[Federal Register Volume 70, Number 186 (Tuesday, September 27, 2005)]
[Proposed Rules]
[Pages 56426-56434]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-18881]
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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
on a Petition To List the Gentry Indigo Bush as Endangered
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 on a petition to list the Gentry indigo bush (Dalea
tentaculoides) as endangered under the Endangered Species Act of 1973,
as amended. After reviewing the best available scientific and
commercial information, we find that listing the species is not
warranted at this time. 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 the status of
the species.
DATES: The finding announced in this document was made on September 14,
2005. Although no further listing 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 the Arizona
Ecological Services Office, 2321 West Royal Palm Road, Suite 103,
Phoenix, AZ 85021-4951. Please submit any new information, materials,
comments, or questions concerning this species or this finding to the
above address.
FOR FURTHER INFORMATION CONTACT: Mima Falk, Plant Ecologist, Arizona
Ecological Services Tucson Sub-Office, 201 North Bonita Ave., Suite
141, Tucson, AZ, 85745; 520-670-6150, ext. 225.
SUPPLEMENTARY INFORMATION:
Background
Section 4(b)(3)(B) of the Endangered Species Act of 1973, as
amended (Act) (16 U.S.C. 1531 et seq.), requires that, for any petition
to revise the List of Threatened and Endangered Species that contains
substantial scientific and commercial information that listing may be
warranted, we make a finding within 12 months of the date of receipt of
the petition on whether the petitioned action is (a) not warranted, (b)
warranted, or (c) warranted but that the immediate proposal of a
regulation implementing the petitioned action is precluded by other
pending proposals to determine whether any species is threatened or
endangered, and expeditious progress is being made to add or remove
qualified species from the List of Endangered and Threatened Species.
Section 4(b)(3)(C) of the Act requires that a petition for which the
requested action is found to be warranted but precluded be treated as
though resubmitted on the date of such finding, i.e., requiring a
subsequent finding to be made within 12 months. Such 12-month findings
must be published in the Federal Register.
On January 7, 2002, we received a petition dated January 2, 2002,
requesting that we list the Gentry indigo bush (Dalea tentaculoides) as
an endangered species, and that critical habitat be designated
concurrently with the listing. In a Stipulated Settlement Agreement,
signed June 14, 2004 [Center for Biological Diversity v. Norton, CV 03-
473-TUC-FRZ (D. Az)], we agreed to submit a 90-day finding to the
Federal Register by January 31, 2005. On January 25, 2005, we made our
90-day petition finding that the petition provided substantial
information indicating that listing may be warranted. The finding and
our initiation of a status review was published in the Federal Register
on February 2, 2005 (70 FR 5401). We are required, pursuant to the
court approved Stipulated Settlement Agreement, to make our 12-month
finding pursuant to the Act [16 U.S.C. 1533(b)(3)(B)] by September 15,
2005.
Biology and Distribution
Gentry indigo bush is an erect perennial shrub that grows from a
woody root crown and can be up to 1 meter (m) (3.2 feet (ft)) tall. It
is a member of the Fabaceae (Pea) Family. The leaves are compound, 3-6
centimeters (cm) (1.2-2.4 inches (in)) long with 9-17 pairs of
leaflets. The leaflets are hairless, notched at the tip, and dotted
with punctuate glands (translucent pitted glands or colored dots) on
the lower surface. The flowers are sessile (lacking a stalk), 6
millimeters (mm) (0.24 in) in length, and are presented in oblong
clusters. The flower petals are rose-purple. Plants flower in the
spring, from late March to mid-May. They may produce a second set of
flowers in late summer and fall in response to monsoon precipitation.
Howard S. Gentry originally described the species in 1950. It is a
distinctive member of the genus Dalea with no closely related species
(Gentry 1950; Barneby 1977). The main distinguishing character that
separates this species from other sympatric species is the presence of
elongate, brown, tentacle-like glands on the calyx (the outer whorl of
flowering parts), lobes, floral bracts (the reduced or modified leaf
subtending a flower), and branches.
Gentry indigo bush is known historically in the United States from
only three areas in southern Arizona: The western and northern slopes
of the Baboquivari Mountains (Tohono O'odham Nation), the Coyote
Mountains (Mendoza Canyon), and Sycamore Canyon (Coronado National
Forest) in
[[Page 56427]]
the Atascosa Mountains. Today, plants are only known to occur in
Sycamore Canyon and on lands within the Tohono O'odham Nation
(Schmalzel 2005).
The plant has also been found at three locations in Mexico. The
first location was found in 1995, northeast of Hu[aacute]sabas in the
State of Sonora. In 2004, the species was documented to occur in Sierra
El Humo, south-southwest of Sasabe, Arizona, in northwestern Sonora,
Mexico (L. Hahn, pers. comm., 2004). Surveys in 2005 documented the
persistence of those two populations and discovered a third in the
Sierra de La Madera (Van Devender 2005).
Surveys in Sycamore Canyon, AZ
Gentry indigo bush grows in scattered patches at elevations of
1,097 to 1,219 m (3,600 to 4,000 ft) in Sycamore Canyon and several
side channels. Plants are usually found on floodplain terraces in sandy
or gravel soils, or, less commonly, on talus slopes (a slope formed by
an accumulation of rock debris) close to the floodplain. The usual tree
canopy for Gentry indigo bush consists of Arizona sycamore (Platanus
wrightii), Arizona ash (Fraxinus velutina), Arizona walnut (Juglans
major), and several oak species. Plants can be found growing under
these trees or out in the open. Where Gentry indigo bush grows in the
semi-active floodplain, plants are exposed to periodic flooding and
scouring events. Observations made by Gori et al. (1992) and Falk
(1993) support the idea that plants are adapted to periodic, low-
intensity floods. Plants that had been covered with sediment were found
to be growing up through the deposited material. The plants can
reproduce vegetatively (asexually), and roots have been found to
connect young plants to nearby larger clumps. The ability to reproduce
asexually presents a problem in estimating population numbers in that
it is impossible to determine if plants are connected, except by
uprooting them. As a result, the number of stems counted may not equal
the number of individuals. Thus, the data from field surveys described
below should be considered only rough estimates of population numbers.
There have been limited observations of sexual reproduction in the
field. Gori et al. (1992) documented some reproduction on the
monitoring plot, although they had difficulty determining if the new
recruits were ramets (vegetative offshoots) or seedlings. Small plants
located in May 2005 were pulled up and were identified as seedlings,
not vegetative offshoots (Baker 2005). It is not known if the seeds had
lain dormant in the seed bank or were from a recent reproductive event.
