Biodiversity & Conservation

SS.SMp.Ang.S4

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Removal of the substratum due to dredging or other activity would result in loss of the reed bed, including aerial stems and rhizomes, together with its associated community. Therefore an intolerance of high has been recorded. Recovery will depend on colonization of the habitat by seed or plant fragments and may be protracted (see recoverability below). Therefore a recoverability of moderate has been recorded.
Smothering
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Little information was found. Haslam (1978) noted that Phragmites australis maintains the same root (rhizome) level as sediment builds up. But reed beds usually accumulate sediment, organic material and litter, through which shoots continue to grow. Smothering with 5cm of sediment (see benchmark) may impair growth if it occurred in spring before or during growth of new shoots. In late spring or summer aerial shoots are considerably higher than 5cm an would be little affected. However, Phragmites was reported to be able to grow through ca 10cm of tarmac, albeit as thin and small shoots (Haslam, 1973 cited in Baker et al., 1989).

Benthic infauna are likely to be little affected. Amphipods, isopods and aquatic insects may be adversely affected if they cannot burrow up through the smothering material or their food source (e.g. benthic microalgae or macroalgae) are destroyed. However, little damage is likely to occur to the bed due to smothering by 5cm of sediment for a month (see benchmark) as any grazers lost in the bed will probably be rapidly replaced from the surrounding area. Therefore, an intolerance of low has been recorded. Recovery would be immediate.

Increase in suspended sediment
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Phragmites australis occurs in low water flow habitats, often with high levels of suspended sediment, e.g. estuaries. In addition, its stems slow water flow further, resulting in increased sediment deposition, and it builds up and binds organic sediment due to accumulation of litter, dead rhizomes and roots. The habitats in which the biotope occurs are depositional environments, so that most aquatic organisms inhabiting the environment are probably also tolerant of sedimentation and suspended sediment. An increase in suspended sediment at the benchmark level is unlikely to adversely affect the reed bed or its associated species. However, in the long term (many years) increased sedimentation will allow the reed bed to colonize deeper water, although it may be out-competed at its inland limit in the absence of management (see emergence). Therefore not sensitive has been recorded.
Decrease in suspended sediment
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Phragmites australis builds up and binds organic sediment due to accumulation of litter, dead rhizomes and roots. A decrease in suspended sediment in the long term could potentially increase the erosion rate. But at the benchmark level (one month) a change in suspended sediment is unlikely to have an adverse effect. Therefore, not sensitive has been recorded.
Desiccation
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Phragmites australis occurs in a variety of water regimes with water tables between 2m above to 1m below the substratum surface. The Phragmites dominated community occurs from permanently deep to shallow water, and from summer-dry and winter flooded areas. Therefore, Phragmites is probably tolerant of desiccation at the benchmark level. Mobile species such as gammarids, mysids and fish will probably avoid drying conditions and move to deeper water, while hydrobids are probably tolerant of desiccation, e.g. Hydrobia ulvae can survive emersed in sediment at the high strandline for over a week. But, bryozoans are restricted to damp habitats on the shore, so that colonies on emergent plants are likely to be adversely affected. The litter and peaty organic substratum generated by Phragmites probably holds water and provides a damp microclimate for aquatic invertebrates such as isopods, amphipods and benthic infauna in tidal sites. Therefore, the reed bed and its associated community is probably not sensitive to increases in desiccation at the benchmark level. However, in the long term, a reduction in the water table, or an accumulation of sediment and litter, may reduce the Phragmites density and allow other species to colonize the reed bed, e.g. as in the Galium palustre sub-community (Rodwell, 1995).
Increase in emergence regime
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Phragmites australis occurs in a variety of water regimes with water tables between 2m above to 1m below the substratum surface, although optimum performance occur in water levels ranges between 50cm above to 20cm below the substratum surface (Rodwell, 1995). As sediment and litter accumulate, the water table effectively falls deeper into the sediment, giving rise to a landward succession of increasingly drier habitats. Succession may be complex (see Rodwell, 1995). However, a reduction in water level usually results in the landward replacement of the Phragmites communities with the Galium sub-community (Rodwell, 1995) or the Atriplex sub-community in saline sites, usually interspersed with other saltmarsh communities (see Rodwell, 1995, 2000). As the soil becomes dryer the reed bed may give way to fen, swamp or alder/willow carr (Rodwell, 1995). Therefore, with increasing emergence and hence lowering of the water table, the monodominant stands of the Phragmites sub-community give way to more species rich sub-communities.

