California buttercup (Ranunculus californicus) recovery strategy: threats

• Table of contents

4. Threats

4.1. Threat Assessment

1 Level of Concern: signifies that managing the threat is of (high, medium or low) concern for the recovery of the species, consistent with the population and distribution objectives. This criterion considers the assessment of all the information in the table).

2 Severity: reflects the population-level effect (High: very large population-level effect, Moderate, Low, Unknown).

3 Causal certainty: reflects the degree of evidence that is known for the threat (High: available evidence strongly links the threat to stresses on population viability; Medium: there is a correlation between the threat and population viability e.g., expert opinion; Low: the threat is assumed or plausible).

4.2. Description of Threats

4.2.1. Alien, invasive or introduced species

One of the most serious and immediate threats to California Buttercup (Table 3) is posed by the encroachment of invasive alien plants (Fairbarns 2010). A large number of invasive alien plant species have encroached into habitats necessary for the survival and recovery of California Buttercup. The most serious invasive shrubs are Scotch Broom (Cytisus scoparius), and Himalayan Blackberry (Rubus armeniacus). Problematic invasive medium-height and tall grasses include Sweet Vernal Grass (Anthoxanthum odoratum), Barren Brome (Bromus sterilis), and Common Velvetgrass (Holcus lanatus). Frequently occurring, low-growing invasive grasses include Cheatgrass (Bromus tectorum), Ripgut Brome (Bromus rigidus), Canada Bluegrass (Poa compressa), and Kentucky Bluegrass (Poa pratensis). Common medium-height and tall invasive forbs include Bull Thistle (Cirsium vulgare), and Sow Thistle (Sonchus oleraceus). Low growing invasive forbs include Stork’s-bill (Erodium cicutarium), Dovefoot Geranium (Geranium molle), Hairy Cat’s-ear (Hypochaeris radicata), Ribwort Plantain (Plantago lanceolata), Sheep Sorrel (Rumex acetosella), Dandelion (Taraxacum officinale), Little Vetch (Vicia hirsuta), and Common Vetch (Vicia sativa). One invasive vine, English Ivy (Hedera helix), forms a dense, spreading mat in some habitat favoured by California Buttercup (Fairbarns 2010).

Invasive alien plants impede the survival and recovery of California Buttercup through suppression, competition, and pre-emption of space. Suppression occurs when shrubs and medium to tall grasses and forbs reduce the amount of light reaching the leaves of California Buttercup, thereby reducing its ability to produce food. Competition occurs when the roots of invasive alien plants capture moisture and nutrients and thereby reduce the availability of these resources to California Buttercup. The availability of safe germination sites suited to California Buttercup is directly reduced when invasive alien plants (particularly perennial rosette and mat-forming species) pre-empt space. The availability of safe germination sites may also be indirectly reduced by alien species when the litter they produce creates an impenetrable thatch (Fairbarns 2010).

Many alien grasses and forbs are successful invaders because they produce abundant seed and thereby saturate germination sites in their vicinity, to the detriment of native species (Fairbarns 2010). This facility is of particular concern in areas where suitable germination sites develop as the result of meso scale (> 50 cm diameter) disturbances and is discussed in the subsequent discussion of changes in ecological dynamics or natural processes. As invasive alien plants are widespread, compete directly with California Buttercup, and can potentially alter the habitat, this threat is of high concern.

