 
TOA in 2001 was tracked by Phillips and Kennedy (2002) who reported 
that 26 percent of the plants seen in Spring of 2001 were present in 
late 2001 and Phillips and Kennedy (2003) who reported that only 0.26 
percent of the plants counted in Spring 2001 survived to Spring 2003. 
In 2003, Phillips and Kennedy (2003) reported that many of the 
germinants were already dead and that large numbers of those remaining 
would likely die. This severe decline in the population in 2003 was 
further documented by Porter (in litt. 2003a), reporting a similar mean 
seedling survival of 0.19 percent in monitored plots for the 2003 
cohort of Peirson's milk-vetch.
    Only 5 of these 71,926 plants encountered were considered to be 
more than one season old (TOA 2001). The observation that only 5 plants 
of the 71,926 individuals were censussed more than 1 season old 
suggests that the seedlings for this species suffered a high degree of 
mortality, or that the age classes were misidentified during the 
survey. In contrast, a study prepared for the ASA (Phillips and Kennedy 
2002) estimated that 26 percent of the plants counted in the spring 
2001 survey survived to the winter of 2001 through 2002. Phillips and 
Kennedy (2002) also found that these persisting plants produced a mean 
of 171 fruits per plant, compared to an estimated 5 fruits per each 
younger plant in the earlier spring survey. Phillips and Kennedy (2002) 
data suggested that older age classes may produce substantially more 
seeds, and that longevity may be an important factor for reproductive 
success.

Public and Peer Review Comments

    On September 5, 2003, we published a Notice in the Federal Register 
(68 FR 52782) that the petition received on October 25, 2001 to delist 
the Peirson's milk-vetch presented substantial information to indicate 
the petitioned action may be warranted. As part of this Notice, we 
requested information on the status of Astragalus magdalenae var. 
peirsonii. In response, we received comments and information from 
several organizations. In addition, to ensure that our status review 
and 12-month finding are based on the best available scientific and 
commercial information available, we solicited peer review of the key 
documents supporting the petition from three scientists with 
demonstrated and significant expertise and backgrounds in studies of 
genetic diversity, seed banks, plant systematics, population genetics, 
Astragalus field studies, and/or dune plant research. Documents 
referenced by the petitioner, sent to the peer reviewers, included 
Willoughby (cited as BLM) (2000, 2001); Thomas Olsen Associates, Inc. 
(TOA) (2001); and Phillips and Kennedy (2002, 2003). These documents 
represent considerable effort to address complex ecological issues. 
They provide some useful data relative to the life history and ecology 
of A. m. var. peirsonii. However, survey methodology and measures used 
in these studies often differed.
    All of the peer reviewers provided comments on some or all of the 
documents provided to them. These included two documents considered 
supportive to the delisting petition although not provided with the 
petition (Phillips and Kennedy 2002, 2003). The peer reviewers 
identified weaknesses in the supporting documents or limitations of the 
data that was used to support the delisting petition. In particular, 
the peer reviewers discussed the limitations of each survey methodology 
used in the various documents and cautioned the use of data 
extrapolation. For example, a few of the peer reviewers cautioned 
against comparing the WESTEC (1977) and Willoughby (2000) studies due 
to the widely different survey methodologies. Several reviewers noted 
that a few statements in TOA (2001) and Phillips and Kennedy (2002, 
2003) were not completely supported by the data presented. The Service 
has incorporated the data from these studies in this finding, however, 
we have taken into account the specific data limitations discussed by 
the peer reviewers. All of the comments and information provided by the 
public and the peer reviewers were considered in the development of the 
12-month finding and are cited in the finding, where appropriate.

Discussion of Listing Factors

    When considering an action for listing, delisting, or reclassifying 
a species, we are required to determine whether a species is endangered 
or threatened based on one or more of the five listing factors 
identified in section 4(a)(1) of the Act. These factors are: (A) The 
present or threatened destruction, modification, or curtailment of its 
habitat or range; (B) over-utilization for commercial, recreational, 
scientific, or educational purposes; (C) disease or predation; (D) the 
inadequacy of existing regulatory mechanisms; and (E) other natural or 
manmade factors affecting the continued existence of the species. 
Delisting a species must be supported by the best scientific and 
commercial data available and only if such data substantiates that the 
species is neither endangered nor threatened for one or more of the 
following reasons: (1) The species is considered extinct; (2) the 
species is considered to be recovered; and/or (3) the original data 
available when the species was listed, or the interpretation of such 
data, were in error (50 CFR 424.11).

