A preliminary floristic classification of southern and ...

Antarctic Science 20 (6), 553–562 (2008) & Antarctic Science Ltd 2008 Printed in the UK

doi:10.1017/S0954102008001454

A preliminary floristic classification of southern and northern Victoria Land vegetation, continental Antarctica NICOLETTA CANNONE*1 and RODNEY SEPPELT2 1

Deptartment of Biology and Evolution, Ferrara University, Corso Ercole I d’Este, 32, 44100 Ferrara, Italy 2 Australian Antarctic Division, Channel Highway, Kingston, TAS 7050, Australia *[email protected]

Abstract: This paper proposes a new objectively-generated vegetation classification for southern and northern Victoria Land (continental Antarctica) based on the floristic composition of the plant communities. The new classification aims to integrate the existing physiognomic classification of the cryptogamic Antarctic tundra, provide useful data on floristic composition and distribution of the vegetation occurring in southern and northern Victoria Land, and develop a suitable tool allowing easy comparison of syntaxa from different locations. Field data from 26 sites along a latitudinal gradient (728 – 778S) were analysed by a hierarchical classification integrated with multivariate statistics, including indirect ecological information (Principal Component Analysis). Similarity of the identified groups was assessed through the Jaccard similarity index. The new classification is compatible with previous ones and is widely applicable to Victoria Land and includes previous classification. This standardized approach relates plant communities to their floristic composition and provides a basis for relating vegetation composition to environmental gradients and to patterns of vegetation dynamics and succession which are still poorly understood in Antarctica. Received 17 September 2007, accepted 18 March 2008

Key words: floristic composition, hierarchical classification, plant communities Introduction

physiognomic dominance are difficult to place within the defined subformations and thus would require intermediate categories. A physiognomic classification of the vegetation does not permit ready comparison of different localities as it does not unequivocally relate each vegetation type to its floristic composition. Plant communities may be classified according to a variety of different criteria (Mueller-Dombois & Ellenberg 1974), including physiognomic and structural criteria. In this context it is possible to emphasize the dominant species in the prevailing synusia, or to focus on significant groups of species (Braun-Blanquet 1964). For continental Antarctic vegetation, there have been only a few studies applying phytosociological criteria for vegetation classification (Nakanishi 1977, Seppelt & Ashton 1978, Longton 1979, Kappen 1985, Smith 1988, Castello & Nimis 1995), in most instances following the subjective scheme developed for the maritime Antarctic (Gimingham & Smith 1970, Smith 1996). A reliable phytosociological classification of the Antarctic vegetation has been difficult to develop and implement due to the inordinate taxonomic difficulties. Any attempt to develop a classification scheme applicable to the whole continental region has been compounded by the lack of biogeographical and phytosociological information for large areas of Antarctica. Despite a recent lichen flora (Øvstedal & Smith 2001) and the preparation of a moss flora (Ochyra et al. in press), many taxonomic difficulties, particularly with lichens, continue to exacerbate the work of the phytosociologist.

Traditionally, plant communities in Antarctica have been classified using the physiognomic-dominance criteria initially developed in the maritime Antarctic region (Longton 1967, Gimingham & Smith 1970) and subsequently extended and adapted to continental Antarctica by Seppelt & Ashton (1978), Longton (1979), Smith (1988, 1990), and Melick & Seppelt (1997). Two main vegetation formations were recognized: the Antarctic herb tundra formation (maritime Antarctic only) and the Antarctic non-vascular cryptogam tundra formation, each with a number of subformations (based on growth form and community dominants), associations and sociations (based on floristic composition) (see Gimingham & Smith 1970). Unlike the maritime Antarctic, where two native vascular plants exist, the vegetation of continental Antarctica is composed entirely of cryptogams (microfungi, cyanobacteria, algae, lichens, bryophytes). In the Antarctic non-vascular cryptogam tundra formation three principal subformations were described (Smith 1988, 1990): short moss turf and cushion subformation (dominated by mosses), foliose and fruticose lichen subformation (dominated by macrolichens), crustaceous lichen subformation (dominated by crustose and microlichens). There are some short-comings in this classification scheme. Communities with similar physiognomy but differing ecology may be grouped together within a single subformation. Communities lacking any prevailing 553

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NICOLETTA CANNONE & R. SEPPELT

unpublished data). In the vicinity of Mario Zucchelli Station, at Boulderclay (74º43’S, 164º05’E) the mean annual air temperature for the period 1997 – 2003 ranged between -16.4ºC and -15.1ºC (Guglielmin 2006). Farther south in Victoria Land the climate is drier and colder with a mean annual air temperature of -17.4ºC at McMurdo Station (77º51’S, 166º40’E) (Bockheim 1995). All sites are characterized by the occurrence of continuous permafrost. At Boulderclay, during the period 1997– 2003, the active layer thickness ranged between 0 – 93cm (Guglielmin 2006) whilst earlier data show it to have been 0 – 60 cm in the McMurdo region (Bockheim 1995). Almost all substrate types (granite, basalt, gabbro, metamorphic rocks, moraine and old marine deposits) were considered, always in ice free areas, sometimes close to glacier margins. In some locations, vegetation colonizing periglacial features (debris islands, gelifluction lobes) was also sampled. Several sites included ornithogenic soils.