None of the adult plants had seed pods, and no seed pods were found on
the ground (Falk, pers. obs. 2005). In fact, plants rarely have been
observed to produce seed (Falk 1993; Gori et al. 1992). This may be the
result of timing, as plants may not have been producing fruit at the
time surveys were conducted. Schmalzel (2005) found seeds within dried
inflorescences (i.e., flowers) during his survey work in July. Staff
from the Desert Botanical Garden collected approximately 15 seeds from
plants they assumed to be Gentry indigo bush in 1998 and 1999, but the
quantities are too small to conduct germination tests (K. Rice, pers.
comm. 2005).
Although this species has adaptations to withstand periodic, low-
intensity flooding, the population in Sycamore Canyon has experienced
population fluctuations, some of those associated with flood events. In
1982, a status report documented only 100 plants from Sycamore Canyon
(Toolin 1982). Following severe winter flooding in 1993, a large
portion of a monitoring plot that had been established on a floodplain
terrace washed away, and the overall population within Sycamore Canyon
declined to 15-30 plants (Falk 1993). Gori et al. (1992) estimated that
there were 1,400 ``individuals'' in Sycamore Canyon before the heavy
rains of 1993. The population in Sycamore Canyon has been monitored
sporadically since 1993. Bertelsen (1997) recorded approximately 500
individuals. Brooks (1999) found 194 plants, including a small group
(15) in Pe[ntilde]asco Canyon. A U.S. Forest Service biologist reported
seeing some patches of Gentry indigo bush while surveying for Sonora
chub in the canyon (2000, 2001). In three separate surveys over
consecutive years the numbers of plants varied. Baker (2003) found 100
plants, and Reina and Van Devender found 36 plants in 2004 (Baker
2005). In 2005, Baker recorded approximately 450 plants, with many
seedlings and some resprouts from plants thought to be dead (bare
branches, no leaves). The latter survey was done in May 2005, when the
biologists (including Service staff) knew the plants would be
flowering, allowing easy identification of Gentry indigo bush.
Additional surveys in Sycamore Canyon were conducted in April and May
(Darling 2005). These surveys were conducted on four separate visits,
and approximately 922 plants were found. Of note was the location of
many plants on talus slopes out of the floodplain. Due to variation in
survey methodologies, the current estimate for Sycamore Canyon is thus
between 450 and 922 plants. Schmalzel (2005) observed during his
surveys that plants were associated with grussy colluvium (i.e., a
loose accumulation of particles from decomposing granite) found on the
sides of canyons, and he believed that locations in the floodplain may
not be as important as those on the sides of the canyon. Schmalzel's
2005 observation is consistent with the results of Darling's 2005
survey report where Gentry indigo bush was found on talus slopes in
Sycamore Canyon.
The distribution of sub-populations in Sycamore Canyon has changed
over time. The overall population in Sycamore Canyon is best described
as a metapopulation, that is, a population consisting of many ``local''
sub-populations or patches. Sub-populations may undergo extirpation
(i.e., loss) while others are created, such that distribution within
the larger population is dynamic in nature and the species persists at
a larger scale-- in this case, throughout the canyon. This pattern
follows Levins' dynamic metapopulation model (1969, 1970) describing
habitat patches, or islands, with some of the patches disappearing but
then undergoing recolonization from the remaining patches. For
instance, a flood event could remove some sub-populations from the
canyon, but the remaining sub-populations would persist and serve as a
source of recolonization.
As a result, it is very difficult to track individual patches in
the canyon over time. Early monitoring efforts documented the location
of patches, but successive surveyors have found that previously
documented patches are not always present. This indicates that patch
location is very dynamic in the canyon. Based on the Baker 2005 survey,
the densest plant patches are located in the central portion of the
canyon (centered around where Pe[ntilde]asco Canyon enters into
Sycamore Canyon) and areas directly to the north and south. The dynamic
nature of plant distribution is likely influenced by drought and
flooding, which is not uncommon for plants found in canyons subject to
episodic climate events.
Additional Survey Work in Arizona and Mexico
Gori et al.(1992) status report included a review of historic
localities in the United States and areas of suitable habitat in
Arizona and Mexico, except areas within the Tohono O'odham Nation. No
plants were found in the Coyote Mountains, and the authors surmised in
the status report
[[Page 56428]]
that the population was extirpated, possibly due to past grazing
practices.
In Mexico, surveys were conducted in areas not previously known to
support Gentry indigo bush plants, but where the habitat appeared to be
suitable. No plants were found in the areas surveyed, which included
canyons in the following mountain ranges in Sonora, Mexico: Sierra
Cibuta, La Colorada, Sierra el Tigre, Sierra los Ajos, Sierra Azul,
Arroyo Las Fresnos, Sierra San Diego, La Angostura, and Sierra San Luis
(Gori et al. 1992).
Extensive survey work has also been completed in other areas of
habitat in Arizona that appear to be suitable, but that were not known
to have ever supported Gentry indigo bush. Specifically, in Arizona in
1991, 1998, 2003, and 2005, surveys were conducted with negative
results in all efforts. Areas surveyed include the Atascosa/Pajaritos
(Upper Peck Canyon, California Gulch, Holden Canyon, and Rock Corral
Canyon), the Baboquivaris (Thomas and Sabino canyons), and the
Patagonia Mountains (Harshaw Creek, Finley and Adams canyons, Flux
Canyon, and upper Mowry Wash) (Gori et al. 1992). Gentry indigo bush
was not found in Atascosa, Pen~asco, or unnamed canyons in the Atascosa
Mountains (Baker 2005), or in the upper reaches of Sycamore Canyon
(Baker 2003). However, in 2005, Gentry indigo bush was located on the
Tohono O'odham Nation (Schmalzel 2005). The Tribe should be contacted
for additional information, if needed.
In 2005, Dr. Tom Van Devender and Ana Lilia Reina conducted
extensive surveys for Gentry indigo bush in Mexico. From April through
June, they visited 22 potential sites in 7 mountain ranges in Sonora,
Mexico. The ranges surveyed west-southwest of Sasabe to southwest of
Cananea were the Sierra El Humo, Sierra Las Avispas, Sierra Cibuta/
Guacomea, Sierra Jojoba, Sierra de Los Pintos, Sierra de La Madera, and
Sierra Azul. Sites surveyed were 1,045 to 1,518 m (3,400 to 5,000 ft)
in elevation and mostly in canyons in desert grassland/oak woodland
transition or oak woodland (Van Devender 2005). They also revisited the
2004 location of Gentry indigo bush in the Sierra El Humo, an isolated
mountain range near the Arizona border in the Municipio of Altar, and a
total of 126 plants were found in 6 patches in an unnamed canyon. A new
population was located in the Sierra de La Madera. This mountain range
is located east of interstate MEX 15 between Imuris and Magdalena.