4.2.2. Changes in ecological dynamics or natural processes

Encroachment by native herbaceous and woody plant species, may impede the survival and recovery of California Buttercup through suppression (shading out the buttercups), competition (for moisture, nutrients and other shared resources), and the pre-emption of space just as do invasive species. The persistence of California Buttercup, however, indicates that a balance once existed between it and other native plants. Historically, First Nations in the area used fire to stimulate the growth of food species and possibly to improve forage for game species (e.g., elk and deer) (Turner 1999; Gedalof et al. 2006). The cessation of First Nations burning may have decreased the supply of suitable habitat for California Buttercup germination and growth. Fire effects change in a wide variety of habitat characteristics including the amount of organic matter, nutrient cycling, soil moisture, and soil biota (Barbour et al. 1999). Fire suppression has allowed fire-intolerant native woody trees such as Red Alder (Alnus rubra), Trembling Aspen (Populus tremuloides) and Douglas-fir (Pseudotsuga menziesii)^[1] to expand into areas where they were previously excluded. Similarly, native shrubs such as Common Snowberry (Symphoricarpos albus) and Nootka Rose (Rosa nutkana) have benefitted from fire suppression^[2]. Native woody species have reduced the amount of light reaching the herb layer where California Buttercup grows, and also compete for moisture and nutrients as well as changing the physical properties of the soil (Broersma 1973). Some of the islands where California Buttercup occurs show signs of forest encroachment, as evidenced by the juxtaposition of abundant small Douglas-firs with the scarcity of older trees. Even the Trial Islands, which show no signs of tree encroachment, have extensive shrub thickets on sites which were likely burned regularly in order to maintain an easily accessed camas (Camassia spp.) crop^[3] (COSEWIC 2008). Consequently, encroachment by native plants through ecological succession is considered a high level of concern.

Hybridization with Western Buttercup is known to occur, producing less fertile intergrades of California Buttercup and Western Buttercup, however, no molecular studies of Canadian populations of California Buttercup have been conducted (Brayshaw 1989; Wilken 1993). Brayshaw (1989) indicates that while there is strong introgression with Western Buttercup, the hybrid plants have less chance of producing viable seeds. California Buttercup is not overwhelmed by Western Buttercup, but rather the two seem to be in balance, perhaps because the site conditions favour California Buttercup close to the ocean where salt spray is a factor. While artificial hybrids can occur in habitats occupied by these two species, further taxonomic and molecular studies are needed to confirm evidence of a threat to California Buttercup survival. Consequently, hybridization frequency and severity are unknown and therefore represent an unknown or low level of concern at this time.

4.2.3. Disturbance or harm

Recreational activities, such as camping, hiking and picnicking, is of medium concern for the Discovery Island population where areas are formally designated for recreational activities. The populations on Alpha Islet and Griffin Island and much of the Trial Islands occur within Provincial Ecological Reserves where visitor use is discouraged. Signs are posted at the aforementioned Ecological Reserves either prohibiting access or encouraging visitors to remain on existing trails. However, visitors do not always comply with prohibitions. In addition, these locations are difficult to access for regular patrols by B.C. Parks to ensure compliance from visitors and boaters. Similarly, the California Buttercup population on West Chatham Island occurs on an Indian Reserve and, while visitors are prohibited from visiting the reserve without permission, compliance is not always followed.

The pressures of recreational use are greatest on the Discovery Island Marine Provincial Park, where the population of California Buttercup extends into a campground. In the past, California Buttercup plants have been disturbed by mowing to create a low turf where tents may be easily erected. Although this no longer occurs, current camper activities do continue to trample plants in the area. Mowing, camping and trampling are activities that can cause physiological stress, damage to individuals, and reduced reproduction and fitness (COSEWIC 2008). Elsewhere on Discovery Island, the population is bisected by walking trails which continue to lead to soil compaction and serve as conduits for the introduction of invasive plants.

There is much less recreational use on the Trial Islands, Alpha Islet, Griffin Island, and West Chatham Islands; campers rarely, if ever, set tents up on these locations. There are numerous well-defined walking trails on the main Trial Island while the other islands and islets receive light recreational use.

In the past, livestock grazing and trampling occurred on portions of the Discovery Island, Griffin Island, Alpha Islet, and the Trial Islands now occupied by California Buttercup. When grazing and trampling occurred on these islands it likely had a negative impact on the California Buttercup populations, but this threat disappeared with the removal of livestock and they are unlikely to be re-introduced to any of these sites. Nevertheless, it is likely that the areas that were most heavily grazed (especially Discovery Island) are no longer able to support California Buttercup as they have been so heavily modified by the introduction of agronomic grasses.