[[Page 31527]]

A. The Present or Threatened Destruction, Modification, or Curtailment 
of Its Habitat or Range

    The final listing rule (63 FR 53596, October 6, 1998) identifies 
OHVs as a serious threat to Astragalus magdalenae var. peirsonii, 
citing the fragile nature of the plants. Numbers and distribution of 
OHVs have increased since the species was listed (BLM 2003 and 
references cited therein).
    Impacts of OHV use on Astragalus magdalenae var. peirsonii plants 
and habitat have been noted by most dune plant studies. For example, 
``The occurrence of dune plants and heavy use areas for vehicles is, to 
a large extent, mutually exclusive'' (TOA 2001). This supports similar 
findings by Willoughby (2000, 2001), WESTEC (1977), Luckenbach and Bury 
(1983), and ECOS, Inc. (1990). Because of the generally transient 
nature of surface structure of the dunes, most quantitative measures of 
OHV impacts are given in terms of numbers of plants impacted. The TOA 
(2001) survey reported finding 667 OHV-impacted plants during 13 survey 
days. Phillips and Kennedy (2003) reported finding 430 impacted plants 
during 6 survey days. But in neither study were plants marked to 
determine survival or reproductive success at a later date. Impacts to 
A. m. var. peirsonii from OHVs continue to be noted (Phillips and 
Kennedy 2003; Willoughby 2004) although no follow-up to measure long-
term impact or relative severity of impact has been done.
    The impacts of OHV use on other types of desert vegetation have 
been documented. Bury et al. (1977) compared eight paired sites in the 
Mojave Desert in 1974 and 1975, examining the impact of OHV use on 
creosote bush scrub and associated wildlife. There were fewer creosote 
shrubs per hectare in plots with higher OHV use, and the proportion of 
shrubs per plot damaged by OHVs increased with increased OHV use.
    The North Algodones Dunes Wilderness (Wilderness) will continue to 
be closed to OHV use. However, the Wilderness alone is not sufficient 
to ensure the long-term survival of Astragalus magdalenae var. 
peirsonii because this area provides only a small percentage of the 
entire habitat for this species within the Algodones Dunes and the area 
provides less available habitat for this plant relative to the areas 
south of State Highway 78 that are open to OHV use.
    The Bureau of Land Management estimates that only approximately 14-
16 percent of the habitat for Astragalus magdalenae var. peirsonii 
occurs within the Wilderness. Between 75-80 percent of all known 
colonies of Astragalus magdalenae var. peirsonii in 1977 were found in 
the areas open to OHV activity; only approximately 20% of the larger 
occurrences were found in the Wilderness (WESTEC 1977). Further, the 
habitat within the Wilderness is not all suitable for this species. 
Creosote bush scrub habitat, which does not support Astragalus 
magdalenae var. peirsonii is more abundant in the Wilderness than in 
the areas south of State Highway 78. The distribution of Astragalus 
magdalenae var. peirsonii from 1998-2000 indicates a higher relative 
abundance of plants in the central dunes south of State Highway 78 (BLM 
2003). Thus, the Wilderness is not sufficient to sustain this species 
because it does not provide sufficient habitat and habitat quality to 
ensure the long-term survival of this species.
    The recently released Recreation Area Management Plan (RAMP) (BLM 
2003) proposes to reopen, to OHV use, all temporarily closed areas of 
the dunes. Re-opening these areas will likely affect the Peirson's 
milk-vetch found in these locations. While many of these areas were 
likely inaccessible prior to the closure, the technological advances, 
such as affordable global positioning system (GPS) units, cell phones, 