Plants were found in Cajon El Chorro, within the Sierra de La Madera. A
total of 98 individuals were found in 2 patches. Van Devender returned
to the 1995 Huasabas site and documented 170 Gentry indigo bush plants.
This site is atypical, as the plants were found under Chihuahua oaks on
gentle north-facing slopes, not in canyon bottoms (Van Devender 2005).
Overall, surveys in Mexico in 2005 documented 394 Gentry indigo plants
at 3 locations. No other populations of Gentry indigo bush were
located, and no historical records are known from any of the other 19
sites surveyed (Van Devender 2005).
In summary, Gentry indigo bush remains a rare, narrow endemic
(i.e., restricted to a particular region) in terms of its overall
numbers, number of populations, and geographic distribution. Dedicated,
extensive surveys conducted over the years have documented few new
locations, and all known populations are small. No new locations have
been found in Arizona despite fairly extensive surveys of apparently
suitable habitat. In Sycamore Canyon, the overall population has
fluctuated greatly since surveys began, and recovery from flooding in
1993 has been slow. Currently, the population constitutes only 32 to 67
percent of the pre-flood numbers. Most of the older plants are gone but
there are many seedlings, which provides some evidence of the species'
resiliency and ability to persist. However, it is not known how many of
these seedlings will survive and contribute to the reproductive
potential of the population. The limited demographic monitoring data
show higher mortality in the small age classes (Gori et al. 1992). In
some locations, larger and older plants were found completely out of
the floodplain and up against the canyon walls, which provides some
assurance that not all of the species' habitat is susceptible to
flooding. The species has persisted at known locations for some time
(based on herbarium records), and it seems likely that other areas that
may support the plant were overlooked in previous survey efforts.
Previous Federal Actions
Gentry indigo bush was determined to be a candidate species as
published in the 1980 Plant Notice of Review (45 FR 82480). A species
with candidate status is one for which we have collected and assessed
information sufficient to propose listing the species. On April 2, 1998
(63 FR 16217), we removed the Gentry indigo bush from candidate status.
The reasons supporting removal from the candidate list were (1) the
taxon was more abundant or widespread than previously believed or not
subject to any identifiable threats; and (2) the Service had
insufficient information on biological vulnerability and threats to
support issuance of a proposed rule to list. Following receipt of the
2002 petition, and pursuant to a stipulated settlement agreement, we
published a 90-day finding on February 2, 2005 (70 FR 5401), finding
that the petitioners had provided sufficient information to indicate
that listing of the Gentry indigo bush may be warranted. In order to
use the best scientific and commercial information available to
determine whether listing of the species was indeed warranted, two
public comment periods were opened. The initial comment period was
opened by the February 2, 2005, 90-day petition finding for a period of
60 days, through April 4, 2005, and the comment period on the 90-day
finding was reopened on July 25, 2005 (70 FR 42520), for an additional
10 days.
Summary of Factors Affecting the Species
Section 4 of the Act (16 U.S.C. 1533), and implementing regulations
at 50 CFR 424, set forth procedures for adding species to the Federal
List of Endangered and Threatened Species. In making this finding,
information regarding the status and threats to this species in
relation to the five factors provided in section 4(a)(1) of the Act is
summarized below.
In general, we have focused much of the five factor discussion
below on the Sycamore Canyon population in Arizona because we have
specific information about it. Where we have information for
populations in Mexico and on the Tohono O'odham Nation, we have
specifically addressed that below.
Factor A: The Present or Threatened Destruction, Modification, or
Curtailment of the Species' Habitat or Range
Modifications and alteration of Gentry indigo bush habitat are
associated with watershed degradation, roads, recreational activities,
undocumented immigrant traffic and associated U.S. Border Patrol
activities to control illegal entry, and the spread of invasive plant
species. All of these factors have the potential to alter and degrade
the species' habitat.
Watershed Degradation
In general, human-related activities can have an adverse impact on
the arid watersheds of the Southwest (Bahre and Bradbury 1978; Bahre
1995; Hadley and Sheridan 1995). Such impacts may include erosion of
stream channels and loss of herbaceous vegetation caused by
overgrazing, altered fire regimes, mining
[[Page 56429]]
runoff, off-road vehicle use, road construction, and other
anthropogenic activities, and all have contributed to reduced quality
and quantity of riparian and wetland habitat (Hendrickson and Minckley
1984; Bahre 1995; Hadley and Sheridan 1995; Ohmart 1995; Whelan 1995;
Debano and Neary 1996; Belsky and Blumenthal 1997; Wang et al. 1997).
Watershed degradation may be a concern in Sycamore Canyon, which is
a small canyon cutting through rugged hills located within the Coronado
National Forest, Nogales Ranger District. Special protection for the
Canyon is provided by inclusion within the Goodding Research Natural
Area (RNA) and the Pajarita Wilderness. Lefevre (2000) concluded that
human influence on Sycamore Canyon is mostly related to downcutting of
the channel system, sediment movement, and sediment yield to the
stream, and has resulted in erosion rates above that which would be
expected under unroaded, unmined, and ungrazed conditions. Within the
Goodding RNA, mining, roads, and grazing are prohibited, as discussed
below. However, such activities occur in the hills outside of the
Canyon and may influence conditions within it.
Grazing Effects on Watershed
The Sycamore Canyon watershed is 6,737 hectares (ha) (16,648 acres
(ac)) in size (Lefevre 2000). All but 874 ha (2,160 ac) are within
grazing allotments. The majority of those lands are on the Coronado
National Forest, where many different types of uses are authorized
(e.g., livestock grazing, mining, roads, wilderness). Livestock grazing
is not permitted within the boundaries of the RNA, including Sycamore
Canyon.
The Bear Valley grazing allotment, which is located in the hills
surrounding Sycamore Canyon, is 9,197.5 ha (22,710 ac) in size. Site-
specific soil surveys (U.S. Fish and Wildlife Service 2002) indicate
that 75 percent of the allotment is in satisfactory condition, 16
percent is considered impaired, 8 percent is unsatisfactory, and 2
percent is in unsuitable condition. Where soils were found to be
impaired, it was attributed to lack of vegetative ground cover. In
addition, the soils had altered structure, which inhibits water
infiltration (Lefevre 2000). Lack of ground cover and compaction of the
soil can lead to increased quantities of sediment and water flowing
into the canyon. Between 1983 and 1997, the percent of ground cover has
increased from 29 percent to 33 percent on this allotment, indicating
that conditions are improving (Lefevre 1999). The majority of this
allotment is in satisfactory condition and on an upward trend. The
number of permitted livestock on this allotment has decreased
dramatically since 1908, when 1,000 cows were allowed. The numbers were
reduced to 650 in 1917, 520 in 1930, and stocking was reduced to almost
zero in 1961 due to range deterioration. Due to improvements in range
condition the allotment is now permitted for 350 cattle. The overall
reduction in livestock numbers from 1,000 to 350 cows indicates that
the current management of this allotment is contributing to the overall
improvement of watershed conditions, and with improved watershed
conditions, the amount of sediment entering into Sycamore Canyon would
be reduced, resulting in improved habitat conditions for Gentry indigo
bush. There will be continued sediment and precipitation run-off
associated with the impaired soils due to livestock grazing, but the
amounts are difficult to quantify and may not be significant.