Fig. 1. Location of the study sites in Victoria Land. Legend: FL ¼ Fryxell Lake, DI ¼ Dunlop Island, MP ¼ Marble Point, FP ¼ Finger Point, KP ¼ Kar Plateau, GI ¼ Gregory Island, CR ¼ Cape Ross, SN ¼ Starr Nunatak, PI ¼ Prior Island, LI ¼ Lamplugh Island, TF ¼ Tarn Flat, II ¼ Inexpressible Island, BC ¼ Boulderclay, MZS ¼ Mario Zucchelli Station, CS ¼ Cape Sastrugi, GO ¼ Gondwana, MK ¼ Mount Keinath, CW ¼ Cape Washington, SC ¼ Simpson Crags, EP ¼ Edmonson Point, CK ¼ Cape King, AI ¼ Apostrophe Island, CP ¼ Cape Phillips, CC ¼ Crater Cirque, LV ¼ Luca Vittuari point (unofficial name), RR ¼ Redcastle Ridge, CH ¼ Cape Hallett.

Despite these difficulties, we here describe a preliminary new floristic approach to the classification of southern and northern Victoria Land vegetation, based on floristic composition. This paper also provides data on the floristic composition and distribution patterns of the plant communities across a large area of continental Antarctica.

Vegetation sampling A standard plot size of 50 50 cm was used for all the vegetation surveys, this being determined by minimal area requirements of all plant community types observed in Victoria Land (Cannone, unpublished data). Within each plot, vegetational data were obtained by visual estimates of percentage cover for each species using a 5%-interval scale (modified by Heilbron & Walton 1984a, 1984b). To avoid overestimating species with very low coverage (, 5%), we also distinguished scattered species (coverage of c. 1%) and very scattered species (coverage 0.1% and/or symbol þ). For each plot elevation, slope, aspect, surface texture and type of substrate were recorded. The habitat type (glacier foreland, slope, crest, beach, ephemeral channel, rock walls, periglacial features, etc) was described for all

Materials and methods Study area Twenty six sites were selected in Victoria Land, continental Antarctica, along a latitudinal gradient from Cape Hallett (72º26’S, 169º56’E) to Lake Fryxell in the Taylor Valley, McMurdo Dry Valleys region (77º35’S, 163º04’E) (Fig. 1). The climate of this region is cold and arid (Øvstedal & Smith 2001). In the Terra Nova Bay area of northern Victoria Land annual precipitation is mostly as snow, (with c. 270 mm y-1 water equivalent), and the mean annual air temperature is c. -15ºC (unpublished data ENEA). The mean summer air temperature (December – February) ranges between -0.1 and -2.08C (Cannone & Guglielmin,



Fig. 2. Dendrogram showing the hierarchical classification of Victoria Land vegetation. The separation of the groups has been carried out at a linking distance . 0.8. The left branch (groups 1–6) identifies the lichen-dominated vegetation, the right branch is composed of transition communities with co-dominance of lichens and bryophytes (groups 7, 8), lichen-encrusted bryophytes (groups 9 –11), crustose lichens (group 12) and pure bryophytes (groups 13, 14).

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CLASSIFICATION OF VICTORIA LAND VEGETATION

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Table I. Floristic composition and average coverage (%) of the groups obtained by the hierarchical classification and proposed for the floristic/ecological classification of Victoria Land vegetation. The % cover of the dominant species within each group is given in bold. Order Alliance Association Number of releve´s Dendrogram groups Total % coverage

1 1 1.1 7 1 60

Usnea sphacelata Umbilicaria decussata Buellia frigida Xanthoria elegans Umbilicaria aprina Acarospora gwynnii Physcia caesia Xanthoria mawsonii Candelariella flava Usnea antarctica Rhizoplaca melanophthalma Prasiola crispa Pseudephebe minuscula Lecidella siplei Schistidium antarctici Syntrichia sarconeurum Bryum argenteum Bryum pseudotriquetrum Ceratodon purpureus Cyanobacteria Lecidea cancriformis Rhizocarpon geminatum Lecanora expectans Candelaria murrayi Buellia cladocarpiza Buellia pallida Physcia dubia Hennediella antarctica Turgidosculum complicatulum Syntrichia magellanica Hennediella heimii Candelariella vitellina Buellia grimmiae Leproloma cacuminum Caloplaca approximata Caloplaca athallina Caloplaca citrina Rinodina olivaceobrunnea Lecanora mons-nivis Rhizocarpon geographicum Lecanora fuscobrunnea Lecanora physciella Lecanora sverdrupiana Buellia papillata Bacidia johnstonii Lecidea andersonii Rhizoplaca mcleanii Tephromela atra Buellia darbishirei Buellia sublobulata

