This summer I am—officially—conducting vegetation surveys of vascular plants. But while I do love the beauty and diversity of tracheophytes, I am a cryptogam biologist at heart. When our team was in Big Thicket National Preserve earlier this summer, I identified (with Reese 1984 and other sources) any moss or liverwort species that covered at least 1% of a survey plot. In Big Thicket, wet floodplains whose non-woody vegetation is dominated by Sphagnum palustre and Pallavicinia lyellii occur frequently throughout the park. Drier upland sites sometimes support Leucobryum glaucum and Atrichum angustatum, although these species are never dominant.
Now we are working at Gulf Islands National Seashore, and the bryoflora is much less conspicuous. Aside from one wet depression in the middle of Quercus geminata shrubland, which at ground level was covered by a Sphagnum sp. I have yet to identify, I have not seen any sites where bryophytes form a dominant component of the vegetation.
But while Gulf Islands hasn’t been a bryologist’s paradise, I have been pleasantly surprised by the prominent role terricolous (soil-dwelling) lichens play in some of the park’s habitats. Three species of Cladonia are of particular note: C. leporina, C. prostrata, and C. evansii. They all seem to be most abundant in the Naval Live Oaks and Fort Pickens areas of the park, although I have seen them, albeit not in any abundance, in other areas.
These three species are all characteristic of the southeast coastal plain and are found growing on sandy soils in full or partial sunlight. Cladonia prostrata has the most restricted range; it is found in Florida and adjoining states. Cladonia evansii can be seen further north along the Atlantic coast, while C. leporina has the broadest range of the three and occurs in more inland areas towards the southern Appalachians (Brodo et al. 2001).
In our field sites, I have seen Cladonia evansii most often in semi-shaded areas under an oak canopy. Cladonia prostrata and C. leporina have seemed more common at more exposed sites, either under a sparse layer of shrubby oaks or in gaps in herbaceous vegetation. Vegetation communities containing Cladonia species have tended to be in areas of stable soil: relic dunes and sandy uplands.
Cladonia species have received some attention in ecological studies of Florida scrubland. They may suppress seedling recruitment in vascular plants (Hawkes and Menges 2003). In addition, they tend to become more abundant in post-fire landscapes (Menges and Kohfeldt 1995) and benefit from larger gaps in shrub vegetation (Menges et al. 2008).
UPDATE, 30 AUGUST 2016: When I originally wrote this post, I hadn’t taken any photos of Cladonia evansii. Below are a couple from today’s fieldwork.
Brodo, I. M., S. D. Sharnoff, and S. Sharnoff. 2001. Lichens of North America. Yale University Press, New Haven, CT, USA.
Hammer, S. 2001. Growth dynamics and the taxonomic status of Cladonia leporina. Rhodora 103(916): 405-415.
Hawkes, C. V. and E. S. Menges. 2003. Effects of lichens on seedling emergence in a xeric Florida shrubland. Southeastern Naturalist 2(2), 223–234.
Menges, E. S. and N. Kohfeldt. 1995. Life history strategies of Florida scrub plants in relation to fire. Bulletin of the Torrey Botanical Club 122(4): 282–297.
Menges, E. S., A. Craddock, J. Salo, R. Zinthefer, and C. W. Weekley. 2008. Gap ecology in Florida scrub: Species occurrence, diversity and gap properties. Journal of Vegetation Science 19(4): 503-514.
Reese, W. D. 1984. Mosses of the Gulf South: From the Rio Grande to the Apalachicola. Louisiana State University Press, Baton Rouge, LA, USA.