and OHVs with greater range have enabled OHV use to penetrate further 
into the dunes. This will likely affect more of the population than was 
previously impacted.
    Visitorship continues to increase in the ISDRA (BLM 2003) and has 
outpaced previous estimations (BLM 1987). Since this plant was listed, 
visitorship to the recreation area has continued to increase. Based on 
the BLM (in litt. 2002), visitorship increased an additional 79 percent 
between 1996 and 1999, and 111 percent over the base year of 1994. The 
visitorship levels recorded in 1999-2000 (BLM in litt. 2002) were 149 
percent higher than those projected for the year 2000 by BLM (1987). 
The BLM (2002) estimated visitorship for 2002 to be 1,005,000. In fact, 
according to BLM figures (Integrated Marketing Systems 2003), there 
were over 1.4 million visitors. This is 400,000 visitors higher than 
were projected. The BLM (2002) estimated range of visitorship projected 
for 2012 is 1,418,000 to 2,071,000. User groups are advocating for 
building as many camping pads as possible until ``Over a span of time, 
100 percent of both sides of the road would be camping pads'' (ASA 
2002). Shifts in visitation have also been reported by the BLM 
(Schoeck, BLM in litt. 2001) indicating that, by the late 1990s and 
early 2000s, day use of the central dunes between State Highway 78 and 
Interstate 8 had become heavy and continues to increase. In the late 
1970s visitation was concentrated primarily to major winter holiday 
weekends, with Thanksgiving week receiving the highest numbers of 
visitors. However, day use has been reported to be increasing on non-
holiday weekends as well (Schoeck, BLM in litt. 2001).
    Significant impacts from OHV use on Astragalus magdalenae var. 
peirsonii habitat have been observed at or near the OHV staging areas 
(Willoughby 2000). The TOA (2001) report supports the BLM findings 
(Willoughby 2000, 2001) regarding limited occurrence of dune plants 
associated with heavy OHV activity: ``The occurrence of dune plants and 
heavy use areas for vehicles is to a large extent mutually exclusive.'' 
This corroborates earlier findings by WESTEC (1977), Luckenbach and 
Bury (1983), and ECOS, Inc. (1990), and was reported in the final 
listing rule (63 FR 53596). The coincidence of timing of seedling 
establishment and the cooler months (OHV season) are among the reasons 
for the plants' susceptibility to impacts from OHVs (Romspert and Burk 
1979). Luckenbach and Bury (1983), in non-replicated studies of paired 
plots along Highway 78 in the Algodones Dunes, report reduced numbers 
of herbaceous and perennial plants, arthropods, lizards, and mammals 
between areas closed to entry (control plots) and those exposed to 
heavy OHV use. Control plots had 2.4 times the number of species, 10 
times the numbers of individuals within these species, 9.4 times the 
vegetative cover, and 40 times the volume of shrubby perennials as 
compared to the OHV-impacted areas (Luckenbach and Bury 1983). These 
data are from localized plots and were not intended to be extrapolated 
to the dune system as a whole but rather are presented here to 
illustrate the effects of OHV use on biota. Willoughby (2001) presented 
data, albeit limited, indicating a higher percentage of A. m. var. 
peirsonii seedlings in the areas closed to OHV use compared to areas 
open to OHV use.
    A map of vehicle tracks (Willoughby 2000) along selected transects 
of the Algodones Dunes on a single day in 1998 showed that considerable 
areas of potential habitat have been impacted. We have no evidence that 
the extent of vehicle tracks, as depicted on this map, will diminish in 
the future. Nor do we know how the distribution and intensity of these 
tracks changes over a growing season or recreation season. Astragalus 
magdalenae var. peirsonii plants, if