The diversity of soil invertebrates is likely to increase to the detriment of aquatic invertebrates. Mobile species (e.g. fish, gammarids and mysids) will probably avoid the factor and filamentous green algae (e.g. Ulva spp.) are probably tolerant of emersion, while emersed bryozoans may be adversely affected due to the increased desiccation risk, potentially reducing aquatic species richness.

Excessive drainage and water abstraction have been implicated in the decline of reed beds in the UK (Anon, 1995). But the succession described above is likely to be a long term effect of a marked reduction in water level. Phragmites australis tolerates a wide range of water levels and a change in emergence at the benchmark level is unlikely to have a marked effect on the reed bed over a period of year, although competition form other species is likely to be increased in that period. Nevertheless, reed beds are intolerant of larger or prolonged changes in water level, as are, therefore those organisms dependent on dense stands of reed such as the bittern and reed bunting. Therefore, an intolerance of intermediate has been recorded to represent the known importance of the emergence regime in the longevity and maintenance of reed beds. Recoverability is likely to be high (see additional information below).
Decrease in emergence regime
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Phragmites australis occurs in a variety of water regimes with water tables between 2m above to 1m below the substratum surface, although optimum performance occur in water levels ranges between 50cm above to 20cm below the substratum surface (Rodwell, 1995). In tidal waters in the Netherlands, Phragmites grows between 1.5m below to 0.25m above mean high water (MHW) and optimally between 1m below and 0m above MHW (Haslam, 1972). The maximum depth that Phragmites can colonize is dependant on their ability to put a photosynthetic canopy above water. The leaves of Phragmites die underwater and greater than about one third of the aerial shoot must be above water for growth (Rodwell, 1995). But maximum depth also varies with trophic status, so that in oligotrophic Scottish lakes it may be only 0.75m but increases in eutrophic lakes or with increasing temperature. Phragmites can survive the low oxygen conditions associated with water logged soils as long as dead aerial stems remain to supply air to the rhizomes (Rodwell, 1995). Where dead aerial stems are cut or removed by wave action, or the stubble flooded too deeply bud growth in late summer and spring is reduced (Rodwell, 1995). Hellings & Gallagher (1992) noted that mixture of cutting and flooding with brackish water resulted in death of experimental stands of reed.

Therefore, increased immersion is likely to limit the seaward extent of Phragmites, perhaps favouring more typical saltmarsh communities (e.g. £IMU.NVC_A12£) and a more marine aquatic fauna and macroalgae. However, the inland extent of the reed bed may increase in the long term. Fell et al. (1998) and Warren et al. (2001) noted little different in macroinvertebrate or fish populations between saltmarsh habitats and saltmarsh invaded by Phragmites in Connecticut, USA, so species richness and community structure may not be affected. Overall, an intolerance of intermediate has been recorded to represent the potential loss of the seaward extent of the biotope, although recovery is likely to be rapid (see additional information below).

Increase in water flow rate
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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. But it was reported to be intolerant of fast flow or flood, presumably due to erosion of the substratum (Haslam, 1978; Connor et al., 1997a). Phragmites is deep rooted with rhizomes between 40-100cm below the surface, sometimes up to 1.5-2m deep, and therefore difficult to erode and strongly anchored in the substratum (Haslam, 1978). But Haslam (1978) reported that Phragmites was intolerant of water movement due to waves or currents. While it could withstand slight scour it was damaged by moderate exposure and absent from severe exposure to wave action or water flow in rivers and lakes (Haslam, 1978).

The crustacean fauna is found in strong water flow and will be probably unaffected by increased water flow directly. However, loss of vegetation, and loosely attached filamentous algal mats will reduce their food supply.