36


3.5 0.5

1

2 1.5

2

1 1 1.2 8 2 100

2 2A 2A.1 16 3 20

2 2A 2A.2 29 4 35

7 27 7 0.5

þ

þ 1 1 5 36 þ þ 2 1 5 8 þ 3 0.5

þ 1 4 0.5 þ þ 13.5

0.5 þ 22 2 3 þ þ þ 0.5

þ

1.5

þ þ þ 0.5 þ þ

þ þ

þ þ 0.5

1.5 þ

þ 1 1 þ þ þ þ þ

2 2A 2A.3 6 5 10 þ 1.5 þ þ þ 0.5 1 5.5

2 2B 2B 11 6 15

þ 8 þ 4 þ þ 0.5 1

þ

þ

þ

þ

þ þ 1 þ 1 þ þ þ þ

þ þ þ 0.5

þ

3 3A 3A 8 7 70

1.5 þ

2 þ 8 þ þ þ 4.5 26 þ 4.5 12 þ 1 þ 2.5 þ 1 þ 0.5

3 3B 3B 5 8 55 0.5 0.5 0.5

þ 2 0.5 42 4

þ 1 þ þ þ þ

4 4A 4A.1 9 9 65

1.5 0.5

8 5.5 5.5 1 þ 4 þ 33 1 0.5 þ 0.5

þ

4 4A 4A.2 9 10 45

4 4A 4A.3 8 11 80

1 þ 2 þ þ

2

18 1 8.5 0.5 þ

5 5 5 5 12 5

0.5

14 3.5 7.5 1 þ

1.5 0.5 2 þ 4 1 þ þ þ

1.5 0.5 1 0.5 31.5 7 5 4 þ þ

þ 3.5

þ þ

þ

þ

0.5

3 3.5

6 6 6.1 27 13 30

6 6 6.2 45 14 60

þ 1 þ þ 1 þ 1

þ þ þ 0.5 þ þ

þ þ

þ þ

þ þ þ 21.5 0.5 1 3 þ

0.5 3.5 þ 14 2 9.5 29.5 þ

þ þ

þ

0.5 þ 1

7.5

10 þ þ þ

þ þ þ

þ þ

þ

þ

þ

þ

þ þ

þ

þ

þ

þ þ

0.5 0.5

þ þ

þ

þ

þ þ

þ þ

þ

0.5

þ þ

þ

1

þ

1

þ þ

þ

þ þ

þ

þ

þ þ

þ þ

þ þ þ

þ þ þ þ 0.5

þ þ

1 þ

þ 0.5 þ

þ þ þ

þ

þ þ

þ


þ

1.5 þ þ þ þ þ

þ þ þ þ

þ þ

0.5 þ þ

þ

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Table II. Floristic composition and species frequency (%) of the groups obtained by the hierarchical classification and proposed for the floristic/ecological classification of Victoria Land vegetation. Species with frequency . 60% within each group are given in bold. The frequency data have been rounded to the nearest 5%. Order Alliance Association Number of releve´s Dendrogram groups Usnea sphacelata Umbilicaria decussata Buellia frigida Xanthoria elegans Umbilicaria aprina Acarospora gwynnii Physcia caesia Xanthoria mawsonii Candelariella flava Usnea antarctica Rhizoplaca melanophthalma Prasiola crispa Pseudephebe minuscula Lecidella siplei Schistidium antarctici Syntrichia sarconeurum Bryum argenteum Bryum pseudotriquetrum Ceratodon purpureus Cyanobacteria Lecidea cancriformis Rhizocarpon geminatum Lecanora expectans Candelaria murrayi Buellia cladocarpiza Buellia pallida Physcia dubia Hennediella antarctica Turgidosculum complicatulum Syntrichia princeps Hennediella heimii Candelariella vitellina Buellia grimmiae Leproloma cacuminum Caloplaca approximata Caloplaca athallina Caloplaca citrina Rinodina olivaceobrunnea Lecanora mons-nivis Rhizocarpon geographicum Lecanora fuscobrunnea Lecanora physciella Lecanora sverdrupiana Buellia papillata Bacidia johnstonii Lecidea andersonii Rhizoplaca mcleanii Tephromela atra Buellia darbishirei Buellia sublobulata


