BSBI Species Accounts ArchiveCarex maritima
Tue, 08/24/2010 - 13:19 | 
markd
The name Carex maritima Gunnerus is accepted by all authorities (Sell 1996; Stace 1997), and antedates the synonym C. incurva Lightf. Its common name is Curved Sedge.
Chromosome No.: 2n = 60 (Stace 2010).
Photograph: A.J. Lockton.
In the British Isles this species is now entirely restricted to Scotland. It used to occur in two places on the Northumberland coast but it has not been seen at either for some time. Some maps show dots on the coast of Lancashire and Cumbria but these are now thought to have been errors. There is a widespread perception (e.g. Preston, Pearman & Dines 2002) that Carex maritima is declining dramatically, but recent surveys by the BSBI have shown that it is still more widespread than was believed (Jermy et al. 2007). The problem with targeted survey like this, however, is that the extra recording effort creates a bias in the data, meaning that any comparisons are open to some doubt. Certainly there are more sites now known for it than ever before, and it is thriving in many of those sites, but that does not necessarily mean that it is increasing. It is widely distributed throughout the sub-arctic region, on coastal dunes and on mountains such as the Alps, Caucasus, Himalaya, Rockies and Andes (David 1982). It also occurs on coasts in the southern hemisphere (David in Stewart, Pearman & Preston 1994).
Photograph: A.J. Lockton.
Click on the map to view full-size on the BSBI Maps Scheme website.
Origin: native in Britain, although some populations inland are accidental introductions.
Rarity: Nationally Scarce in Britain (Stewart, Pearman & Preston 1994), but extinct in England and absent from Wales and Ireland.
Threat: currently classified as Endangered (Cheffings & Farrell 2005), but if it is not declining it would be more appropriately listed as “Least Concern.”
Conservation: all recorders regard it as an axiophyte, being an indicator of active dune systems. Sometimes it occurs on golf courses and airfields, where it is short-lived and has presumably been spread by mechanical means, and in these situations it is of less value as an ecological indicator.
David (1982) describes four habitats for it in Britain: on open, damp sand; at the mouth of a stream debouching on to a beach; in wet dune slacks; and in turf beside rock pools. It is tolerant of erosion but can stand little competition from other plants (David in Stewart, Pearman & Preston 1994). It reproduces vegetatively by deeply-rooted rhizomes and can form extensive stands quite rapidly. It seems likely that it is a vigorous coloniser, able to exploit available eroded habitats when they become available. By contrast, there are numerous instances of it disappearing from closed swards or successional vegetation communities. C. maritima plants can produce abundant large fruits which may be adapted to long periods of dormancy. The existence of a large viable seedbank may be the reason why it sometimes appears in huge numbers in dune slacks, golf courses, airfields and quarry floors, only to disappear completely after a few years. It is also known to crop up in sand dumped by roadsides or used in inland construction projects but, again, it doesn’t tend to last long. Rodwell (2000) gives no NVC communities for Carex maritima, but in the new Sedge Handbook Jermy et al. (2007) suggest that it occurs in communities ‘such as’ SM16 Festuca rubra and SM19 Blysmus rufus saltmarsh.
Photograph: A.J. Lockton.
To know how C. maritima is faring in the long term, we need to how many sustainable ‘natural’ sites there are - the ones by streams in dune systems, and how many temporary ‘un-natural’ sites there are. This situation is complicated by the fact that some of the temporary sites, such as dune slacks, may be part of the natural cycle. In essence, the key question about C. maritima is: ‘Is the seedbank increasing or decreasing?’ But we have no direct way to measure that. Potential threats to this species include coastal erosion, sea-level rise, and development in coastal areas. Drainage and agricultural improvement of coastal grasslands could threaten sites, as could a change in rainfall patterns as a consequence of climate change. On the other hand, several of these factors could work to increase populations and create new sites. Continued detailed recording is needed before any of these questions can be answered. Another question of interest is why it is not found on the west coast of Scotland. One theory that has been put forward is that it cannot adapt to falling sea levels, whereas it can stand rising ones (the west coast of Scotland is slowly rising by isostatic rebound, following the last Ice Age). There is no way of testing this theory yet, but perhaps similar conditions occur elsewhere.
- David, R.W. 1982. The distribution of Carex maritima Gunn. in Britain. Watsonia 14, 178-180.
- Jermy, C., Simpson, D., Foley, M. & Porter, M. 2007. Sedges of the British Isles, 3rd ed. Botanical Society of the British Isles, London.
- Lockton, A., Pearman, D. & Metherell, C. 2009. Is Carex maritima extinct in England? BSBI Recorder 13, 10-11.
- Pearman, D. & Lockton, A. 2007. Progress with the Carex maritima survey. BSBI Recorder 11, 11-12.
- Pearman, D. & Lockton, A. 2008. Carex maritima update. BSBI Recorder 12, 11.
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