The Subnival Vegetation of Moquegua, South Peru: Chasmophytes, Grasslands and Cushion Communities

: The present work is a phytosociological synthesis and syntaxonomic overview of the vegetation of the highest subnival parts (superpuna) of the open alpine vegetation of the high plateaus (puna) of the Andes of Moquegua, South West Peru, as related to the main environmental gradients. Using TWINSPAN and DCA ordination analysis, 153 phytosociological relev é s were analyzed. For each association, subassociation and community, the syntaxonomy, ﬂoristic diversity and relation with environmental variables are described. The syntaxonomy and synecology of superpuna vegetation was studied in 19 localities at an altitude of 4450–4800 m. The study area has a pluviseasonal climate with yearly rainfall (December-April). Four main highland vegetation types were distinguished: 1. slope and scree chasmophyte vegetation composed of shrubs, cushions, ground rosettes and grasses, 2. grasslands (grazed and ungrazed) characterized by great species richness in shrubs, cushions, ground rosettes, grasses and herbs, 3. vegetation of plateaus with cushions, shrubs, ground rosettes, herbs and grasses and 4. nitrophilous vegetation with high cover and low species richness. Within the vegetation of the orotropical and cryorotropical bioclimatic belts three phytosociological classes can be distinguished: Argyrochosmetea niveae (chasmophytic vegetation), Calamagrostietea vicunarum (grasslands with cushions), Anthochloo lepidulae-Dielsiochloetea ﬂoribundae (highland slopes and plateaus) and a nitrophylous community. One new association from rock and scree slopes was described within the Saxifragion magellanicae ( Argyrochosmetea niveae ). Within the Calamagrostion minimae , which comprises grasslands with cushions and mat-forming plants, one new association with two subassociations could be distinguished. Within the grassland and cushion associations of the Azorello-Festucion ( Calamagrostietea vicunarum ), three new associations were described, comprising nine subassociations. In the Anthochloo - Dielsiochloetalia one new and one previously described association and one community are distinguished. In addition, the nitrophilous community of Tarasa nototrichoides and Urtica ﬂabellata has been described. In total the vegetation comprised 172 vascular species belonging to 32 families. Our study provides the ﬁrst syntaxonomic revision of chasmophytes, cushion associations and high-altitude grasslands in the Andes of North Moquegua. The proposed syntaxonomic scheme contains the associations distributed under similar habitat conditions throughout the Southern Andes of Peru, but also the associations reﬂecting the local ﬂoristic and environmental patterns. The subnival vegetation of Moquegua hosts some rare endangered and/or protected plant species.


Introduction
The puna is one of the world's largest pastoral ecosystems in the tropical mountains and its flora, (including many endemic species) and vegetation are vulnerable to human pressure. A reference and tool for nature conservation is highly needed. Its vegetation is however still insufficiently studied. An overview of plant species assemblages and their relation to environmental conditions is largely missing. This especially applies to the highest part of the Moquegua study area over 4400 m. The relation between diversity and species composition of the superpuna vegetation and environmental factors such as altitude, slope aspect and angle, cover of rocks and stones and soil properties is largely unknown.In the traditional vegetation classification of Bolivia and Peru, the term puna is used to identify the open alpine vegetation of the high plateaus of the Central Andes [1][2][3][4][5][6]. Reference [7] defined the puna as a level area termed Altiplano. References [8,9] use the term superpuna to refer to the highest subnival parts of the puna with isolated patches of snow. The subnival zone of tropical mountains is characterized by a variable climate. This means cold freezing nights and low to moderate temperatures during daytime [7,[10][11][12][13]. Night temperature is lowest at ground level before sunrise. Nightly freezing causes daily frost heaving with a number of phenomena at soil surface level, which also has an impact on plant life.
In this research we define the superpuna as the zone between 4450 and 4800 m (permanent snowline in Moquegua) with average annual temperatures ranging from 6 degrees C at 4500 m to 0 degrees C at 4800 m a.s.l. Mean annual precipitation is low: between 400 and 600 mm per year [14].
Growth forms in the extreme habitat of the subnival zone of the puna correspond mainly to low evergreen shrub, low herbs with thick cuticle and/or hairy leaf surface, and lax and compact cushions [7].
In the north of Moquegua growth forms of the superpuna vegetation include the scarce presence of dwarf and erect shrubs, tussock grasses, and annual herbs. More abundant is the presence of ground rosettes, cushions, mats and annual grasses. Cushions are abundant in the superpuna as well; they are known to enhance diversity by nursing other species [8,15,16], although some cushions appear to be non-facilitators [17]. Due to the near absence of tussock grasses grazing and fire are practically absent.
The continuous fumarolic activity of the Ubinas volcano [18] could have strong negative effects (not studied) on the plant communities in North Moquegua.
South Peru. The study area is located at 70 • Table 1) at an altitude between 4450 and 4800 m a.s.l. Average annual precipitation at the Ichuña meteorological station at 3790 m a.s.l. is 460 mm, the mean minimum temperature is 3.7 • C and the mean maximum is 19.4 • C [14]. Precipitation is markedly seasonal, with over 80% of the annual rainfall (600-800 mm) falling between December and April [14] and significant interannual variability [37,38]. Recent floods correspond to the El Niño phenomenon by increased annual precipitation. Soil moisture ranges from 0 in the dry season to below 10% in the rainy season [39]. No glaciers have been observed on the highland mountains of North Moquegua. Nevertheless, after heavy rainfall, snow accumulates temporarily above 4700 m altitude. On the summit of the Ubinas volcano (5672 m a.s.l.), snow can be permanent during the rainy season (December-April) and occasionally during the dry season (May-November).  Table 1.