It is not clear what grazing and trampling pressures affect the potential Saturna Island population but nearby meadow areas have been heavily altered by livestock, most notably feral goats. As the current threat of grazing and trampling may only occur at a single potential population, this threat is considered a low level of concern.

4.2.4. Habitat loss or degradation

Habitat conversion appears to present a moderate level of threat to the habitat of extant populations of California Buttercup. The locations supporting California Buttercup in Canada have potential for further habitat loss and degradation due to a range of potential activities such as habitat conversion (i.e., residential development, development and maintenance or modification of existing structures), industrial and commercial activities such as excavation, and potential impacts from ongoing use and operation of existing facilities. If habitat conversion does occur it can disrupt life cycle processes and cause physiological stress to the plant populations. This threat is a medium level of concern.

5. Population and Distribution Objectives

In Canada, California Buttercup is found in maritime meadow habitats associated with Garry Oak ecosystems and as such had a naturally, highly restricted range. Within this range, significant habitat loss since European settlement (Lea 2006) has likely resulted in population reductions. Encroachment of vegetation and effects resulting from recreational activities continue to exacerbate the situation (COSEWIC 2008). There are currently four confirmed California Buttercup populations in Canada (COSEWIC 2008, Fairbarns 2010).

In general, it is believed that multiple populations and thousands of individuals are likely required to attain a high probability of long-term persistence for a species (Reed 2005; Brook et al. 2006; and Traill et al. 2009). In an analysis of several published estimates of minimum viable population (MVP) sizes, Traill et al. (2007) found that the median population size required for plants to achieve a 99% probability of persistence over 40 generations was approximately 4,800 individuals (but see Flather et al. 2011; Garnett and Zander 2011; and Jamieson and Allendorf 2012 for critical evaluations of the analyses and the applicability of the results). Such information provides a useful guide, but developing specific quantitative and feasible objectives must consider more than just generalized population viability estimates, including the historic number of populations and individuals, the carrying capacity of extant (and potential) sites, the needs of other species at risk that share the same habitat, and whether it is possible to establish and augment populations of the species (Parks Canada Agency 2006; Flather et al. 2011; Jamieson and Allendorf 2012). Because not enough of this information is available for California Buttercup, it is currently not possible to determine to what extent recovery is feasible and therefore it is not possible to establish quantitative long-term objectives. Recovery planning approaches (see Section 6) are designed to respond to knowledge gaps so that long-term, feasible, and quantitative recovery objectives regarding size and number of populations can be set in the future. At this time it is possible to set short-term objectives that focus on maintaining the four confirmed extant populations and preventing a decline in distribution while exploring the feasibility of establishing and/or augmenting populations to increase abundance and distribution:

Objective 1: Maintain the four confirmed extant populations (1-4 in Table 2) of California Buttercup.

Objective 2: Prevent a decline from the 2008 distribution^[4] of California Buttercup in Canada.

Objective 3: Establish and/or augment populations to increase abundance and distribution^[5] if determined to be feasible and biologically appropriate for California Buttercup.

6. Broad Strategies and General Approaches to Meet Objectives

Broad strategies and approaches to meet the population and distribution objectives for California Buttercup include:

• Stewardship: foster landowner understanding , appreciation, and involvement in work towards the survival and recovery of California Buttercup;
• Habitat and species protection: protect populations and habitat from destruction (e.g., from land conversion) by developing mechanisms/instruments for protection;
• Public education and outreach: increase public awareness of the species, its needs and conservation value;
• Population monitoring: gather information to make decisions and fill knowledge gaps pertaining to species distribution, population dynamics, and population trends;
• Population restoration: restore extant populations and establish new population(s) to recover the Canadian population of the species;

Population research: address critical knowledge gaps;

6.1. Strategic Direction for Recovery

6.2. Narrative to Support the Recovery Planning Table

Protecting and maintaining habitat at the known sites supporting California Buttercup is essential to its recovery in Canada (Table 4). The successful implementation of habitat protection initiatives and stewardship plans relies upon establishing strong relationships with land owners, land managers, and recreational land users. The threat of most concern is encroachment of invasive alien plants and woody shade plants into California Buttercup habitat. Continued maintenance by land managers is important in order to mitigate key threats such as native and non-native plant encroachment and the effects of ongoing fire suppression. Collaboration between government, land managers, environmental groups and others is key to recovery of California Buttercup populations. An effective monitoring program is also essential to evaluate the success of site protection and stewardship measures.

