Cladonia submitis is an endemic macrolichen native to the Mid-Atlantic coast of North America, inhabiting primarily pine barren and sand dune habitat. It has a restricted area of occupancy (AOO = 196 km2), and is considered to be severely fragmented. The species shows evidence of decline due to habitat loss resulting from land use changes and development. Based on recent large-scale surveys, there has been a 59.3% decline in AOO and a 39.3% decline in extent of occurrence (EOO) in the past century (Hoffman et al. 2020). A similar range of decline in the population size is inferred based on the reduction in EOO and AOO. Overall, therefore, the species is listed as Endangered under criteria A2c; B2ab(i,ii,ii,iv).
Cladonia submitis is endemic to eastern North America, with occurrences as far north as southern Maine and as far south as central North Carolina, from the coastline to eastern West Virginia (Brodo et al. 2001, Hoffman et al. 2020). However, occurrences in the western extent of its range are presumed no longer to be extant. The species has also been recorded from Honshu and Hokkaido, Japan, and Sakhalin Island, Russia, but the taxonomic identity of these collections is unlikely to be C. submitis. The morphology and habitat differences are notable enough to suggest that the East Asian collections are not C. submitis (Ahti 1961, Hoffman et al. 2020), and thus are not included here.
Across most of its range, the population of Cladonia submitis is naturally patchily distributed, occurring primarily in exposed patches among forested habitats. However, the species is typically locally abundant where it occurs. The current population size is estimated to exceed 4,200 individuals based on counts at each site until the number exceeded 100 distinct thalli (Hoffman et al. 2020). As population size estimates were made only at a subset of occurrences for the species, and at most of these sites the number of individuals was considerably greater than the maximum count recorded, this estimate of population size is most likely highly conservative. However, the conversion of habitat to commercial and residential land has extirpated the species at 14 of its historical occurrences. All of the known disjunct occurrences in mountainous regions consist of small numbers of individuals in spatially restricted rock outcrop habitats, and some of these have not been relocated in 30 years or longer. These declines have caused a notable reduction to the area of occupancy (AOO) and extent of occurrence (EOO). Hence, we infer a population decline for the species due to these anthropogenic effects within the last 3 generations. As the processes that have caused past declines in the core area of the population along the coast have not ceased, and are ongoing, we infer that the there is also a continuing decline in the AOO and EOO, as well as in overall habitat quality due to increased fragmentation and habitat loss.
Population Trend: decreasing
Cladonia submitis is primarily restricted to exposed sections of sand and sparse grass or shrubs among pine barren and sand dune habitat. In pine barrens, the species occurs along roadsides or in exposed areas with reduced canopy coverage, among pitch pine (Pinus rigida) and oaks (Quercus marilandica, Q. berberidifolia). On dune habitat, the species typically inhabits the inter dune, with beach plum (Prunus maritima) beach heather (Hudsonia tomentosa) and occasional pitch pine. In both habitat types, the species grows in a large assemblage among other Cladonia species, including C. subtenuis, C. rangiferina, C. uncialis, C. atlantica and C. boryi. Cladonia submitis has also historically been reported from a small number of scattered locations on exposed rock outcrops in the Piedmont and Appalachian Mountains, in assemblage with other Cladonia species.
The most immediate threat that Cladonia submitis faces is that of habitat loss and degradation (historical and ongoing) from land use changes and development. In the majority of its range, C. submitis inhabits land around a metropolitan area which has grown and developed considerably over the last century. Many places where the species had been collected in the past were recently found to be transformed into residential or commercial land (Hoffman et al. 2020). While the species can occasionally be found on sandy roadsides, creating small pockets where the species can occur, the overall trend of land development threatens the species in the majority of its range, leading to more than a 50% decline in its area of occupancy.
Cladonia submitis also faces threats from climate change, particularly in the form of modified fire regimes and sea level rise. The species primarily occupies pine barren and sand dune habitats. Pine barrens, once influenced by a natural fire regime, are an at-risk habitat due both to fire-suppression and because fire disturbances are projected to become more frequent and intense under climate change (Keeley and Syphard 2016). Suppression of the natural fire regime can result in overgrowth of vegetation which can overshade and exclude C. submitis. This overgrowth also leads to increased fuel loads, which leads to more intense fires, that will also impact remnant individuals (Ray et al. 2020). This forecasted change in the fire regime poses a risk to C. submitis inhabiting pine barrens. Sand dunes on the other hand, are threatened by erosion caused by sea level rise, projected to become more significant under climate change (Sweet et al. 2017). The species appears to have been lost from inter dune habitat along Cape May, New Jersey following a significant storm in 1962, in which the majority of the dunes were destroyed (see Jordan 2003, Hoffman et al. 2020).
Cladonia submitis inhabits a range of public and protected land. While the species is more protected from urbanization and land use changes in state and federal protected areas, such as Island Beach State Park and Wharton State Forest in New Jersey, it is threatened by those effects outside of such boundaries. An increase in the public awareness and education about the species, and particularly its threatened habitat (pine barrens and sand dunes), is needed. Additionally, further research that will aid in the conservation of this species includes population assessments and monitoring, population genetics studies, and ecological studies that incorporate threats to the species. Additionally, a species recovery plan needs to be written. Studies into the true identity of specimens collected in Japan and Russia should also be conducted.