According to Van Devender (2005), none of the three Mexican
populations are accessible to cattle, so grazing does not constitute a
threat there. On the Tohono O'odham Nation, the influence of grazing is
unknown, but the species is still present (Schmalzel 2005).
In summary, the watershed condition of the Bear Valley livestock
grazing allotment has been improving since the early 1900s. There has
been an overall decrease in the permitted numbers of cattle on the Bear
Valley allotment and ground cover has improved to the point where 75
percent of the allotment is in satisfactory watershed condition. The
continuation of these sound livestock-management practices will likely
result in improved habitat conditions for Gentry indigo bush. Sediment
will continue to move off the allotment, due to the 16 percent of
impaired soils, but the amounts are difficult to quantify and may or
may not result in significant effects to the ecosystem. The Mexican
populations are not subjected to grazing, but watershed conditions
there are unknown. Similarly, there is little information available
from the Tohono O'odham Nation.
Roads
Many roads are present in the Sycamore Canyon watershed, and they
have contributed to overall watershed degradation. However, it is not
known how these roads affect ongoing erosion and, more importantly, how
much of the eroded material ends up in the Sycamore Canyon drainage.
The amount of sediment and surface runoff within the Sycamore Canyon
watershed may affect Gentry indigo bush and its habitat. The plants
have adaptations for persisting in spite of flood events that have
caused sediment to enter Sycamore Canyon, but it is unknown whether a
threshold exists which, if crossed, may eliminate the metapopulation
from the canyon. However, as noted above, the species does have the
ability to recolonize after flood events, and plants located out of the
floodplain and on associated talus slopes may provide the source for
recolonization of the plants within the floodplain. The U.S. Forest
Service maintains a road density of 0.58 km/km2 (0.93 mile/
mi2) within the watershed, and considers these roads to be
``a primary source of erosion and sediment'' (Lefevre 2000). This
translates to 38.8 km (24.1 mi) of roads within the watershed,
occupying 22.2 ha (55 ac) (Lefevre 2000).
The U.S. Forest Service has no immediate plans to address the
effects of roads in the Sycamore Canyon watershed; thus sediment
deposition and scouring in and along the stream channel could still
occur. Again, we do not know if the sediment production associated with
the roads is resulting in significant effects to the ecosystem and the
habitat of Gentry indigo bush. However, we do know that the
metapopulation has persisted in the canyon under the current road
conditions. We also note that the U.S. Forest Service closed
unauthorized roads that crossed the stream at several locations near
the mouth of Sycamore Canyon and built a bridge where Forest Road 39
crosses Sycamore Creek, thus eliminating some erosion threats
associated with roads. It is not known whether roads are a threat to
either the Mexican or Tohono O'odham populations, but we have no
evidence that roads have adversely affected the species there.
Recreation
Sycamore Canyon is close enough to Tucson and Nogales, Arizona, to
make it a popular destination for hiking and birding. The flora of the
canyon supports 624 species of vascular plants, and birders come from
all over the world to see various species considered rare in the United
States. Because there are no designated trails within the RNA,
trampling and compaction of soils from the resulting foot traffic can
negatively affect the Gentry indigo bush in Sycamore Canyon. Gentry
indigo bush plants grow on the floodplain terraces where hikers often
create trails to avoid walking in the stream. Due to its narrow width,
there are limited terraces in the canyon intensifying the use of Gentry
indigo bush habitat as places to create trails. Many of the remaining
plant
[[Page 56430]]
locations are near recreational trails, and plants were found that had
been trampled (Falk, pers. obs. 2005). Even when the plants are
flowering, they are not particularly showy and are quite fragile. When
they are not flowering, they do not stand out, and it is fairly easy to
step on them without noticing. Although no overnight camping is allowed
in the RNA, there is unauthorized camping occurring, as evidenced by
fire rings and obviously trampled areas where human activities had
taken place. These activities degrade habitat and may reduce the areas
potentially occupiable by Gentry indigo bush. They may also alter and
reduce the amount of habitat available for plant germination. This in
turn affects the ability of the plant to reoccupy sites after
disturbance events.
We know of no plan to address the effects of recreation in this
area or the larger watershed. The degree to which recreational
activities may affect the population in Sycamore Canyon is not known.
However, recreation has been ongoing in the canyon in the past, and the
Gentry indigo bush continues to persist and increase in number;
therefore, we do not believe recreation is affecting the overall
population in Sycamore Canyon. We have no evidence that recreation is
adversely affecting the Mexican or Tohono O'odham populations.
Undocumented Immigrant Traffic/U.S. Border Patrol Actions
The cutting and/or disrepair of the border fence along the U.S.-
Mexican border by undocumented immigrants is an ongoing concern due to
the potential for cattle trespassing and trampling of habitat. It is
very difficult to monitor the status of this fence because it is a long
hike or horse ride of over six miles down the canyon. The U.S. Forest
Service does not monitor this fence as part of its allotment
monitoring. It is possible that the fence could be cut or knocked down
and livestock could enter the canyon without detection; however, the
fence has apparently excluded trespass cattle since 1998. Given the
seemingly slow recolonization of the Gentry indigo bush population in
Sycamore Canyon since the 1993 flood, a single incursion of cattle
could have a significant effect on individual clusters of plants in the
canyon bottom. Currently, the majority of the sub-populations are in
areas that would be accessible by cattle from the southern end of the
canyon, absent a functional fence. On the other hand, the
metapopulation has persisted even through times when the fence was
down. We do not know what the long-term effects to the metapopulation
would be from livestock grazing, but it seems unlikely that the entire
metapopulation in Sycamore Canyon would be severely affected by
occasional use by trespass livestock.