Overall, an increase in water flow from very weak to moderately strong (see benchmark) is likely to remove the litter layer, increase scour and erode the substratum, resulting in loss of plants at the seaward edge, although some rhizomes will probably remain. Over a period of a year, the reed bed will probably be damaged and reduced in extent. A reduction in the extent of the reed bed and hence the available habitat may have adverse effects on the associated terrestrial fauna, e.g. insects and birds (see Tscharntke, 1992). Therefore, an intolerance of intermediate has been recorded. Once flow returns to prior conditions and sediment builds up, recover will probably be rapid (see additional information below).
Decrease in water flow rate
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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. A further reduction to negligible water flow is unlikely to have any adverse effects.
Increase in temperature
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Phragmites australis occurs from north of 70° N to the tropics. Growth, fertility and the length of the growing season increase with increasing temperatures (Haslam, 1972). For example, reeds may grow up to 4m in Malta even with a water level ca. 6m below ground, up to 6m tall in the Danube Delta and up to 6.7m in Uganda (Haslam, 1972). However, Haslam (19720 noted that the increase in height was controlled by several factors rather than just temperature.

The majority of the characterizing species have broad temperatures tolerances or are widely distributed to the north or south of Britain and Ireland, and unlikely to be affected by changes in temperature at the benchmark level. But an acute increase in temperature may adversely affect spring populations of Neomysis integer (see species review).

Overall, an increase in temperature at the benchmark level may benefit the growth, expansion rate and fertility of the reed bed, potentially to the advantage of the associated species. Therefore, not sensitive* has been recorded.
Decrease in temperature
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Phragmites australis occurs from north of 70° N to the tropics but becomes sterile towards its northern limit (Haslam, 1972). Shoots cannot grow in cold weather and are killed by severe frost. Spring frost can markedly affect growth and shoot density. Moderate spring frost may kill the dominant dormant buds, so that subsequent shoots are thinner and shorter. Haslam (1972) noted that light spring frost can cause an increase in shoot density, and standing crop. Buds lost in spring may be replaced, whereas replacement shoots that emerge later cannot. Very heavy or repeated frosts can kill all emergent shoots, preventing their replacement in that season, causing marked short-term variation in reed beds that can take several seasons to recover. A build up of litter provides some protection against frost, so that reed beds exhibit variation in their susceptibility to frost (Haslam, 1972; van der Toorn & Mook, 1982; Rodwell, 1995).

The majority of the characterizing species have broad temperatures tolerances or are widely distributed to the north or south of Britain and Ireland, and unlikely to be affected by changes in temperature at the benchmark level.

Overall, a long term decrease in air temperature is likely to increase the risk of frosts. Severe frosts in spring could potentially result in loss of a years growth of reed, with resultant reduction in primary productivity within the biotope and the wider ecosystem, loss of food plants to insects and hence bird species. Therefore, an intolerance of intermediate has been recorded. Recovery will probably be rapid (see additional information below).
Increase in turbidity
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Phragmites australis forms aerial stems up to 4m in height with leaves above water level. It is an effective competitor for light, excluding many other species in monodominant stands. Haslam (1978) suggested that the common reed was relatively tolerant of shading. Therefore, Phragmites itself is unlikely to be adversely affected by an increase in water turbidity. Increased turbidity will probably reduce the growth of epiphytic or filamentous green algae and charophytes (e.g. Lamprothamnium papulosum) but most invertebrates are unlikely to be affected directly, although loss of algal productivity will reduce the food supply for grazers and ultimately decomposers and deposit feeders. On balance, not sensitive has been recorded.
Decrease in turbidity
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A decrease in turbidity (or shading) may allow submergent or emergent macrophytes (e.g. the charophyte Lamprothamnium papulosum)) to increase in abundance. However, the dominance of Phragmites probably has a greater effect on the availability of light within the reed bed. The growth of algal epiphytes, periphyton and benthic microalgae may be increased by increased light availability, resulting in a minor increase in primary productivity, when compared to Phragmites. Overall, a decrease in turbidity is unlikely to have any adverse effects.
Increase in wave exposure
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Phragmites dominated communities and saltmarsh communities occur in wave sheltered environments. Although, saltmarsh plant communities and reed beds bind sediment and attenuate wave energy, an increase from extremely wave sheltered to 'sheltered' may adversely affect the habitat. Haslam (1978) reported that Phragmites was intolerant of water movement due to waves or currents. While it could withstand slight scour it was damaged by moderate exposure and absent from severe exposure to wave action or water flow in rivers and lakes, and wave action may result in the formation of mats of rotting reed (Haslam, 1978).

