Coast Microseris (Microseris bigelovii) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

In Canada, Microseris bigelovii is restricted to a small area of southeastern Vancouver Island. This area, which is highly correlated with the distribution of Garry oak, has mild winters and dry, cool summers.

Winters are mild as a result of relatively warm, low pressure areas which dominate coastal areas. The Coast Mountains impede the westward movement of cold high pressure systems. Winter temperatures along the coast are moderated by proximity to the ocean, which is dominated by mild waters of the California Current all year long.

January, the coldest month, has a daily mean temperature of 4.6° C and a mean daily minimum of 2.5° CFootnote1. Mild winter temperatures characterize the southeast coast of Vancouver Island. Southeast Vancouver Island also has drier winters than elsewhere in south coastal British Columbia. It lies in the rain-shadow of the Vancouver Island and Olympic Mountains, which intercept moisture from the prevailing systems that move in from the Pacific. December, which is also the wettest month, receives an average of 108 millimetres (mm) of precipitation (but very little snow).

Summers are cool and dry. A large semi-permanent high pressure area extends over the northeastern Pacific, dominating the general circulation in western Canada. The Olympic and Vancouver Island Mountains continue to intercept much of the moisture from systems moving into the region. May, June, July and August each bring less than 25 mm of mean monthly precipitation and pronounced moisture deficits develop. Temperatures are greatly mediated by proximity to the ocean and daily maximum temperatures often increase by several degrees as one moves inland on a warm summer day.

The combination of mild, relatively clear winters and dry clear summers, along with a southern location, determine that southeast Vancouver Island has the greatest annual amounts of sunshine in British Columbia. The scarcity of snow and rarity of hard frosts allow vegetation to remain green throughout the winter. Strong moisture deficits turn the meadows brown in mid-summer.

Edaphic factors strongly limit the distribution of Microseris bigelovii within southeastern Vancouver Island and the adjacent Gulf Islands. The low-elevation band of coastal environments is narrow and quickly gives way to uplands that lack the necessary mesoclimatic conditions. Broken terrain over much of the lowland band creates many cool north- and east-facing slopes where forest plants have a comparative advantage. Well-to moderately well-drained soils favour forests; consequently, potential habitat is quite patchy due to natural causes. This natural level of patchiness is exacerbated by the extensive human development in the area (see below).

In Canada, Microseris bigelovii is restricted to open sites without tall vegetation. These areas remain open because of wind exposure along shore, summer drought stress in thin soils, or winter seepage that waterlogs soils preventing taller vegetation from dominating. Microseris bigelovii is restricted to areas within 50 m of the coast where frequent coastal fogs occur in the autumn and winter and the ocean buffers against deep frosts in the winter.

Some populations occur on rock-ledge sites and have a significant cover of ‘shrubby’ fruticose lichens – primarily Cladina portentosa. Associated species often include Selaginella wallacei, *Gnaphalium purpureumFootnote2, Grindelia integrifolia, *Hypochaeris radicata, *H. glabra, Lotus micranthus, *Rumex acetosella, *Teesdalia nudicaulis, Triteleia hyacinthina, Brodiaea coronaria, Danthonia californica, Elymus glaucus, Festuca rubra, *Holcus lanatus, *Vulpia bromoides, Polytrichum piliferum, Racomitrium lanuginosum, and R. elongatum. Cytisus scoparius may also root in rock fractures but is rarely tall or thick.

Other populations occur on the margins of shallow, winter-wet depressions which have little or no Cladina, but are covered with low plants including Aphanes microcarpa, Cerastium arvense, *Gnaphalium purpureum, *Hypochaeris glabra, *H. radicata, Plagiobothrys scouleri, Plantago elongata, Trifolium spp., Triphysaria pusilla, *Aira praecox, Brodiaea coronaria, *Poa annua, Triteleia hyacinthina and *Vulpia bromoides.

Habitat trends

The amount of potential habitat has declined greatly over the past century as coastal areas in southeast Vancouver Island have been developed for residential and recreational use.

Most large areas of suitable habitat have been surveyed for Microseris bigelovii but it is not practical to survey all of the small fragments of suitable habitat. Trends in suitable habitat for Microseris bigelovii may be indirectly estimated according to the following indicators.

Microseris bigelovii typically occurs within a matrix of Garry oak ecosystems, so the decline of these ecosystems provides an indirect measure of the loss of habitat for M. bigelovii. Overall, Garry oak systems have, over the past century, been reduced to less than 5% of their original extent in the Victoria area (Lea 2002). Garry oak ecosystems persist largely as isolated communities that are heavily fragmented and lack connections that would allow substantial genetic interchange. Microseris bigelovii prefers shoreline situations, which are also sought after for residential development, while Garry oak ecosystems are more broadly distributed, so the actual decline in suitable habitat is probably even higher.

Much of the remaining habitat suitable for Microseris bigelovii has been heavily altered due to invasion by alien weeds including several grasses (Agrostis capillaris, Aira caryophyllea, A. praecox, Anthoxanthum odoratum, Bromus hordeaceus, Cynosurus echinatus, Dactylis glomerata, Hordeum spp., Lolium perenne, Poa annua, P. bulbosa, Vulpia bromoides) and forbs (Bellis perennis, Cerastium semidecandrum, Geranium molle, G. pusillum, Hypochaeris glabra, H. radicata, Plantago lanceolata, Rumex acetosella, Silene gallica, Stellaria media, Trifolium dubium, T. subterraneum, Vicia lathyroides).

The distribution of Microseris bigelovii in Canada lies at the heart of one of North America’s fastest growing regions. The Victoria Metropolitan Area includes all but one of the extant populations of M. bigelovii and all but one of the apparently extirpated populations. The population of metropolitan Victoria has increased from approximately 180,000 in 1966 to 318,000 in 1996 and is projected to increase to more than 400,000 by 2026. The Capital Regional Plan adopted in 1959 led to expansion into rural areas surrounding Victoria over the past 44 years and this pattern of expansion may continue in order to accommodate population increases (Capital Regional District Regional Growth Strategy 2003a). During past the 18 years, average prices for single family residences in Metropolitan Victoria have increased 330% from $94,000 to $313,000, reflecting the pent-up demand for property (Capital Regional District Regional Growth Strategy 2003b). The most expensive and sought-after properties are ocean frontage, the favoured habitat of M. bigelovii.

Several historic populations (Beacon Hill, Thetis Lake, Mount Tolmie, Uplands Park subpopulation, and Gonzales Hill) in the Victoria area have apparently disappeared as a result of habitat loss or degradation and the same trend holds in adjacent San Juan County (Washington State) where the species has been extirpated.

Habitat protection/ownership

Only the Hornby Island population occurs in a protected area. British Columbia’s Parks and Protected Areas do not have a management plan with specific protection for Microseris bigelovii, although under the Parks Act it cannot be collected in Provincial Parks or Protected Areas.

One of the populations is on private land designated as a National Historic Site and managed with guidance from Parks Canada. Two populations occur in municipal parks where they are protected from residential development but subject to very high levels of recreation use. Neither municipality has plans or programs designed to manage for species at risk. The two Rocky Point populations occur on Department of National Defence (DND) property managed by CFB Esquimalt. The Department of National Defence does not have any management plans in place for M. bigelovii, although their regular operations make little use of the areas where Rocky Point population #2 occurs.

Four populations (Thetis Lake, Mount Tolmie, Beacon Hill/Dallas Road and Gonzales Hill) have been extirpated despite occurring on municipal or regional park lands.

None of the sites where it occurs have weed or vegetation management plans to protect the habitat of Microseris bigelovii from alien invasives or succession.

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