1 1 1.1 7 1 85 60 30

30

15 40 15

40

1 1 1.2 8 2 50 75 60 35 10 75 60 85 100 35 10 50 25 50 35 25 10 10

15

2 2A 2A.1 16 3 5 60

5 25 75 55 20 5 95 20 20 25 25 5 10

10 10

25 10 5

35 20

2 2A 2A.2 29 4 10 15 95 55 25 25 5 20 30

2 2A 2A.3 6 5

30 5 5 15 5 5 25 5

100

15 65 35 15 15 50 50

15

35

5 15 5 15 15 5 5 5 5

2 2B 2B 11 6

3 3A 3A 8 7

20 100

25 25

10 35 25 25 25 20 10

25

10 25 10 10

10

35 25 75 10 25 10 35 75 25 85 60 25 35 10 35 35 35 10 10

3 3B 3B 5 8 20 20 20

40 20 20 100 20

40 20 20 20 40 40

4 4A 4A.1 9 9 20 40 40

80 80 80 40 40 20

4 4A 4A.2 9 10 20 10 45 10 10

4 4A 4A.3 8 11

5 5 5 5 12

6 6 6.1 27 13

25

20

80 40 90 20 20

60 50 75 25

5 10 5 5 10 5 30

5 5 10

10 10

5 5

15 10 5 100 25 5 40 5

15 30 5 95 60 50 95 5

15 5

10

45 35 80 20 20 10 20 10 35

60 50

10

10

20 40 100 20 40 40 40

60

20 50 10 35 50 100 75 25 25 50 10

40

60 40

5 20

10 10 10 25

10 10 10 10

15

10

20

20

10 10

20

20

10

5

10

15

10 20

10 15

10

15

10 25

25

10

15

20

15 5

15

10 10

35

5

15

35 10

5 5 10

10

5

10

25 10 0

10 5 5 5 5

20 20

10

20 20 20

20 20 20

20

10 10


5 5 5 5 5 5

10 20 20 20

10 5

5 5 5

5

5 10 5

5 5 5

20

15

10

6 6 6.2 45 14

20

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releve´s. Additional descriptors such as the presence of ornithogenic soils and qualitative estimates of snow and moisture conditions were recorded. A total of 189 releve´s were assessed for the analysis. Samples of terricolous and epilithic plants were collected for later taxonomic verification. Species nomenclature follows Castello & Nimis (2000), Øvstedal & Smith (2001) and Castello (2003) for lichens, and Ochyra (1998) and Seppelt & Green (1998) for bryophytes. Data analysis The original field data from 24 locations along a gradient of five degrees of latitude in Victoria Land (Cannone 2005, 2006) were analysed using Statisticaw. A hierarchical classification (dendrogram) was derived, applying the unweighted pair-groups average joining rule and the l-r Pearson coefficient as linkage distance, based on floristic composition. The hierarchical tree matrix comprised 189 releve´s. The separation of the two main vegetation groups used a linking distance . 0.95, while the separation of the sub-groups used a linking distance between . 0.95 and . 0.6. The suitability of the separation between groups was tested analysing the similarity of the identified groups using the Jaccard index computed by EstimateS (Colwell 2005). Further analysis by multivariate statistics (ordination by Principal Components Analysis - PCA) allowed us to characterize, although indirectly, which environmental gradients might be related to the vegetation communities identified. In particular, the ordination by PCA was carried out using logarithmic transformation of the original data, applying the scaling through inter-species correlation, the centred standardization by species and the normed standardization by samples using the software CANOCO for Windows (ter Braak & Sˇmilauer 1998). Results Nine species of moss, 54 lichens, the chlorophycean alga Prasiola and the general category Cyanobacteria were recorded in this study. The lichen species recorded represent around 95% of all taxa known to occur in the region 71– 77ºS and 162– 170ºE (Castello & Nimis 2000, Castello 2003) and 72% of all the mosses (Seppelt & Green 1998, Adams et al. 2006). Hierarchical classification The dendrogram generated by the hierarchical classification (Fig. 2) (Tables I & II) has two main branches (which are separated at a linking distance of 0.96): the left branch (groups 1 – 6) is characterized by a dominance of lichens and its sub-branches are characterized mainly by: macrolichens (foliose and fruticose lichens; groups 1, 2), and macro- and microlichens (foliose and crustose lichens;



Fig. 3. Species-site diagram of the Principal Component Analysis (X ¼ 0.239; Y ¼ 0.96). In the lower right-hand corner there are gradients subjectively derived from the PCA. The numbers represent the fourteen groups of releve´s identified by the hierarchical classification (dendrogram of Fig. 2). Legend. Releve´s symbols: open circles ¼ releve´s of the left branch of the dendrogram (groups 1–6), open squares ¼ releve´s of the right branch of the dendrogram (groups 7–14). Species abbreviations: Aca.gwy ¼ Acarospora gwynnii, Bry.arg ¼ Bryum argenteum, Bry.pse ¼ Bryum pseudotriquetrum, Bue.fri ¼ Buellia frigida; Cal.app ¼ Caloplaca approximata, Cal.cit ¼ Caloplaca citrina, Can.fla ¼ Candelariella flava, Can.mur ¼ Candelaria murrayi, Cer.pur ¼ Ceratodon purpureus, Cyanob ¼ Cyanobacteria, Lec.an ¼ Lecidea cancriformis, Lec.sip ¼ Lecidella siplei, Phy.cae ¼ Physcia caesia, Pra.cri ¼ Prasiola crispa, Pse.min ¼ Pseudephebe minuscula, Rhi.geo ¼ Rhizocarpon geographicum, Rhi.mel ¼ Rhizoplaca melanophthalma, Syn.sar ¼ Syntrichia sarconeurum (previously named Sarconeurum glaciale), Shi.ant ¼ Schistidium antarctici, Umb.apr ¼ Umbilicaria aprina, Umb.dec ¼ Umbilicaria decussata, Usn.ant ¼ Usnea antarctica, Usn.sph ¼ Usnea sphacelata, Xan.ele ¼ Xanthoria elegans, Xan.maw ¼ Xanthoria mawsonii.

