Photo Credit: Mark Dodero, RECON
Goal: Maintain existing Shaw's agave occurrences to ensure multiple conserved occurrences with self sustaining populations to increase resilience to environmental and demographic stochasticity and improve chances of persistence over the long term (>100 years) in coastal bluff, coastal sage scrub, and Torrey pine forest vegetation communities.
Management units: 1, 6, 7
In 2021, inspect extant Shaw's agave occurrences on Conserved Lands (see occurrence table) using the regional rare plant IMG monitoring protocol to record abundance and collect habitat and threats covariate data to determine management needs.
| Action | Statement | Action status | Projects |
|---|---|---|---|
| IMP-1 | Based upon occurrence status and threats, determine management needs including whether routine management or more intensive management is warranted. | on hold | |
| IMP-2 | Submit project metadata, monitoring datasets and management recommendations to the MSP Web Portal. | on hold |
| Criteria | Deadline year |
|---|---|
| Surveys Completed in 2021 with Management Recommendations | 2021 |
| Threat Name | Threat Code |
|---|---|
| Human uses of the Preserves | HUMUSE |
| Invasive plants | INVPLA |
Management units: 1, 6, 7
Beginning in 2017, conduct routine management actions as identified through the IMG monitoring conducted in 2016 and 2021 at Shaw's agave occurrences on Conserved Lands (see occurrence table). Depending on the type and level of threat, management should be conducted as needed, not necessarily every year, and using BMPs with precautions to do no harm.
| Action | Statement | Action status | Projects |
|---|---|---|---|
| IMP-1 | Perform as needed routine management activities, such as protecting occurrences from disturbance through fencing and enforcement and controlling invasive non-native plant species =20% absolute cover. | available for implementation | |
| IMP-2 | Submit project metadata and management data to the MSP Web Portal. | available for implementation |
| Criteria | Deadline year |
|---|---|
| Routine Management Completed as Needed Based Upon Monitoring Recommendations | 2021 |
| Threat Name | Threat Code |
|---|---|
| Human uses of the Preserves | HUMUSE |
| Invasive plants | INVPLA |
|
Rare Plant Inspect and Manage Monitoring 2014-2026
From 2014-2026, a Management and Monitoring Strategic Plan (MSP Roadmap) monitoring objective for 30 rare plant species is to inspect occurrences to determine management needs. The inspect and manage (IMG) objective is implemented to document the status of rare plant occurrences and assess habitats and threats to develop specific management recommendations. IMG monitoring is implemented by a combination of land managers and contracted biologists in coordination with the SDMMP. Available rare plant data is posted below. New annual updates are typically posted in March. Based upon an evaluation of these data, a 2014-2026 monitoring schedule has been developed for the 30 rare plant species (attached below). Coordinating data collection across the region allows analyses of species and population trends over time and provides a better understanding of the association between habitat and threat covariates and population dynamics.
|
| File name | Lead Author | Year | Type |
|---|---|---|---|
| Management Strategic Plan (MSP) 2014 Monitoring Protocol for Rare Plant Occurrences on Conserved Lands in Western San Diego County | San Diego Management and Monitoring Program | 2014 | report |
| Management Strategic Plan (MSP) 2015 Monitoring Protocol for Rare Plant Occurrences on Conserved Lands in Western San Diego County | San Diego Management and Monitoring Program | 2015 | report |
| San Diego Rare Plant Monitoring Plan: Fiscal Year 2011 | Greer, Keith; McEachern, Kathryn; Tracey, Jeff | 2011 | report |
Occurs from San Diego County to approximately the 30th parallel in coastal Baja California, Mexico (near El Rosario) [1].
Native range restricted to a single natural occurrence in San Diego County at Border Field State Park in MU1 [1]. A second occurrence of partially native origin is found on the Point Loma Naval Base in MU1. There are 4 other transplanted occurrences in MUs 1 and 7.
None [2].
Restricted distribution, occurring only in maritime succulent scrub near coast [1]. Mean annual rainfall where found in California is 423 mm, falling mostly between October and April [3]. Mean annual maximum and minimum temperatures are 19 C and 13 C, respectively. Moderately cold sensitive, with damage starting at -5 degrees C and becoming extensive at -8 degrees C [4; cited in 1].
Perennial monocot in Agavaceae family [1]. The only natural occurrence in San Diego County was restricted to one genetic individual during the construction of the border fence. Chromosome number is 2n = 60 [5; cited in 1]. Low seedling recruitment and low viable seed production may impact genetic diversity [1].
