Macoun’s meadowfoam (Limnanthes macounii) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

General characteristics

Macoun's meadowfoam occurs in open places or light open forest, usually close to the shore of the Pacific Ocean. All localities are characterized by being wet or submerged in winter and completely dry in summer. Depressions in shallow soil lining bedrock (a form of vernal pools) and intermittent seepage streams along fractures in bedrock are typical spots where the water regime is suitable for its growth.

Most populations grow close to the sea level with elevation from 5 to 35 m above the sea level (a.s.l.). Several localities, however, are as high as 195 m a.s.l.

Climate

A maritime climate with mild and wet winters is essential for the existence of Macoun's meadowfoam. The regional macroclimate is Mediterranean, temperate rainy with dry warm summers (Csb in Koppen's classification). The area in which meadowfoam occurs is in the rain shadow of the Olympic Mountains, Sooke Hills and Vancouver Island Mountains, and has the lowest amount of precipitation of all Vancouver Island. Most of the precipitation is in the winter months; there is a sharp decline during the spring and drought in summer. The growing period of Macoun's meadowfoam spans from late September or October to May and relatively mild temperatures and high rates of precipitation in this period are essential for the plant's survival. Dry summers are important for the "rest period" of the seeds.

The proximity of most of the localities to the ocean shore suggests microclimates milder than those more inland. The ground temperatures are higher in winter than inland, and the sites are generally moister. These two factors are again important to the growing period of Macoun's meadowfoam. The most adverse influences on the development and growth of Macoun's meadowfoam are low temperatures in winter and unusually dry periods in early spring. Low temperatures in the fall can impede germination, and winter frosts can kill the plants. According to our observations, however, temperatures slightly below freezing (about -2 °C or -3 °C) do not harm the plants but can suppress the growth of other plant species competing with Macoun’s meadowfoam for space. There is usually no water deficit in the growing period of Macoun's meadowfoam. Unexpected dry weather in the fall months can harm those seedlings that germinated too early after the first heavy rains, but in order for the seeds to germinate, so much water must have accumulated in meadowfoam localities that there is almost no danger of a later water deficit.

With regard to light requirements, Macoun's meadowfoam can be considered to be shade intolerant. It usually occurs in open places. When it grows in shade (among tall grasses in open light forests), the plants are thin and elongated and usually produce fewer nutlets.

Physiographic and topographic characteristics

Localities of Macoun’s meadowfoam are situated on rocky shores. Bedrock depressions, such as glacial grooves, collect water. Fractures in rocks collect seepage water running to the shore and provide another possible location for the plant. The bedrock is predominantly volcanic, with the exception of the Yellow Point area, Gabriola Island and Hornby Island, where it is sandstone. The bedrock substrate must be impermeable so that vernal pools and seepy places retaining water can develop. The surface is generally not covered by glacial till; but if it is (e.g., [3] or [18]), the till layer is very thin (less than 15 cm).

Edaphic factors

Populations of Macoun's meadowfoam grow on shallow soils that range from being a few cm to about 30 cm thick. These soils are classified as Orthic Humic Regosols (Canada Soil Survey Committee 1978), or as Protoranker or Mull Ranker in Kubiena's classification (Kubiena 1953). The soils are rich in humus, which gives them their distinctive black colour. Most of the localities are rich in nutrients, especially nitrogen and phosphorus. Meadowfoam can tolerate high amounts of nutrients, as is shown by several populations occurring around rocks where sea birds gather and deposit layers of guano ([7.1] or [14]). Preliminary tests show that soils are quite acidic (pH <5.5) and rich in nutrients (Coger 1985).

The main edaphic factor is the abundance of moisture during the winter (the water table is either at the soil surface or about 5 cm above the surface). The soil remains fresh and moist until the end of April when it starts to dry out. It is bone dry during the summer.

Biological characteristics

According to Krajina's biogeoclimatic classification (Krajina 1965), the area in which Macoun's meadowfoam occurs belongs to the drier subzone of the Coastal Douglas fir zone. The climax vegetation of this area are dry Douglas fir forests in which Douglas fir (Pseudotsuga menziesii) may be accompanied with arbutus (Arbutus menziesii) and Garry oak (Quercus garryana), with mahonia (Mahonia nervosa), western fescue (Festuca occidentalis), and Eurhynchium oreganum in the undergrowth. Open Garry oak (Quercus garryana) stands are characteristic of the driest part of the Douglas fir zone.

