Introduction

Syntaxonomic work on plants in the Netherlands started shortly before 1930 (Sýkora and Sýkora 1987). Few years later some young syntaxonomists developed an ardent bryological interest (Harmsen 1999). However, when Beijerinck (1934) published a booklet entitled ‘Sphagnum en Sphagnetum' the term Sphagnetum – though labeled as an ‘independent association’ – was not used in a standardised syntaxonomic way. In early Dutch syntaxonomical literature several bryophyte and lichen species were mentioned as important diagnostic (character or differential) species, e.g. the liverworts Fossombronia dumortieri (today F. foveolata) and F. wondraczeki (today F. wondraczekii) (Cicendietum filiformis Allorge’22, Nanocyperion flavescentis W.Koch’26), the mosses Brachythecium rivulare and Philonotis fontana (Cardamineto-Montion Br.-Bl.’26) and the lichens Cladonia uncialis, C. squamosa, C. gracilis, C. chlorophaea, C. sylvatica (today C. arbuscula) and Cornicularia aculeata (today Cetraria aculeata) (Ericetum tetralicis Schwickerath’33 cladonietosum Tx. ‘37, Rhynchosporion albae W.Koch’26) (Westhoff et al. 1942). Publications on bryosociological and lichenosociological studies remained scarce in the Netherlands until Barkman published his voluminous study on phytosociology of cryptogamic epiphytes in Europe (Barkman 1958). In later years, most Dutch bryosociological studies focused on non-epiphytic communities, e.g. thatched roofs (Ringelberg-Giesen 1958), springs and rivulets (Maas 1959, Weeda 1994), inland dunes and heaths (Touw 1963, 1969, Hovenkamp 1975), coastal dunes (Boerboom 1960, Coesel 1963, During 1973, Bruin et al. 1999), peat banks (Barkman 1989), and epilithic communities (Kruijsen 1982, Greven 1990). Considerably less Dutch lichenosociological studies were published during this period, Barkman (1969), Masselink (1994) and Spier and Aptroot (2000). At the end of the twentieth century, the vegetation in the Netherlands was phytosociologically described in detail (Schaminée et al. 1995a, 1995b, 1996, 1998, Stortelder et al. 1999), and updated in 2017 (Schaminée et al. 2017). In the latter six publications, 46 classes were described, the vast majority of associations dominated by vascular plants, although many bryophytes and some lichens and algae were incorporated as diagnostic species. Incidentally, bryophyte-dominated syntaxa were incorporated within vascular plant classes, e.g. Pellio-Conocephaletum Maas 1959 and Pellio endiviifiliae-Cratoneuretum commutati Rivola 1982 (Montio-Cardaminetea Braun-Blanquet et Tüxen 1943), Didymodon recurvirostris-Tortella flavovirens-ass. – today Tortello-Bryoerythrophylletum Boerboom 1960 (Koelerio-Corynephoretea Klika in Klika et Novák 1941), and Sphagnetalia medii Kästner et Flössner 1933 (preferred over Sphagnetalia magellanici Kästner et Flössner 1933 as Sphagnum magellanicum is not present in Europe; Hassel et al. 2018) (Oxycocco-Sphagnetea Braun-Blanquet et Tüxen ex Westhoff et al. 1946) (Maas 1959, Boerboom 1960, Schaminée et al. 1995b, 1996, 2017). Shortly before 2000, Siebel and Van Dort published a list of bryophyte syntaxa which were known from the Netherlands (Van Dort and Siebel 1995, Siebel and Van Dort 1999). No such lists existed for lichen syntaxa at that time.