The study area is located in the high-altitude sectors of the southwestern Andes with Pacific tributaries. Here the geology is volcanic and sedimentary with intercalations of conglomerates and sand. Ravines and crevices have infill of sandy silt and calcareous sediment [40]. The fieldwork area comprises the high plateaus and rocky slopes of the two mountain chains of volcanic origin that form the watersheds of the upper Tambo, Paltuture and Ichuña rivers and their tributaries.
Reference [35] presented the vegetation zonation of the upper Tambo River in the Moquegua region and distinguished the orotropical and cryorotropical bioclimate [41] occurring between 4150 and 4650 m and characterized by chasmophytic associations and grasslands with cushions, which occur above 4500 m in Moquegua. The cryorotropical zone was identified at altitudes above 4870 m where cushion associations are also present.  (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) in the superpuna of the Andes of Moquegua, Peru. #rel = number of relevés at the site in question, year = year(s) in which fieldwork was done, Elevation = the altitudinal range within which the relevés were made, Slope ( • ) = minimal and maximal slope angle, Aspect. = orientation, and vegetation = general description of the vegetation structure.

Data Collection
Floristics. The plant species were identified directly in the field; unidentified species were collected and later deposited in various herbaria (USM, HUSA, MOL, CPUN, CUZ, HSP, MO, L, WAG; acronyms according to [42]. Information on the taxonomy and species distribution was obtained from the literature. The nomenclature of the taxa is in accordance with [43], the electronic versions of [44][45][46]. Specific information on the taxonomy and species distribution was obtained from different sources [43,[47][48][49][50][51][52]. Vegetation. Fieldwork was conducted over a period of five years (2009,(2011)(2012)(2013)(2014) during the months of February, March, April and September.
A total of 153 relevés was made in 11 sites within an altitudinal range of 4450-4800 m a.s.l. Plot size was 25 m 2 for grasslands and cushion vegetation and 16 m 2 , or 25 m 2 for chasmophyte and 1 m 2 for nitrophilous vegetation [9].
Within the different biotopes, sample plots (relevés) were randomly selected and positioned according to the principle of homogeneity as defined by the Zurich-Montpellier method [53]. We ensured that no sample relevés traversed ravines, clefts or streams. In chasmophytic environments, relevés were selected on pure rock stands including soil pockets and crevices. Contact with zonal grassland vegetation was avoided.
For each relevé, the presence of species was noted and its percentage actual cover was estimated [54,55]. Due to insufficient expertise only the presence of bryophytes and lichens was noted, but the species were not identified.

Environmental Variables
For each relevé we collected data on altitude (meters above sea level = m a.s.l.), slope inclination (degrees) and slope orientation (compass), cover of rocks and stones (percentage). Within each relevé, five subsamples were taken from the upper 10 cm of the soil and combined into one bulked sample for pH analysis in the laboratory (only for the relevés done in 2009). The presence of manure was determined by the amount of dung found in each relevé and classed as 0: absence; I: 1-30%; II: 31-70%; III: >71% (dung cover). Grazing intensity was determined by the percentage of tussock grasses showing signs of grazing at the moment of field analysis, and was later converted into the same I-III values.

Classification
The relevés were classified by means of TWINSPAN [57]. In Table 2 species constancies are given in percentage values.
The first cluster analysis with 373 nr of relevés (153 this survey and 220 nr from literature) revealed an outgroup (61 relevés by [4,20,22,28,31,32,35,[58][59][60][61] which was removed prior to the second run with the remaining 312 relevés including the relevés from the present survey as well as relevés from literature ( Table 3, see heading of Table 3 for detailed description of the communities from other studies included in the analysis). Table 2. Table with the type relevés of associations and subassociations described as new (including one community and a pro-visional association). Community # indicated for each association and subassociation; Relevé# for the type relevé or representa-tive relevé. Altitude (meters above sea level). Inclination (degrees). Orientation. Total number of species (# SPP). VEGC % for vegetation cover percentage in that single relevé. Rocks and stones in percentage cover. Grazing and manure (expressed as I: 1-30%; II: 31-70%; III: >71%).          The second TWINSPAN analysis was run with 6 cutlevels resulting in 64 clusters. The clusters were checked for the presence of differentiall species in different hierarchical TWINSPAN cut-levels. Species are considered to be differential by their occurrence in clusters and contrasted with their absence or less frequent occurrence or smaller total estimate in other clusters [56]. Clusters without diferentials species were fused resulting in a final number of 27 clusters.
Full association tables are presented in Supplementary Tables S1-S9. The character and differential species in the description of the associations are mentioned in order of their diagnostic value.
The assignment to class order, alliance, association and subassociation is based on the presence of diagnostic species as mentioned in relevant syntaxonomic publications. Besides the hierarchical structure of the table clearly shows the syntaxonomic level allowing the distinction and assignment of associations on the lowest level but one and characterised by their own diagnostic species. At the lowest level subassociations are distinguished based on the presence of differential species. Two vegetation types could not be described within the Braun-Blanquet system due to lack of data and were simply named community.
The relation between each syntaxon and the environmental variables rocks, stones, slope degree and the vegetation cover was presented as box-and-whisker charts. Besides a chart is presented showing their altitudinal distribution.

Gradient Analysis
Detrended Correspondence Analysis (DCA; CANOCO 4.5, [63]) was used to study the relation between species composition and environmental variables.