A large shrub-like rosette-forming perennial monocot [1]. Occurrences differ considerably in growth form. Some consist entirely of individual rosettes, while others form groups of clones via suckering, or “budding†from the roots. Average age to flowering is 20-40 years [6]. Low proportion of reproductive individuals in the US in any given year is a factor of the minimal sexual reproduction and low seed set [1].
Flowers from February to May in California (as early as November in Baja California), but may take decades to do so. Monocarpic rosettes that die after flowering [1].
Capable of reproducing by suckering, but occurrences vary considerably with some consisting entirely of individual unbranched rosettes and others consisting of clumps or colonies of clones [1]. Sexual reproduction and seedling recruitment are low throughout its range. Belief that Shaw's agave may be shifting from an ancestral habit of bat-pollinated toward pollination by bees or other diurnal pollinators due to selection pressures [7]. Large bees and hummingbirds are probable pollinators as they are often seen visiting flowers, but empirical data to substantiate these claims are lacking [1]. Fruits and inflorescence stalks are persistent and seeds are shaken from the tall dry inflorescences by wind or other forces. Seedling recruitment in California occurrences is visibly low and viable seed production appears to be low in recent years for all occurrences. It is not documented whether this taxon is self-compatible and can set seed without pollen from another individual or genotype. Data is also lacking on compatibility between clone rosettes. Distances between occurrences are considerable in the northern range and may be impacting effective cross-pollination.
Physical loss of plants and habitat through human interference [1]. Unrestricted collecting and habitat alteration have significantly reduced occurrences and numbers [8]. Nonnative plant species may be negatively impacting seedling recruitment [Jon Rebman, pers. comm. 2007; cited in 1]. May be due to impacts of nonnative species on the local environment or to direct competition for resources. Depletion of unique genotypes may be the biggest threat to the long-term survival of this species [9].
Does well in cultivation, and is easily propagated clonally, with many rosettes surviving transplanting at reintroduction sites [10]. Recommendations for conserving Shaw's agave include: development of a binational conservation plan (and consideration of endangered species listing in both nations); implementing a monitoring program with standardized protocols; maintaining an exÂ-situ conservation seed collection; research into the causes of limited seed set and low seedling recruitment; a laboratory study on the genetic variation between all California and Baja California occurrences; an assessment of the genetic distance between Shaw's agave and its sister subspecies to the south; a survey of zones of potential interspecific hybridization; assessing occurrences in northern Baja California for long-term conservation; and developing a long-term cross-border conservation initiative [1].
[1]  Vanderplank, S. E. 2014. “A Conservation Plan for Agave Shawii.†Rancho Santa Ana Botanic Garden Occasional Publications 14.
[2] CNPS, Rare Plant Program. 2016. Inventory of Rare and Endangered Plants (online edition, v8-02). California Native Plant Society, Sacramento, CA. http://www.rareplants.cnps.org, accessed 25 August 2016.
[3] National Oceanic and Atmospheric. 2007. “National Weather Service, Imperial Beach Climate Data.†http://www.wrh.noaa.gov/sgx/climate/san-nrs.htm.
[4] Turner, R. M., J. E. Bowers, and T. L. Burgess. 1995. Sonoran Desert Plants: An Ecological Atlas. Tucson, Arizona: The University of Arizona Press.
[5] Lenz, L.W. 1959. “Chromosome Numbers of Some Western American Plants, I.†Aliso 2: 317–19.
[6] Gentry, H. S. 1978. “The Agaves of Baja California.†In Occasional Papers of the California Academy of Sciences, 130. San Francisco: California Academy of Sciences.
[7] Hogue, J. 1981. “Pollination Biology of Agave Utahensis Var. Nevadensis.†Claremont Graduate School, Claremont, California.
[8] Reveal, J. L., and W. C. Hodgson. 2003. “Agave.†In Flora of North America Editorial Committee, Eds. 1993+. Flora of North America North of Mexico. 12+ Vols, 26:455. New York, NY. http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=100796.
[9] Vanderplank, Sula E. 2012. “Conservation Plan for Shaw’s Agave (Agave Shawwii Subsp. Shawii) Agavaceae.†Rancho Santa Ana Botanic Garden Occasional Publications.
[10] San Diego Multiple Species Conservation Plan. 2006. California Coastal Sage and Chaparral (NA1201) 2001. MSCP Covered Species Prioritization For Task B of Local Assistance Grant #P0450009. http://www.dfg.ca.gov/habcon/nccp/pubs/mscpsppmonpriorities1-06.pdf.Pollination Biology 29: 50.