Many authors studied vegetation communities dominated by bryophytes separately from lichen-dominated communities (for example, bryophyte communities: Demaret 1939, Von Hübschmann 1953, 1986, Philippi 1965, Lecointe 1978, Messe 1982, Drehwald and Preising 1991, Dierßen 2001, Bardat and Hauguel 2002, Schlüsslmayr 2005, Marstaller 2006, Schubert 2009; lichen communities: Klement 1955, Massé 1964, Delzenne-Van Haluwyn 1976; James et al. 1977, Wirth 1980, 1995, Roux 1981, Drehwald 1993, Schubert and Stordeur 2011). However, these two species groups have not always been separated strictly, as expressed by the name of the cryptogam class Cladonio digitatae-Lepidozietea reptantis Ježek and Vondráček 1962, a class including an alliance with diagnostic bryophyte species (Tetraphidion pellucidae Von Krusenstjerna 1945) and an alliance with diagnostic lichen species (Cladonion coniocraeae Duvigneaud ex James et al. 1977). One of the arguments against the separate treatment of bryophyte syntaxa and lichen syntaxa is that some lichen groups show a strong ecological (notably the genus Peltigera) or physiological (particularly the genera Leptogium, Collema, Parmeliella; Barkman 1958) resemblance with bryophytes. Barkman (1958), though keeping lichen syntaxa apart from bryophyte syntaxa, even placed an alliance characterized by at least 19 lichen taxa Lobarion pulmonariae in a bryophyte order Neckeretalia pumilae on ecological and physiological grounds. Recently, Mucina and colleagues (2016) published separate lists of vascular plant communities, bryophyte communities, lichen communities and algal communities of Europe, based on Braun-Blanquet syntaxonomy. However, they state that “an important future task will be combining bryophyte and lichen (and algal) communities into one consistent syntaxonomic system” (Mucina et al. 2016).

Since Barkman's publication in 1958, both species presences and frequencies have changed. For example, bryophyte species density in Dutch forests has increased considerably in the period 1984–1994 (Dirkse and Martakis 1998). The classification of Dutch vegetation relevés, the majority recorded after the year 2000, resulted in the first complete overview of bryophyte-lichen syntaxa of the Netherlands (Van Dort et al. 2017). When appropriate, we joined previously described bryophyte and lichen phytosociological units. Our bryolichenosociological study included synoptic tables and ecological information (Van Dort et al. 2017). Additionally, we used actualized distribution data and Red List status of character species (Aptroot et al. 2011, Siebel et al. 2013, BLWG 2017) to assess the distribution, trend, rarity and Red List status of vegetations representing each (sub)association on a national level (Schrijvers-Gonlag et al. 2018). In the current paper, we present the full list of current Dutch bryophyte-lichen syntaxa and for each (sub)association the Red List status of corresponding vegetations. To put the bryophyte-lichen vegetation in the Netherlands in an international context, we make some comparisons with syntaxa elsewhere in Europe. We present synoptic tables for 13 newly described syntaxa. Additionally, we present graphical information about the abiotic habitat variables moisture, light availabilty, nutrient richness and acidity for each class.

The bryophyte-lichen syntaxa of the Netherlands

We selected more than 5000 relevés from the Netherlands, based on Braun-Blanquet syntaxonomy and the majority recorded in the period 2000–2017, to compile our syntaxonomic lists. Our main goal was to produce a scientifically based overview of bryophyte-lichen vegetation useful for both scientists and nature managers in the field (as illustrated by Haveman and De Ronde (2021): “the proof of the classification is in its usage”). For this reason, we simplified syntaxon names whenever appropriate. As an example, we renamed the T. pellucidae Von Krusenstjerna 1945 to the simpler form Tetraphidion Von Krusenstjerna 1945 as only one Tetraphis species Tetraphis pellucida is known in Europe, leaving no room for confusion. Therefore, the epithet ‘pellucidae’ is not neccessary in the name of the alliance to interpret the syntaxon correctly. On the other hand, we used the name Rhizocarpetalia geographici Klement 1949 instead of the proposed valid name Rhizocarpetalia Klement 1949 (with the addition nom. conserv. propos. in Mucina et al. 2016), to prevent confusion with the Rhizocarpetalia reducti Wirth 1980 (Rhizocarpetalia obscurati Wirth 1980 in Mucina et al. 2016).