The majority of the associated aquatic invertebrate species are probably adapted to wave sheltered conditions, or fine sediments associated with wave sheltered conditions. Mobile species such as mysids, gobies and sticklebacks will probably move to deeper water to avoid wave turbulence. More sedentary gammarids or hydroids may be washed away, while the benthic infauna may be changed due to changes in the substrata from fine to coarser sediment, and a proportion of the epifauna (including insects) and epiflora will be lost on removed vegetation. Increased wave action may result in loss of the litter layer and hence loss of nesting material or nesting sites for reptiles (e.g. the grass snake) and the bittern.

Overall, an increase in wave action at the benchmark level may result in loss of a proportion of the biotope at its seaward limit, together with its associated community. Therefore, an intolerance of intermediate has been recorded. Recovery will probably be rapid (see additional information below).
Decrease in wave exposure
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Phragmites australis is characteristic of negligible or slow water flow and IMU.NVC_S4 was recorded from saline lagoons in extremely to ultra wave sheltered conditions. A further reduction in wave exposure is unlikely.
Noise
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The vascular and non-vascular plants and invertebrate species within the biotope are unlikely to be adversely affected by noise. But wildfowl are intolerant of disturbance from noise from e.g. shooting (Madsen, 1988) and from coastal recreation, industry and engineering works. For example, Percival & Evans (1997) reported that wigeon were very intolerant of human disturbance and, where wildfowling was popular, wigeon avoided Zostera noltii beds at the top of the shore. Birds are likely to be most intolerant of disturbance during the mating season, where noise may interfere with mating calls, or interrupt nesting or food gathering for their young. But the intolerance to noise and visual presence probably varies with species. For example brent geese, redshank, bar-tailed godwit and curlew are more 'nervous' than oyster catcher, turnstone and dunlin. Turnstones will often tolerate one person within 5-10m but one person on a tidal flat can cause birds to stop feeding or fly off affecting c. 5 ha for gulls, c.13ha for dunlin, and up to 50 ha for curlew (Smit & Visser 1993). Goss-Custard & Verboven (1993) report that 20 evenly spaced people could prevent curlew feeding over 1000 ha of estuary. No information concerning the effects of noise of the bittern or reed bunting was found. However, an increase in noise at the benchmark level could potentially affect feeding and reproduction in important bird species, possibly driving nesting birds away from the site, and an intolerance of intermediate has been recorded albeit at very low confidence. Recovery of birds population may be immediate for some species, while shy species may find more isolated sites and take longer to return.
Visual Presence
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The vascular and non-vascular plants and invertebrate species within the biotope are unlikely to be adversely affected by noise but birds are likely to be more intolerant. Disturbance is species dependant, some species habituating to visual disturbance while other become more nervous. For example, brent geese, redshank, bar-tailed godwit and curlew are more 'nervous' than oyster catcher, turnstone and dunlin. Turnstones will often tolerate one person within 5-10m. However, one person on a tidal flat can cause birds to stop feeding or fly off affecting c. 5 ha for gulls, c.13ha for dunlin, and up to 50 ha for curlew (Smit & Visser 1993). Goss-Custard & Verboven (1993) report that 20 evenly spaced people could prevent curlew feeding over 1000 ha of estuary. Disturbance causes birds to fly away, increasing energy demand, or cause them to move to alternative sites. Least human disturbance is likely in winter, however during breeding periods for some species and moulting periods of northerly breeding species in late summer and early autumn most recreational activity takes place, potentially reducing reproductive ability. Therefore an intolerance of intermediate has been recorded for birds in general. Recovery of birds population may be immediate for some species, while shy species may find more isolated sites and take longer to return.
Abrasion & physical disturbance
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The aerial stems of Phragmites australis are cut as part of management, either as a crop or to prevent succession. Cutting and burning may increase plant diversity, and winter cutting of dead stems also increases the next season's crop (Haslam, 1972; Cowie et al., 1992; Rodwell, 1995). Cutting in spring or summer removes causes a reduction of the crop due to loss of irreplaceable shoots, the effects possibly lasting several seasons (Haslam, 1972; Rodwell, 1995). Loss of the winter material and litter may expose the reed to frost damage (see temperature).