groups 3 – 6). The right branch (groups 7 – 14) is characterized by a dominance of bryophytes and is divided into three sub-branches characterized by: fruticose lichens and bryophytes (groups 7 – 8), lichen-encrusted bryophytes (groups 9 – 11) and by crustose lichens (group 12) and pure bryophytes and Cyanobacteria (groups 13 –14). The separation of the main groups within each main branch has been carried out at a linking distance . 0.8 for all groups except for groups 13 and 14 (separated at the linking distance of 0.66). The macrolichen vegetation is characterized by the dominance of Usnea sphacelata (group 1) and of

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Table III. Similarity of the dendrogram groups calculated by the Jaccard similarity index (computed by the software EstimateS, Colwell 2005). Values 0.6 are given in bold. Groups 1 2 3 4 5 6 7 8 9 10 11 12 13 14

1

2

3

4

5

6

7

8

9

10

11

12

13

0.33 0.27 0.37 0.30 0.30 0.32 0.24 0.31 0.25 0.11 0.25 0.30 0.49

0.49 0.54 0.40 0.46 0.53 0.58 0.63 0.64 0.60 0.12 0.56 0.49

0.55 0.36 0.42 0.46 0.32 0.50 0.52 0.53 0.14 0.49 0.46

0.36 0.61 0.55 0.33 0.44 0.53 0.43 0.26 0.54 0.44

0.42 0.24 0.30 0.31 0.33 0.20 0.15 0.40 0.37

0.43 0.29 0.34 0.36 0.34 0.28 0.50 0.47

0.46 0.50 0.56 0.53 0.20 0.45 0.46

0.45 0.57 0.44 0.15 0.32 0.41

0.61 0.58 0.10 0.41 0.46

0.59 0.13 0.46 0.56

0.09 0.56 0.53

0.12 0.13

0.67

Umbilicaria decussata– Usnea antarctica – U. sphacelata (group 2), respectively. The vegetation dominated by macrolichens and microlichens includes a range of communities characterized by the constant occurrence of Buellia frigida, associated with different species, including Prasiola crispa and Xanthoria mawsonii (group 3), Umbilicaria aprina (in group 4 as associated species to the dominant Buellia frigida), Rhizoplaca melanophthalma (group 5), Xanthoria elegans and Physcia caesia (group 6). In contrast to the left branch, the right branch of the dendrogram is more heterogeneous, and is characterized by the almost constant occurrence of bryophytes. It includes a range of vegetation types dominated by different growth forms including bryophytes, macrolichens and microlichens. Groups 7 and 8 represent a transition from the lichendominated to the bryophyte-dominated communities and are characterized by the dominance and high frequency of the fruticose lichen Pseudephebe minuscula, associated with the crustose lichen Lecidella siplei, occurring with scattered bryophytes Bryum argenteum and B. pseudotriquetrum. Groups 9, 10 and 11 are composed of lichen-encrusted bryophytes with a common pool of muscicolous lichens, including Physcia caesia, Candelariella flava, Xanthoria mawsonii, and different prevailing species of bryophytes such as Schistidium antarctici (group 9), Bryum argenteum (group 10), and Syntrichia sarconeurum (formerly Sarconeurum glaciale) (group 11). Group 12 is anomalously nested within the bryophyte communities and it is completely different from all the other groups of the dendrogram. It is characterized by crustose epilithic lichens with the dominance and high frequency of Lecidea cancriformis and of Rhizocarpon geminatum. The positioning of this group within the dendrogram is confused. The pure bryophyte communities are represented by groups 13 and 14, the former characterized by the clear dominance of Bryum pseudotriquetrum and the latter by the dominance of



Cyanobacteria with Bryum argenteum, Ceratodon purpureus, B. pseudotriquetrum and Schistidium antarctici.

