Nugget moss (Microbryum vlassovii) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

British Columbia has received considerable survey effort for mosses (bryophytes) and the flora of a large portion of the province has been well documented (Figures 3, 4). Among the areas best collected are the south-central and south-western parts. The dryland areas of south-central British Columbia, in particular, were the focus of intense survey during the early 1980’s as part of a PhD dissertation by T. McIntosh (McIntosh 1986).

In 1997, T. McIntosh initiated a further survey of British Columbia arid-land areas to complement his earlier work (McIntosh 1986) in preparation for a research paper describing and providing keys for the bryophytes of these regions. From 1997 to 2002, 17 suitable lacustrine (glacial lake-derived) banks in the semi-arid portions of the province were surveyed for Microbryumvlassovii, as well as other uncommon species. This survey included lacustrine banks near Penticton, Naramata, and Summerland, in the Okanagan Valley, near Merritt, near Kamloops, and near Spences Bridge (place names are labelled in Figure 4). Additional populations of Microbryumvlassovii were not found during these surveys.

This moss is highly inconspicuous and may be overlooked in its habitat, as it is both small and grows only as scattered individuals or small patches. Notwithstanding these characters, this moss is not impossible to find. Its size and habit are similar to those of many other unrelated mosses whose occurrences are in fact well known, and that are frequently collected by non-experts. Moreover, because mosses are restricted to, and often found in only a small range microsites, searchers will generally focus their efforts on these to effectively narrow their search.

Nugget moss appears to be restricted to relatively undisturbed, yet early successional, sites where competition from other species is restricted. These types of sites are not common relative to other habitats in the dry interior. T. McIntosh extensively surveyed lacustrine banks during his PhD studies and many times since then (all major lacustrine banks have been surveyed at one point or another). Many of the other rare and localized lacustrine bank-restricted mosses (including Grimmia plagiopodia and Crossidium seriatum, also small and inconspicuous species) have been collected or observed a number of times during these surveys, yet Microbryum vlassovii has only been seen twice. The microsite that this species inhabits appears to be relatively rare in lacustrine bank habitats.

Figure 3. Collecting effort for mosses in British Columbia. Each open circle with central dot represents a general, non-targeted, collecting site for mosses. Locations were obtained from voucher data of approximately 40% of the holdings in the Bryophyte Herbarium at the University of British Columbia (UBC) in addition to several thousand records at the University of Alberta (ALTA) and Devonian Botanic Garden (ALTADBG). This map does not include many of the sites surveyed by T. McIntosh since 1987.

Collecting effort for mosses in British Columbia

Figure 4. Distribution of Microbryum vlassovii in Canadaand general collecting effort for bryophytes in the regions of the Bunchgrass Biogeoclimatic Zone. Each triangle is a general, non-targeted collecting site for bryophytes. Locations were obtained from voucher data of approximately 40% of the holdings in the Bryophyte Herbarium at the University of British Columbia (UBC). This map does not include many of the sites surveyed by T. McIntosh since 1987 but labelled place names show areas where T. McIntosh surveyed 17 suitable lacustrine bank sites from 1997 to 2002.

Distribution of Microbryum vlassovii in Canadaand general collecting effort for bryophytes in the regions of the Bunchgrass Biogeoclimatic Zone

Potential sites for nugget moss are defined as sites separated by at least 0.5 km and separated by landscapes that do not contain the potential habitats (for example water near Penticton, and an urban centre at Kamloops). Through examination of representative specimens and information from locations of this taxon in Europe and

Asia, T. McIntosh considers only four areas (sides of valleys) at two locations as having habitat potential for the nugget moss:

  • Okanagan Valley, both sides of valley from about 12 km south of central Penticton to 18 km north
  • South Thompson River, both sides of valley from about 18 km west of central Kamloops to about 20 km east; mainly on the south side of the river

Further, T. McIntosh has examined more than 75% of these banks and has made over 300 collections of lichens and mosses. Early in 2005, he initiated a thorough survey of the banks running south of Summerland (north-west of Penticton). Over 90% of the potential habitat for this species was examined in this ~4 km stretch and it was not found, although a number of locations for its associated species were recorded.

Abundance

Only the Penticton population was re-located during the recent survey for the species. Here, it is very rare, found in two small patches which were composed of at least 6 individuals and 2 individuals, respectively. In an earlier collection from this site (Collections Examined #2; 1980), it was found in a relatively large patch (2x4 cm), and a note on the collecting bag states that it was relatively frequent.

Fluctuations and trends

No precise information is available on population trends for Microbryum vlassovii in British Columbia.

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