Light grazing by wildfowl, livestock, and deer may be tolerated resulting in a denser bed of reed more suitable for bittern (Rodwell, 1995). Heavy grazing may be more damaging. Grazing removes young shoots while the resultant trampling damages upper rhizomes and decreases bud density (Haslam, 1972). Grazing by Canada and grey lag geese was reported to have contributed to the decline of reed beds in Broadland, although non-native coypu (now extinct) probably had a greater impact (Rodwell, 1995). Amsberry et al. (2000) suggested that physical disturbance of salt marsh plant communities may allow Phragmites to colonize low marsh habitats

Cowie et al. (1992) and Dithlogo et al. (1992) reported that their management regimes (cutting, burning and unmanaged) had little effect on the species richness, species diversity and distribution of macroinvertebrates, including soil invertebrates.

Overall, physical disturbance due to anchorage will probably damage a few stems and rhizomes but otherwise have little effect on the reed bed.. But the combined effects of grazing and drainage has been implicated in the decline reed beds (Rodwell, 1995). In addition, Wade (1999) reported that the mooring developments resulted in significant local damage of reed beds in Llangorse lake, south Wales, although no effect of water-based recreation could be demonstrated. Therefore, Phragmites reed beds are probably sensitive to the effects of grazing, trampling, and moorings and an overall intolerance of intermediate has been recorded. Recoverability is probably high (see additional information).

Displacement
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Phragmites australis would probably be severely damaged and fragmented by displacement, resulting in loss of filamentous algae, epiphytes, epifauna and the associated fauna. The mobile invertebrates, gammarids, mysids, fish and birds will probably be unharmed and migrate to adjacent areas. However, the community would probably be lost and a sensitivity of high has been recorded. Recoverability is probably moderate, although Phragmites is probably able to root from fragments of rhizome and stem, which may aid recovery (see additional information below).

Chemical Factors

Synthetic compound contamination
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Little information was found, however, herbicides are used to control or remove Phragmites beds, especially where beds may block water courses or it is considered an invasive species (e.g. the USA). For example, Hawke & José (1996) suggest that herbicides are an effect method for eliminating reed from areas to maintain or create open water. Therefore, it is likely that reed beds are intolerant of herbicide contamination, e.g. from agricultural runoff, especially in isolated areas where contaminants may accumulate such as lakes and lagoons. Pesticide contamination will by definition kill terrestrial insects, aquatic invertebrates, especially crustaceans, and may affect the reproductive success of bird species. Therefore, an intolerance of intermediate has been recorded. Recoverability of the reed and associated invertebrates is probably high, although some bird species may take longer to colonize the habitat.
Heavy metal contamination
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Haslam (1978) suggested that macrophytes were little affected by heavy metals, since a countrywide survey had not been able to detect any correlation between plant distributions and heavy metal concentrations of Cr, Co, Cu, Fe, Pb, Mn, Ni, Sn and Zn. Windham et al. (2001) reported that Phragmites australis sequestered Pb (and by inference other heavy metals) into its rhizome system, reducing the availability of Pb to the wider ecosystem. But growth of Phragmites in sediment containing 68 µg/g Pb resulted in a 40-70% decrease in biomass (Windham et al., 2001).

Cole et al. (1999) suggested that Pb, Zn, Ni and As were very toxic to algae, while Cd was very toxic to Crustacea (amphipods, isopods, shrimp, mysids and crabs), and Hg, Cd, Pb, Cr, Zn, Cu, Ni, and As were very toxic to fish. Gobies were reported to be particularly intolerant of Hg (see Pomatoschistus minutus). Bryan (1984) reported sublethal effects of heavy metals in crustaceans at low (ppb) levels.

