|Applegate's milkvetch, Applegate's milk-vetch|
|Edward Guerrant, Ph.D.|
The following Participating Institutions are custodians for this species in the CPC National Collection:
Rae Selling Berry Seed Bank & Plant Conservation Programs
The conservation of Astragalus applegatei is fully sponsored.
Edward Guerrant, Ph.D. contributed to this Plant Profile.
In the mid-1980s, a significant portion of the largest remaining Applegate's milkvetch population was paved over to make way for an auto dealership and grocery store. Since the site, which was just outside Klamath Falls, Oregon, contained the largest remaining population, this destruction was especially detrimental to the future of this species. Even before this unfortunate event, however, Applegate's milkvetch had reached a critical point. Land development, noxious weed introduction, and the suppression of fires within its limited range had dramatically reduced suitable habitat. Consequently, Applegate's milkvetch is only found at three sites. Of the approximately 12,000 individuals that remain, nearly all are found at the one location outside of Klamath Falls.
While conservation efforts are underway, Applegate's milkvetch is still severely threatened. The Nature Conservancy purchased a portion of the land that contains the vital Klamath Falls population, but the remaining area is still at risk of development. Alarmingly, this protected population has decreased to fewer than 8,000 individuals. The other two locations are on public lands and are protected by its listing as Endangered by the Fish and Wildlife Service. Nevertheless, these two sites contain very few individuals, only 500 and 3, respectively. Due to these small population sizes, persistence is uncertain as these sites are especially susceptible to random disturbance and the lack of genetic variation may cause problems associated with inbreeding.
Applegate's milkvetch is distinguishable in mid-summer by its small, whitish flowers with purple tips. This plant is also unique because it is only found in flat, seasonally moist meadows and flood plains of the Lower Klamath Basin. The US Fish and Wildlife Service has developed a recovery plan that aims to increase the number of plants to six populations with a minimum of 4,500 plants each. At that point, Applegate's milkvetch will be considered for downlisting to threatened status.
Distribution & Occurrence
Flat, open, seasonally moist remnants of floodplain alkaline grassland of the Klamath Basin (Williams and Parenti 1991, USFWS 1997).
Habitat was historically characterized by sparse, native bunch grass and patches of bare soil (USFWS 1997).
Elevation 4,100 ft (1250 m).
|As of 1998: 3 populations:
One with 11,500 individuals (seven acres with the greatest number and density of plants is owned and managed by The Nature Conservancy, while the remainder is on private land).
Another with fewer than 500 individuals (owned and managed by the Oregon Department of Fish and Wildlife).
A third with only 3 plants (discovered in 1997) (USFWS 1998).
Conservation, Ecology & Research
The above ground portion of Astragalus applegatei dies back completely after flowering, then in the fall re-sprouts short (0.5-2 inch) stems bearing immature leaves. Reproduction is achieved exclusively by seeds. Bumblebees, butterflies and polylectic bees are the most likely pollinators (Gisler and Minke 1998 and USFWS 1998). Autogamy (self-pollination) is common in the Astragalus genus and is facilitated by simultaneous ripening of anthers and stigmas (Barneby 1964 in Gisler and Meinke 1998). Astragalus applegatei seeds that are produced by self-fertilization do not appear to have lower viability than those produced by outcrossing (Gisler and Meinke 1998). It is likely that autogamy is a vital life-history strategy for rare, locally endemic flora that might otherwise be especially vulnerable to inconsistent pollinators (Karron 1987 and Greer et al. 1995 in Gisler and Meinke 1998).
Flowering occurs in early June through August. Seeds show no specialized mechanisms for long distance dispersal. Species may have historically existed on bare patches of soil, possibly allowing for wind movement of seeds along soil surface. Present day dense coverage by introduced grasses and weeds likely reduces this wind caused movement (USFWS 1998).
Even though each fruit typically contains 8-10 ovules, production of greater than 3 (if any) seeds per pod is rare (USFWS 1997). Flowers attract a large variety of bees and other insects and equally low seed set has been documented among individuals grown under presumably optimum greenhouse conditions. It is therefore suspected that low seed set is due to genetic constraints as opposed to resource and/or pollinator limitations (Gisler and Meinke, 1998).
Difficulties with cultivation using conventional propagation techniques suggests that A. applegatei may have evolved a complex reliance on particular soil ecosystem properties (Gisler and Meinke 1998). Results from a soil symbiont study indicate that there may be a certain degree of specificity. Specificity between host and symbionts is generally thought to be uncommon, but in a recent study there was no evidence of symbiont root colonization with commercial mixtures of Rhizobium bacteria and VAM fungi. It is possible that the commercial inoculums contained nonviable propagules. Regardless of viability, this study showed the value of simply using field soils inoculums and has important restoration implications (Geisler and Meinke 1998).
In a recent study, Astragalus applegatei grown in native soil treated with fungicide were far less vigorous than in the untreated native soil, but performed better than when grown in soil inoculated with a commercial soil inoculum. Since the fungicide selectively removed VAM fungi, leaving Rhizobium to colonize in its absence, these results suggest that VAM fungi provide the majority of symbiont benefits. However, there may be a synergistic relationship between VAM fungi and Rhizobium, and the relative benefits from VAM fungi and Rhizobium cannot be definitively concluded (Gisler and Meinke 2001). Additional research on this subject is being conducted.