Many bryophyte and lichen species share the same habitat and substrate and are subject to the same (a)biotic conditions. Therefore, whenever possible, we integrated bryophyte and lichen syntaxonomy. As a result, our choice of syntaxa and syntaxon names fits the Dutch situation well but is not always in accordance with the International Code of Phytosociological Nomenclature (ICPN) (Weber et al. 2000). To illustrate this, we combined the ‘bryophyte class’ Frullanio dilatatae-Leucodontetea sciuroidis Mohan 1978 and the ‘lichen class’ Physcietea Tomaselli and De Micheli 1952 into one integrated class divided into the bryophyte-dominated order Orthotrichetalia Hadač in Klika and Hadač 1944 (originating from the Frullanio-Leucodontetea) and the lichen-dominated order Physcietalia Hadač in Klika and Hadač 1944 (originating from the Physcietea). According to the ICPN, the new name should be: Physcietea Tomaselli and De Micheli 1952. As in our integrated class both bryophyte and lichen species play a more or less equally important role, we combined both the original class names into the new name Orthotricho-Physcietea Tomaselli and De Micheli 1952 (Fig. 1), although not valid according to the ICPN. Why we chose to follow the ICPN in specific cases, and why we chose to divert from it in many other cases, is extensively explained in Schrijvers-Gonlag (2019). We aimed at easy-to-use names for our syntaxa. Haveman (2016) quotes the famous Shakespeare sentence ‘What’s in a name? that which we call a rose By any other name would smell as sweet’ (Shakespeare 1597) to illustrate that plant names are just code words to facilitate communication among humans. The same is valid for syntaxa: names are just names, as stated in the ICPN: “Names are only labels and, as such, they can never be wholly adequate. [...] It is far more important to know exactly what is meant by a name than to find one that seems in every respect to be characteristic” (Weber et al. 2000).

Figure 1.

A Physcietalia vegetation with a large cover of Orthotrichetalia moss species, or an Orthotrichetalia vegetation invaded by Physcietalia lichen species? We prefer an integrated approach with both bryophytes and lichens included: several moss species (Lewinskya speciosa, Nyholmiella obtusifolia (both species formerly in the genus Orthotrichum, hence the name Orthotrichetalia; Goffinet et al. 2004, Sawicki et al. 2010, Lara et al. 2016), Pylaisia polyantha) and many lichen species (Athallia pyracea, Caloplaca cerina, Candelariella xanthostigma, Myriolecis dispersa, Phaeophyscia orbicularis, Physcia adscendens, P. aipolia, P. stellaris, Toniniopsis subincompta, Xanthoria parietina) were identified in an Orthotricho-Physcietea vegetation on a Populus tremula trunk (Koppang, Norway 2020). Photo: Marcel Schrijvers-Gonlag. The length of the scale bar (white piece of paper) is 10.0 cm.

The list with Dutch bryophyte-lichen syntaxa (Table 1) consists of 11 former classes (Mucina et al. 2016) existing of mainly bryophyte or lichen species, supplemented with five classes where existing bryophyte and lichen classes have been integrated, often merged at order level: Hymenelio lacustris-Fontinalietea antipyreticae, Verrucario nigrescentis-Schistidietea crassipili, Racomitrio heterostichi-Rhizocarpetea geographici, Orthotricho-Physcietea and Ceratodonto purpurei-Polytrichetea piliferi. The overview includes 168 syntaxa: 16 classes, 27 orders, 37 alliances, 82 associations and 6 subassociations (Table 1). From these, 13 are new syntaxa and described in detail (with the addition ‘nov. hoc loco’ in Van Dort et al. (2017): two alliances, nine associations and two subassociations (further down: New syntaxa). As 46 tracheophyte-dominated classes have been described in the Netherlands recently (Introduction), the 16 bryophyte-lichen-dominated classes in Table 1 are numbered 47–62.