It will be important to develop population augmentation techniques for California Buttercup to improve the long-term viability of this species in Canada by reducing the risks associated with stochastic events or other potential impacts to an extant population. Identifying additional habitat for the establishment of an experimental population may also provide a range of benefits as workers test habitat suitability models, propagation methods, and conduct monitoring that will provide opportunities for further insights into the species’ life history. New populations are unlikely to become established without human intervention, even if suitable habitat is available. Development of any experimental populations will require the development of a translocation plan and its careful implementation in a precautionary, adaptive management framework. There are also risks associated with translocations which must be accompanied by a program to monitor not only the success of translocations, but the impacts of translocation on non-target species, communities, and ecological processes. Suitable habitat may also require additional stewardship and management actions (e.g., invasive alien species control) prior to establishing new populations of California Buttercup.

Site protection and stewardship will not, by themselves, guarantee the persistence of existing populations: due to their small size some populations may require augmentation. A population may also collapse as the result of other factors, not all of them predictable. Demographic studies will help identify whether populations are inherently self-sustaining and may indicate which life stages are most at risk.

7. Critical Habitat

Areas of critical habitat for California Buttercup are identified in this recovery strategy. Critical habitat is defined in the Species at Risk Act as “...habitat that is necessary for the survival or recovery of a listed wildlife species and that is identified as the species’ critical habitat in the recovery strategy or in an action plan for the species” (Subsection 2(1)). Habitat for a terrestrial wildlife species is defined in the Species at Risk Act as “…the area or type of site where an individual or wildlife species naturally occurs or depends on directly or indirectly in order to carry out its life processes or formerly occurred and has the potential to be reintroduced” (Subsection 2(1)).

7.1. Identification of the Species’ Critical Habitat

Critical habitat for California Buttercup is identified in this recovery strategy to the extent possible based on best available information. It is recognized that the critical habitat identified below is insufficient to achieve the population and distribution objectives. Critical habitat has been fully identified for three of four known populations (at five locations listed in Table 2: Trial Island, Lesser Trial Island, Discovery Island, Alpha Islet, and Griffin Island), further study is required (see below) in order to identify critical habitat for the West Chatham Island population. The schedule of studies section (Section 7.2; Table 5) outlines activities required to identify additional critical habitat necessary to support the population and distribution objectives of the species.

Attributes of critical habitat follow; the critical habitat attributes below cover the range of attributes found at studied sites and may not reflect attributes at new or unstudied sites:

• Sunny areas with short or sparse vegetation (trees are absent and the cover of shrubs is never substantial).
• Elevations between 0 to 20 m above sea level.
• Terraces and low slopes (0-10%).
• Shallow soils (< 5 cm organic surface layer) over bedrock with very small amounts of exposed mineral soil and fine litter.
• Moderately well drained soil that is moist early in the growing season (October to March) with water deficits by early summer.

The habitat of California Buttercup in Canada generally occurs in coastal meadows on small islands and islets along the southeast coast of Vancouver Island in Garry Oak and associated ecosystems. The habitat is characterized as open areas without tall vegetation, reliant on seasonal seepage, and have thin soils stressed by summer droughts (COSEWIC 2008). Field investigations at Trial Island, Lesser Trial Island, Discovery Island, Alpha Islet, and Griffin Island were used to further characterize the habitat of California Buttercup (Fairbarns 2010).