Undocumented immigrants crossing the border into the United States
from Mexico cross through Sycamore Canyon. Although we did not detect
high levels of use during our 2005 survey, we did observe trash and
many foot trails in canyons and uplands associated with Sycamore Canyon
(i.e., Pe[ntilde]asco, Atascosa, Hank, and Yank Canyons). Human traffic
associated with this activity in the canyon bottom may directly trample
plants and is likely contributing to Gentry indigo bush habitat
degradation. It follows that areas receiving heavy use will be under
surveillance by the U.S. Border Patrol. The U.S. Border Patrol's
activities could also create additional disturbance by using the same
foot trails, as well as increasing use of existing roads. We do not
know if these types of activities are likely to increase in the future
and cause detrimental effects to Gentry indigo bush and its habitat.
Undocumented immigrants may also set fires. Although these fires are
usually accidental (e.g., an escaped campfire), they may be the
ignition source for a future grassland fire in the watershed.
The border fence in Sycamore Canyon has remained intact since 1998.
Border activity ebbs and flows, and it is difficult to predict where
increased activity will take place. Currently, the level of border
activity is not threatening the continued existence of the plant in
Sycamore Canyon.
Invasive Plants
The invasive buffelgrass (Pennisetum ciliare) is used throughout
Sonora, Mexico, as a pasture grass, and large natural grassland areas
have been converted to buffelgrass. Buffelgrass lines the major highway
in Sonora to the U.S. border. Noxious weed seeds can be spread by the
wind, on the soles of shoes, and in the tire treads of vehicles.
Riparian areas can also function as dispersal corridors for the
movement of invasive plant species (Stohlgren et al. 1998; Parendes and
Jones 2000). With the increase in border activity, it is probably only
a matter of time before this highly invasive grass species is found in
Sycamore Canyon. The U.S. Department of Agriculture's Agricultural
Research Service has developed and released a cold-tolerant variety of
buffelgrass, ``Frio'', which is intended to be used at higher
elevations and in regions where current buffelgrass cultivars
experience winter damage (Hussey et al. 2005). These cultivars will
increase the potential area of invasion.
Buffelgrass grows very quickly and out-competes native grass for
water and nutrients. Once stabilized, it rapidly becomes the dominant
plant cover. Should it become the dominant plant species on floodplain
terraces, it could replace Gentry indigo bush along with other native
riparian species in Sycamore Canyon, but it is not known to occur there
at this time. We do not know if buffelgrass is found near the
populations of Gentry indigo bush in Mexico, but it may be a potential
threat to these populations in the future since so much planting of the
grass has taken place in Sonora, Mexico. As of 1997, over one million
ha (2,471,000 ac) of desert and thorn scrub in central Sonora had been
cleared to plant bufflegrass (Van Devender and Felger 1997), but we do
not know how close it is to invading canyons occupied by Gentry indigo
bush.
Baker (2005) found at least one, and possibly two, species of
Pyracantha in Atascosa and Sycamore canyons. This nonnative, aggressive
species, should it become established and spread in Sycamore Canyon,
could potentially reduce suitable habitat for Gentry indigo bush.
Many areas of Sonoran desert grasslands in southeast Arizona have
been colonized by Lehman lovegrass (Eragrostis lehmanniana), an
invasive species from South Africa. This grass has become so firmly
established in southern Arizona that there may be no feasible control
for it. Lehman lovegrass produces more fine fuel than native grass
species (Cable 1971; Cox et al. 1984), leading to increased fire
spread. Lehman lovegrass also increases after fire (Ruyle et al. 1988;
Sumrall et al. 1991). Currently, the Bear Valley allotment does not
seem to have continuous patches of Lehman lovegrass, so the effects
from an altered fire regime due to its presence may not pose a threat
to Gentry indigo bush. If the density and distribution of Lehman
lovegrass were to increase on the allotment, then more frequent and
higher intensity fires would be expected. This could potentially result
in increased erosion and precipitation run-off, possibly leading to
more frequent flood events in Sycamore Canyon. More frequent and
greater intensity flooding may not allow for the recolonization of
habitat and reestablishment of sub-populations in Sycamore Canyon
during flood-free intervals, resulting in overall habitat and
population reduction.
Establishment of these nonnative grasses in Sycamore Canyon or
other
[[Page 56431]]
occupied habitat could compromise habitat quality and possibly endanger
the long-term survival of metapopulations because the change in fire
frequency and intensity could increase the frequency and intensity of
flood events, placing sub-populations at increased risk. However, the
threats from invasive species are considered to be only potential at
this time, as there are no populations of the grass species present in
Sycamore Canyon. We do not know if the populations in Mexico or on the
Tohono O'odham Nation are threatened by invasive species.
In summary, there are ongoing and potential threats to the habitat
of Gentry indigo bush in Sycamore Canyon. Many of the threats
identified have been minimized (e.g., protection from livestock
grazing, reduction in livestock numbers, overall improvement in
watershed health) and while other threats are possible in the future,
there is no evidence that they are currently affecting the population,
and certainly not at a level that threatens the species (e.g., invasive
species, recreation impacts, undocumented immigrant traffic, U.S.
Border Patrol activities, and wildfire). Because they occupy similar
habitat (i.e., canyon bottom), the populations in Mexico may be
affected by the threats discussed in this section; however, due to a
lack of detailed information regarding these sites, there is no direct
evidence of threats to Mexican populations. The status of the
populations in Mexico and on the Tohono O'odham Nation are not known,
but some of the populations have persisted over time.
Factor B: Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
There are no known threats to Gentry indigo bush from over-
utilization for commercial, recreational, scientific, or educational
purposes.
Factor C: Disease or Predation
Grazing Effects on Plants
This section discusses the threat from cows directly eating the
plant. Gentry indigo bush plants are palatable, as are most Dalea
species. Gori et al. (1992) concluded, ``Our surveys of Sycamore and
Mendoza Canyons lead us to believe that grazing constitutes a threat to
D. tentaculoides. We observed direct evidence of livestock browsing on,
and even uprooting, the species in lower Sycamore Canyon where trespass
cows from Mexico enter the canyon up to an impassable narrows.''
As discussed above, Sycamore Canyon is found within the Goodding
RNA and the Pajarita Wilderness within the boundaries of the Coronodo
National Forest, Nogales Ranger District. Livestock grazing is not
permitted within the boundaries of the RNA, but trespass cattle use has
been a sporadic problem (U.S. Department of Agriculture 1998). Trespass
cattle can enter the canyon from the mouth of the canyon at the
northern end, and also from the southern end on U.S.-Mexico border. The
sides of the canyon are generally too steep for livestock. Cattle have
been observed in the northern reaches of the canyon (Brooks 1999), and
Brooks noted heavy cattle use in the southern end of the canyon (i.e.,
below ``the narrows'') most likely attributable to trespass livestock
from Mexico. In 1997, the U.S. Forest Service proposed a set of actions
in Sycamore Canyon to protect the federally threatened Sonora chub
(Gila ditaenia). One of those actions included building a fence at the
northern portion of the canyon to restrict livestock access to the
riparian areas. As long as this fence is maintained and remains
effective, no direct threat of cattle in the upper reaches of Sycamore
Canyon exists.