Principal Component Analysis The PCA results (Fig. 3) indicate a continuum rather than a discontinuous distribution of both species and releve´s, although it is possible to identify some target (and/or more important and/or dominant) species (characterized by the longer vectors) and a separation of the releve´s compatible with the groups already identified by the hierarchical classification (Fig. 2, Tables I & II). The distribution of the target species allows recognition of three main groups: a) a group of mainly epilithic lichens dominated by Buellia frigida with Xanthoria elegans, Acarospora gwynnii, Umbilicaria aprina, Usnea sphacelata and Umbilicaria decussata, b) a group of both epiphytic (muscicolous) and ubiquitous lichens and bryophytes characterized by Xanthoria mawsonii, Candelariella flava and Physcia caesia with Prasiola crispa, Usnea antarctica, Syntrichia sarconeurum, Rhizoplaca melanophthalma and Pseudephebe minuscula, c) a group dominated by bryophytes and Cyanobacteria with Bryum argenteum, B. pseudotriquetrum and Ceratodon purpureus as target species for the bryophytes. The 14 groups of releve´s already identified by the hierarchical classification are located in different parts of the diagram: groups 1 – 6 (lichen dominated vegetation) are located in the left part of the graph (x , 0) and mainly in the upper part (y . 0). The lichen-bryophyte vegetation (groups 7 and 8) and the lichen-encrusted bryophytes (groups 9 – 11) occur in the lower left part (x , 0; y , 0) of the diagram, while the pure bryophyte communities lie in the right part of the graph (x . 0). The anomalous group 12 is close to the origin, indicating the lack of specific links to the other groups and confirming its anomalous nesting within the dendrogram.

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4. Physcia caesia –Candelariella flava– Xanthoria mawsonii encrusting bryophytes

5. Lecidea– Rhizocarpon–Rhizoplaca– Lecanora 6. Bryum spp. –Ceratodon– Cyanobacteria

Lichen-encrusted bryophytes

Microlichens Pure bryophytes

3. Pseudephebe minuscula –Lecidella siplei– Bryophytes Mixed (macro)lichen and bryophyte communities

2B. Xanthoria elegans– Physcia caesia 3A. Lecidella siplei –Bryophytes (Bryum pseudotriquetrum B.argenteum, Hennediella) 3B. Pseudephebe minuscula– Lecidella siplei –Bryophytes 4A. Physcia caesia– Candelariella flava– Xanthoria mawsonii encrusting bryophytes (Schistidium –Syntrichia– Bryum) 5. Lecidea– Rhizocarpon –Rhizoplaca–Lecanora 6. Bryum spp.– Ceratodon–Cyanobacteria

2. Buellia frigida–Physcia caesia–Xanthoria spp. Macrolichens and microlichens

2A. Buellia frigida

Association

1. Usnea –Umbilicaria

Alliance Order

The International Code of Phytosociological Nomenclature (ICPN) (Weber et al. 2000) recognizes four principal ranks in the hierarchical system of syntaxa: association, alliance, order and class. An “association (type of stands) is a plant community of definite floristic composition which presents a uniform physiognomy and which is grown in uniform habitat conditions”. Ranks such as “sociation” and “consociation” are not considered under the ICPN, while a subassociation (a rank subordinate to an association but which must be established with reference to the association to which it belongs) is recognized. At least 10 vegetation releve´s are required for the original diagnosis of an association or subassociation and that for each proposed association, a releve´ must be indicative and serve as the

Macrolichens

Floristic classification of Victoria Land vegetation

Formation

Results obtained from the hierarchical classification were compared to and integrated with those of the PCA to elaborate a synthetic table containing species (rows) and clusters of releve´s (columns) as a database from which to compute a similarity matrix. The similarity between the identified groups was tested using the Jaccard similarity index (Table III). Separation of the identified groups (obtained by the dendrogram and confirmed by the PCA) is consistent with results of the Jaccard similarity index which indicates the highest similarity a) between groups 13 and 14, b) among groups 2, 9, 10, 11, c) between 9 and 10; and a high similarity d) between groups 4 and 6. In particular, the high similarity among groups 2, 9, 10, 11 could be linked to the occurrence in all groups of Schistidium antarctici, Syntrichia sarconeurum, Usnea antarctica, Candelariella flava, Xanthoria mawsonii, Physcia caesia and Buellia frigida. The high similarity between groups 13 and 14 suggests they are two different associations belonging to the same alliance and order. Group 12 is isolated from all the other groups, again confirming that it was anomalously nested within the dendrogram.

Table IV. Scheme of the proposed new floristic classification of Victoria Land vegetation.

Similarity indices

1. Usnea –Umbilicaria

The distribution patterns of the 14 groups and of the target species within the PCA diagram allows us to suggest, although indirectly, the existence of some main environmental determinants, particularly moisture (increasing from left to right) and nutrient gradient (increasing from top to bottom). The patterns outlined by the PCA confirm the separation of communities dominated by epilithic lichens from those dominated by epiphytic and ubiquitous lichens and by bryophytes, respectively. Also, the releve´s of the groups 7 and 8 of the dendrogram (Fig. 2, Tables I & II) are located in the PCA (Fig. 3) at a position representing a transition from the lichen-dominated to mixed lichen-bryophytes communities.