The California Buttercup depends directly on canopy openings to provide certain habitat attributes. Although California Buttercup plants have been found growing in shaded areas (one subpopulation on Discovery Island) these are not optimum growing conditions for California Buttercup. Minimum canopy openings must be large enough that California Buttercup plants are not sheltered by surrounding vegetation, nor smothered by fallen trees. When tall vegetation falls it will cover an area of ground for a distance equal to its height. The minimum size of openings can be determined based on the height of vegetation able to grow in the area and cast shade or smother the California Buttercup (Spittlehouse et al. 2004). The presence of surrounding vegetation (e.g., trees and shrubs) within these canopy openings will also compete with California Buttercup for water and nutrients.

California Buttercup is a conspicuous perennial plant but, as is the case with many species, it may not produce flowers every year. In non-flowering years it is essentially indistinguishable from the closely related Western Buttercup, which is a widespread and abundant species of similar habitats on southeastern Vancouver Island. Consequently, only flowering plants surveyed in 2010 could be identified as California Buttercup and used to identify critical habitat. Since species identification is difficult, known California Buttercup plant locations require further surveys to ensure the entire population is captured.

Within the geographical boundaries identified in Figure 4 and Figure 5, critical habitat required for the survival of each California Buttercup patch^[6] is the minimum canopy openings supporting the plants and was mapped by Fairbarns (2010).

At West Chatham Island, no recent surveys have been conducted to confirm the presence of suitable habitat or plants in over five years so data is currently unavailable upon which to define critical habitat.

The known critical habitat for the two subpopulations, occurring within the two parcels, is approximately 0.3 ha.

Figure 5. Areas (~26ha) within which critical habitat for California Buttercup is found on Discovery Island (within Discovery Island Marine Provincial Park), Alpha Islet and Griffin Island (within Oak Bay Islands Provincial Ecological Reserve).

7.2. Schedule of Studies to Identify Critical Habitat

7.3. Activities Likely to Result in the Destruction of Critical Habitat

Examples of activities likely to destroy critical habitat are provided below, but are not limited to those in Table 6. Destruction of critical habitat will result if any part of the critical habitat is degraded, either permanently or temporarily, such that it would not serve its function when needed by the species. Destruction may result from single or multiple activities at one point in time or from the cumulative effects of one or more activities over time.

8. Measuring Progress

The performance indicators presented below provide a way to define and measure progress toward achieving the population and distribution objectives. Progress towards recovering California Buttercup in Canada will be assessed using the following measures:

Objective 1: Maintain the four confirmed extant populations (1-4 in Table 2) of California Buttercup.

• By 2017 best management practices are developed and implemented at two or more sites.
• The populations remain extant.
• By 2022, all populations show a stable or increasing trend in population size.

Objective 2: Prevent a decline from the 2008 distribution of California Buttercup in Canada.

• There is no decrease in the known distribution (extent of occurrence and area of occupancy) of California Buttercup in Canada.

Objective 3: Establish and/or augment populations to increase abundance and distribution if determined to be feasible and biologically appropriate for California Buttercup.

• By 2017, additional sites have been identified for establishment or restoration of California Buttercup population(s).
• By 2017, propagation techniques have been developed.
• By 2022, one or more (re)introduction or augmentation experiments are underway at suitable site(s).

9. Statement on Action Plans

One or more action plans will be completed by 2018.

10. References

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Brayshaw, T.C. 1989. Buttercups, waterlilies, and their relatives (the Order Ranales) in British Columbia, Victoria. Royal British Columbia Museum Memoir 1. Royal British Columbia Museum, Victoria, British Columbia.

Broersma, K. 1973. Dark soils of the Victoria area, British Columbia. M.Sc. Thesis. Department of Soil Science, University of British Columbia. Vancouver, B.C. 110 pp.

Brook, B.W., L.W. Traill, and J.A. Bradshaw. 2006. Minimum viable population sizes and global extinction risk are unrelated. Ecology Letters 9:375-382.

COSEWIC. 2008. COSEWIC assessment and status report on the California Buttercup Ranunculus californicus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 24 pp.