In the lower reaches of Sycamore Canyon, trespass cattle from
Mexico may present another problem. Although the U.S.-Mexican border
fence had been in a state of disrepair,in the fall of 1998, 2.4 km (1.5
mi) of fence was repaired and information provided to us during our
status review of the species indicates that the fence is currently
functional in preventing livestock trespass and has not been recently
cut (Parker 2005). Thus, while sporadic grazing was historically
considered a potential threat to Gentry indigo bush, we do not believe
that trespass cattle from Mexico pose a threat at this time in Sycamore
Canyon. This determination is based on the protective status of the
area as an RNA and the measures taken by the U.S. Forest Service to
construct and maintain a fence preventing cattle from entering the
canyon from Mexico.
We know that livestock grazing occurs on Tohono O'odham Nation in
the general area where the plants were known to be in the southern
Baboquivari Mountains, but have no recent information on plant numbers.
We are currently working with the Nation to gather information on this
population. We anticipate that, if livestock grazing is determined to
be a concern, we can work cooperatively with the Nation to resolve
those issues.
We do not know if the populations in Mexico are affected by
livestock grazing; nothing was reported on the grazing regime in the
areas surveyed. Van Devender (2005) noted that the populations he found
were in areas not accessible to livestock.
Gentry indigo bush is palatable to other species beside livestock.
Brooks (1999) provided one observation of a plant being almost totally
eaten by a rabbit. Schmalzel (2005) also noted one Gentry indigo bush
that had evidently been clipped at the base by a valley pocket gopher
(Thomomys bottae), but we do not consider this to be a major threat. We
acknowledge that rabbits, gophers, and other herbivores may eat plants,
but we do not think this constitutes a major threat to the species
because of the size of mature plants and the abundance of other
herbaceous plants in the canyon available for food.
We know of no diseases threatening this species.
Factor D: The Inadequacy of Existing Regulatory Mechanisms
The population in Sycamore Canyon is on the Coronado National
Forest and subject to the general Federal regulations of the National
Forest System. Gentry indigo bush is on the Coronado National Forest's
Sensitive Species List. Populations that may be present on the Tohono
O'odham Nation are not protected by any regulation of which we are
aware. Mexican populations have no protection because they are on
private land and are afforded no protection under Mexican laws. The
Arizona Native Plant Law (State of Arizona) does consider this species
as highly safeguarded, and thus a permit is required from the Arizona
Department of Agriculture to salvage the plant; however, no other
protection is afforded to the species or its habitat.
U.S. Forest Service (Sycamore Canyon, AZ)
The metapopulation of Gentry indigo bush in Sycamore Canyon is
within the Goodding RNA and the Pajarita Wilderness. There are no other
locations on U.S. Forest Service land. The U.S. Forest Service has
stated that Gentry indigo bush is afforded a high level of protection
because it shares its habitat with critical habitat of the federally
listed Sonora chub. The U.S. Forest Service has done much work to
improve the habitat of Sonora chub, including removal of a road at the
mouth of Sycamore Canyon, protection of riparian areas at the northern
end of Sycamore Canyon, and the expansion of the Goodding RNA. These
actions have contributed to improvement of Sonora chub habitat and are
likely to improve Gentry indigo bush habitat, as discussed above. Many
activities are prohibited within the RNA; livestock grazing,
[[Page 56432]]
timber harvest, and overnight camping are examples. A mining withdrawal
has also been completed for lands within the RNA, for a period of 25
years. In addition to the Sonora chub, the canyon also supports
populations of the federally listed Chiricahua leopard frog (Rana
chiricahuensis) and Mexican spotted owl (Strix occidentalis lucida).
The surrounding watersheds are also under U.S. Forest Service
management. A multiple-use policy allows for grazing, recreation, and
other activities that may be affecting the habitat of Gentry indigo
bush. These issues were discussed under Factors A and C above.
In summary, the U.S. Forest Service has completed a number of
conservation actions in Sycamore Canyon that have improved habitat for
Gentry indigo bush. Road closures and the protection of riparian areas
at the canyon mouth have undoubtedly increased the overall health of
the riparian ecosystem in the canyon. We believe that U.S. Forest
Service actions and the amount of protection the canyon receives by
virtue of its wilderness and RNA designation will promote the long-term
conservation of Gentry indigo bush in Sycamore Canyon.
The Tohono O'odham Nation
The Tohono O'odham Nation has not drafted specific regulations to
address sensitive species on their sovereign lands. We have a Statement
of Relationship with the Nation, and provide technical assistance with
wildlife and plant issues at their request. The Nation is currently
working with us on allowing us access to the Baboquivari Mountains so
that we may assist them in survey and assessment of their Gentry indigo
bush populations.
Mexico
Three locations of Gentry indigo bush have been documented in
Mexico. We have basic information (e.g., plant community, associated
plant species, elevation, and substrate) and population estimates for
these sites. We are not aware of any protection for these areas, but
Van Devender observed during his 2005 survey work that the sites do not
have obvious direct threats. Furthermore, all of the sites are in
remote locations and in canyons with no livestock access (Van Devender
2005).
Factor E: Other Natural or Manmade Factors Affecting the Continued
Existence of the Species
The known extant Gentry indigo bush populations are small,
isolated, and threatened by unpredictable variation in demographic and
environmental characters (i.e. flooding). Genetic factors, such as
reduced genetic variation due to small population size, may also
contribute to this species' overall status. Inbreeding depression and
loss of genetic diversity may occur in small populations of less than a
few hundred individuals; such loss may reduce the fitness of
individuals and the ability of the population to adapt to change
(Frankel and Soule 1981). Both of these genetic considerations result
in an increased likelihood of extirpation (Lande and Barrowclough
1987). Climate change may influence precipitation patterns in ways that
could affect the long-term persistence of the metapopulations.
Flooding
The past movement of water and sediment in Sycamore Canyon has
affected the plants and their habitat. After the 1993 El Ni[ntilde]o
winter rains, most of the monitoring plot was washed away, and the
then-known overall plant population declined dramatically, with more
than 90 percent of the known individuals washed away or covered with
sediment. Recolonization has slowly occurred; at last count there were
450 to 922 plants recorded in Sycamore Canyon (Darling 2005), fewer
than the estimated 1,400 that were documented in 1992.