Dutch bryophyte-lichen syntaxa in an international context

Our classification is based on recent national data and European classifications. For each syntaxon, the set of diagnostic species reflects the conditions of the Netherlands, but the allocation may also fit other European lowland regions with temperate climatic influences. Here, we make some comparisons with syntaxa elsewhere in Europe.

Our classification of epiphytic syntaxa broadly follows Barkman's study of cryptogamic epiphytes in Europe (Barkman 1958). Barkman limited himself to the level of order but he discussed two possible ways of grouping his nine epiphytic orders into four classes. However, he refrained from drawing up ‘premature’ classes, leaving the final decisions about ecological criteria and the selection of faithful species to future phytosociologists (Barkman 1958). Much research has been done in recent years. Although our knowledge of floristic affinities between syntaxa is still far from being complete, it seems appropriate to publish an updated overview based on contemporary data. However, it should be kept in mind, that a comprehensive, stable phytosociological system is largely a matter of wishful thinking. In modern times, environmental factors (below) and changes in land use lead to rapid changes in the floristic composition of assocations, so adaptations, or additions, of the syntaxonomic units will always be necessary (Bout and Dirkx 2012, Schaminée et al. 2017, Haveman 2021, Haveman and De Ronde 2021).

Table 1.

Bryophyte-lichen syntaxa in the Netherlands. Red List status for vegetations representing syntaxa at association or subassociation level is given (Van Dort et al. 2017, Schrijvers-Gonlag et al. 2018). Classes (in bold) are numbered 47–62, succeeding 46 classes which have been described previously (text). When a syntaxon name does not correspond with the International Code of Phytosociological Nomenclature (Weber et al. 2000) its ‘valid name’ (the name according to Weber et al. 2000; Mucina et al. 2016) is given between parentheses []. If a syntaxon name is valid, but Mucina et al. (2016) propose a different name, this is also indicated between parentheses, with the addition ‘nom. conserv. propos. (Mucina et al. 2016)’. C: character species, D: differential species. Red List status of corresponding vegetations (RL): LC = Least Concern, NT = Near Threatened, VU =Vulnerable, EN = Endangered, CR = Critically Endangered, EX = Extinct (categories according to The IUCN Red List, iucnredlist.org).

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Until recently, climatic conditions prevented the occurrence of xero-thermophilous species as Fabronia pusilla in the Netherlands (BLWG 2023a). The Fabronion pusillae Barkman 1958 is therefore not mentioned on the Dutch list (Table 1). Mucina et al. (2016) consider the F. pusillae synonymous with the Syntrichion laevipilae, widespread and common in the Netherlands – although F. pusilla is not indiginous (yet?) (BLWG 2023a). Fabronia pusilla may spread from populations on the stems of garden trees, imported from the Mediterranean countries, and become part of Syntrichion vegetations in the Netherlands in the near future.

Due to sulphur dioxide and ammonia emissions and depositions in the last century (Asman et al. 1988, Mylona 1996, De Ruiter et al. 2006, De Haan et al. 2008, Van der Swaluw et al. 2011, Van Zanten et al. 2017, Dammers et al. 2022, Wever et al. 2022), acidophilous cryptogams have decreased in distribution while epiphytes favoured by eutrophication have spread rapidly. Nitrophytes invaded vegetations to such an extend that formerly obvious floristical characteristics have been obscured. In particular vegetations representing Hypogymnietea physodis associations have impoverished and decreased in area (Van Herk and Spier 1994, Van Herk et al. 2000, Sparrius and Timmerman 2014). Within the Hypogymnietea, both alliances Usneion barbatae Ochsner 1928 and Vulpicidion pinastri Ochsner ex Kušan 1933 (synonym Cetrarion pinastri), two in many European boreal and mountain areas well represented alliances, are missing from the Dutch list with bryophyte-lichen syntaxa (Table 1). Some of the diagnostic species are known from lowland countries, but exist here on the edge of their natural distribution area due to climatic conditions. The epiphytic lichens Bryoria fuscescens, Platismatia glauca, Tuckermanopsis chlorophylla, Usnea filipendula, U. subfloridana (all diagnostic for the U. barbatae), Parmeliopsis ambigua and Vulpicida pinastri (diagnostic for the V. pinastri) have declined tremendously in the last century, mainly due to the mentioned sulphur dioxide and ammonia emissions and depositions in the Netherlands (Aptroot et al. 2011, Van der Pluijm and Boesveld 2016, BLWG 2023b). All present vegetations in the Netherlands with one of these species are ‘floristically blurred’ and can hardly be distinguished syntaxonomically from the Hypogymnion physodis. We use a broad concept of the H. physodis and the impoverished Usneetum filipendulae and Parmeliopsidetum ambiguae vegetations are placed within the H. physodis (Table 1), while in our neighboring country Germany these associations still are included in the U. barbatae and V. pinastri (Drehwald 1993, Wirth 1995, Schubert and Stordeur 2011).