[[Page 31528]]

present in those areas, may have been impacted; however, on-the-ground 
counts coincident with the vehicle track mapped areas were not 
performed. Because of the transient nature of sand dunes, impacts from 
OHVs are usually reported in terms of plant numbers impacted or the 
condition of the impacted plants. In their report, TOA (2001) found 667 
plants impacted by OHVs over the course of 13 survey days. A seedling's 
roots are especially sensitive to drying out if the plants or sand 
surface are disturbed. There are potential direct impacts if OHVs run 
over the delicate seedlings and indirect impacts, such as higher soil 
and root desiccation, if sand disturbance occurs in close proximity to 
the seedlings. Seedling death may result from both types of impacts. 
Seedlings that sustain broken branches and live will produce fewer 
flowers, fruits, and seeds that they otherwise would have produced. 
Most recently, during their short survey period, Phillips and Kennedy 
(2003) report that they found several hundred A. m. var. peirsonii 
plants that had been impacted by OHVs. Neither TOA (2001) nor Phillips 
and Kennedy (2003) described the degree, pattern, or frequency of 
impacts to the habitat occupied by the plants, or to adjacent suitable 
habitat used as access avenues to the impacted site. Follow-up surveys 
to determine the effects of the impacts on the plant's survival and 
reproductive output were also lacking. Willoughby (2004) did not record 
the area associated with the OHV-impacted plants he recorded. The 
early, and most sensitive, life history phases of Peirson's milk-vetch 
plants occur between late October and late February. This period 
directly overlaps five of the peaks of visitorship to the Algodones 
Dunes that occur in the same time frame. These peaks in visitor use 
include Thanksgiving (250,000), New Years (150,000), and Presidents Day 
(100,000) as well as Halloween and Martin Luther King Day. Only two 
other visitor peaks over 50,000 visitors occur during a typical 
recreation year. The early elimination of a portion of a seedling 
cohort means that there will be fewer plants to potentially survive to 
become older plants. Older plants have been shown to produce many more 
seed pods per plant than younger first year plants.
    In a very limited study, Pavlik (1979) quantified the immediate 
physical effects of direct contact with an OHV to four specimens of 
each of three psammophytic plant taxa found on the Eureka Dunes in Inyo 
County, California. One was Astragalus lentiginosus var. micans 
(shining milk-vetch), a short-lived perennial to annual desert plant 
similar to Astragalus magdalenae var. peirsonii. Damage to each of the 
plants impacted was assessed in terms of percentage of shoots severed, 
apices removed, flowers removed, foliage loss or damage, and damage to 
underground parts of the plants. In this study, A. l. var. micans lost 
50 to 90 percent of the shoots and stem apices with light to moderate 
OHV activity.
    Willoughby (2000) notes a similar abundance trend in both the 
closed and open areas for OHV activity for five of the six monitored 
plant taxa, including Peirson's milk-vetch. Willoughby (2000) states 
that this is likely due to the fact that intensive OHV use did not 
encroach on much of the plant's habitat over relatively large portions 
of the open area (all of the dunes except the wilderness area at that 
time). Willoughby (2000) further notes that this trend may be expected 
to continue unless OHV use patterns change. Patterns of visitorship 
have reportedly changed according to BLM with the advent of GPS units 
and cell phones, which apparently embolden riders to use more remote 
areas (Schoeck in litt. 2001). Also, the projected 82 percent increase 
in visitorship by 2012-2013 over 1999-2000 levels (BLM 2002) will 
