Assessment Notes

Justification

Idaho Grouse Pellet (Rhizoplaca idahoensis) is narrowly endemic to the Little Lost River and Birch Creek Valleys in Idaho, United States of America. Its total area of occupancy is 48  km², and its extent of occurrence is 996 km². It grows over deep gravel calcareous alluvium soils and remains unattached to any substrates. The most serious threats to this species are sheep grazing, which reduces the population size and area of occupancy, and road building, which fragments subpopulations and reduces the population size (Rosentreter 1997). Both threats have reduced the extent and quality of habitat for the species over the past decade and are expected to continue to do so. Thus, R. idahoensis is Endangered B1ab(ii,iii,iv,v)+2ab(ii,iii,iv,v).

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Taxonomic notes

Leavitt et al. (2019) confirmed the circumscription of this species.

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Geographic range

Rhizoplaca idahoensis is restricted to the Little Lost River and Birch Creek Valleys in Idaho, United States of America.

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Population and Trends

Rhizoplaca idahoensis can be very locally abundant, with subpopulation sizes in the thousands. However, subpopulations are very isolated. Subpopulations have likely been fragmented by sheep grazing and road construction. Due to human activities, there are likely now over 20 sites, where in the past they would have been contiguous. Sheep grazing has the potential to affect an entire valley, and thus this species occurs at only two locations. Native pronghorn antelope also eat this species in the winter, but it is unknown to what extent this herbivory affects populations or changes over time (Thomas and Rosentreter 1992).

Population Trend: decreasing

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Habitat and Ecology

Rhizoplaca idahoensis grows on deep gravel calcareous alluvium basins and benches between 2,100 and 2,400 m. It is unattached to the soil or rocks and is considered a 'vagrant' lichen. The climate where it occurs is cold, arid, and continental, an unusual climatic combination in the region.

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Threats

The main threat to Rhizoplaca idahoensis is sheep grazing (Rosentreter 1997). Cattle apparently do not impact this species. Road construction is another major threat as it fragments subpopulations because these 'vagrant' lichens tend to be trapped by and accumulate into road ditches which are unfavourable microsites (Rosentreter 1993, 1997, Rosentreter and McCune 1992). Some invasive species, including Alyssum desertorum, Bromus tectorum, Centaurea stoebe ssp. micranthos, Lepidium perfoliatum, Rhaponticum reptans, may tend to exclude this lichen. Wind farm development may be an additional threat, along with powerlines and telephone poles.

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Conservation Actions

This species is state listed in Idaho as S2 and subpopulations occur on two types of federally held lands, Bureau of Land Management and National Forest Land. Excluding sheep grazing from areas where the species remains is essential, along with site protection and management. Raising awareness of the threats facing soil-dwelling lichens, including Idaho Grouse Pellet, is an additional conservation need.

There are multiple outstanding research questions that must be addressed to aid in recovery of Rhizoplaca idahoensis, including: 1) developing methods for mitigating the obstructive effects of gravel roads and reducing mortality in ditches, 2) on the ground surveys to locate possible additional locations (e.g. other valleys with similar geology and climate), and 3) monitoring projects to quantify the rate of decline in population sizes.

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Use and Trade

There are no known commercial uses of this lichen.

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Source and Citation

Root, H., Rosentreter, R. & Hollinger, J. 2021. Rhizoplaca idahoensis. The IUCN Red List of Threatened Species 2021: e.T194662185A194678184. https://dx.doi.org/10.2305/IUCN.UK.2021-2.RLTS.T194662185A194678184.en .Accessed on 1 October 2023

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