Bryan (1984) suggested that polychaetes are fairly resistant to heavy metals, based on the species studied. Short term toxicity in polychaetes was highest to Hg, Cu and Ag, declined with Al, Cr, Zn and Pb whereas Cd, Ni, Co and Se were the least toxic. He also suggested that gastropods were relatively tolerant of heavy metal pollution.

The intolerance of crustaceans to heavy metal contaminants suggests that amphipod and isopod grazers would be lost, allowing rapid growth of epiphytes, and reduced turnover of the detrital food chain. Overall, in the absence of other evidence, the Phragmites beds would probably survive, with reduced productivity but several members of the community may be lost (e.g. fish and crustaceans) resulting in a reduced species richness. Therefore, an intolerance of intermediate has been recorded. Heavy metals are persistent and remain in the sediments for some time after their source is removed, so that recovery will probably be delayed. But once heavy metals return to prior conditions recovery would probably be rapid.

Hydrocarbon contamination
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Phragmites australis was regarded as relatively tolerant of oil pollution by Baker et al. (1989). Their evidence can be summarized as follows:
  • most seaward reed stems were coated in oil after the Sivand oil spill in Humberside in September 1983 but no adverse effects were seen on shoots in 1984;
  • in experiments, Phragmites australis survived 10 successive oiling with Forties crude or heavy fuel oil at Slapton Ley;
  • in water-logged substrata, growth of Phragmites was stunted by hydrocarbon concentrations of 57% but growth was good at 20% and near control levels at 3%, and
  • In Crymlyn Bog, Phragmites grew well at up to 1500ppm hydrocarbons in the substratum although the shortest reeds were encountered where the substratum reached 7000ppm hydrocarbons.
Baker et al. (1989) reported that oil on the substratum surface may weather to a crust, which could potentially inhibit plant growth but noted that Phragmites was reported to be able to grow through ca 10cm of tarmac, albeit as thin and small shoots (Haslam, 1973 cited in Baker et al., 1989).

Suchanek (1993) noted that gastropods, amphipods, infaunal polychaetes and bivalves were particularly sensitive to oil spills. For example substantial kills of Nereis, Cerastoderma, Macoma, Arenicola and Hydrobia were reported after the Sivand oil spill in the Humber (Hailey, 1995). Single oil spills were reported to cause a 25-50% reduction in abundance of Arenicola marina (Levell, 1976). The toxicity of oil and petrochemicals to fish ranges from moderate to high (Cole et al., 1999). The water soluble fraction of oils was shown to cause mortality in sand gobies and fish, especially their larvae, are thought to be intolerant of polyaromatic hydrocarbons (PAHs) (see Pomatoschistus minutus). PAHs are significantly more toxic when exposed to sunlight (Ankley et al., 1997) , and may have a greater effect in clear shallow waters inhabited by pondweed communities.

While Phragmites may be relatively tolerant of oil spills, the associated aquatic invertebrate and fish fauna, and probably the terrestrial invertebrate fauna are likely to be adversely affected. The effects of bird oiling is well known. Therefore, an intolerance of intermediate has been recorded to represent the presence of sensitive species within the habitat. Recovery is likely to be rapid once the site regains its prior condition, although some bids species may take longer to recolonize the habitat.
Radionuclide contamination
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No information found.
Changes in nutrient levels
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Nitrogen and phosphorus are limiting, and nutrient deficiency limits bud density, development and subsequent aerial growth (Rodwell, 1995). Phragmites is characteristic of eutrophic conditions (Haslam, 1995). In oligotrophic conditions, Phragmites may be out-competed by other emergent macrophytes and swamp species, or may be represented NVC S4 sub-communities e.g. the Menyanthes sub-community S4c. Eutrophic conditions favour monodominant stands of Phragmites, although with increasing eutrophication the reed beds may give way to various kinds of Phragmites-Urtica fen (NVC S26), possibly including nitrophilous tall herbs (Rodwell, 1995). Amsberry et al. (2000) suggested that increased nutrients favoured expansion and colonization by Phragmites, and Bertness et al. (2002) suggested that shoreline development, removal of the woodland buffer between terrestrial and salt marsh communities and eutrophication was precipitating the invasion of salt marsh habitats by Phragmites in the New England, USA.