likely result in intensification and dispersal of OHV impacts. 
Willoughby (2000) also states that the BLM surveys are monitoring 
programs and not research, and there are limitations to using the 
information to assess the impacts of OHV use on the plants monitored. 
This indicates the observational nature of the monitoring rather than 
research that tests hypotheses related to measures of OHV impacts on 
plants.
    The early, and most sensitive, life history phases of Peirson's 
milk-vetch plants occur between late October and late February. This 
period directly overlaps five of the peaks of visitorship to the 
Algodones Dunes that occur in the same time frame. These peaks in 
visitor use include Thanksgiving (250,000), New Years (150,000), and 
Presidents Day (100,000) as well as Halloween and Martin Luther King 
Day. Only two other visitor peaks over 50,000 visitors occur during a 
typical recreation year.
    The period of plant sensitivity, approximately late October to late 
February, includes seed germination as well as seedling emergence. A 
seedling's roots are especially sensitive to drying out if the plants 
or sand surface are disturbed. There are potential direct impacts if 
OHVs run over the delicate seedlings and indirect impacts, such as 
higher soil and root desiccation, if sand disturbance occurs in close 
proximity to the seedlings. Seedling death may result from both types 
of impacts. Broken seedlings will produce fewer branches which results 
in fewer flowers and seeds than undamaged seedlings leading to a 
gradual diminishment of the seed bank.
    The early elimination of a portion of a seedling cohort means that 
there will be fewer plants to potentially survive to become older 
plants. Older plants have been shown to produce many more seed pods per 
plant than younger first year plants. Surveys that found hundreds of 
plants impacted in 2001 (TOA 2001) and 2003 (Phillips and Kennedy 2003) 
were conducted between early March and mid May. The magnitude of impact 
described in these reports is likely conservative, in that the surveys 
occurred after the highest vehicular use.
    One of the mechanisms of survival for this species is a seed-
setting strategy for producing large numbers of seeds per plant, 
particularly by older plants. Additionally, as is the nature of seed 
banks, not all of the seeds in the soil germinate the following year, 
as a safety measure against population failure. Natural ecological 
processes diminish the Peirson's milk-vetch seed bank. Natural factors 
affecting the seed bank include seed viability, seed parasitism, seed 
deposition in suitable habitat and at appropriate depth, age of the 
seeds, and failure of an entire seedling generation due to range-wide 
environmental conditions. Each of these factors can limit the number of 
seeds available for germination. The timing of the germination of 
seedlings, the most sensitive life-stage of PMV, also overlaps with the 
onset and peak levels of OHV activity within the Algodones Dunes. 
Several studies document plants that were run over by OHVs at the 
Algodones Dunes and this activity likely results in the direct loss and 
damage to seedlings. The likely mortality of seedlings and older plants 
by OHV activity precludes their future contribution to the seed bank 
further threatening the long-term recovery potential and viability of 
this plant.
    The available documentation attests to historical and ongoing, 
heavy OHV impacts to Astragalus magdalenae var. peirsonii (WESTEC 1977; 
ECOS, Inc. 1990; Willoughby 2000, 2001, 2004; TOA 2001, Phillips and 
Kennedy 2003). Based on information noted above, visitorship is 
expected to continue to increase (BLM 1987, 2002, 2003). and OHV use 
will continue to pose a threat to the survival of A. m. var. peirsonii. 
In summary, OHV use generally reduces the number of species and density 
of

