Fragrant popcornflower (Plagiobothrys figuratus) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements

The only site currently known to support fragrant popcornflower in Canada is a grassy, undeveloped waste area adjacent to a road and housing development on the coast of Hornby Island. Numerous non-native grass species are present, as are moisture-tolerant native grasses such as California oatgrass (Danthonia californica). Although the site does not have the characteristics of a true vernal pool, it likely contains some standing water for brief periods during the year (R. Martin, pers. comm. 2006). Another native species, Nuttall’s quillwort (Isoetes nuttallii), blue-listed in BC and critically imperilled in Washington State (S1), is also known to occur in the vicinity of this site in a similar roadside depression habitat. Meadow popcornflower (Plagiobothrys scouleri), a more common native species, also occurs in the area in the same habitat type. Clearly fragrant popcornflower is a native species that has been known in Canada for over 120 years.

Hitchcock et al. (1959) describe the habitat of fragrant popcornflower as non-alkaline meadows, low ground and moist fields. In Oregon’s Willamette Valley it is known from wet prairies and vernal pool systems (NatureServe 2005). In Washington and Oregon it has been collected from a range of microsites including stream banks, ditches, damp open ground, vernally flooded fields, and wetland prairies (Gilkey and Dennis 1967), while in southeastern Alaska it is described as a weedy species of disturbed soils (Welsh 1974). In the U.S., the species is federally classified as a facultative wetland species and a wetland indicator (USDA-NRCS 2002).

Douglas et al. (1998, 2002) describe its British Columbia habitat as "moist to mesic sites in the lowland Coastal Douglas-fir zone," also as "moist to mesic coastal bluffs." Unfortunately, the few museum collection notes available for fragrant popcornflower in B.C. tend to lack detailed habitat descriptions; most references are simply either to "hillsides," roadsides, or vernally wet areas. The best known fragrant popcornflower site, at Whaling Station Bay on Hornby Island, is a former coastal meadow now occupied by a housing development and grass lawn. The plant community in the original habitat was a short turf maintained by grazing sheep. The only remaining near-natural habitat, less than 100 m to the northeast, consists of a flat meadow with several slight depressions and with some areas of shallow soil over bedrock. This habitat is currently dominated by various introduced species along with fool’s-onion (Triteleia hyacinthina). The range of preferred habitat conditions may be summarized as follows on the basis of the literature and observations made by the third author:

Habitat trends

Structure and successional stage: Occasional fire has played a historical role in maintaining open habitats in the wet prairies of Washington and Oregon (Wilson 1999; Newhouse 2003) and possibly on Vancouver Island, although this has not been documented for the latter. Fire prevention would have caused a build-up of thatch and ultimately colonization by shrubs and trees, effectively making such wetter sites unsuitable for small annuals such as Plagiobothrys.

Early collections from a range of Canadian locations suggest that fragrant popcornflower was more widespread historically on the coastal plains of southern Vancouver Island. Because it occurs in low-lying areas, seeds may have been dispersed by flood waters or waterfowl, resulting in a patchy clumped distribution. Natural processes such as flooding and fire likely maintained open, wetland habitat. However, increasing urbanization around Victoria and Nanaimo, combined with the draining of wetlands for agricultural uses and road construction, has evidently altered the original hydrology of the region to such an extent that the total area of suitable habitat for fragrant popcornflower is now significantly reduced.

The historical range of fragrant popcornflower encompasses a broad mosaic of maritime meadows, coastal bluffs, grasslands, and wet meadows associated with the Garry oak ecosystem. During the past century, this environment has been substantially altered by urbanization, land development, and fire suppression, to the point where only an estimated 1-5 % remains in a near-natural (i.e., pre-contact) condition (Fuchs 2001; Lea 2002). Despite ongoing efforts to protect what is left of this system, most remnant fragrant popcornflower habitat remains under threat from continued urban development.

Even so, there is presumably still available sufficient suitable habitat, in the form of low-lying wet meadows, seepage areas, and marine bluffs, to support a viable population of fragrant popcornflower in Canada in situ, should it turn out that reintroduction is deemed necessary. At the same time, the writers do not entirely discount the possibility that this species may still exist somewhere on Vancouver Island or elsewhere on the Gulf Islands.

Habitat trends for Plagiobothyrs figuratus ssp. figuratus in Washington and Oregon are not currently tracked as this subspecies is not considered at risk there. However, two closely related taxa, P. figuratus ssp. corallicarpus (coral-seeded allocarya), and P. hirtus (rough popcornflower), are rare in Oregon (S1). The latter is a U.S. federally listed endangered species with a rating G1N1S1. Referring to its endangered Oregon habitat, where it is limited to a few known occurrences, the recovery plan for this species (USFWS 2003) states: "Land use patterns since the time of European settlement have greatly influenced vegetation patterns throughout the West, and habitat destruction has been of particular importance to the loss of vernal pool and seasonal wetland species. Conversion of wetlands to agricultural fields was identified as a major contributor to the extinction of vernal pool species as early as 1941 (Hoover 1941), and researchers currently estimate that 60 to 90 percent of pools extant at the time of European settlement have now been destroyed, along with the endemic plant and animal species associated with them (Keeley and Zedler 1998; King 1998). In the Umpqua Valley, conversion of wetlands to agricultural lands through hydrological alterations has drastically reduced the number of seasonal wetlands that can support the rough popcorn flower."

The Willamette Valley wetland prairies, where the majority of fragrant popcornflower collections have been made, are one of the rarest and most endangered ecosystems in the U.S. (Noss et al. 1995). The Willamette Floodplain Natural Area, which contains perhaps the best and most extensive system of the wetland phase of these prairies, have become degraded over the past decades, mostly as a consequence of fire suppression and subsequent invasions of shrubs, trees, and exotic herbaceous weeds (Wilson 1999).

Habitat protection/ownership

The only site known to still support fragrant popcornflower in British Columbia (Whaling Station Bay, Hornby Island) is on private land with no protective management. Ownership status at all other historical sites is unknown.