The forest species Lobaria pulmonaria and Lobarina scrobiculata, character species of the L. pulmonariae Ochsner 1928, disappeared long ago from the highly fragmented forests in the Netherlands (BLWG 2023c), and most European lowland forests. Therefore, the Lobarion appears under ‘Disappeared climax vegetation’ in the class Neckeretea complanatae in Van Dort et al. (2017). Another example of an epiphytic syntaxon absent in Table 1 is the Nowellion curvifoliae Philippi 1965 (Cladonio digitatae-Lepidozietea reptantis) (Barkman proposed the name Blepharostomion trichophylli for this alliance). Representatives of the N. curvifoliae are common in many conifer dominated forests in Europe. Due to adjusted forest management (Wijdeven 2005, Schelhaas et al. 2022), the diagnostic species Nowellia curvifolia, Riccardia latifrons and more recently also R. palmata are increasing in the Netherlands (BLWG 2023d), responding to an increased availability of large diameter logs at late decay stages (important for critical epiphytes; Ódor and Van Hees 2004, Ódor et al. 2006). Nevertheless, their current distribution does not yet justify the existence of an independent alliance in the Netherlands.

Epilithic bryophyte-lichen vegetation is widespread in the densely populated Netherlands. However, exposed acidic rock surface is nearly absent. Acidophytic epilitics are restricted to just a few imported graveyard stones, sea dikes constructed with granitic boulders from the ‘hunebedden’ (ancient tombs similar to dolmens;  www.sketchfab.com/gia), few remaining hunebedden and some weathered walls from old churches and historical buildings. As a consequence, the number of syntaxa belonging to the Racomitrio heterostichi-Rhizocarpetea geographici is very small in the Netherlands (Table 1). Moreover, Racomitrio-Rhizocarpetea associations are poor in character species compared to corresponding associations in other European countries, especially in mountainous regions. Several reasons exist: the relatively small area available, the young age (no late succession stages present: graveyard stones, hunebedden and stone sea dikes were absent before 1700, or not exposed: hunnebedden were buried in the ground), eutrophication (particularly with nitrogen-containing compounds as mentioned earlier), and increasing shade and restauration measures of graveyard stones, hunebedden and granite sea dikes (Masselink and Van Zanten 1976, Boele and Van Zanten 1984, Siebel et al. 2000, Colpa and Van Zanten 2006, Bijlsma et al. 2009). On the other hand, epilithic vegetations with calcicolous species (Verrucario nigrescentis–Schistidietea crassipili, N. complanatae) are abundant in the Netherlands on anthropogenic substrate as buildings, extensively used roads and pavements. The species composition does not differ substantially from vegetation on natural calcareous and other base-rich siliceous rock surfaces. As species preferring chalk, limestone or other base-rich porouse rock surface are rare or absent in the Netherlands, so are the corresponding vegetations belonging to the Verrucario nigrescentis–Schistidietea crassipili, the Ctenidietea mollusci Von Hübschmann ex Grgić 1980 and the Clauzadeetea immersae Roux in Roux et al. 2009. The latter two classes are absent in Table 1, in spite of the fact that some impoverished communities or fragments do occur. For example, a characteristic Ctenidietea species like Ctenidium molluscum is rather widespread in the Netherlands (be it on antropogeneous substrata), and not rare in the southeastern part of the country (Mergelland) on nutrient-poor limestone substrates (BLWG 2023e).