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1.1. Usnea sphacelata 1.2. Usnea antarctica– Umbilicaria decussata 2A.1 Prasiola crispa –Xanthoria mawsonii 2A.2 Buellia frigida 2A.3 Rhizoplaca melanophthalma 2B. Xanthoria elegans– Physcia caesia 3A. Lecidella siplei –Bryophytes (Bryum pseudotriquetrum B. argenteum, Hennediella) 3B. Pseudephebe minuscula– Lecidella siplei – Bryophytes 4A.1 Epiphytic lichen encrusted Schistidium antarctici 4A.2 Epiphytic lichen encrusted Bryum argenteum 4A.3 Epiphytic lichen encrusted Syntrichia sarconeurum 5. Lecidea–Rhizocarpon– Rhizoplaca–Lecanora 6.1. Bryum argenteum– Cyanobacteria 6.2. Cyanobacteria –Bryum argenteum– Ceratodon


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Table V. Distribution patterns of the vegetation associations in the investigated sites at Victoria Land. FL

Edaphic characteristics Granites Metamorphic rocks Balsalts Marine deposits Ornithogenic soils Periglacial features Ephemeral streams Vicinity to penguin rookery

MP

FP

KP

GI

CR

B

B

B

B

B

B B

B

B

PI

LI

B B

B B B B

B

B

B

B B

B

B

SN

B B

B

B

B B

II

BC

CS

GO

MK

CW

B

B

B

B B

B

B B

B

B

B

B

B

B

CK

AI

CP

CC

LV

RR

B

B

B

B

B

B

B B

B

B

B B B

B

B B

B B

B B B

B B

B

B

B

B

B

B

B

B

B

B

B B

B B B

B

B B

B B B

B

B B B

B B

B

B

B

B B

B

B

B B

B

B

B B B

B

B

B

B

B B

B B

Site acronyms: FL ¼ Fryxell Lake, DI ¼ Dunlop Island, MP ¼ Marble Point, FP ¼ Finger Point, KP ¼ Kar Plateau, GI ¼ Gregory Island, CR ¼ Cape Ross, SN ¼ Starr Nunatak, PI ¼ Prior Island, LI ¼ Lamplugh Island, TF ¼ Tarn Flat, II Inexpressible Island, BC ¼ Boulderclay, CS ¼ Cape Sastrugi, GO ¼ Gondwana, MK ¼ Mount Keinath, CW ¼ Cape Washington, SC ¼ Simpson Crags, EP ¼ Edmonson Point, CK ¼ Cape King, AI ¼ Apostrophe Island, CP ¼ Cape Phillips, CC ¼ Crater Cirque, LV ¼ Luca Vittuari point (unofficial name), RR ¼ Redcastle Ridge, CH ¼ Cape Hallett.


CH

B

B

B

EP

B

B B

SC

B

B B B

TF


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1.1 Usnea sphacelata 1.2 Usnea antarctica –Umbilicaria decussata 2A.1 Prasiola crispa –Xanthoria mawsonii 2A.2 Buellia frigida 2A.3 Rhizoplaca melanophthalma 2B Xanthoria elegans– Physcia caesia 3A Lecidella siplei –Bryophytes 3B Pseudephebe minuscula– Lecidella siplei– Bryophytes 4A.1 Epiphytic lichen encrusted Schistidium antarctici 4A.2 Epiphytic lichen encrusted Bryum argenteum 4A.3 Epiphytic lichen encrusted Syntrichia sarconeurum 5 Lecidea–Rhizocarpon 6.1 Bryum argenteum– Cyanobacteria 6.2 Cyanobacteria –Bryum– Ceratodon

DI


name-bearing type. In Antarctica, local environmental constraints often make it difficult to acquire 10 such releve´s and it is proposed here that a minimum of 5 should be required for the diagnosis of associations and subassociations in continental Antarctic regions. The rules of the ICPN are complex. Considering that the aim here is to provide a useful and easily applicable tool for standardized field measurement and subsequent data analysis and comparison, a simplified nomenclature (easily usable in the field) is proposed. The hierarchical classification of the original data (Fig. 2, Tables I & II), integrated with the results of PCA (Fig. 3) and similarity indices (Table III), permits an elaboration of a floristic classification of the vegetation derived from the average percentage cover of each species (Table I), species frequency (Table II), and the general syntaxonomical scheme (Table IV), organized according to the ICPN rules (Weber et al. 2000). The distribution patterns of each identified association in the sites sampled in Victoria Land together with some environmental data, such as lithology, occurrence of ornithogenic soils, periglacial features, ephemeral streams and proximity to penguin rookeries/colonies are reported in Table V. These data are referred only to the releve´s presented in this paper and do not attempt to cover all the environmental variability of the conditions where these associations may occur. Discussion The data obtained from field studies in Victoria Land were compared to those available from existing Antarctic literature (Kappen 1985, Wynn-Williams 1985, Schwarz et al. 1992, Castello & Nimis 1995, Smith 1999) to develop a proposed standardized system for floristic classification of the vegetation. The floristic classification proposed here distinguishes six different orders which could be grouped in two main classes of vegetation: a) dominated by lichens (orders 1, 2, 5 of Table IV corresponding to the dendrogram groups 1 – 6 and 12) (further divided into units dominated by macrolichens - groups 1, 2, and by crustose lichens groups 3, 4, 5, 6, 12), and b) mainly dominated by bryophytes (orders 3, 4, 6 of Table IV and dendrogram groups 7 – 14 with the exception of group 12). It is comparable with the main formations described for the vegetation of other continental Antarctic regions (e.g. Smith 1988, Melick & Seppelt 1997). The proposed new classification groups associations on the basis of floristic composition. The sequence of associations within each alliance emphasis ecological requirements, often indicative of a range of moisture and/or nutrient regimes, as indirectly indicated by PCA (Fig. 3). The distribution of bryophytes is compatible with a gradient in ground moisture. Recent data on soil properties