Commercial development on habitat of largest (and only genetically viable) population. Negotiations to lease the land from the owner were unsuccessful. The area is now an auto
Greenhouse experiments revealed that native soil inoculation was successful at facilitating abundant colonization of mycorrhizal fungi. Plants were grown in both non-inoculated and inoculated soil, and only those plants from the inoculation treatment survived (Barroetavena et al. 1998).
Growth and survival of individuals grown under greenhouse conditions in six experimental soil treatments were compared: 1) field soil from natural habitat, 2) field soil subjected to heat sterilization (control treatment), 3) field soil treated with fungicide, 4) commercial grade Rhizobium inoculum, 5) commercial grade mycorrhizal (VAM) inoculum, and 6) mixture of commercial grade Rhizobium + VAM inoculate. Plants were not fertilized. Results from the trials clearly indicate that A. applegatei grew best under the field soil treatment. Astragalus applegatei grown under the field soil treated with fungicide treatment performed slightly better than the control and commercial inoculum treatment, but not nearly as well as the untreated field soil treatment (Gisler and Meinke 2001).
Growth and survival of individuals grown with sterilized soil inoculated with a small amount of field soil were compared. Only one tablespoon of field soil was needed to promote healthy growth for each individual, posing little threat of depleting natural populations of their soil. Alternatively, a self-sustainable source of inoculum can be developed from a field soil inoculum starter in the greenhouse using other species of host plants (Gisler and Meinke 2001).
Germination trials at The Berry Botanic Garden. For scarified seeds, all treatments (Either 8 weeks cold stratification or no cold stratification and either constant 68F (20C) or alternating 50/68F (10/20 C) treatments yielded between 40 and 60 % germination (BBG File).
Grazing does occur at the Klamath Wildlife Area (Gisler and Meinke 1998).
Experimental prescribed burning, herbicide application, and mowing at site managed by The Nature Conservancy to examine the influence of invasive species on Astragalus applegatei populations (USFWS 1997)
Recovery plan finalized in 1998.
1,500 individuals were cultivated for introduction to the Klamath Wildlife Area. Seeds were collected from the Klamath Wildlife Area population being augmented. Despite consistently high (~ 90%) germination rates after scarification, the fungal root pathogen Fusarium oxysporum stunted growth and greatly reduced the number of plants available for outplanting. Fungicide, fertilization, and irrigation treatment failed to decrease infection. In all cases, only 12 and 14% of plants were usable, and even those plants available for outplanting were of questionable vigor. Of these plants, few survived one growing season (Gisler and Meinke 1998).
Monitoring at the site managed by The Nature Conservancy. At this site, recruitment is decreasing and seedlings have become rare within the macroplots that were established in 1988 for long term monitoring. This population initially showed an increase from 1988 to 1991, when it hit a high at nearly 30,000 estimated individuals. Since 1995, the population has been hovering at lowest record levels of abundance (between ~4,500 to ~10,000 individuals). Though poorly documented, distribution of Astragalus applegatei individuals outside the macroplot suggests that the population may be expanding westward. It is important to note that the suitability of habitat is this new area is questionable, and that slow dispersal rate may limit the extent of colonization (Borgias 2001).
Seed from one population is stored at The Berry Botanic Garden.
Study outcrossing rates, and relative fitness between individuals resulting from self- and cross-pollinated seeds (USFWS 1997).
Research impacts of competition from weeds and other plants. Explore whether the presence of other plants facilitate pollination by attracting pollinators or reduces pollination due to competition for pollinators (USFWS 1997).
Investigate the benefits of controlled burning (USFWS 1997).
Determine alkalinity tolerance, and to what degree soil specialization may prevent competitive exclusion by other less alkaline-tolerant native taxa (USFWS 1997).
Study salinity and hydrological tolerances (Borgias 2001).
Identify the abundance and geographic distribution of soil symbionts. In habitats lacking such symbionts, it may be possible to inoculate sites with field soil from natural populations to increase potential habitat for A. applegatei (Gisler and Meinke 2001).
Further research on the extent, impacts, and possible control of herbivory and predation (USFWS 1997).
Study age structure and levels of recruitment population dynamics in order to assess the long-term viability of population in terms of age/growth stage structure (USFWS 1997).
Monitor the westward expansion of A. applegatei at the site managed by The Nature Conservancy (TNC) population (Borgias 2001).
Determine the long term effect of quackgrass colonization on the TNC Astragalus applegatei population (Borgias 2001).
Investigate whether appropriate soil microfauna in field soil samples can survive dry frozen storage.
If techniques can be developed, collect and store field soil samples containing appropriate soil microflora to aid in population establishment or reintroduction.
Isely, D. 1998. Native and Naturalized Leguminosae (Fabaceae) of the United States (exclusive of Alaska and Hawaii). Salt Lake City, Utah: Monte L. Bean Life Science Museum, Brigham Young University.