In the Netherlands, both small and large freshwater bodies are common. Most of these are both mineral-rich and base-rich and therefore aquatic (amphibious and (semi-) permanently submerged) communities belonging to the Hymenelio lacustris–Fontinalietea antipyreticae are widespread. A rare cryptogam vegetation on pebbles and stones in clear, mineral-poor streams resembles the habitat of the montane association Verrucarietum siliceae Wirth and Ullrich in Wirth 1972 as described in Drehwald (1993). The species composition shows more affinities to the Verrucarietum rheitrophilae Coste 2011, belonging to the alliance Verrucarion rheitrophilae Coste 2011. We updated and modernized the syntaxon names to Hydropunctarietum rheitrophilae and Hydropunctarion rheitrophilae, respectively (Table 1). In the Netherlands, vegetations representing the alliances H. rheitrophilae and Racomitrion acicularis (common in montane and subalpine areas) have the Red List-status ‘endangered’ (Table 1). Our classification of these syntaxa is based on a limited number of relevés poor in diagnostic species and our description is probably incomplete. For example, only one character species (Scapania undulata) is distinguished in the Chiloscypho rivularis-Scapanietum undulatae, whereas in German literature Dichodontium pellucidum figures either as a second character species for this association (Marstaller 2006), or is present in the Chiloscypho-Scapanietum (Schubert 2008) or R. acicularis (Von Hübschmann 1986, Dierßen 2001). Interestingly, in a German province with relatively low elevation and bordering the Netherlands, D. pellucidum is characteristic for the Brachythecietalia plumosi (Drehwald and Preising 1991). Frey et al. (2006) describe D. pellucidum as a mountainous species, sparse in the lowlands. In the Netherlands, D. pellucidum is very rare and mainly growing in Leptodictyo-Fissidentetum crassipedis vegetation.

The bryophyte-lichen communities affected by saltwater (Hydropunctarietea maurae) are also common in the Netherlands. Bryophytes are almost absent in these coastal communities. Noteworthy is that, unlike many other places in Europe, natural rock formations are lacking along the sandy North Sea coast line. Salt-tolerating lichens are almost exclusively restructed to dikes (often made of basalt, chalk stone or granite), and other antropogenic constructions as wooden poles. Sporadically, H. maurae communities are found on shells and other hard substrate from animals in the littoral zone (e.g. Littorina spp., Ostrea spp., Sessilia spp.) and on weathered bones or plant material (see the synoptic table of the Lecanoretum zosterae below).

Our interpretation of the Psoretea decipientis, pioneer epigaeic bryophyte-lichen vegetations on exposed, nutrient-rich, subneutral to calcareous soil differs from many other European classifications. The syntaxonomic interpretation of these vegetations is greatly influenced by the scale used (both temporal and sparial) and such vegetations are sometimes considered synusiae, microcoeni, microcommunities, or other dependent communities and not independent syntaxa. For a discussion about the classification of ephemeral small-scale bryophyte-lichen vegetations see Van Dort et al. (2017). Here we only mention some differences with other European classifications. Two orders are recognized in the P. decipientis: the Barbuletalia and Funarietalia hygrometricae (we don't distinguish a separate Psoretalia decipientis Mattick 1951; Table 1). In the F. hygrometricae, Von Hübschmann (1986), Drehwald and Preising (1991) and Marstaller (2006) distinguished a Physcomitrellion patentis Von Hübschmann 1957, whereas Bültmann placed this alliance in the Dicranelletalia heteromallae (Mucina et al. 2016). In the Netherlands, the P. patentis diagnostic species Physcomitrium eurystomum, P. sphaericum and Physcomitrella patens represent the Eleocharito acicularis-Limoselletum Wendelberger-Zelinka 1952 (Bidentetea tripartitae Tüxen et al. in Tüxen 1950) (Weeda et al. 1998, Nieuwkoop 2011, 2016), whereas Physcomitrium pyriforme is diagnostic of the Funarion hygrometricae. A peculiar feature of the Netherlands is the overall-presence of nutrient-enriched habitats (mainly resulting from a high ammonia deposition, see before). Therefore, the P. patentis elements are largely replaced by nitrophilous species diagnostic of the F. hygrometricae and consequently the P. patentis is absent in Table 1.

