Alkaline wing-nerved moss (Pterygoneurum kozlovii) assessment and status report: chapter 7

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Habitat

• Habitat Requirements
• Trends
• Protection/Ownership

Habitat Requirements

Pterygoneurum kozlovii is restricted to the edges of open, seasonally wet and alkaline ponds, lakes, sloughs, and seepage slopes, where vegetation remains low and patches of soil are available. In this habitat, it grows on open or litter-covered soil amongst vascular plants, especially salt grass (Distichlis stricta), sedges (most commonly Carex praegracilis), and, sometimes, foxtail barley grass (Hordeum jubatum). It is most often found within a narrow band around the edges of the wetland where the topography is flat to very slightly sloping. It has not been found in alkaline sites where tall rushes and sedges dominate. The alkaline nature of these areas arises from evaporation of water during warmer months over many years, leaving minerals behind.

Alkaline wetlands are relatively common in the south-central portions of the province, along river valleys and adjacent lowlands. They are most common in a relatively large area south and west of Williams Lake, but are also fairly common in relatively narrow bands in the drier portions of the Fraser, Thompson, Nicola, Similkameen, and Okanagan Valleys. Scattered alkaline areas are also present in the Rocky Mountain Trench.

Although alkaline wetlands probably number in the hundreds in British Columbia relatively few appear to have suitable habitat for Pterygoneurum kozlovii. Based on field experience, Terry McIntosh has defined 'potential habitat' for this taxon as:

1. In seasonally wet alkaline areas where bare soil is available; these alkaline areas are either distinct ponds, pocket complexes comprised of small ponds and seepage areas, or seepage slopes. The species appears to be most common near ponds and least common on seepage slopes.
   
2. On a flat to very gentle slope within a low-growing vegetation zone above, but not in, a zone defined by a complete alkaline-deposit crust; the low-growing vegetation is often defined by the presence of two graminoid species: Carex praegracilis and Distichlis stricta. The species has not been found where taller sedges and rushes predominate.
   
3. In open areas (no shade) at relatively low elevations in sagebrush, grassland, and open forested (ponderosa pine/Douglas-fir/lodgepole pine, although less commonly with the latter two species)
   
4. In areas where erect-growing moss species predominate; P. kozlovii has not been found in sites where creeping moss species, and in particular where Drepanocladus (probably D. aduncus) are present.

Table 1 gives estimates of potential sites, by regions. Potential sites are defined as sites separated by at least .5 km., (but usually much more) and separated by landscapes that do not contain the potential habitats. Based on examinations of maps and through field work, between 93 and 111 distinct sites (geographically isolated ponds, lakes, seepage slopes, or complexes) may provide suitable habitat for this species in the province. Although more work needs to be completed, this species appears to be restricted to those alkaline areas in warmer locations (lower elevation/more southerly latitude). This is supported by the concentration of this species in the Okanagan and Kamloops areas. Alkaline wetlands are found in the Bunchgrass, Ponderosa Pine, and dry Interior Douglas-fir Biogeoclimatic Zones.

Over the past seven years and during his Ph.D. work, T. McIntosh has investigated the edges of probably more than 75% of the alkaline wetlands that have potential habitat for this species in British Columbia (see Table 1), and has confirmed the presence of Pterygoneurum kozlovii at only 13 sites. However, the edges of many of these ponds and the potential habitat for this species are extensive, covering hectares in some sites, and, because of collection time constraints, this species could have been overlooked at some of the sample locations.

Trends

In 1997, T. McIntosh initiated a survey of provincial arid-land areas in order to complement his Ph.D. work (McIntosh 1986) in preparation for a research paper describing and providing keys for the bryophytes of these regions. From 1997 to 2001, some 45 alkaline wetlands of potential habitat for this species were visited at various locations throughout the semi-arid regions of south-central British Columbia (about 20 sites were visited in the Cariboo Region from north of Clinton to west of Williams Lake, and another 25 were visited in the Kamloops/Merritt/Okanagan areas, where this species appears to be more common; these sites were not documented with UTM information). The primary focus of these visits was to look for a number of rare bryophytes, including Pterygoneurum kozlovii. Five new populations were found for this species during this survey. 

Thirteen populations were examined by T. McIntosh in 2002-03 (Table 2; the White Lake population, 25, was confirmed in the field and a collection not made due to paucity of material). Of the nine original populations in British Columbia (field work conducted 1980-83, McIntosh 1986), six may have been extirpated (Sites 2, 3, 4, 6, 8, and 9), four in the Osoyoos area, one west of Kamloops, and one near Riske Creek. The Saskatchewan population and Populations 20 and 24 southwest of Williams Lake were not visited in 2002.

Thirty additional alkaline wetland sites were also visited in the 2002-03 period, including an attempt at relocating the original sites found by McIntosh during field work for his Ph.D. (field work conducted 1980-83, McIntosh 1986). Only two of them were probably relocated (precise location information was not available for these earlier collections, and some sites were probably destroyed). The investigations during this survey were more intense than the earlier survey, and more time was spent at each site. Nine new populations were found.

Table 3 lists habitat condition and trends for each known population, as well as at the Spotted Lake area, although Pterygoneurum kozlovii was not found there in 2002. Habitat notes were made for Populations 20 and 24 south-west of Williams Lake in earlier years. There has been no monitoring of habitat condition trends for this species, since the earlier surveys were not designed to report on these factors. However, some general observations can be made based on the 2002 survey. Eight of the known sites are undisturbed to relatively undisturbed, and eight are moderately to heavily disturbed. Site monitoring is required in order to comment on habitat stability in most sites.

Numbers in brackets following population number refer to collections examined; the White Lake population, #25, was confirmed in the field but a collection was not made due to paucity of material.

Protection/Ownership

Most of the extant populations appear to be on provincially owned lands, in particular Crown lands, although ownership needs to be confirmed for some sites (Table 3). Populations 19 and 25 are protected within cattle exclosures. Although Site 20 is in the Churn Creek Protected Area, grazing by cattle occurs there. Site 11, an extensive population in apparently good condition, is in a horse paddock, but horse use of the area appears minimal.

Population 25 is found adjacent to White Lake in the southern Okanagan Valley. In the past, cattle and horses utilized the area around White Lake. However, the Nature Trust (J. Hope, pers. comm. 2002) recently signed a 99 year lease in order to establish a study area on federal lands at White Lake in accordance with their 2000 Biodiversity Ranch Management Plan. As part of this plan, White Lake and the surrounding riparian vegetation, including the known location for Pterygoneurum kozlovii, have been permanently excluded from grazing and other potential large-scale disturbances through the construction and maintenance of a fence. It is expected that the habitat will improve in the riparian area, although data are lacking on how changes will affect the population of this species.

Notes (in all cases, ‘?’ refers to ‘unknown’ or ‘uncertain’, and a letter in brackets refers to ‘minor importance’):

1. With respect to Column B: Limiting Factors and Threats: A refers to grazing impacts, B refers to human impact, C refers to impact by burrowing animals.
2. With respect to Column C: Habitat Condition: A refers to relatively undisturbed, B refers to moderately disturbed, C refers to heavily disturbed; Habitat Trend: A refers to possibly improving, B refers to possibly stable, C refers to possibly degrading.
3. With respect to Column D: Population Size: A means widespread in area surveyed, B means uncommon across site, and C rare across site; Population Trend: A may be improving, B may be stable, C may be degrading, X possibly extirpated.
4. With respect to Column E: Protection and Ownership: P refers to private ownership and G refers to Government ownership, either municipal (m) or provincial (p, usually Crown land).