[[Page 31529]]

those species in a given area. The Pierson's milk-vetch seedling 
establishment timing coincides with the heaviest use of OHV use, which 
impacts seedlings reducing the number of older plants. The older plants 
produce more seed, ultimately contributing the most seed to the seed 
bank. Without establishment of the older plants the seed bank will 
likely decrease. Given that this plant survives in a dry dune habitat 
that is highly disturbed by its nature and experiences periods of long 
periods of drought, increasing the size of the seed bank is key to the 
long term survival and eventual recovery of the species.

B. Overutilization for Commercial, Recreational, Scientific, or 
Educational Purposes

    Current data do not indicate that these factors constitute a threat 
to Astragalus magdalenae var. peirsonii at this time.

C. Disease or Predation

    Herbivory was reported for some of the taxa of Astragalus in the 
final listing rule (63 FR 53596). As part of a series of reports on the 
natural history of Astragalus magdalenae var. peirsonii, Porter (in 
litt, 2003a) noted the general poor health of adult plants and 
attributed it to evidenced rodent and insect herbivory. Porter (in 
litt. 2002a) reported ``nearly ubiquitous'' harvesting of leaflets and 
young inflorescences by rodents in A .m. var. peirsonii populations. 
Most of the plants had leaves, leaflets, and/or terminal portions of 
the stems removed, likely by unidentified rodents that had left 
abundant tracks around the milk-vetch plants. Porter (in litt. 2003a) 
also found similar results in 2003. To the extent that rodents remove 
photosynthetic tissue and young inflorescences, plants are likely to 
exhibit a loss of vigor and reduction in reproductive output (i.e., 
seeds). Indeed, Phillips and Kennedy (2002) noted that seed bank counts 
were lower in areas where they noted kangaroo rat (Dipodomys spp.) 
tracks and dens and suggested that this should be investigated. Pavlik 
(in litt. 2003) noted that rodents may be a constant, long-term source 
of high seed mortality that could dramatically reduce the seed bank. As 
yet unidentified weevils were observed to strip the epidermis from the 
stems, which would affect the movement of food and water in the plants 
(Porter in litt. 2003a).
    Beetles, in the family Bruchidae, were reported to contribute to 
the high mortality of seeds and reduced seed crop for Astragalus 
magdalenae var. peirsonii by Romspert and Burk (1979). Larvae of these 
beetles eat the contents of the seeds before emerging as adults. Fruits 
collected in April continued to release beetles, into October (Romspert 
and Burk 1979). Porter (in litt. 2003a) found between 45 and 86 percent 
of the fruits on the few Astragalus magdalenae var. peirsonii plants, 
where he could find fruits, were infested with bruchid beetles. The 
range was 0 to 29 percent for dispersed fruits on the ground. 
Similarly, for the obligate dune plant Astragalus lentiginosus var. 
micans, Pavlik and Barbour (1985) found that dispersed fruits had about 
66 percent of the seeds eaten or damaged by insect larvae compared to 
86 percent of the seeds in fruits still on the plant. Also the number 
of undamaged seeds decreased by more than 60 percent between April and 
May, indicating that predation is highest at dispersal time. The 
reduction of productivity of any given cohort of A. m. var. peirsonii 
from seed predation is unknown but may locally be considerable in a 
given year. Seed predation has been reported to cause significant loss 
of ovules or seeds in Astragalus canadensis (Boe et al. 1989), and in 
two other species of Astragalus (Green and Palmbald 1974).
    Available information shows that rodent herbivory and seed 
predation, as noted above, are not detrimental to the species by 
themselves but, may be additive threats to Peirson's milk-vetch in the 
presence of the other stressors that the population is currently 
undergoing.

D. The Inadequacy of Existing Regulatory Mechanisms

    The lack of regulatory protections for Astragalus magdalenae var. 
peirsonii by the State of California cited in the final listing rule 
(63 FR 53596) still hold true. Pursuant to the Native Plant Protection 
Act (California Department of Fish and Game (CDFG) Code) and the 
California Endangered Species Act (CESA), A. m. var. peirsonii was 
listed as endangered in 1979. This plant is known to occur primarily on 
BLM managed lands. BLM is not subject to the provisions of the CESA. 
The BLM and the CDFG developed a habitat management plan in 1987 that 
included provisions for monitoring transects every other year until 
trends were established. However, little monitoring specific to 
sensitive species was carried out by the BLM prior to the listing of A. 
m. var. peirsonii. Since the listing, the BLM and the CDFG have been 
conducting periodic monitoring for the rare plants on the Algodones 
Dunes.
    The BLM temporarily closed areas of the Algodones Dunes to OHV and 
other traffic on November 3, 2000. However, the recent RAMP for the 
ISDRA (BLM 2003) proposes to reopen those areas temporarily closed to 
OHV activity. The opening of the temporarily closed areas will increase 
the threat to Astragalus magdalenae var. peirsonii to some degree from 
current levels. This would open all areas of the dunes to OHV use, 
except for the Wilderness Area, which was the case when this species 
was listed in 1998 (63 FR 53596). To help protect the plant, BLM has an 
adaptive management and monitoring strategy in place. This will provide 
corrective measures should existing management be found to cause 
excessive, unacceptable impact to the plant. The majority of OHV users 
are responsible recreationists on the dunes and avoid vegetated sites 
(TOA 2001). However, there may be significant damage to populations of 
A. m. var. peirsonii and its habitat, especially closer to the staging 
areas. This would be the result of the focus of increased OHV activity 
in a smaller area.
    The designation of the North Algodones Dunes Wilderness was fully 
considered and was one of the reasons for changing the listing status 
from endangered, published in the proposed rule (57 FR 19844), to 
threatened in the final rule (63 FR 53596). As stated in the final 
listing rule (USFWS 1998), ``While this taxon remains vulnerable to the 
OHV use occurring over most of its dune habitat, the Service believes 
that the dispersed nature of its colonies and the wilderness 
designation reduce the potential for immediate extinction.''
    Available information does not indicate that adequate regulatory 
mechanisms are in place to protect Peirson's milk vetch.