The first DCA run with all 153 relevés resulted into two floristically and environmentally very dissimilar groups. The grassland and cushion vegetation was clearly separated from the vegetation from rock fissures (chasmophytic vegetation), scree (cryoturbate vegetation) and the nitrophylous vegetation. In order to better reveale the inner gradients DCA analysis was performed again, but now on both groups separately: the grassland and cushion vegetation with 112 samples and 153 speciesand the rock fissures, scree and the nitrophylous vegetation with 41 samples and 56 species.

Classification of Relevés and Description of Vegetation Units
The classification resulted in 17 clusters separated by differential species (see Supplementary Tables S1-S9, in Table 2 Figure 2). Physiognomy and composition: Association of chasmophyte vegetation, with a variable cover by cushions, herbs and grasses. It consists of 4-20 cm tall cushions and herbs with a cover of 10-20% in combination with tussock grasses and dwarf shrubs (Ephedra rupestris) with a cover of 5%. Among the surface layer species with substantial cover are Leucheria dauciflora, Saxifraga magellanica, Calandrinia acaulis, Weberbauera spathulifolia and Microsteris gracilis. The cushion Pycnophyllum molle, present in two relevés, facilitates the presence of the rare orange-flowered Gentianella incurva. The grass layer is composed of the tussock Stipa ichu and the small grass Anthochloa lepidula. Ecology and distribution: This Andean chasmophyte association is generally found delimited by grassland, plateaus and steep rock formations, at edges of slopes or on hilltops. It is located at altitudes of 4580-4590 m, on south-facing slopes of 5-25 • . The soils are mainly formed by unstable scree high in copper minerals, with stone particles and grayishgreen mottling in the upper soil horizons. This association can be found on the rocky slopes of the Ichuña River valley, in the north of the Ichuña district.
Astragalo minimi-Azorelletum diapensioidis ass. nov. (  Figure 3A). Physiognomy and composition: Grassland vegetation with high density and diversity of dwarf shrubs, cushions, grasses, ground rosettes and annual herbs. Vegetation cover is between 20-80%, 57% on average. The 20-40 (50) cm tall resinous shrubs of Parastrephia quadrangularis cover 10% in four relevés only. Cushions attain 15-30% of the total cover and are represented by Azorella diapensioides and Pycnophyllum molle. Pycnophyllum glomeratum attains low cover in two relevés only. The grasses are mostly represented by Festuca orthophylla, which reaches high cover in most of the relevés. The ground layer is represented by few species with relatively higher cover: Dissanthelium calycinum, Hypochaeris meyeniana, Brayopsis calycina, Werneria pectinata, Belloa piptolepis, Astragalus minimus, Werneria apiculata, Aciachne pulvinata, Bouguiera nubicola, Oreomyrrhis andicola, the dwarf shrub Tetraglochin cristatum, among others. The absence of Festuca dolichophylla and Baccharis tricuneata is diagnostic. Ferns are absent. The mat-forming Astragalus minimus is dominant and forms dwarf and compact mats that extend to 30-40 cm in diameter; in common with other species of cushion plants, these cushion plants also host other species. This association is negatively characterized by the absence of Azorella compacta.
Ecology and distribution: The association develops between 4460-4670 m altitude, covering extensive plateaus on slopes of about 11 • with varied aspect. Soil texture is composed of fine scree, clay and sandy clay, with few rocks and stones. The association occurs in the highlands of the Ichuña district, near Cachilaya, Coriri, Jatun Puqio and Qhaqhaskinkri and the southern lower slopes of Pirhuani peak (Ubinas district). The association borders the syntaxa formed by Azorella compacta, grasslands and chasmophytic units.
Subassociation Typicum ( . Physiognomy and composition: By comparison with the subassociation typicum, the herb layer is more species-rich, herbs and cushions are more abundant; Azorella diapensioides is common.
Ecology and distribution: The vegetation of this subassociation grows on extensive plateaus covered by clayey sand and with a relatively high cover of stones; rocks are almost absent. The subassociation develops at altitudes between 4460 and 4670 m a.s.l. greatly in slope orientation, rockiness percentage and grazing.

Physiognomy and composition:
The association is characterized by the co-occurrence of the aromatic shrub Senecio nutans and the leptophyllous shrub Parastrephia quadrangularis. Ref. [19] refer to this association as orotropical and dry, situated on volcanic sediments and alluvial materials from the Pleistocene, which form large rocky slopes with soils of variable depth.
Ecology and distribution: The Astragalo pusilli-Parastrephietum quadrangularis is widespread on the southern slopes of Peru in areas with intense grazing. In our study area it occurs between 4450-4560 m a.s.l. The association develops on slopes (mean inclination: 22 • ) with a relatively high cover of rocks (mean: 28%) and stones (20% Physiognomy and composition: Characterized by the relative abundance of Sisyrinchium trinervis together with Pycnophyllum molle, Paronychia andina and Parastrephia quadrangularis. Annual herbs are relatively abundant but low in cover; like the cushions and shrubs, their cover is between 15 and 20%. The cushion Azorella compacta is present in four relevés.
