White meconella (Meconella oregana) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Meconella oregana requires the specialized habitat of open rocky or grassy sites that have early spring seepage but dry out in the summer (Douglas et al. 1999; NatureServe 2003). It is generally found at low elevations, below 300 m in the north and slightly higher in the south, on gradual to steep slopes (Flora of North America Editorial Committee [eds.] 1993+; Douglas et al. 1999; California Native Plant Society 2003;Washington Natural Heritage Program 2004).

In the southern United States the species is commonly found in association with bryophytes and lichens along with species of Dodecatheon, Plectritis, Ranunculaceae and Saxifagaceae (Ernst 1967). In Washington, Meconella oregana grows in mixed forest/grassland sites with Douglas fir, ponderosa pine, Garry oak and with shootingstar (Dodecatheon poeticum), woodland star (Lithophragma bulbiferum) and Douglas’ blue-eyed-grass (Sisyrinchium douglasii); see Rush et al. 1999; NatureServe 2003; Washington Natural Heritage Program 2004. The Flora of North America describes the habitat as part sun, and mentions “sandy bluffs” (Flora of North America Editorial Committee [eds.] 1993+).  However, Dr. Gary Hannan (pers. comm. 2004) states that seepage slopes are a more typical habitat.

Much of the above-mentioned habitats and even the species combinations coincide remarkably with those of the majority of the British Columbian populations. The sites surveyed in the spring of 2004 were generally in the close vicinity of seepage areas. However, the plants also occupied nearby well-drained micro-habitats. It is likely that the seepage areas themselves serve as habitat where this small annual can survive in exceptionally dry years. All visited subpopulations were on steep south to southwest-facing slopes, their specific micro-habitats on these slopes being often on more gentle benches. The shallow soils, averaging only 6 cm thick and directly underlain by bedrock, were rich in organic matter, but never entirely free of a sandy to pebbly mineral component. All occupied microsites had plant communities that formed a very short turf with some of the cover consisting of bryophytes and were largely free of dense and taller growing vascular plants. The other common features of the sites were a very high diversity of native species and the presence of other rare vascular plants, mosses and liverworts. Two provincially red-listed vascular plants also found in Meconella habitats are Idahoa scapigera and Plagiobothrys tenellus. Frequently associated species were documented in a vegetation table; this supplementary information is available upon request. The 10 most frequently encountered associated vascular plants were Collinsia parviflora, Aira praecox, Aphanes occidentalis, Saxifraga integrifolia, Triteleia hyacinthina, Bromus hordeaceus, Selaginella wallacei, Silene gallica, Brodiaea coronaria, andMontia fontana. The two most frequent bryophytes were Rhacomitrium canescens and Mnium miniatum.

Trends

In Canada Meconella oregana occupies only a small fraction of what appears to be identical and potentially suitable habitat. However, the trend for all this habitat, occupied and unoccupied, is to become increasingly overrun by non-native species. In a few instances the invasive Scotch broom (Cytisus scoparius) was found in the vicinity of Meconella. At the actual Meconella growing sites, however, the soils are too shallow for broom to survive; the greater threat here are introduced annuals such as Aira, Vulpia and Bromus species, Cynosurus echinatus, Erodium cicutarium, Silene gallica, Geranium molle and many others which collectively degrade the micro-habitat forMeconella. Several sites for which old Meconella records exist, but which are close to densely populated areas, now have highly altered plant communities consisting of mostly non-native species, apparently incapable of supporting Meconella (writer’s observation, 2004, based on comparison between occupied sites as shown in Table 2 and unoccupied sites). This degradation of habitats by non-native species may be considered to be equally or more important than outright habitat loss for the species.

Of five sites for which old records exist, but where the species was not found in the 2004 surveys, three have retained what may be considered “good habitat” and two marginal or poor habitat. The potential for the species reappearing in these good habitats should be kept in mind for future surveys.

Habitat protection/ownership

In British Columbia old Meconella records exist for six areas that enjoy protection of some sort (Table 1) including a provincial park, an ecological reserve, regional and municipal parks. The report writer's recent fieldwork included all these areas, but confirmed only one single extant population for these locations. Another extant population is partly on federal (NRC’s Hertzberg Institute for Astrophysics) and partly on private property. Four extant populations, including the two largest, are on private land. In terms of numbers of individuals counted in 2004, only 368 were on the protected land (Regional District Park) and 151 on federal land, while 2806 were on privately owned land.

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