Foothill sedge (Carex tumulicola) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements 

Across its range, Carex tumulicola is typically found in upland prairies, dry to moist meadows, and open woodlands (Peck 1961, Hitchcock et al. 1969, Mastrogiuseppe 1993, Wilson 1999, B. Newhouse, pers. comm. 2001).

In Canada, Carex tumulicola is restricted to the dry coastal lowland zone (Coastal Douglas-fir Biogeoclimatic Zone, moist maritime subzone) of southeast Vancouver Island, British Columbia (Douglas et al. 2001). This region lies within the rain shadow of the Vancouver Island and Olympic mountains and is characterized by a sub-Mediterranean climate with warm, dry summers and mild, wet winters. The mean annual temperature in Victoria, the core of the Canadian range of C. tumulicola, is 10 °C. Mean daily temperatures range between 4°C in December and 15.6 °C in July. Summer drought is an important feature determining the character of the vegetation in this region. Of the 690 mm of average annual precipitation in Victoria, less than 5% falls during July and August. The annual moisture deficit exceeds 350 mm (McMinn et al. 1976, Fuchs 2001). Carex tumulicola is not widelydistributed throughout the dry coastal lowland, being found only at elevations of less than 50 m and generally within 200 m of the coastline. Its restriction to low elevation coastal sites suggests that poor frost-hardiness may limit its distribution.

The bedrock underlying southeastern Vancouver Island is primarily igneous, metamorphic, and to some extent sedimentary in origin (McMinn et al. 1976). Many populations of Carex tumulicola occur in openings in Garry oak woodlands, where the soils tend to be Orthic Sombric and Lithic Sombric Brunisols, with a well-developed Ah horizon and Moder to weak Mor humus formations (Roemer 1972). Population #7 occurs on a Lithic Dystric Brunisol overlying gently sloping sandstone or conglomerate(Jungen et al. 1985). The soils become moistened with arrival of autumn rains and remain moist (sometimes saturated) through the winter and early spring. Soil moisture levels decline as the summer drought progresses and by mid-summer most of the surrounding vegetation has withered, although the foliage of C. tumulicola often remains bright green into the fall.

Carex tumulicola may have been an important species in coastal meadows and prairies of southeastern Vancouver Island prior to European settlement. Currently, C. tumulicola persists on San Juan Island, WA (15 km from Victoria) in large patches of several hundred plants in damp, undisturbed meadows, and at lower abundances in more disturbed meadows (P. Zika, pers. comm. 2004). It is one of the few species of native grasses or sedges that could have dominated these systems prior to the arrival of invasive European forage species (Chappell and Caplow 2004).

Population #1 

This population consists of several scattered Carex tumulicola patches within a remnant Garry oak woodland-meadow complex presently dominated primarily by weedy native and non-native shrubs (e.g., Symphoricarpos albus, Cytisus scoparius, Ulex europaeus) and introduced grasses (e.g., Holcus lanatus, Lolium perenne,Agrostis stolonifera) and herbs (e.g., Allium vineale). Several C. tumulicola occurrences are in small strips of woodland habitat along the margins of shrub thickets, appearing to persist along the lightly trampled margins of paths where foot-traffic has held back encroachment by shrubs such as Symphoricarpos albus. Elsewhere, C. tumulicola occurs as small tussocks within meadow fragments (dominated by introduced grasses) where competition is reduced by summer mowing intended to reduce the build-up of fire fuels.

Population #2 

A portion of this population is located beside a footpath in an upland Garry oak meadow, with introduced grasses (e.g., Bromus sterilis) predominating. The other localities consist of small tussocks in weedy areas along footpaths and roadsides, with understories typically dominated by invasive native and non-native shrubs, grasses and herbs (e.g., Symphoricarpos albus,Rubus discolor, Lolium perenne, Poa pratensis, Agropyron repens, Hedera helix, and Taraxacum officinale).

Population #3 

This population is located next to a dry, mown trailside in a rocky upland area adjacent to an overgrown bog. Here, Carex tumulicola occurs near the trail edge beneath an overstory of Populus tremuloides and Crataegus monogyna in association with several introduced species of herbs and grasses.

Populations #4 & #5 

These populations occur in remnant Garry oak savannah within a few metres of the marine shoreline. Several of the patches are found in grassy swales, dominated by a mix of native and non-native herbs, amid rock bluffs. Other patches occur in mown meadows dominated by non-native grasses and forbs (e.g., Poa pratensis, Bromus hordeaceus, Lolium perenne, Bromus sterilis, Geranium dissectum, G. molle, Vicia spp.,Myosotis discolor, Trifolium dubium, and Cynosurus echinatus). Associated native species includeCarex macloviana, Juncus tenuis, Lomatium nudicaule, Triteleia hyacinthina, Pteridium aquilinum, Camassia leichtlinii, Cerastium arvense, and Plectritis congesta.