We do not accept many of the associations placed within the P. decipientis, particularly Barbuletalia, by other authors (Schlüsslmayr 2005, Marstaller 2006, Schubert 2009). Some character species of these associations occur or may be present occasionally in the Netherlands, but they appear periodically while forming a diffuse bryophyte layer in vegetation types dominated by vascular plants (e.g. the Riccio-Anthocerotetum punctati Koppe ex Neumayr 1971 vegetation in the Netherlands is appointed to the Centunculo- Anthocerotetum punctati Koch ex Libbert 1932 in the N. flavescentis Koch ex Libbert 1932 (Isoeto-Nanojuncetea Braun-Blanquet et Tüxen 1943) (Lemaire et al. 1998, Siebel and Van Dort 1999)). A second reason to ignore these Psoretea-syntaxa is that many of the vegetations, representing associations recognized in other countries, originate from pioneer habitats, e.g. river banks. In the Netherlands, fluviatile vegetation develops within an extremely short period. Bryophytes do sometimes build up quite large populations, always in combination with vascular plants. As both groups are fairly inseparable, both spatially and temporarily, they do not meet the definition of an independent bryophyte community (Siebel and Van Dort 1999). These vegetations therefore have to be considered as synusiae, or pioneer phases of the already mentioned Eleocharito acicularis-Limoselletum.

Two associations figure in the Splachnetea in Table 1. The coprophilous bryophytes in this class (all in the moss family Splachnaceae) occur widely on dung, carcasses, antlers and bird's pellets (Frey et al. 2006, Hallingbäck et al. 2008, Blockeel et al. 2014). In boreal, arctic and alpine habitat, these substrates decay slowly. In the Netherlands, the decomposition rate is generally too high to allow Splachnaceae to complete their life cycle (Cameron and Wyatt 1986, Bijlsma 2010). Suitable habitat, e.g. wet heathland, edges of fens and moorland and ombotrophic peat areas, have become extremely rare. Moreover, large herbivores which provide suitable dung are often absent. The two Splachnetea species known from the Netherlands most likely became extinct (Splachnum ampullaceum, last record in 2010; Tetraplodon mnioides, last record in 2002; BLWG 2023f). As Splachnaceae almost have disappeared from the surrounding countries, colonization from foreign populations is unlikely, but not impossible (Walsh 1951, Blockeel et al. 2014, Van Landuyt et al. 2020, BLWG 2023f, NBN 2023, PMD 2023).

New syntaxa

All 13 new syntaxa that are described in detail (with the addition ‘nov. hoc loco’) in Van Dort et al. (2017) are listed below, including a synoptic table (species cover according to an adjusted Braun-Blanquet cover-abundance scale; Van Dort et al. (2017)). Also the type relevé (‘holotypus hoc loco’ in Van Dort et al. (2017), Weber et al. (2000)) and a reference to the original publication are given.

Synoptic table Cinclidotetum fontinaloidis cinclidotetosum danubici (Table 47-9 in Van Dort et al. 2017).

Synoptic table Cinclidotetum fontinaloidis leskeetosum polycarpae (Table 47-10 in Van Dort et al. 2017).

