Campylopus introflexus

The rapid spread of the moss, C. introflexus within its newly colonized continents (Europe in 1941, North America in 1975) is attributed to its high dispersal capacity, locally by fragmentation and over longer distances by small spores. It can quickly and effectively establish on acidic open sites with low competition from other plants and often benefits from disturbances (burning, trampling and digging by animals, wind erosion). C. introflexus can form extensive carpets that have impact on habitat conditions and on the native flora and fauna. Van der Meulen et al. (1987) first pointed out the negative impact of the moss invasion on the Netherlands coastal dunes. Today (2009), the species is listed as an environmental weed on the “Global Compendium of Weeds” (http://www.hear.org/gcw).

C. introflexus is considered native in the southern hemisphere where it is common in temperate and sub-Antarctic regions, between 22 and 57°S (Gradstein and Sipman, 1978; Ochyra et al., 2008). The most northwards locality is on the island of Réunion at approximately 21°S (Frahm, 1985a). Records are known from southern South America (Argentina, Brazil, Chile, Paraguay, and Uruguay), southern Africa (Botswana, Lesotho, Namibia, and South Africa), Australia, New Zealand, and many islands throughout the southern oceans (e.g. South Sandwich Islands, Kerguelen Islands, Juan Fernández Islands, and Saint Helena). This species invaded the northern hemisphere, where it was first recorded in 1941 in Europe and 1975 in North America. At present, it ranges between approximately 35°N (California; Norris and Shevock, 2004) and 66°N (Iceland; Weidema, 2006). 

Presently (2009), there is no evidence that the spread of C. introflexus has stopped and more records will probably emerge. No measures are known to counteract this spread, which probably originates from the dispersal of tiny spores dispersed by the wind over long distances. The number of sites where the species is considered to be invasive is also still increasing.

C. introflexus is most widespread in low elevations of up to a few hundred metres, but occurs up to 1000 m.a.s.l. (e.g. Equihua and Usher, 1993; Nieuwkoop and Arts, 1995; Bisang et al., 1998). In southern Africa it was found above 3000 m (Germishuizen and Meyer, 2003). It prefers temporarily dry to humid, non-calcareous, nutrient-poor, humus or mineral soil or peat in fairly open situations; it is also found on bases of trees, rotten wood, and gravel on roofs and rarely on rocks (Gradstein and Sipman, 1978; Stieperaere and Jacques, 1995; Smith, 2004). Roadside banks, open sites and trails in poor shrub and forest, sparse grassy ground, swamps and fire sites are typical habitats. In the subarctic and subantarctic region (Iceland, South Sandwich Islands) this species is confined to geothermal ground where the soil is warmed up. A common factor of all these habitats is that they are, to some degree, exposed to natural or man-made disturbance and that competition from higher plants is low.

In Europe, C. introflexus is recorded as most invasive in stands of the grass Corynephorus canescens on stabilized and decalcified sand dunes on the coast (van der Meulen et al., 1987; Biermann, 1999; Ketner-Oostra and Sýkora, 2004) and inland (Biermann and Daniëls, 1997). It also invades heathlands (Stiperaere and Jacques, 1995), light forests and pine plantations, and raised and blanket bogs where it prevails on bare peat (Equihua and Usher, 1993; Lambdon, 2009). Furthermore, it can cover large areas of recently exposed and abandoned sandy ground in post-mining land.

In North America, the moss occupies similar habitats and is very abundant in sand dunes along the coast, for example (Frahm, 2007).

In Europe, C. introflexus performs best in the oceanic and suboceanic regions where precipitation is above 700 mm/year. It tolerates precipitation as low as approximately 500 mm/year. Microclimatic conditions can sometimes outrank macroclimate as the occurrences on geothermal ground show. In dune areas, C. introflexus is reported as having difficulties in dominating south-facing slopes most exposed to the sun (Ketner-Oostra et al., 2006). However, C. introflexus is still rather drought-resistant. Robbins (1952) showed that moss carpets can recover after a period of drought of 25-28 weeks maximum. In periods of drought, the leaves of the moss twist around the stems to impede evaporation. The hyaline hair tips reflect irradiation and thus keep the temperature within the carpets relatively moderate (van der Meulen et al., 1987).

The pH value of the substrate ranges from 3.5 to 7.0 with a peak at about 4.5 (e.g. Biermann, 1999; Hasse, 2005; Isermann, 2005). Values above 6.5 are reported only from fen peat (Equihua and Usher, 1993). In addition to the Soil Tolerances list, special soil tolerances for C. introflexus include organic substrates such as peat, rotten wood, and tree bases.

With reference to the Habitat List, the harm caused by C. introflexus in managed forests, plantations and orchards; disturbed areas; natural forests; wetlands (raised and blanket bogs); and cold lands/tundra (referring to geothermal warmed ground only), is evaluated to be local and not as severe as in coastal dunes.

In the northern hemisphere, C. introflexus is not a weed of agricultural land, but occurs on low-productive soils. In the southern hemisphere, the moss also occurs in pasture (Robbins, 1952), but is not mentioned to have major impact there.