Eutrophication and the resultant increase in turbidity and phytoplankton may result in loss of submergent macrophytes. For example, it was suggested that the nationally rare foxtail stonewort Lamprothamnium papulosum was intolerant of nutrient enrichment being absent from water with >20 µg/l P as phosphate and preferring nutrient poor sites (Bamber et al., 2001). Therefore, if present the foxtail stonewort will probably be lost due to nutrient enrichment. Loss of submergent macrophytes in the Broadland forces herbivores to concentrate of swamp species, to the detriment of Phragmites (Rodwell, 1995). It has also been suggested that smothering by filamentous algal mats my deprive young shoots of oxygen and light by smothering but see smothering above.

Gammarus salinus has been associated with polluted waters (see reviews), while most epiphytic and epistatic grazers would probably benefit from the increased algal growth stimulated by eutrophic conditions.

Overall, the extent and growth of Phragmites may benefit from nutrient enrichment and 'not sensitive*' has been recorded.

Increase in salinity
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Phragmites tolerates salinities between 2 -12 psu (g/l) but up to 22 psu (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 psu (g/l). However, stands of Phragmites have been reported to grow at salinities of up to 65 psu (g/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.

The nationally rare foxtail stonewort Lamprothamnium papulosum was reported to prefer 8-28psu but tolerate up to 32psu. Most brackish water species are adapted to a wide range or variable salinities, e.g. Hydrobia ulvae, Gammarus salinus and Gammarus insensibilis, however the mysid Neomysis integer is predominantly brackish water and has an upper tolerance limit of 20 - 25psu (see review).

Overall, a short term increase in salinity e.g. from reduced or low to variable or full for a week would probably stress the pondweeds and a few members of the invertebrate community but otherwise has limited effects. But, a long term change from e.g. from reduced to variable salinity would probably result in decreased growth rates of the established Phragmites bed and increased competition with salt marsh vegetation such as Puccinellia maritima or Spartina species. In the long term the seaward extent of the biotope will probably be reduced. The invertebrate community would probably change to include more marine species with a minor decline in species richness.

Overall an intolerance of intermediate, with a recoverability of high has been recorded (see additional information below).

Decrease in salinity
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A decrease in salinity from reduced to low or freshwater would probably benefit the Phragmites allowing it to colonize a wider area, potentially invading other salt marsh communities, e.g. Spartina communities. Fell et al. (1998) and Able & Hagan (2000) did not detect any significant difference in macroinvertebrate, decapod and fish populations between salt marsh and Phragmites dominated communities. Therefore, 'not sensitive*' has been recorded. However, the marine invertebrate community is likely to decrease with decreasing salinity, being replaced by freshwater representatives. Species richness is generally low in estuarine or brackish water conditions, increasing in marine or freshwater conditions, therefore, overall species richness may rise with decreasing salinity.
Changes in oxygenation
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Phragmites australis grows well in poor oxygenated, water-logged substrata as long as the rhizomes remain aerated through the dead aerial stems. But if the stubble of aerial stems is cut too low, removed by wave action or flooded too deeply, especially by saline water, the Phragmites stand may be killed (Hellings & Gallagher, 1992). Water logging and reducing conditions may prevent Phragmites from colonizing sediment as seed or plant fragment but Phragmites may colonize such sediments by vegetative expansion (Amsberry et al., 2000).

Most of the species identified as characterizing can probably tolerate low oxygen concentrations (e.g. benthic infauna and Conopeum spp.) as they are characteristic of wave sheltered and low water flow environments or are able to avoid low oxygen conditions, e.g. mobile gammarids and fish. Anoxic conditions are not relevant to aerial insects and vertebrates.

Therefore, an established stand of Phragmites will probably survive a reduction in oxygen concentration within the water column or substratum and an intolerance of low has been recorded.