Ecology and distribution: The sisyrinchietosum trinervis grows on bare soils on slopes with 5-20 • inclination and facing N to NE. Rocks cover between 25-50% and stones between 10-15%. Three out of ten relevés appeared to be intensively grazed. The sisyrinchietosum trinervis occurs around 4450 m a.s.l. in the Rancho-Pirhuani area, near Tassa locality in the Ubinas district and it borders the chasmophytic Loricario graveolentis-Pycnophylletum mollis [51] and the Calamagrostion minimae (this study, [51] . Physiognomy and composition: By comparison with the other subassociations of the Astragalo pusilli-Parastrephietum quadrangularis, the vegetation cover and species richness are higher. The species composition comprises several companions such as: Adesmia spinosissima, Astragalus peruvianus, Bartsia diffusa, Calamagrostis curvula, Galium corymbosum, Geranium sessiliflorum, Lepidium meyenii, Luzula vulcanica, Microsteris gracilis, Paronychia andina, Senecio nutans and Stipa ichu, the last species probably as an effect of grazing. The shrub Parastrephia quadrangularis is abundant and covers 10-15%, the cushion Azorella compacta also attains a high cover compared to the other units, and so does the spiny shrub Tetraglochin cristatum. Diagnostic species: This subassociation is mainly differentiated by Astragalus pusillus, Sisyrinchium brevipes and Conyza sp. (# 2601), but also by the low frequency of Cardionema ramosissimum and Mancoa hispida.
Ecology and distribution: The subassociation typicum occurs at altitudes averaging 4500 m on stony slopes in the Coriri and Qhaqhaskinkri sites in the Ichuña district. On average, the measured pH was 5.6.
Senecioni moqueguensis-Pycnophylletum mollis ass. nov. (  Figure 4). Ecology and distribution: The vegetation represented by the Senecioni moqueguensis-Pycnophylletum mollis spreads over areas with partial rock cover (13%) and stones (28%) on the extensive plateaus at an altitude of 4500-4830 m in North Moquegua. The slopes (about 11 • with varied aspect) for this association are characterized by the abundance of the cushion Pycnophyllum molle and, with less presence, Azorella compacta. Wild animals were seen in the landscape during fieldwork. Dung from domesticated bull (Bos taurus), vicuña (Vicugna vicugna) and deer (Hippocamelus antisensis) was recognized in a few relevés across the sites. There were no signs of grazing. The wild animals tend to graze other species such as small grasses and herbs. The distribution is limited to Gasawasi-Witopata plateaus, the northern lower slopes of Pirhuani peak, the extensive plateaus surrounding the group of lakes upslope Coalaque and Querala localities, the Matazo locality environs (Ubinas district) and the Choco-Choco lower mountain slopes in Yunga district.
Subassociation typicum (   Physiognomy and composition: Characterized by the low abundance of Xenophyllum weddellii and of Stangea wandae. Pycnophyllum molle, Senecio moqueguensis, Werneria aretioides and Belloa piptolepis attain high cover. Other differences include the absence of shrubs, except for Tetraglochin cristatum, which acquires a decumbent habit on the slopes. The cushion Azorella compacta is less frequent in the company of Pycnophyllum molle. Species richness is relatively high, probably due to the presence of species related to grazing and manure. Diagnostic species: The senecionetosum tassaensis is mainly differentiated by species such as Senecio tassaensis, Xenophyllum weddellii, Oritrophium sp. (# 2194b) and Werneria heteroloba.
Physiognomy and composition: Association of vegetation growing on a mixture of scree and volcanic sand deposits, with low diversity of species and extensive bare soils. It consists of 4-20 cm tall resinous shrubs (Senecio trifurcifolius) with a cover of 5-10% in combination with few grasses and herbs attaining less than 5% cover. The cushion Mniodes coarctata and mat-forming Xenophylum poposum co-occur with a cover of 5-7%.
Ecology and distribution: This Andean chasmophyte subassociation is generally found on the extensive plateaus formed by the volcanic lower slopes and locally known as "puna desert". It is located at altitudes of 4700-4710 m (probably extending up to 4800 m a.s.l.), and a slope of 5-10 • facing southeast. The soils are mainly formed by scree and white volcanic sand deposits. This vegetation can be found on the Janchata lower slopes (Carumas district) and presumably also occur on the lower pumice slopes of the Huaynaputina and Ticsani volcanoes. It is worth mentioning that several herds of vicuña (Vicugna vicugna) were seen during fieldwork.
Poo aequiglumae-Xenophylletum dactylophylli ass. nova ( Physiognomy and composition: Characteristic are the rocky and scree slopes with low vegetation cover and low species diversity. The resinous dwarf shrub Xenophyllum dactylophyllum is common, together with the short grass Anthochloa lepidula and the ground rosette Nototriche obcuneata. Vegetation cover is about 10-15%. Cushion plants are almost absent, except for Pycnophyllum glomeratum, which was found in only one relevé, with low cover. Shrubs are represented by Senecio nutans and Parastrephia lucida with very low cover. Tussock grasses are absent. Diagnostic species: Character species are Xenophyllum dactylophyllum, Nototriche sp.3 (# 2447), Poa aequigluma and Poa spicigera.
Ecology and distribution: Cryorotropical association with SSW aspect, with extension to an altitude of 4800 m a.s.l. The association was only found on the Choco-Choco rocky slopes (Yunga district) and is assumed to occur on other slopes and summits above 4800 m in the neighboring departments in South Peru.

Community of Senecio algens
( Physiognomy and composition: Almost bare scree slopes with low species diversity. The unique appearance of the shrub Senecio sp.5 (# 3942) (apparently a new species) is very characteristic of the landscape and the less than 10 cm high Senecio algens develops with low cover between the scree stones. 90% of the soils are formed by white scree and rarely by volcanic rocks (except in one relevé). Vegetation cover is about 5%, the slope is 35-45 • , facing W or NW.
Diagnostic species: Characteristic species are Senecio algens and Senecio sp.5 (# 3942). Stangea rhizantha is differential against the other units of the alliance.
