Golden paintbrush (Castilleja levisecta) COSEWIC assessment and status report: chapter 5
Habitat
Habitat requirements
In Canada, golden paintbrush is restricted to maritime meadows associated with Garry oak ecosystems. These are low-elevation (< 30 m), herb-dominated ecosystems largely confined to coastal situations (within 3 km of the shoreline) along southeastern Vancouver Island and a subset of islands in the Straight of Georgia, Haro Strait and the Strait of Juan de Fuca. Summer temperatures are greatly moderated by proximity to the ocean. Coastal fogs bring heavy dew in the late summer and early fall, stimulating germination and breaking shoot dormancy in many perennials even as inland areas remain dry and brown. Coastal fogs and the proximity to shoreline also tend to moderate winter frosts (particularly at night), retard the accumulation of heat and may slow down the development of plants, particularly in the late spring. Maritime meadows may be largely free of woody vegetation for a variety of reasons, including strong summer moisture deficits (particularly on wind-exposed sites and/or those with thin, coarse-textured soils), salt spray and a long history of burning by First Nations. These forces may act alone or in concert, consequently some maritime meadows are subject to forest ingrowth while others remain open despite fire suppression (Parks Canada 2006).
Habitat trends
Habitat loss
The amount of potential habitat on southeast Vancouver Island and the adjacent offshore islands has declined greatly over the past century as maritime meadows have been developed for residential and recreational use. There are no reliable estimates of the rate of loss of maritime meadows and it is difficult, if not impossible, to determine the original extent of this ecosystem type. The proportion of maritime meadows which has been lost probably exceeds the rate of loss of Garry oak ecosystems in Victoria because the maritime meadows were more concentrated along the desirable shoreline locations and provided more level building sites. The extent of Garry Oak ecosystems in Victoria decreased 95% from 10,510 ha in 1800 to 512 ha in 1997 (Lea 2002). This loss is almost entirely attributable to agricultural conversion followed by residential and recreational development.
Surveys conducted in support of this status report showed that there are only approximately 24 ha of maritime meadow habitat within the current range of golden paintbrush in Canada. If one rejects the Wellington report (apparently based on a misidentification) there are only approximately 27 ha of maritime meadow habitat within the entire historic range of the species in Canada.
The distribution of golden paintbrush in Canada lies at the heart of one of North America’s fastest growing regions. The population of metropolitan Victoria has increased from approximately 180,000 in 1966 to 338,738 in 2005 and is projected to increase to 407,600 by 2026 (CRD 2006). The most expensive and sought-after properties are ocean frontage where golden paintbrush commonly occurs. As a result, there will be continued pressure to develop maritime meadow habitat capable of supporting the species.
Habitat invasion by exotic species
Golden paintbrush is now restricted to open meadows a few metres above sea level on offshore islands and islets. There have been long periods of livestock grazing in approximately 90% of the current area of occupancy as well as much of the apparently suitable, but unoccupied habitat within its extent of occurrence. Invasive grasses and forbs have entered and now dominate much of the area that has been grazed. Even areas of suitable habitat that were not grazed have often been invaded by exotic plants (pers. obs.).
Several invasive woody and semi-woody species have invaded maritime meadow habitat in the historic range of golden paintbrush. The following species already occur within populations of golden paintbrush and are frequent in similar maritime meadows.
Scotch broom (Cytisus scoparius) is present at all sites and in some places it has increased to the point where there is little if any native vegetation under its canopy. Where it has not yet created a closed canopy, size-class distributions suggest its cover is increasing rapidly. Attempts to control Scotch broom have had little success. Most control efforts have involved uprooting which creates soil disturbances that favour invasion by rapidly dispersed invasives. Efforts to control the species by stem-cutting have failed because it resprouts prolifically from cut stumps. In almost every case, control efforts have been followed by heavy recruitment from the large, long-lived soil seed bank (pers. obs.). Recruits may begin reproducing when as little as 3 years old (Bossard n.d.).
Gorse (Ulex europaeus) is an increasing threat to maritime meadow habitats. It spreads more slowly than Scotch broom because its seeds are not dispersed as far from the parent plant. It has become established on most maritime meadow sites in the current golden paintbrush area of occupancy and some of the older populations now form a continuous canopy cover (pers. obs.). Where it is established, gorse quickly forms a dense canopy and produces a thick layer of acidic litter that discourages the growth of all other species (see William 1983). Gorse is even more difficult to control than Scotch broom, because it quickly establishes branching rhizome and root systems that are not easily removed.
English ivy (Hedera helix) is the third major woody invasive of maritime meadows. It is less widespread than Scotch broom but appears to be increasing its distribution and may soon be present on most sites. Once established, it spreads rapidly to blanket the herb layer. Rooting readily from even small rhizome fragments, it is even more difficult to control than Scotch broom and gorse(pers. obs.).
Other serious and widespread woody invaders of maritime meadow habitats include spurge-laurel (Daphne laureola) and Himalayan blackberry (Rubus armeniacus). These species appear to present serious threats to maritime meadow ecosystems and the former appears to be rapidly spreading across the region. As well, a few meadows have significant infestations of English holly (Ilex aquifolium) and Cotoneaster sp. (pers. obs.).
Habitat changes related to fire
Burning by First Nations, to improve camas bulb crops, maintained maritime meadow habitat in the past. Fire suppression now favours the development of dense patches of native shrubs and trees where golden paintbrush cannot survive. Paradoxically, an attempt to improve camas harvest by restoring fire has favoured invasion by rapidly dispersing non-native grasses and forbs rather than restoring the native plant cover (pers. obs.).
Protection/ownership
One of the extant populations lies entirely within an Ecological Reserve managed by BC Parks. The other population is split between another Ecological Reserve, a Canada Coast Guard site and a communications lease on BC crown land. Plants on ecological reserves are protected under the BC Parks Act and plants on the Canada Coast Guard site are protected under the Species at Risk Act. Recently, BC Parks and the Canada Coast Guard have taken steps to control invasion by woody species. In contrast, maritime meadow habitat on the communications lease that is occupied by golden paintbrush has no formal protection. Habitat quality on the communications lease is declining as the cover of gorse and Scotch broom increases. Operational activities on the communications lease (e.g. trail maintenance and storage of supplies and waste) have directly impacted habitat quality (pers. obs.).
Most of the unoccupied maritime meadow habitat that remains within the extent of occurrence is in municipal parks, which lack formal policies to protect species at risk. Nevertheless, most of these municipalities have taken measures to map species at risk and some have established programs to try to protect maritime meadow habitat by controlling invasive shrubs (pers. obs.).
Federal lands occurrence
One extant population (Trial Island) extends onto federal lands.
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