Biological Factors

Introduction of microbial pathogens/parasites
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Several insect species damage reed stems or rhizomes and reduce the standing crop.
  • The larvae of the twin-spotted wainscot Archanara geminipuncta feeds on growing internodes from the inside, killing the shoot and causing thinner, shorter side shoots to grow from beneath the point of damage. The larvae requires three shoots before they pupate and over-winter inside thick stems (Tscharntke, 1992; 1999). In outbreaks up to 96% of stems may be affected (Tscharntke, 1992). Mook & van der Toorn (1982) reported that heavy frost or twin-spotted wainscot damage reduced shoot biomass by 25-35%.
  • The larvae of the large wainscot Rhizedra lutosa eat the inside of young spring shoots, entering and feeding on rhizomes and pupating in the soil. The insect could only complete its life-cycle in dry conditions (van der Toorn & Mook, 1982). Loss of spring shoots resulted in the production of thinner side shoots. Heavy infestation in dry plots resulted in losses of yield of 45-60% (see van der Toorn & Mook, 1982; Mook & van der Toorn, 1982).
Phragmites australis also supports several species of gall forming flies and midges, which benefit from the activities of the twin-spotted wainscot (Tscharntke, 1992; 1999). Many species of invertebrates, including crustaceans and gastropods are secondary hosts for fish or bird parasites (see individual species reviews for examples). Gastropod molluscs may also be castrated by heavy trematode infestation.

Given the evidence of loss of shoot biomass reported above an intolerance of intermediate has been recorded. Recovery is likely to be rapid.

Introduction of non-native species
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Extraction
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Phragmites australis reed beds have long been exploited commercially as a crop (see importance). Careful cutting and management is an important tool in the long term conservation of reed beds. Reed beds are more likely to decline as a result of poor management (inappropriate cutting or burning) or lack of management than as a result of harvesting. Therefore, not sensitive has been recorded.

Additional information icon Additional information

Recoverability
Existing reed beds may expand and colonize new substratum by vegetative growth. Phragmites australis produces horizontal rhizomes that spread across the surface producing new vertical shoots and roots at each internode (Hawke & José, 1996). Hawke & José (1996) reported expansion rates of 1-10m per year, sometimes faster, depending on temperature and water depth. Amsberry et al. (2000) noted that underground rhizomes spread horizontally about 1-1.5m per year. Hawke & José (1996) reported that allowing marginal reed to colonize an area of Hickling in Norfolk, resulted in 50ha of harvestable reed within 5 years. Sowing of large volumes of seed resulted in 7-500 plants/m² within 3 years, although in the wild seed set and survival is low. Therefore, in favourable conditions or favourable management regime, recovery or colonization from existing, adjacent populations is likely to occur within about 5 years. However, spring frosts, insect or grazing damage, and changes in the emergence regime may hinder recovery.

Where the population is completely removed, recovery will depend on colonization by seed or fragments of plant, especially rhizome. Seedlings are rare in the field and usually associated with mineral soils and areas of habitat disturbance, i.e. devoid of other macrophytes (Haslam, 1972; Amsberry et al., 2000). Boedeltje et al. (2001) studied colonization of created shallow water zones along navigation canals in the Netherlands. Phragmites australis communities occurred late in the succession in plots older than 3-5years, requiring areas in which a thick layer of sediment had accumulated, for example, a well developed Phragmites - Urtica community (NVC S26) characterized 13 year old zones. NVC S26 is more characteristic of dryer zones than NVC S4 and probably represents a later stage in the hydrosere than NVC S4. Therefore, where the community is removed completely recovery may be protracted.

The epiphytic species will probably recruit to the available habitats quickly, as will mobile species such as crustaceans, insects, and fish (see recruitment). Rare species, e.g. bittern, foxtail stonewort, the reed leopard moth and Fenn's wainscot, may take longer to recruit to the developing reed bed, partly due to isolation of breeding populations and partly due to their different habitat size requirements. Species that need large reed beds would probably not recruit until an adequate reed bed size was attained.

This review can be cited as follows:

Tyler-Walters, H. 2002. Phragmites australis swamp and reed beds. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 29/07/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=304&code=2004>