Ecology and distribution: Cryorotropical community distributed at about 4750 m a.s.l. The community was only found on the Choco-Choco scree slopes (Yunga district) and is assumed to occur on other mountain summits above 4700 m in the neighboring departments of South Peru. Ref. [22] recognized the occurrence of the community at lower altitude with a mixture of species belonging to grasslands. Ref. [64] indicates that S. algens can be found on chasmophytic rocky slopes as well as in cryoturbate conditions, however, [22] recognized the occurrence of the community at lower and higher altitude with a mixture of species belonging to the puna grasslands.
Tarasa nototrichoides and Urtica flabellata community (  Figure 8). Physiognomy, composition and syntaxonomy: Due to the nitrogen-rich accumulations of manure, species such as Urtica flabellata become dominant; in some areas, together with other species, it covers almost 100% of the soil surface.
Ecology and distribution: Nitrophilous community growing on llama and alpaca patches in grassland plateaus near grazing sites. The vegetation typically develops during the rainy season within a short 2-3-month period. The community of Tarasa nototrichoides and Urtica flabellata can be found between 4460 to 4650 m in North Moquegua, in a wide variety of habitats. Ref. [46] Includes the distribution of Urtica flabellata in the high Andes from Colombia to Argentina; there fore this puna and superpuna community can be assumed to occur in a wide geographical area in the high Andes. The ecological and floristical optimum for this unit is found in the orotropical and cryorotropical bioclimatic belts. The distribution range of the unit is approximately between 4000-4800 m a.s.l.

Gradients and Zonation
As after the first DCA with all 153 samples the relevés clearly fell into two very dissimilar groups representing very different site conditions, subsequently two separate analyses were performed. One group contains the grasslands and tussock vegetation of the Calamagrostion and Azorello-Festucion and the other group consists of vegetation growing on mobile scree slopes (Nototrichion). The DCA diagrams (Figures 9 and 10) show the relation between the vegetation units and environmental variables. In Figure 9, the main gradient in species composition (axis 1) is strongly correlated with altitude (r = 0.65), scree (r = 0.31), vegetation cover (r = −0.24), grazing (r = −0.22), manure (r = −0.16), stones (r = 0.03) and number of species (r = −0.06). The relation between the second axis and environmental variables is low, except for number of species (r = 0.34), vegetation cover (r = 0.31) and slope inclination (r = 0.27). Figure 9. Ordination diagram (DCA, axis 1 and 2) of associations 2-5. The relevés belonging to the 4 different associations have been delineated. # SPP refers to the total number of species, % rocks and stones = estimated cover of rocks and stones in each relevé. VC refers to total vegetation cover, altitude is expressed in meters above sea level, manure and grazing is expressed in I: 1-30%; II: 31-70%; III: >71%, and scree is expressed by the percentage total cover. The grasslands with cushions (Astragalo pusilli-Parastrephietum quadrangularis and Astragalo minimi-Azorelletum diapensioidis) are positively correlated with grazing, number of species, vegetation cover and manure. The cushion association (Senecioni moqueguensis-Pycnophylletum mollis) is correlated with rocks, altitude and scree. The other cushion associations from higher altitudes (Calamagrostio trichophyllae-Azorelletum compactae) are correlated with altitude, percentage of stones, slope and rocks.
The Nototricho obcuneatae-Xenophylletum poposi correlated positively with number of species and negatively with manure and vegetation cover. The community of Senecio algens shows a positive correlation with scree, stone percentage and slope degree.
The relation between vegetation and environmental factors as shown by the ordination diagrams corresponds to the results as shown by Figure 11 in which the mean values for (a) slope degree, (b) vegetation cover, (c) rocks and (d) stones are given. The Calamagrostio trichophyllae-Azorelletum compactae develops on steeper slopes, as does the community of Senecio algens. In contrast, the community of Tarasa nototrichoides and Urtica flabellata develops on level surfaces. In graph b, vegetation cover is higher in the following units: community of Tarasa nototrichoides and Urtica flabellata, Astragalo pusilli-Parastrephietum quadrangularis subassociation typicum, Astragalo minimi-Azorelletum diapensioidis aciachnetosum pulvinatae and Senecioni moqueguensis-Pycnophylletum mollis subassociation typicum. The lowest vegetation cover (less than 20%) was recorded for the community of Senecio algens, Nototricho obcuneatae-Xenophylletum poposi senecionetosum trifurcifolii, Poo aequiglumae-Xenophylletum dactylophylli and Astragalo pusilli-Parastrephietum quadrangularis sisyrinchietosum trinervis. Astragalo pusilli-Parastrephietum quadrangularis grows on sites with a high rock cover. This is especially the case in two subassociations belonging to this association: the sisyrinchietosum trinervis and baccharidetosum tricuneatae. The mean rock cover is less than 10% in the Saxifrago magellanicae-Leucherietum daucifoliae (comm. 1), Astragalo pusilli-Azorelletum diapensioidis (comm. 2) and community of Senecio algens (comm. 8). The community of Tarasa nototrichoides and Urtica flabellata (comm. 9) grows on sites without bare rock. In the community of Senecio algens (comm. 8) the surface is almost fully covered by stones (>90%) as well as in the Nototricho obcuneatae-Xenophylletum poposi senecionetosum trifurcifolii. Within the Saxifrago magellanicae-Leucherietum daucifoliae (comm. 1) the stone cover is 40 to 50%. Stones are almost absent in the community of Tarasa nototrichoides and Urtica flabellata (comm. 9). Figure 12 shows the observed and expected altitudinal distribution of the syntaxa described in this overview. The gray boxes represent the distribution as based on the present field survey and the boxes in dashed lines the expected distribution based on the co-occurrence of the following character species of the syntaxa distinguished [48,[65][66][67]:  Family composition shows the same trend as observed in the Andean prepuna and puna of Moquegua [35,36], where the Composites dominate the vegetation. In the grasslands of Moquegua, species richness is greatest within the woody species belonging to the Composites, Fabaceae and Orobanchaceae, while in the ground layer the number of species is highest in the Malvaceae, Caryophyllaceae and Poaceae, followed by Plantaginaceae and Violaceae.
