Biodiversity & Conservation

This biotope is widespread in lowland Britain and has a scattered distribution in estuaries and inlets and coastal lagoons around the British Isles. It is recorded from the Tay in east Scotland, south to the Wash, south east England, the Solent, Seven estuary, Gower Peninsula, Cardigan Bay, Morecambe Bay, Solway Firth, and west Scotland.

Temperature range preferences - See additional information

Water clarity preferences - Not relevant

Limiting Nutrients - Nitrogen (nitrates)
Phosphorus (phosphates)

Other preferences - Wet or periodically waterlogged habitats

Marine records of this biotope are restricted to Scottish saline lagoons (JNCC, 1999) but the equivalent NVC S4 community is widespread in lowland Britain and has a scattered distribution in estuaries and inlets and coastal lagoons around the British Isles (Rodwell, 1995). NVC S4 occurs in a variety of permanently wet or periodically waterlogged habitats, with different substrata and trophic states. Reed stands are common in open-water transitions around lakes, estuaries, flood-plain mires, along dykes, canals and sluggish lowland rivers, peat cuttings, salt marshes and saline lagoons (Rodwell, 1995).

Habitat preferences

• Phragmites survives in a variety of water regimes with water-tables varying between 2m above the substratum to 1m below. Optimal performance occurs with water levels between 50cm above the substratum to 20cm below, and flooding for at least several months of the year. Healthy growth is favoured by a regular water regime, and Phragmites is uncommon in areas subject to erratic variation in water level (Haslam, 1978; Rodwell, 1995).
• Phragmites tolerates water-logging and reducing conditions (low oxygen) as long as the rhizomes remain aerated through dead aerial stems (Rodwell, 1995).
• The depth of the bed is limited by photosynthetic ability since the leaves of Phragmites die underwater, and about one third or more of the shoot needs to be above water.
• In tidal waters in the Netherlands, Phragmites grows between 1.5m below to 0.25m above mean high water and optimally between 1m below and 0m above (Haslam, 1972).
• Nutrients (N and P) are limiting, and Phragmites grows best in eutrophic conditions (Rodwell, 1995).
• Where nutrients are in adequate supply, Phragmites shows few substratum preferences, growing on mineral or organic soils, but seedlings show a preference for mineral soils, while the common reed is a good peat forming species and, hence, often associated with organic soils. The common reed forms only a thin cover on nutrient poor silts or acid peats.
• Phragmites australis is characteristic of negligible or slow water flow and IMU.NVC_S4 was recorded from saline lagoons with very weak tidal streams in extremely to ultra wave sheltered conditions, although it was intolerant of fast flow or flood, presumably due to erosion of the substratum (Haslam, 1978; Connor et al., 1997a).
• Phragmites tolerates salinities between 2 -12 g/l, but up to 22 g/l in Poole Harbour, although bud formation is reduced at high salinities (Rodwell, 1995). Hellings & Gallagher (1992) reported that shoot density, height, biomass, underground reserves and rhizome carbohydrates decreased with increasing salinity, from 0 to 15 and 30 g/l. However, stands of Phragmites have been reported to grow at salinities of up to 65g/l (Hellings & Gallagher, 1992). Amsberry et al. (2000) reported that colonization of new habitats by Phragmites was restricted by physical factors including salinity but that the expanding reed bed could colonize low salt marsh habitats and hence higher salinities by clonal, vegetative growth.
• Phragmites occurs from tropical areas to above 70° N (Haslam, 1972).
• Phragmites becomes more sterile towards its northern European limit, and shoots cannot grow in cold weather and are killed by severe frost. In Britain it must complete its annual growth between April and September, while its growing season is longer in Malta. Warmer temperatures stimulate growth (Haslam, 1972; Rodwell, 1995).

For further details see Haslam (1972, 1978) and Rodwell (1995). Detailed accounts of the physical and chemical tolerances of Phragmites australis in fresh waters and sediments are given by Haslam (1978) and an overview of factors affecting growth is provided by Boar (1992). The habitat requirements for the associated bird species are discussed by Tyler (1992).