E. Other Natural or Manmade Factors Affecting Its Continued Existence

    The vast majority of OHV users likely avoid Astragalus magdalenae 
var. peirsonii and other biota on the dunes for safety and aesthetic 
reasons. The impacts from OHVs can be incidental or purposeful. 
Although the range-wide impact is difficult to assess, there has been 
an increase in reports of vandalism to the habitat and individuals of 
A. m. var. peirsonii. This was a specific concern expressed in the 
critical habitat discussion of the final listing rule (63 FR 53596). 
There has been no monitoring specifically for the distribution, extent, 
and impact of vandalism to the plant across its range. Porter (in litt. 
2002) describes both tracks and incursions of OHVs into areas outside 
of the Wilderness Area that were closed to OHV traffic. Three of the 20 
plants in one of Porter's monitored plots (Porter in litt. 2002) were 
destroyed by vandals. There have

[[Page 31530]]

been other reported incidents of vandalism, some by our staff, and 
others, but because of the time, lack of knowledge of intent, precision 
of the description of the location, frequency of occurrence, and 
percentage of the plant's range involved, it is difficult to assess the 
cumulative impact to the species.
    This species is also threatened by low numbers of reproducing 
individuals, a circumstance that occurs from time to time. Movements 
and fluctuations of populations have not been recorded long enough to 
assess the full impact of significance to the survival of the taxon. 
The BLM (Willoughby 2001) reported a total of only 86 plants throughout 
its transect areas in the 2000 survey. TOA (2001) found only five 
plants more than a year old in their survey of all of the areas open to 
OHV use. This would be an extremely important fact requiring 
explanation and assessment if only five plants of an herbaceous 
perennial taxon had persisted from the previous season, especially in 
light of seed production as mentioned before. The older, larger plants 
contribute more to the seed bank than younger flowering juveniles 
(Romspert and Burk 1979; Phillips and Kennedy 2002). Random events may 
have a significant detrimental effect on the species when so few 
individuals are present or when the habitat requirements are so narrow 
that random environmental conditions can result in the demise of an 
entire cohort. This was apparently the case with the loss of the entire 
2003 cohort of seedlings (Phillips and Kennedy 2003; Porter in litt 
2003). The ecological impact of any cyclic depletion and restoration of 
the seed bank is unknown.
    Astragalus magdalenae var. peirsonii, like some other narrow 
endemic dune taxa, is subject to debilitating or lethal environmental 
conditions, such as drought or excessive unseasonal winds, across its 
entire range that can affect an entire cohort of plants. Pavlik and 
Barbour (1988), noting the establishment/survivorship pattern of 
Astragalus lentiginosus var. micans, another dune endemic plant, 
reported a complete crash of the 1984 through 1985 seedling cohort. 
Even though 54 percent of the 1985 through 1986 cohort of seedlings 
survived, none of these plants reached reproductive maturity within the 
year. This was apparently the case for the 2003 cohort of A. m. var. 
peirsonii. Phillips and Kennedy (2003) noted that many of the 
germinants were already dead and that large numbers of those remaining 
would likely die. Porter (in litt. 2003a) reports a similar mean 
seedling survival of 0.19 percent in monitored plots for the 2003 
cohort of A. m. var. peirsonii. Environmental conditions unsuitable for 
this plant can occur at irregular intervals or can persist for several 
years. Low numbers combined with periodic, range-wide, debilitating 
environmental conditions pose an ongoing potential threat to this 
plant.