In Figure 13, box-and-whisker plots show the species diversity of the different associations, subassociations and one community. The species richness of the Chasmophytic association can not be compared to the richness of the grassland and cushion vegetation as with 16 m 2 the plot size is 9 m 2 smaller (see Figure 13). The chasmophytic association Saxifrago magellanicae-Leucherietum daucifoliae) has a maximum of 15 species and a median of 11 species. The highest species diversity was recorded in the Senecioni moqueguensis-Pycnophylletum mollis (comm. 4) and Calamagrostio trichophyllae-Azorelletum compactae (comm. 5), which have a median of 15 species and a maximum of 26 and 25 species respectively. Within the grasslands with cushions, species diversity in the Astragalo minimi-Azorelletum diapensioidis (comm. 2, median of 18 species and maximum of 23 species) is greater than that of the Astragalo pusilli-Parastrephietum quadrangularis (comm. 3), median of 13 species and maximum of 22 species. The species diversity is least in the Nototricho obcuneatae-Xenophylletum poposi (comm. 7) and in the community of Senecio algens (comm. 9), with a median of 6 species and maximum of 16 species; this is probably due to the extreme conditions in their high altitude growth sites.
The plot sizes of the relevés made in the nitrophilous community are only 1 m 2 and only 4 to 6 species were counted per plot.
Within the chasmophytic association species richness generally decreases with elevation. However, species richness was observed to increase locally between 4500 and 4700 m in the cushion associations, probably as a result of nursing effects, sometimes in great abundance as seen in Azorella and Pycnophyllum [8,16]. Although lichens and mosses were not included in our phytosociological analysis, we noted their low diversity in the study sites. Low cover of Thamnolia vermicularis was observed in the Poo aequiglumae-Xenophylletum dactylophylli.
The vegetation vegetation of rock crevices, grassland and cushion vegetation, and vegetation of mobile scree slopes could respectively be assigned to the Argyrochosmetea niveae, Calamagrostietea vicunarum, Anthochloo lepidulae-Dielsiochloetea floribundae. The class, order and alliance of the nitrophilous community should be defined by further research.
Based on the presence of Saxifraga magellanica, the new association Saxifrago magellanicae-Leucherietum daucifoliae has been assigned to the class Argyrochosmetea niveae, the order Saxifragetalia magellanicae and the alliance Saxifragion magellanicae. It grows on deep soils with fine scree across rock crevices, in the north of Moquegua, South Peru. Ref. [61] described the class Argyrochosmetea niveae as occurring at an altitude of 2500-3500 m in Junín (Central Peru), with Argyrochosma nivea, a fern species characteristic of rock crevices. Ref. [20] confirmed the presence of this species in the south of Peru, and we refer to the Argyrochosmetea niveae based on the occurrence of the superpuna alliance Saxifragion magellanicae [19] represented by Saxifraga magellanica.
The order and alliance combine the basaltic and andesite soils along the Andes of Peru, from Lima to Tacna regions [22].
Saxifraga magellanica grows on the south-facing highlands of the Yanahuara River in the Ichuña district. Saxifraga magellanica is a cushion-forming herbaceous rosette with whitish flowers; its distribution area is from Ecuador to South Argentina [46].
Four new associations were assigned to the order Parastrephietalia quadrangularis of the class Calamagrostietea vicunarum based on the presence of Calamagrostis vicunarum and many species of the Parastrephietalia (see Table 3).
Reference [22] proposed the class name Deyeuxietea vicunarum. According to [46] Deyeuxia vicunarum should be considered to be a synonym for Calamagrostis vicunarum and The Calamagrostietea vicunarum grows on clay and loamy clay (rarely on sand) on rocky slopes, plateaus and hills at 4450-4800 m a.s.l. in the Andean regions of North Moquegua, downslope it is in contact with the grassland vegetation dominated by Lupinus paruroensis and the giant bromeliad Puya raimondii and upslope with units of the Anthochloo-Dielsiochloetea.
The Parastrephietalia quadrangularis combines the puna grasslands extending from southwest Peru to West Bolivia, Northwest Argentina and Northwest Chile.
The Astragalo minimi-Azorelletum diapensioidis ass. nov. is assigned to the alliance Calamagrostion minimae. It is characterized by the presence of cushion plants, dwarf shrubs, tussock grasses, annual grasses and herbs. The high cover of the cushion Azorella diapensioides together with the mat-forming Astragalus minimus characterizes the association described within this alliance. The alliance occurs in the grassland puna known as "cesped de puna" formed by small herbs and ground rosettes with long root systems, mostly developing on open and uniform slopes with shallow soils. The alliance is known to occur in the highlands of Peru and Bolivia, between 4500 and 5000 m [29,58].
The Astragalo minimi-Azorelletum diapensioidis (Calamagrostion minimae) differs greatly from the Belloo piptolepis-Dissanthelietum calycini azorelletosum diapensioidis [20] and Baccharido caespitosae-Azorelletum diapensioidis [36] because of the absence of Festuca dolichophylla, Baccharis caespitosa and other elements of the puna. We have included this association in the Calamagrostion minimae [29] because of the abundance of cushion plants such as Azorella diapensioides and the presence of small grasses such as Calamagrostis minima, and the absence of some species characterizing the Azorello-Festucion and Nototrichion obcuneatae.
