Bentgrass  (Agrostis trachychlaena)

Classified as Endangered (EN) on the IUCN Red List (1).

Agrostis trachychlaena is a small, creeping grass that grows in loose clumps or tufts, and spreads by putting out horizontal stems, called stolons, along the ground. The leaf blades of this grass measure around 2 to 7 centimetres long and 0.5 to 2 millimetres wide, and have a ribbed surface and a pointed tip (2).

Agrostis trachychlaena is endemic to Inaccessible and Nightingale Islands, Tristan da Cunha (1).

This grass grows on rocky slopes and in open patches amongst tussocks of the grass Spartina arundinacea, and is often found around the nesting sites of albatrosses (1).

Agrostis trachychlaena is a perennial species, living for more than two seasons and not dying after flowering. The flowers are borne on a branched inflorescence, up to 5.5 centimetres long and 1.6 centimetres wide, comprising a cluster of small units known as ‘spikelets’ (2). Little other information is available on the biology of this species.

The population of Agrostis trachychlaena is though to number fewer than 250 mature individuals. The species has only been found once on Inaccessible Island, and on Nightingale Island the dense cover of Spartina arundinaccea makes it difficult to accurately estimate the population size. It is thought that Agrostis trachychlaena occupies a total area of less than ten square kilometres, and, together with its small population, this makes it particularly vulnerable to extinction (1). Although thought to be naturally scarce, possibly because of natural erosion of the volcanic islands and the subsequent loss of habitat, potential man-made threats include the introduction of non-native plant species, and fire (1). In particular, introduced New Zealand flax (Phormium tenax) has the potential to exclude native plant species, and increasing tourism on the islands means an increasing potential for future introductions of alien species (3). Non-native invertebrates, including earthworms, slugs and woodlice, have also been introduced to Inaccessible Island, with unknown effects on its ecology (3).

Both Inaccessible and Nightingale Islands are subject to management plans, and Inaccessible Island was declared a Nature Reserve in 1997 (1) (3). Fieldworkers from the Tristan da Cunha Darwin Initiative Project have already undertaken measures to remove invasive New Zealand flax from the islands, although frequent follow-up visits are likely to be needed to ensure the islands remain free of this and other alien plants. It will also be important to inform visitors about the risk of accidentally introducing exotic species, and to take necessary precautions to prevent introductions (3) (4). Further research may be needed into Agrostis trachychlaena before more specific conservation measures can be put into place for this species.

To find out more about Agrostis trachychlaena, and about conservation on the islands of Tristan da Cunha, see:

• Royal Botanic Gardens, Kew - GrassBase:
  http://www.kew.org/data/grasses-db/www/imp00293.htm
• Tristan Island Government. (2006) Tristan da Cunha Biodiversity Action Plan (2006-2010). Tristan Island Government, RSPB, and University of Cape Town. Available at:
  http://www.rspb.org.uk/Images/TristanBiodiversityActionPlan2_tcm9-180968.pdf