Lefevre, a U.S. Forest Service hydrologist (1999), notes that the
changes observed in Sycamore Canyon after the 1993 flood were, in his
professional opinion, geologic in nature. Large flood events (e.g.,
greater than the 25-year event) and their effects on channel morphology
will likely overshadow any management activity of the U.S. Forest
Service.
In summary, above-average flood events (greater than the 25-year
event) will likely affect the dynamics of the metapopulation in
Sycamore Canyon, but U.S. Forest Service actions are not likely to
influence or minimize the effects from such events. The species does
have the ability to recolonize after flood events, and plants located
out of the floodplain and on associated talus slopes (i.e., the sides
of the canyon) may provide the source for the recolonization of the
plants in stream habitat.
Population Size and Stochastic Events
Estimated numbers of the metapopulation in Sycamore Canyon have
fluctuated dramatically since the early 1990s. The sub-populations had
seemingly been reduced to very low numbers in 1993, after the canyon
was subjected to a large flood event. Since that time, overall numbers
and patches have been increasing. In 2005, we observed many seedlings
and resprouts, alleviating some of our concern regarding the plant's
seemingly low reproductive output. We still do not know the
environmental factors that allow for successful seed germination, and
do not know how many seedlings will survive. We observed no seedlings
away from patches, although some patches contained only a few larger
plants and were dominated by seedlings.
This species could potentially be negatively affected by
environmental stochasticity (variations over time in the population's
operational environment) and natural catastrophes (Menges 1991). The
minimum viable metapopulation (MVM) size is an important estimate of
the minimum number of interacting local sub-populations necessary for
the long-term persistence of a metapopulation (Hanski 1999). In
general, 15 `` 20 well-connected patches are required for MVM
(Maschinski, in press). Baker (2005) found 12 patches in Sycamore
Canyon, but that is only an estimate from one of the five known
populations. There were likely more patches than he detected. More
consistent monitoring could help us determine the patch dynamics of
Gentry indigo bush more accurately. A decrease in the overall number
and size of patches, and a lack of recolonization of extirpated
patches, could indicate that the metapopulation is not at equilibrium.
The most likely adverse scenario in Sycamore Canyon is that of
catastrophic flooding. Increased rainfall combined with an altered
hydrograph in Sycamore Canyon may result in many patches being washed
out. Long-term drought, such as the one the region is experiencing
currently, may affect the species' ability to recolonize vacant
patches. In Sycamore Canyon, the combination of small patch size,
uncertain persistence of the patches, highly variable overall number of
patches, and a highly dynamic and uncertain environment due to flooding
and drought could make this population vulnerable to extirpation,
although it has continued to persist despite such climatic events.
The species is located in at least five locations, reducing the
risk of stochastic events affecting all of the known populations
simultaneously. The population in Sycamore Canyon, despite a severe
reduction in overall numbers, still persists and is recolonizing the
canyon. Recent observations of seedling recruitment and resprouting
indicate that the metapopulation can recover from
[[Page 56433]]
environmental stochastic events. Given the population's persistence in
Sycamore Canyon, we do not believe that its continued existence is
threatened now or in the foreseeable future.
Genetic Factors
Harmful genetic effects, such as genetic bottlenecks and founder
effects, are often associated with small plant populations (Hedrick and
Miller 1992). A genetic bottleneck is a significant reduction in the
genetic diversity of a population resulting from a significant
reduction of the number of individuals of a species in a specific place
or time. It is often associated with a stochastic event and can result
in a loss of genetic diversity. The founder effect (Mayr 1963) refers
to the establishment of a new population from only a few colonizing
individuals, which may represent only a small portion of the overall
genetic variation of the original population. Reductions in genetic
diversity from these and other causes can have profound effects on both
short- and long-term population survival, as genetic variation is
related to a population's ability to survive stochastic events
(Huenneke 1991; Rogers and Montalvo 2004; Falk et al. in press). In
Sycamore Canyon, the small number of individuals, small size of the
metapopulation, and the type and severity of environmental factors to
which the metapopulation is exposed could influence the genetic
diversity of the metapopulation.
The ability of a species to persist over time is related, in part,
to genetic variation in a population, which provides the basis of
adaptation to changing environments. The greater the heterozygosity
(number of different types of alleles) present, the higher the
probability that at least some plants in a population will be able to
adapt to changing circumstances (Huenneke 1991; Reed and Frankham
2003). As populations become depauperate (less variation) in their
genetic make-up, the ability of the populations to adapt to changing
environmental factors, like climate change or changes in the local
environment, may decrease.
The long-term persistence of a population is also related to the
fitness of the individuals within the population, where fitness is
typically measured in terms of survival and reproduction. Inbreeding
depression is a relative decrease in fitness of offspring resulting
from either selfing (pollination within the same plant as opposed to
between two different plants) or mating between closely-related
individuals compared with outcrossed individuals (Barrett and Kohn
1991). The reduction in fitness is associated with a higher rate of
expression of recessive and often lethal alleles (parts of genes that
control certain characters, i.e., flower color) in a population. This
condition leads to an overall reduction of fitness in a population
until the population cannot produce viable offspring. We do not know if
this is a factor for Gentry indigo bush because we have not identified
the type of breeding system (e.g., obligate outcrosser, selfing, or
combination). Thus, we have no information to indicate that genetic
factors and small population size are a threat to Gentry indigo bush
now or in the foreseeable future. Further, we have no documentation
that this species historically persisted in significantly higher
numbers than it does today, so its rarity is not necessarily an
indication of excessive vulnerability to extinction.
Climate Change
Mean annual temperatures rose 1.1-1.7 degrees Celsius (C) (2.0-3.1
degrees Fahrenheit (F)) in the American Southwest in the 20th century,
and are predicted to rise 4.5-6.1 degrees C (8.1-11.0 degrees F) in the
21st century. Predictions of changes in precipitation are less certain;
however, some models predict as much as a doubling of annual
precipitation, with the largest increases in winter precipitation
(Southwest Regional Assessment Group 2000). But these predictions
contrast with current trends of a warming North Atlantic and cooling
tropical Pacific, with associated changes from a relatively wet period
to drought, insect outbreaks in Southwestern forests, and increasing
wildfires (Patterson 1997; Betancourt 2004). Some models predict
dramatic changes in Southwestern vegetation communities as a result of
climate change (Thompson et al. 1997). Climate change can occur
abruptly, with associated major changes in the environment (National
Academy of Sciences, Committee on Abrupt Climate Change 2002). Climate
change could affect metapopulations of Gentry indigo bush in
unpredictable ways. For example, changes in precipitation may increase
the frequency and magnitude of flood events, possibly affecting the
distribution and persistence of patches in occupied habitat. Rainfall
patterns may shift towards more summer precipitation and less winter
precipitation. The germination of seeds may be linked to seasonal
rainfall events, and changes in rainfall patterns may affect the
population dynamics of this species. We have no information to indicate
that climate change constitutes a threat to Gentry indigo bush now or
in the foreseeable future.