The grassland with cushion vegetation of South Peru is grouped into the Azorello compactae-Festucion orthophyllae [20,21,59]. Azorella compacta can be found in some restricted Andean regions in South Peru [6,39,65,69], Bolivia [70], Argentina [71,72] and Chile [73,74]. The Azorello compactae-Festucion orthophyllae represents the large tracts of superpuna grasslands in South Peru, in the Moquegua region where Festuca orthophylla, Tetraglochin cristatum, Parastrephia quadrangularis and P. lucida are common. Festuca orthophylla is the tussock grass that dominates the superpuna grasslands of Moquegua in association with the resinous shrub Parastrephia quadrangularis, which is replaced by Parastrephia lucida at altitudes higher than 4500 m and is well represented in the superpuna.
The Azorello compactae-Festucion orthophyllae comprises vegetation represented by grasslands with cushions, open plateaus with cushions, vertical cushion formations and scree units with cushions and dwarf shrubs. The relatively high presence and cover of the composite resinous shrub Parastrephia lucida that replaces Parastrephia quadrangularis in the altitudinal gradient characterize the associations described. The cushions Pycnophyllum molle and Azorella compacta are relatively abundant, together with the relative high cover of the tussock Festuca orthophylla which replaces Festuca dolichophylla as well as from the higher altitudinal gradient context. Festuca dolichophylla (which is a species from the lower altitudinal gradient) This alliance dominates extensive areas in the puna and superpuna of North Moquegua [36], occurring in the Arequipa, Tacna and Puno departments [20,59]. In our study region, it occurs between 4450-4800 m a.s.l. The inclination varies from 0 to 90 • and the orientation is variable. Grazing intensity varies; some grasslands are heavily grazed while others can be considered to be ungrazed.
The tussock Festuca orthophylla is distributed in our study sites at altitudes between 4450 and 4800 m, becoming more abundant at 4650 m and higher. The tussock grass distribution is in agreement with [75], who recorded Festuca dolichophylla in the subhumid puna of Bolivia at 3500-4000 m and 4500 m and Festuca orthophylla at higher altitudes, in the super puna and subnival puna (uppermost part of the superpuna). Above 4500 m Festuca orthophylla co-occurs with cushion plants such as Azorella and Pycnophyllum.
The new associations and subassociations with Azorella compacta described here differ from each other not only in species composition but also in altitude and distribution.
In the Calamagrostio trichophyllae-Azorelletum compactae ass. nov. the character species of the alliance Azorello-Festucion, Azorella compacta and Festuca orthophylla are very frequent. Anthochloa lepidula, considered to be a character species of the Anthochloo-Dielsiochloetea, appears to have a very wide syntaxonomic amplitude. Anthochloa lepidula, Dissanthelium calycinum and Senecio adenophyllus, character species of the Nototrichion obcuneatae, are only present at low frequency. By contrast, Azorella compacta and Baccharis caespitosa, both character species of the Azorello-Festucion, are relatively frequent. Consequently, this association is considered to belong to the Azorello-Festucion instead of the Anthochloo-Dielsiochloetea and Nototrichion obcuneatae.
Two associations and one community have been assigned to the alliance Nototrichion obcuneatae of the order and class, Anthochloo lepidulae-Dielsiochloetalia floribundae Rivas-Martínez & Tovar 1982 and Anthochloo lepidulae-Dielsiochloetea floribundae (for diagnostic species see Table 2).
According to [29] Anthochloa lepidula and Dielsiochloa floribunda are character species of the Anthochloo lepidulae-Dielsiochloetea floribundae. According to our table, however, although Anthochloa lepidula has a higher presence in this class, it appears to have a very wide syntaxonomic amplitude. Although the associations are well represented by character species, these are almost absent from the higher units. This might be due to the very extreme climatic conditions on the mountain summits.
The Anthochloo-Dielsiochloetea is highland vegetation characterized by ground rosettes, cushion and dwarf subshrubs, herbs and grasses. Soils are of cryoturbate origin with sparse stoniness and fissures in gelid rocks, located near the vegetation line [29] in the superpuna region.
The alliance of Nototrichion obcuneatae [19], combines a series of subnival associations identified in the Andean regions of the Moquegua department.
The cryorotropical units described within Nototrichion obcuneatae (Supplementary  Tables S6-S8) under the names Nototricho obcuneatae-Xenophylletum poposi [20] and Poo aequiglumae-Xenophylletum dactylophylli are similar to those described in Peru [60] and Bolivia [28,32] as having similar floristic affinities, such as Anthochloa lepidula, Nototriche obcuneata and Senecio adenophyllus. Both associations are more similar to those units described in Arequipa by [22] and Bolivia [32]. Our knowledge about the structure of these cryorotropical communities is incomplete because of the lack of studies in the different geographical regions of South Peru and Nortwest Bolivia.
The alliance is found on mobile scree slopes. As a consequence of solifluction, the plants are dispersed in sheltered hollows [20]. Based on the distribution of its character elements (Nototriche obcuneata, Xenophyllum poposum) it is a cryorotropical (dry-humid) alliance of the southern highlands of Peru and Bolivia [20,22,43,76]. It is characterized by the presence of ground rosettes with thick roots, resinous shrubs and cushions, herbs and small grasses. The associations belonging to this alliance can further be found in South Peru [20,22], SW Bolivia and NW Argentina (described as Chaetantherion sphaeroidalis by [20] where the species Chaetanthera sphaeroidalis is absent in our study region.