Genetics

Stech and Dohrmann (2004) resolved that C. introflexus is monophyletic. It is unknown to what extent hybridization plays a role. However, molecular relationships (Stech and Dohrmann, 2004) and morphological characteristics (Gradstein and Sipman, 1978) of C. introflexus and Campylopus pilifer might indicate hybridization between both species. Chromosome numbers (n = 12) of specimens from Australia (Ramsay, 1974) and Poland (Ochyra and Kuta, 1990) were checked.

Reproductive Biology

C. introflexus is dioecious. In favourable habitats, the moss produces numerous tiny spores (10-15 µm). These are distributed by the wind over long distances and are therefore presumably primarily responsible for the rapid range expansion of the species within Europe and North America (Hassel and Söderström, 2005; Frahm, 2008).

Vegetative propagation by shoot tips plays an important role in local dispersal and the forming of invasive stands (Hallingbäck et al., 1985; Söderström, 1992). The abundance of these deciduous leafy buds shed from the upper leaves is highest in the young moss carpets, only a few millimetres high (Biermann, 1999). They are dispersed by the wind or animals and enable a very efficient and rapid occupation of gaps, a strategy which is often superior to strategies of native pioneer mosses.

Another advantage for colonizing new habitats is the ability of fragments of the moss carpets to survive for years after being detached and displaced, and to give rise to new individuals if conditions are suitable (Robbins, 1952; van der Meulen et al., 1987; Hasse, 2007). Animals frequently disperse them and thus assist the local spread of the moss.

Succession

C. introflexus is perennial. Under adequate conditions the moss can form carpets of 2-10 cm thickness. These barely allow other plants to colonize once they are established and therefore often form monotonous stands of up to several hundred square metres. These carpets persist over several years before being succeeded by other plants (Daniëls et al., 2008) or being rejuvenated with new individuals of the moss, often due to disturbance. The dry moss carpets are often observed to fragment and break loose from the ground, due to birds in search for food or trampling and digging or scraping animals. Alternate wetting and drying of moss carpets leads to the forming of polygon-shaped cracks and thus facilitates fragmentation.

C. introflexus may be grazed to some extent by typical moss herbivores such as slugs or pill beetles (Bhyrridae) (Lambdon, 2009).

Ornamental

• Potted plant

If well-developed, C. introflexus is easily recognized by its typical strongly reflexed hair tips. These hair tips are sometimes poorly developed, especially in semi-shady habitats, and confusion with other Campylopus species in the field is possible. It is most difficult to separate C. introflexus from Campylopus pilifer. Characteristics for the separation of both species were discussed by Richards (1963), Frahm (1974) and Gradstein and Sipman (1978), but they are still subject to discussion. Frahm and Stech (2006) put the hitherto known characteristics into perspective by describing intermediate forms between both species from France. In the southern hemisphere both species are even less clearly separated by morphological characteristics than in Europe (Gradstein and Sipman, 1978).

C. introflexus can best be distinguished from its near relative C. pilifer with a transverse section of the leaf nerve. C. introflexus’ dorsal lamellae are composed of 1 (to 2) cell rows whereas C. pilifer has (1 to) 2 to 4 (to 6) cell rows (Frahm and Stech, 2006). Furthermore, the seta is longer (ca. 4 mm for C. pilifer) and spores are smaller (12 to 19 mm for C. pilifer; Gradstein and Sipman, 1978).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Invasive Species Management

Disturbance is a key factor in many ecosystems invaded by C. introflexus. It is essential to maintain different successional phases that contribute to overall species richness, as many native species in these ecosystems rely on the creation of open habitats. There are several natural sources of disturbance (e.g. wind and water erosion, animals, fire) and management practices often target for the same factor. These open habitats are prone to invasion by C. introflexus.

Management measures such as the removal of pine plantations to restore heathland (Wilton-Jones and Ausden, 2005), and natural disturbances such as wild fire (Ketner-Oostra et al., 2006) were reported to result in an increased emergence of the alien moss.

Prevention

No prevention methods have been described for C. introflexus. It seems impossible to prevent its dispersal because it is very fertile and the tiny spores are distributed by the wind over long distances.

Control

Management options to control moss encroachment can be categorized into direct interference with the moss plants or the control of habitat conditions to the disadvantage of the moss as an indirect measure. However, all management options have been of limited success.

The use of the herbicide asulam (Asulox), tested in experiments with different mosses, showed little impact on C. introflexus (Rowntree et al., 2003). Sod-cutting of a 200 m² plot did not successfully remove C. introflexus long-term, and the moss reclaimed dominance 3 years later (Ketner-Oostra and Sýkora, 2000).

This moss does not tolerate burial in calcareous sand (van der Meulen et al., 1987; van Boxel et al., 1997; Ketner-Oostra and Sýkora, 2000; 2004), thus stimulating sand drift from the first foredunes and the beach could be a protective measure against moss invasion on the coast. Burial under a thin layer of decalcified sand was tolerated by C. introflexus (Hasse and Daniëls, 2006).

It is uncertain whether airborne eutrophication and acid rain facilitate the spread of C. introflexus (van der Meulen et al., 1987; Nentwig, 2006).

24/07/09 Original text by:

T Hasse, Consultant, Germany