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in different vegetation and permafrost conditions in continental Antarctica (Cannone et al. in press) show that Bryum species, Ceratodon purpureus and Syntrichia magellanica (formerly named Syntrichia princeps) are generally found where ground moisture is relatively high (. 25%), while Schistidium antarctici and Syntrichia sarconeurum generally occur where soil moisture is , 13%. However, in many localities in Victoria Land species show adaptation to variable ground moisture conditions (e.g. C. purpureus and B. pseudotriquetrum are able to tolerate also relatively dry conditions according to Selkirk & Seppelt 1987). At Cape Hallett and some nearby localities, Bryum argenteum occurs in the wettest sites and Syntrichia magellanica in dry sites with ephemeral moisture. Schistidium antarctici occurs in habitats spanning a wide range of substrate moisture levels. Syntrichia sarconeurum appears to be the only consistent indicator of dryer habitats. The gradient in lichens distribution is complex and is determined in part by substrate characteristics, the availability of nitrogen (as NHþ 4 ), the physiological response of individual habitat moisture regime, and in part by latitude. The Usnea –Umbilicaria order (and alliance) includes the following communities previously described for northern Victoria Land: the Usneetum purum and the Usneetum mixtum (Kappen 1985), and the groups G1 and G2 of the fruticose and foliose lichen subformations (Castello & Nimis 1995). Similar communities occur in other northerly locations of continental Antarctica (e.g. for the Windmill Islands region of Wilkes Land: Smith 1988, Melick et al. 1994, Melick & Seppelt 1997). The Buellia frigida – Physcia – Xanthoria alliance and its orders and associations are compatible and may include the communities formerly described within groups G5, G6, G7 of the subformations of crustaceous lichens in Victoria Land (Castello & Nimis 1995). An additional order and alliance is characterized by Pseudephebe minuscula, Lecidella siplei and bryophytes, and is separated from the traditional Usnea – Umbilicaria – Pseudephebe alliance. From the dendrogram, this alliance is located close to the bryophyte-dominated communities and may indicate that Pseudephebe has similar moisture requirements to bryophytes and may, therefore, be a potentially useful target species for long-term monitoring of climate change impacts on vegetation, in particular to snow, because it is reliant on snow melt for its water supply. The Physcia caesia – Candelariella flava – Xanthoria mawsonii encrusting bryophytes order and alliance is compatible with, and may include, the lichen-encrusted bryophytes communities formerly described as G8 (Castello & Nimis 1995). The identification of a Lecidea cancriformis–Rhizocarpon– Rhizoplaca–Lecanora order and alliance raises problems concerning both its position within the dendrogram and its representativeness within the classification system. To address

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this problem it seems appropriate to place it in isolation but representative of the epilithic crustose lichen communities, although investigation is needed to represent adequately its floristic composition and ecological requirements. The pure bryophytes communities are represented by the Bryum spp. – Ceratodon– Cyanobacteria order and alliance. Proposals for future research include: a) analysis of the ecological requirements of the proposed syntaxa, particularly for substrata moisture and nutrients, b) assessment of the successional stages to reconstruct patterns of vegetation development and succession, c) inclusion of new study sites and of a wider range of environmental, latitudinal and geographical conditions to increase the representativeness of these data, and d) development of the present objective floristic classification to encompass the vegetation of all continental Antarctica.

Acknowledgements We wish to thank for their comments and suggestions Prof Ryszard Ochyra and two anonymous reviewers which allowed us to significantly improve this paper. We wish to thank Prof Mauro Guglielmin, the coordinator of the Permafrost and Global Change in Antarctica Project (funded by PNRA), for his scientific cooperation and help in the field. We are grateful to PNRA (Progetto Nazionale Ricerche in Antartide) for their scientific collaboration and logistic support to Nicoletta Cannone.

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