COSEWIC. 2010. COSEWIC's Assessment Process and Criteria. Committee on the Status of Endangered Wildlife in Canada, Ottawa. 19 pp.Web site: http://www.cosewic.gc.ca/pdf/assessment_process_e.pdf [accessed February 2012].

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Fairbarns, M. 2010. Towards a recovery strategy for the California Buttercup (Ranunculus californicus) in Canada. Parks Canada Agency, Victoria, B.C. v + 28 pp.

Garnett, S.T., and K.K. Zander. 2011. Minimum viable population limitations ignore evolutionary history. Trends in Ecology and Evolution 26(12): 618-619.

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Lea, T. 2006. Historical Garry Oak Ecosystems of Vancouver Island, British Columbia, pre-European Contact to the Present. Davidsonia 17:34–50.

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Spittlehouse, D. L., R.S. Adams, and R.D. Winkler. 2004. Forest, edge and opening microclimate at Sicamous Creek: Research Report 24. British Columbia Ministry of Forests, Research Branch, Victoria, B.C. vii+ 43 pp. Web site: http://www.for.gov.bc.ca/hfd/pubs/Docs/Rr/Rr24.htm [accessed January 2013].

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Turner, N.J. 1999. “Time to burn:” Traditional use of fire to enhance resource production by aboriginal peoples in British Columbia. Pp 185-218. in R. Boyd (ed.). Indians, Fire and the Land in the Pacific Northwest, Oregon State University Press, Corvallis, OR.

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The majority of the proposed recovery activities will lead to better site protection, broader public appreciation of rare species, reduced human impacts and reduced pressure from non-native species. Accordingly, they will have positive effects on most non-target native species, natural communities and ecological processes. Recovery activities aimed to reduce the impacts associated with encroachment from native trees and shrubs (see section 4.2.2, Changes in ecological dynamics or natural processes), which have occurred as the result of fire suppression, will have negative impacts on the targeted woody species themselves as well as plant and animal species which rely upon them.

A number of species at risk and provincially rare species occur within or adjacent to populations of California Buttercup (Table 7). Most recovery activities proposed for California Buttercup can be expected to have a net positive effect on the habitat of these other non-target species and communities. Nevertheless, it is possible that specific management actions carried out during the course of California Buttercup recovery (e.g., weed removal, shrub clearing, population augmentation, and species translocations) could have unforeseen collateral impacts on co-occurring non-target species. While probably slight, the chances of negative impacts accruing due to recovery activities must be duly considered. One method of mitigating such negative effects is to monitor the results of California Buttercup management. In keeping with the principles of adaptive management, an important component of recovery action planning will be anticipating, monitoring and mitigating collateral impacts (both positive and negative) on non-target species, communities, and ecological processes.

[1] While mature Douglas-fir are quite tolerant of fire, young seedlings and saplings are not. Frequent burns, conducted in order to maintain the productivity of camas populations, would have prevented Douglas-firs from surviving long enough to become fire-tolerant.

[2] Common Snowberry and Nootka Rose can resprout from buried rhizomes after a fire destroys above-ground plant parts but frequent, regular burning will greatly reduce or eliminate them.

[3] Camas was historically managed for the growth as a traditional food crop among First Nations.

[4] Distribution is measured by the extent of occurrence (currently about 20km²) and area of occupancy (currently estimated at 2 ha; COSEWIC 2008). If new populations are discovered, these baseline figures should be updated as required.

[5] The intent is to increase the area of occupancy and maintain the extent of occurrence.

[6] Patch is a term used to refer to a single plant or group of several plants in close proximity. A specific mapping scale and minimum separation distance have not been used to quantitatively define a patch; the identification of patches is based on survey work performed by a biologist familiar with the species. Lacking any detailed information on seed bank extent, the seed bank is assumed to be included within each patch: the only information pertaining to the spatial extent of the California Buttercup seed bank is derived from the physical characteristics of the seeds, and dispersal distance is probably very limited (COSEWIC 2008).