In summary, Gentry indigo bush remains a rare, narrowly distributed
endemic plant species throughout its range in southern Arizona and in
Mexico. Extensive survey work in the United States and Mexico has
increased the documentation of populations by one and reconfirmed the
existence of two populations in Mexico. In total, there are
approximately 1,400 individuals, distributed among 5 sites. There are 2
confirmed populations in the United States, containing over 66 percent
of the known individuals. At this time, the majority of Gentry indigo
bush in the United States is located within Sycamore Canyon; we do not
have an accurate assessment of the numbers of Gentry indigo bush on the
Tohono O'odham Nation. We have no information indicating that
populations in Mexico or on the Tohono O'odham Nation are experiencing
any direct threats. The populations, based on observations of the
Sycamore Canyon metapopulation, have the ability to recover from floods
and drought. We have seen seedlings and plants resprout, alleviating
our concern regarding the plant's ability to reproduce and recover from
flood events and sediment deposition. Threats to the Sycamore Canyon
population have been minimized by U.S. Forest Service actions, and
ongoing activities are not immediately threatening the population.
Finding
We have carefully assessed the best scientific and commercial
information available regarding past, present, and future threats faced
by the species. We reviewed the petition, available published and
unpublished scientific and commercial information, and information
submitted to us during the public comment periods on our 90-day
finding. This finding reflects and incorporates information we received
during the public comment periods. We also consulted with recognized
plant experts, including those most familiar with this species, and
other Federal resource agencies. On the basis of our review, we find
that the petitioned action of listing the Gentry indigo bush is not
warranted.
In making this finding, we recognize that one historical population
in the United States has been extirpated and is presumed lost. We also
recognize that populations are still present on the Tohono O'odham
Nation, but that those populations are under the management of a
sovereign nation and subject to their laws. The same is true for
populations in Sonora, Mexico. There are ongoing
[[Page 56434]]
activities and natural events that may be affecting the habitat and
reestablishment of the species. Other threats, like undocumented
immigrant traffic, are larger than one agency's jurisdiction. However,
we believe that existing regulatory mechanisms are sufficient to
protect the species. The overall existing management of the U.S. Forest
Service is protecting much of the habitat in Sycamore Canyon. We also
acknowledge that, due to small population size, demographic or genetic
factors may apply to each of the locations in Arizona and Sonora,
Mexico, but we have no genetic information to determine whether this is
indeed the case.
We conclude that the Gentry indigo bush does not warrant listing at
this time. In order to make a warranted finding, the species must, at a
minimum, meet the definition of a threatened species. In accordance
with section 3(19) of the Act, a threatened species is one which is
likely to become endangered within the foreseeable future throughout
all or a significant portion of its range. Based on all the information
we have gathered and reviewed, we do not conclude this to be the case
for the following reasons.
Populations have persisted in all but one of the known locations
over time. A new population was located in Mexico and offers hope that
there may be more populations located with additional surveys. Areas
that were previously overlooked as suitable habitat outside of the
floodplain appear to support Gentry indigo bush. Thus, populations may
not be as vulnerable to extirpation from flood events as previously
thought since the species does have the ability to recolonize after
flood events, and plants located out of the floodplain and on the sides
of the canyon could provide a source for the recolonization of plants
in stream habitat. The largest known population occurs in Sycamore
Canyon within the Goodding RNA, where mining, roads, and grazing are
prohibited and where the U.S. Forest Service has completed a number of
conservation actions that have improved the habitat for Gentry indigo
bush. Additionally, as noted above, the actions of the U.S. Forest
Service and the protection that the canyon receives by virtue of its
wilderness and RNA designations will continue to provide for the long-
term conservation of Gentry indigo bush in Sycamore Canyon. The
metapopulation in Sycamore Canyon has persisted through some dramatic
environmental events, and its numbers have increased; thus, we believe
it will continue to persist into the future. Other factors (e.g.,
watershed degradation, invasive species, undocumented immigrant and
U.S. Border Patrol activities, recreation, fire, climate change, and
genetic factors associated with small population size) discussed above
have not been documented as more than low magnitude or potential
threats, and therefore it is not reasonably foreseeable that these
factors pose threats over a significant portion of the species' range.
We anticipate that we will have the opportunity to work cooperatively
with the Tohono O'odham Nation, as we have in the past, to census their
populations and address potential concerns, if necessary. We also plan
to emphasize the need for and participation in future monitoring
efforts, surveys, and genetic studies.
The Service does not believe the Gentry indigo bush is likely to
become a threatened species throughout either all or a significant
portion of its range in the foreseeable future. The only population for
which we have a thorough threats assessment is the one on U.S. Forest
Service land in Sycamore Canyon. While the Sycamore Canyon population
is not entirely devoid of potential threats, we believe that U.S.
Forest Service management (e.g., RNA and Wilderness designations,
exclusion of both domestic and Mexican cattle from the habitat)
sufficiently ameliorates human-influenced threats, while its
persistence over time through droughts and floods, and its discovery
outside the floodplain, render it unlikely to be extirpated from the
canyon as a result of natural factors.
Threats facing the other populations are less well known. Three
populations are known from Mexico. One population in Mexico has been
present since its original discovery in 1995, another one was relocated
in 2005 after it was initially detected in 2004, and the remaining
population was only detected in 2005. Based on this information, two of
the populations are known to have persisted. In addition, according to
information received during the public comment period, the Mexico
populations are in areas not accessible to cattle. We can verify that
plants still exist on the Tohono O'odham Nation. The fact that the
Mexican and Tohono O'odham Nation populations have persisted under
current management and through various climatic conditions provides
evidence that whatever threats may exist, if any, are not significant.
In summary, we have no evidence to indicate that any portion, let alone
a significant portion, of the species' range is threatened to the
extent that listing under the Act is warranted.
We will continue to monitor the status of this species and will
accept additional information and comments at any time from all
concerned governmental agencies, the scientific community, industry,
and any other interested party concerning this finding. This
information will help us monitor and encourage beneficial measures for
this species.
References Cited
A complete list of all references cited herein is available upon
request from the Field Supervisor at the Arizona Ecological Services
Office (see ADDRESSES section).
Author
The primary author of this document is the Arizona Ecological
Services Office (see ADDRESSES section).
Authority: The authority for this action is the Endangered
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).
Dated: September 14, 2005.
Marshall Jones,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. 05-18881 Filed 9-26-05; 8:45 am]
BILLING CODE 4310-55-P