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Synoptic table Lecanoretum zosterae (Table 48-8 in Van Dort et al. 2017).

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Synoptic table Lecanoretum pannonicae (Table 49-9 in Van Dort et al. 2017).

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Synoptic table Porpidietum soredizodis (Table 50-8 in Van Dort et al. 2017).

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Synoptic table Protoparmelietum oleaginae (Table 52-7 in Van Dort et al. 2017).

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Synoptic table Ramalinetum fastigiatae (Table 53-7 in Van Dort et al. 2017).

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Synoptic table Pertusarietum coccodis (Table 53-5 in Van Dort et al. 2017).

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Synoptic table Fissidentetum gymnandri (Table 56-4 in Van Dort et al. 2017).

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Synoptic table Sciurohypno populei-Anomodontetum viticulosi (Table 56-6 in Van Dort et al. 2017).

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Synoptic table Cladonietum digitatae (Table 57-6 in Van Dort et al. 2017).

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Synoptic table Trapeliopsidetum flexuosae (Table 57-9 in Van Dort et al. 2017).

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Table 2.

Weighing of species to calculate mean habitat indicator values on association level. For each association, all species present in the association (and corresponding subassociations) in the synoptic table of the actual class (Van Dort et al. 2017) are considered. The weight per species is given, used to calculate, per association, a mean habitat indicator value (moisture, light availabilty, nutrient richness, acidity; Siebel 1993, 2005, Sparrius et al. 2015a, b). Species not identified on species level (e.g. Collema sp.) are excluded. If several subspecies or variants of one species are present, indicator values are averaged and used only once in the calculations. Additionally, character and differential species not present in the synoptic table, but present in the association table or mentioned as such in the accompanying text (in Van Dort et al. 2017), are also included with similar weights as in the table below. ‘Species presence’ under ‘Note’ is the species presence (%) in the actual association in the corresponding synoptic table. *Aptroot et al. (2011), Siebel et al. (2013).

Figure 2.

Relationships between classes for the habitat variables moisture, light availabilty, nutrient richness and acidity. For each class, the minimum and maximum ecological indicator values of their associations are indicated by a solid green box. Values for other classes are indicated by transparent green boxes. Moisture: 1 = very dry, 11 = in water; light availability (‘Light’): 2 = shadow-deep shadow, 9 = very open; nutrient richness (‘Nutrients’): 1 = very poor, 9 = excessively rich; acidity (‘pH’): 1 = extremely acid, 9 = extremely basic. Class names truncated if necessary.

Ecological relationships between classes

In Van Dort et al. (2017) we analysed almost all associations on the abiotic habitat variables moisture, light availabilty, nutrient richness and acidity to compare habitat preferences of all associations within a class, using ‘ecological indicator values’ specifically designed for Dutch bryophyte and lichen species (Siebel 1993, 2005, Sparrius et al. 2015a, b). The class Fellhaneretea bouteillei with epiphyllic lichen species contains only three diagnostic species. One is a character species on class level F. bouteillei which also grows in completely different habitats than typical for this class. Also, its diagnostic value for one of the two associations is not fully clear (yet). Furthermore, this class contains two very rare character species on association level (Fellhaneropsis vezdae and Fellhaneropsis rhododendri; BLWG 2023g). Therefore we decided to exclude this class (two associations) from our analyses. For all other 80 associations in the remaining 15 classes, species indicator values were used to calculate an average value per association. In this calculation, species were weighted: character species were more important than differential species and diagnostic species on association level were more important than diagnostic species on other levels (Table 2). Here, we use this analysis to indicate, for these four habitat variables, the position of each class (except the F. bouteillei) relative to the other classes, using minimum and maximum values of all associations from each class (Fig. 2). Analyses performed in R ver. 4.2.2 ( www.r-project.org). Figures in Fig. 2 made with R-package ‘ggplot2’ ( www.r-project.org, Wickham 2016).