Nitrophilous Vegetation
Nitrophilous communities dominated by nitrophytes are found on patches of llama and alpaca dung in grassland plateaus and slopes in the South Andes of Peru. The communities have been found in rock shelters, where cattle and wildlife shelter during the night and heavy rain, and near traditional cattle corrals and farmhouses. Little is known about the occurrence of these specific plant communities in the Andes. It seems that populations of Urtica flabellata are widespread in the C Andes [77]. According to [6], Urtica flabellata as a ruderal species and colonizer of llama dung that can often be found in puna regions together with Cajophora cirsiifolia and tall Lupinus species.
We distinguished two nitrophylous communities, the community of Senecio algens and the Tarasa nototrichoides and Urtica flabellata community. As these vegetation types are still insuffiently studied and suggestions of proper alliances or associations are still missing in literature, no association names were suggested in this paper.
The community resembling the community of Senecio algens [22] was named accordingly. Nitrophilous communities, but floristically more impoverished, can also be recognized in northern, Central and southern Peru [60,61], and Bolivia [60,61,77]. Reference [61] was based on data from the Central Andes; he was not aware of Bolivian records. Ref. [60] describe the close affinity of these communities to the class Nicotiano glutinosae-Ambrosietea arborescentis Galán de Mera & Cáceres in [19], which represents ruderal vegetation from lower altitudes with a very distinct structure and floristic composition.
In the prepuna (supratropical belt) in Central Peru (Prov. Yauli, dept. Junín) [61] described the Urtico flabellatae-Cajophoretum sepiariae between 3600 and 3800 m in the region South of La Oroya. He supposed that this association could belong to a still undescribed class. Additional observations were made of alpine Urtica flabellata communities on the West slope of the Andes between 3000 and 3600 m, above Huánuco 3900-4000 m, in North Peru above Cajamarca and near Huaraz and Cusco. We agree with the concept of Gutte that a true ruderal class seems to exist in the alpine zone of Peru. However, in our relevés of the superpuna of Moquegua the only species in common with [61] are the character species Urtica flabellata and Perezia multiflora. Urtica flabellata is also shared with the Urtico flabellatae-Urocarpidetum peruviani [60] (3320-3850 m a.s.l.). Urtica flabellata is found throughout the country and also from neighbouring Bolivia. It is known that Urtica flabellata also occurs in the páramos of Ecuador and Colombia [9]. On calcareous bedrock (Colombian Páramo Almorzadero) Lachemilla pinnata is associated with Urtica flabellata as well. For an adequate description of the class on the level of order and alliances, more relevés are needed. Thus far there are no relevés available for páramos. We conclude that these communities need further research using relevé data collection from both puna and páramo.

Discussion
There are few previous studies on species composition and diversity of superpuna grassland syntaxa in South Peru for comparison with our vegetation description. Refs. [4,[20][21][22]60,61,77] address the phytosociological classification and description of plant associations and communities in the central and southern Peruvian Andes. Other studies from North Chile [24,25] and Bolivia [27,28,[31][32][33]; were compared with our results and appear to differ significantly in species composition and distribution. Refs. [35,36] describe the prepuna shrublands, puna chasmophytes and grassland associations and communities occurring in the north of Moquegua under the classes Echinopsio-Proustietea cuneifoliae (prepuna shrublands) occurring at an average altitude of 3500 m, Argyrochosmetea niveae (chasmophytic vegetation) and Calamagrostietea vicunarum (puna grasslands) occurring between 3800 and 4500 m a.s.l. These associations lack the presence of cushion plants (Azorella compacta, Pycnophyllum spp.) and the tussock grass Festuca orthophylla.

Nitrophilous Vegetation
Class, order and alliance: Still to be defined by further research. Community of Tarasa nototrichoides and Urtica flabellata

Concluding Remarks
Our vegetation research in northern Moquegua (South Peru), an area not studied previously, extends the knowledge of the syntaxonomy, floristic diversity and synecology of Azorella compacta and Pycnophyllum molle vegetation structure, and of chasmophytic and nitrophilous communities. It comprises four alliances, seven new associations and thirteen subassociations, representing an important basis for a future overview and synopsis of the Andean vegetation of tropical South America. The vegetation studied in Moquequa appears to be floristically different from comparable vegetation in North Chile and Bolivia. Further research is needed, however, to study the relation with chasmophytic and plateau associations with cushions in the highlands of other mountainous regions in South America.
The present overview is also important as a reference and tool for nature conservation. Apart from the impressive cushions plants, many endemic species are found in the newly described syntaxa, highlighting the need for conservation schemes and measures. In recent years, the superpuna syntaxa have been increasingly affected by grazing and road construction. The natural vegetation is being disturbed and cushions of Azorella compacta have regularly been removed for use as fuel. Fire has been regularly observed on several mountain slopes. These fires were probably set on purpose as part of a festivity in June. Fortunately, due to advice and information given to the local communities by the first author, this practice is now gradually decreasing (personal observation), and conservation programs have been started. At the same time, interviews with the local communities suggest that the pastures are being grazed in a way that prevents overgrazing. Negative effects have been observed only in some grassland syntaxa where livestock and wild grazers are abundant. In addition to livestock, wild grazers including vicuñas (Vicugna vicugna), viscacha (Lagidium peruanum), taruca (Hippocamelus antisensis) and suri (lesser rhea, Rhea pennata) are known to occur in the region. This highlights the vulnerability of the flora and vegetation of the Andes to human pressure, and requires further studies.