Nugget moss (Microbryum vlassovii) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements

In British Columbia, Microbryum vlassovii is found in the Bunchgrass Biogeoclimatic Zone where it occurs on undisturbed and exposed compact silts and clays on post-glacial lacustrine banks in semi-arid steppe and low-elevation grassland environments (Brink 1997). There is a variety of potential bryophyte habitats on these banks defined by aspect, slope, and associated vegetation cover. Examination of earlier collections and observations made during recent fieldwork show that this species either grows on highly exposed or partially shaded steep slopes where few other moss species are able to grow. It has not been found growing in the late successional lichen-dominated crust that predominates over most low-elevation and undisturbed lacustrine bank environments. Therefore, M. vlassovii may be more characteristic of early successional situations, including sites that are relatively less disturbed than other portions of the banks, and where potentially competitive lichens and mosses are unable to colonize (however, an earlier collection at Penticton had a relatively large patch of this species growing with Barbula unguiculata, a species characteristic of more shaded conditions). During the 2004 survey by T. McIntosh at the Penticton site, M. vlassovii was found on an exposed, south-facing, early successional steep face; associated moss species included Aloina bifrons andPseudocrossidium obtusulum, and these were poorly developed. A few early successional lichen species were present as well. Zander (1999) lists the substrate and elevational range as unknown; the Californian collection was found on clay soil in a pastured hillside.

Lacustrine bank habitats are common landforms within the Bunchgrass Biogeoclimatic Zone, which is restricted to a number of narrow valleys in the south-central part of the province. Common plants in this zone are bluebunch wheatgrass (Pseudoroegneria spicata), needle-and-thread grass (Heterostipa comata), big sage (Artemisia tridentata), and, in the southern portions of the Okanagan Valley, antelope brush (Purshia tridentata).

Lacustrine banks can be very extensive and kilometres in length, such as those near Kamloops and Penticton, or can be quite small, less than a hectare in extent, such as found in smaller adjacent valleys. Although lacustrine banks are common in British Columbia, relatively few appear to have suitable habitat for the nugget moss. Based on field experience and close examination of the known habitats, T. McIntosh has defined 'potential habitat' for this taxon as:

1. Only on extensive lacustrine banks in the hottest and driest portions of the province, specifically in the South Thompson Valley near Kamloops and in the south Okanagan. Some of its associated lichens and mosses are only common or restricted to these banks, and
2. Only on very steep portions of these banks which appear in an early successional state.

Habitat trends

Both British Columbia sites appear to be, in general, relatively undisturbed, although there appears to be occasional human activity at bothknown sites. Hiking on the lacustrine banks in the Penticton site is apparently discouraged by the local residents. Small patches of bank erosion on the steep banks above the roadside ditch at the Penticton site are present but sporadic.

Habitat protection/ownership

Both sites are near residential areas within city limits and there doesn’t appear to be any specific protection for either site.