Population #6 

This population is located within heavily disturbed meadows near the marine shoreline. The sites have been mown and/or grazed in the past and are dominated by non-native shrubs, forbs and grasses.

Population #7 

This population consists of a single tussock growing at the edge of a moist, shrubby (Symphoricarpos albus, Rosa nutkana, Crataegus monogyna) seep within a Garry oak woodland.

Population #8 

This population occurs on bare soil in a small opening beneath a mixed second growth forest canopy of Pseudotsuga menziesii, Quercus garryana, and Arbutus menziesii.

Population #9 

This population occurs in a grassy, coastal, mesic meadow interrupted with some patches of Scotch broom (Cytisus scoparius) and Nootka rose (Rosanutkana).

Population #10 

This population occurs on Sidney Spit, owned by Parks Canada, in an abandoned rough (unseeded) grassy pasture with a mix of native plants and a large component of invasive species.

In summary, Carex tumulicola tends to occupy meadow and open woodland habitats in Canada, many of which are now dominated by invasive forage species or are being taken over by shrubs and trees. The most vigorous populations tend to occur where tree and shrub cover is slight and where invasive forage grasses are either less common, or subject to mowing.

Habitat trends 

The amount of potential habitat has declined substantially over the past century as coastal areas on southeastern Vancouver Island have been developed for residential and recreational use. Less than 1% of the Coastal Douglas-fir zone is currently protected (Eng 1992). Garry oak ecosystems in the Victoria region have declined in area from 10,510 ha in 1800 to 512 ha in 1997, a decrease of nearly 95% (Lea 2002). Even more has been lost since then. Most of what remains has been heavily altered through invasion by exotic grasses and shrubs. Habitats suitable for Carex tumulicola were probably never as abundant as Garry oak ecosystems in general. Their habitat has certainly experienced at least an equally sharp decline since price and demand for residential and commercial development are greatest in coastal areas where C. tumulicola tends to occur. Specifically, populations #1, 2, 3, & 7 occur in small green spaces within or immediately adjacent to large residential areas built on similar sites that were formerly capable of supporting C. tumulicola.

Habitat quality has also declined throughout the coastal meadow and woodland habitats that persist (see Limiting Factors and Threats section). Fire suppression has favoured in-growth of native and non-native shrubs and trees, reducing light to the forest floor. A number of highly competitive forage grasses and forbs have been deliberately introduced since the mid-19th century and have spread unassisted throughout meadow and woodland habitats (Fuchs 2001). Carex tumulicola tends to persist only as small and/or low-vigour populations on sites where there is significant tree or shrub encroachment or where forage grasses and forbs are abundant.

Habitat protection/ownership

The type of land ownership and protection corresponding to each occurrence of Carex tumulicola in Canada is shown in Table 1. Of the ten Carex tumulicola populations identified to date, three occur in municipal parks within Greater Victoria (with one straddling the boundaries of an educational institution), four are on federal DND land, with one extending onto an adjacent Indian Reserve, one is completely within Indian Reserve lands, one occurs on private land, and one in a National Park. None of the populations is under any legal protection, although several sites are afforded some measure of effective protection from urban and residential development due to their location on managed municipal, DND or Parks Canada Agency lands (Table 1). Federal land managers are generally concerned with the inventory of taxa that are currently designated under federal Endangered Species legislation (SARA) as well as those that are of concern provincially or candidates for SARA designation.

The Department of National Defence lands are administered by both the Maritime Forces Pacific (MARPAC) and Canadian Forces Base, Esquimalt (CFB –Esquimalt). The Environmental Science Advisory Committee (ESAC) supports research and inventory on species-at-risk and candidates for species-at-risk designation under SARA. Decisions regarding management of species are considered within the context of the Natural Resources Program and therefore, some needs may not get addressed. Although this species has yet to be SARA-listed, DND has mapped all the known C. tumulicolasites on their GIS layers. For the moment the sites on DND lands remain inaccessible to the public and are effectively protected from development.

The three populations occurring on municipal parklands also have no formal protection under park management policies. Portions of Population #2 occur on the campus of a post secondary institution and are afforded neither formal nor informal protection. Population #7 occurs on private land that has been repeatedly proposed for residential development.

Population #1 is under the jurisdiction of the District of Oak Bay, while populations #2 & 3 are managed by the District of Saanich. Because they are located in municipal parks in close proximity to some of the most densely populated areas of Victoria, all three sites experience steady recreational use throughout the year. Here, long term prospects for the survival of the species will be tied closely to any future land use decisions made with regard to the management of these popular areas. A stewardship plan for the municipal park containing Population #1 is currently being drafted jointly by the University of Victoria’s Restoration of Natural Systems Program and the Municipality of Oak Bay. The site supporting Population #3 has been designated as a Conservation Area by the Municipality of Saanich, which is currently developing management strategies to protect known occurrences of rare species at the site. Population #10 is on property owned by Parks Canada Agency.