Finding

    We have carefully assessed the best scientific and commercial 
information regarding the biology of this species and its threats. We 
reviewed the petition and associated documents, information available 
in our files, other published and unpublished information submitted to 
us during the public comment period following our 90-day petition 
finding. We reviewed new data and information on the life history and 
ecology of Peirson's milk-vetch; however, we did not find convincing 
information that Peirson's milk-vetch was listed in error.
    The North Algodones Dunes Wilderness (Wilderness) will continue to 
be closed to OHV use. However, the Wilderness alone is not sufficient 
to ensure the long-term survival of Astragalus magdalenae var. 
peirsonii because this area provides only a small percentage of the 
entire habitat for this species within the Algodones Dunes and the area 
provides less available habitat for this plant relative to the areas 
south of State Highway 78 that are open to OHV use.
    The Bureau of Land Management estimates that only approximately 14-
16 percent of the habitat for Astragalus magdalenae var. peirsonii 
occurs within the Wilderness. Between 75-80 percent of all known 
colonies of Astragalus magdalenae var. peirsonii in 1977 were found in 
the areas open to OHV activity; only approximately 20% of the larger 
occurrences were found in the Wilderness (WESTEC 1977). Further, the 
habitat within the Wilderness is not all suitable for this species. 
Creosote bush scrub habitat, which does not support Astragalus 
magdalenae var. peirsonii is more abundant in the Wilderness than in 
the areas south of State Highway 78. The distribution of Astragalus 
magdalenae var. peirsonii from 1998-2000 indicates a higher relative 
abundance of plants in the central dunes south of State Highway 78 (BLM 
2003). Thus, the Wilderness is not sufficient to sustain this species 
because it does not provide sufficient habitat and habitat quality to 
ensure the long-term survival of this species.
    This species likely depends on the production of seeds in the 
wetter years and the persistence of the seed bank from previous years 
to survive until appropriate conditions for germination occur again. 
However, assertions that the reproductive success of Peirson's milk-
vetch is not dependent on the longevity of individual plants but on 
each plant's ability to produce and drop seeds in their first year is 
not supported by the available documentation. First year plants produce 
substantially less seeds than older plants (5 fruits per plant as 
opposed to 171 fruits per plant) (Phillips and Kennedy 2002). TOA 
(2001) reported plants produce seeds their first year, however those 
age classes may have been misidentified. In addition, an entire cohort 
of seedlings may die off in a given year without producing seeds 
(Phillips and Kennedy 2003, Porter in litt. 2003). Therefore, the key 
to survival and recovery is having a large seed bank. The available 
information on the rate of seed deposition to the seed bank and the 
longevity of seeds in the seed bank does not support claims of a 
healthy seed bank. Given, the low numbers of Pierson's milk-vetch, 
other natural predators (seed predatory beetles and kangaroo rats) 
further threaten the species by depleting an already low seed bank 
reserve. Peirson's milk-vetch also exhibits a wide variation in numbers 
of standing individuals found in any given year. Plant count data 
between years is often not directly comparable due to differences in 
rainfall amounts and methodologies. Long-term studies need to be 
undertaken to show the population trends for the species.
    Documentation available attests to historical and ongoing OHV 
impacts to Peirson's milk-vetch (WESTEC 1977, ECOS 1990, Willoughby 
2000, 2001, 2004, TOA 2001, Phillips and Kennedy 2003). Areas within 
the dunes subject to intensive OHV use have a lower abundance of 
Peirson's milk-vetch (e.g., staging areas). Plants within the interior 
portions of the dunes have remained less affected by OHV use, however, 
the advent of GPS and increased vehicle fuel efficiency now enable OHV 
users to travel further into the interior of the dunes without getting 
disoriented and lost. Available information suggests OHV use will 
continue to pose a threat to the survival of Peirson's milk-vetch. 
Given the low numbers, other threats such as rodent and insect 
herbivory, seed predation, and vandalism are contributing to the 
cumulative threats to the Peirson's milk-vetch.
    After a thorough review and consideration of all information 
available, we find that delisting Peirson's milk-vetch is not warranted 
at this time and that this species should remain classified as a 
threatened species. In making this determination we have followed the 
procedures set

[[Page 31531]]

forth in section 4(a)(1) of the Act and regulations implementing the 
listing provisions of the Act (50 CFR part 424).
    We will continue to monitor the status of the species, and to 
accept additional information and comments from all concerned 
governmental agencies, the scientific community, industry, or any other 
interested party concerning this finding.

References Cited

    A complete list of all references cited in this finding is 
available on request from the Carlsbad Fish and Wildlife Office (see 
ADDRESSES above).

Author

    The primary author of this finding is the staff of the Carlsbad 
Fish and Wildlife Office.

    Authority: The authority for this action is the Endangered 
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).

    Dated: May 28, 2004.
Marshall Jones,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. 04-12659 Filed 6-3-04; 8:45 am]
BILLING CODE 4310-55-P