Macoun's meadowfoam grows in the following vegetation formations (photographs are on file with COSEWIC):

  1. Vernal pools - open depressions with a large number of annual plants ([5.4], [21.1], [23.1], [24.1], [24.3], [29.6], etc.).
  2. Ephemeral seepage streams on open slopes ([10.5], [13.1], [21.2], [22.4], [26.2], [28.4], etc.).
  3. Seagull roosting places - wet depressions and the end of seepage streams in places where sea birds gather and feed, areas extremely rich in nutrients ([7.1], [14.1], and [16.1]).
  4. Open light forests - depressions and seepy places in open light mixed forests of Douglas fir, Garry oak, arbutus, Rocky Mountain juniper (Juniperus scopulorum), or lodgepole pine (Pinus contorta) ([5.9], [6.1], [11.1], and [29.1]).

Populations of Macoun’s meadowfoam are more viable in shallow soils than in deeper ones. In shallower soils (up to about 4 cm), the species does not encounter the competition of introduced perennial grasses, namely bentgrass (Agrostis spp.), orchard grass (Dactylis glomerata), rye grass (Lolium perenne), and velvet grass (Holcus lanatus) or some shrubs, such as Scotch broom (Cytisus scoparius) or Himalayan blackberry (Rubus armeniacus).

Habitat trends

Suitable habitats for Macoun’s meadowfoam are disappearing. Natural vegetation of Garry oak savanna that once occurred on southern part of Vancouver Island has diminished. Lea (2002) estimated only about 5% of the original area of Garry oak ecosystems still exists in more or less natural state. In the Victoria area, the majority of open Garry oak forests and open grasslands on shallow soil were developed for housing and many suitable natural habitats disappeared. With this development pressure, many historical habitats of native plants associated with Garry oak disappeared (e.g., open spaces at “Cloverdale”, Royal Oak, Oak Bay, and Saanich Peninsula).

Before the introduction of European fodder plants, the open habitats of southern Vancouver Island had only a few native perennial grasses: California wild oat grass (Danthonia californica), blue wild rye (Elymus glaucus), Roemer's fescue (Festuca roemeri), and prairie Koeler's grass (Koeleria micrantha), or perennial graminoids (such as Carex tumulicola). None of these perennial graminoids represents a real competition to Macoun’s meadowfoam, because they have different ecological requirements than Macoun’s meadowfoam and seldom occurred together with it.

Even the remaining Garry oak vegetation has been significantly altered. Introduced plants now represent almost 50% of all vascular plant species and often are the main dominants of the herb layer. Introduced perennial grasses now dominate herb layer of vegetation associated with Garry oak. Scotch broom (Cytisus scoparius), with its nitrogen-fixing abilities, changed the structure and composition of areas that remained undeveloped in the Garry oak ecosystems.

Perennial grasses such as sweet vernal grass (Anthoxanthum odoratum), orchard grass (Dactylis glomerata), bent grass (Agrostis capillaris, and A. stolonifera), velvet grass (Holcus lanatus), perennial rye grass (Lolium perenne) and Kentucky blue grass (Poa pratensis) has changed the herb layer. The annual introduced grasses also play a significant role in sites with Macoun’s meadowfoam. These are: bristly dog's tail grass (Cynosurus echinatus), early silver-hair grass (Aira praecox), common silver-hair grass (Aira caryophyllea), brome six-weeks grass (Vulpia bromoides), rat-tail six-weeks grass (V. myuros), soft brome (Bromus hordeaceus), and bald brome (Bromus racemosus). These annual grasses are not direct spatial competitors as are the perennial grasses, but they significantly contribute to the build-up of soil and filling in of wet depressions.

Habitat protection/ownership

Macoun’s meadowfoam occurs in areas that have a full range of the ownership holdings as summarized in Table 1.

Table 1. Ownership status and number of subpopulations in various ownership types
Ecological Reserve 3
National Historical Site 3
ProvincialPark 7
CRD - Regional Park 3
MunicipalPark 8
DND 27
Federal 2
First Nation Reserve 17
Golf Club 4
Private 25
Total 99

An Ecological Reserve to protect Macoun’s meadowfoam was established on Trial Island. Provincial, Regional and Municipal Parks provide a certain degree of protection, but in general, protection of rare plants is not the main objective of these parks. Populations or subpopulations on private land, Indian Reserves and at the golf course are not protected with the exception of one protective covenant.

Page details

Date modified: