MARTÍNEZ CARRETERO, E., A. DALMASSO, J. MÁRQUEZ & M. MARTINELLI (2010). Plant communities and phytogeographical units from NW San Juan Province (High Central Andes of Argentina). Candollea 65: 69–93. In English, English and French abstracts.
Vegetation of the High Central Andes of Argentina was studied in NW San Juan Province (MAB Reserve of San Guillermo) from a phytosociological point of view. Four new associations are proposed: two shrubland associations, Artemisietum paramilloensis and Lycio-Ephedretum rupestri, and two grassland associations, Jaravetum chrysophyllae and Jaravetum absconditae. The latitudinal and altitudinal boundaries of the Monte, Puna and High Andean phytogeographic provinces were established for the study area. This area constitutes the floristic and biogeographic transition between northern (Bolivia) and southern (Mendoza, Argentina) Puna elements, belonging to the Calamagrostietea vicunarum class, and to the Stipo-Lycietea class, respectively.
Introduction
The arid Puna region, bordered by Andean ranges in the southeast of Peru, southwest and centre of Bolivia and northwest of Argentina, is characterized by xerophytic steppe vegetation. In Argentina, the Puna extends southwards to La Rioja, San Juan and North of Mendoza (Roig, 1985, 1987; Ambrosetti & al., 1986; Roig & Martínez Carretero, 1998). Cold, drought and summer frost characterize both the Puna and High Andean regions.
The Central Andes of Argentina comprise two mountain ranges: the western range with Paleozoic metamorphic rocks, and the eastern one with Devonian sedimentites and Permo- Triassic intrusive rocks, that border high Andean valleys covered, in part, with aeolian sands. According to Furque (1972) the Llanos de San Guillermo (San Guillermo plains) would have originated from sediments resulting from the uplift of an ancient foothill. Phytogeographically this region belongs to the Arid Puna (Martínez Carretero, 1995) that reaches the southern altiplano in Bolivia (Navarro, 1993).
Geologically the study area is included in the Cordillera Frontal, separated from the Precordillera by the Blanco river. Faults are the most common structures; those located north of 29°S are north/northeast-south/southwest in direction, whereas the southern ones are oriented north-south and north/northwest- south/southeast. All faults are parallel or sub-parallel to the hill ranges and separated by distances of 5 to 20 km. They are inverse faults due to compressive forces starting since the Miocene. Devonian deposits appear intensively folded, whereas intrusive and Permian-Triassic vulcanite rocks show traces of a distensive pre-Tertiary tectonic activity (Caminos, 1972; Zambrano, 2007).
In relation to the vegetation, few studies have been conducted in the study area, particularly in the North-West of San Juan and South-West of La Rioja provinces; most of those studies consist of plant collections with general comments on the phytogeography (Roig, 1960; Cabrera, 1971, 1976; Cabrera & Willink, 1973; Martínez Carretero, 1995).
The northwest of San Juan province is important from the phytogeographic and floristic points of view; in addition, due to the interest in mining (copper and gold) and the impact of this activity on natural resources (water, vegetation), it is necessary to study the plant communities and their distribution in the area. In this study, we present a floristic analysis of the vegetation along the whole altitudinal gradient, and establish the boundaries between the vegetation belts of the Monte, the arid Puna and the High Andean belts.
Material and methods
Study area
The North-West area of San Juan province (28°25′N 30°25′S – 70°00′W 69°05′E), that includes the San Guillermo MAB Reserve, is a wide high Andean region with extensive areas covered by detritus and aeolian sands called ‘'pampas or llanos'' (i.e Llano de los Leones, Llano Negro, Llano de San Guillermo). On occasions, foothills show considerable development (10–12 km long). Wetlands constitute an important water reservoir and are spots of high biodiversity.
Altitude in the study area varies from 1700 m (East) to more than 5000 m (West), which means that megathermic elements belonging to the Monte formation as well as elements of cryogenic environments in the High Andean region can be found.
Scarce climate information is available for the study area. Winds reach 120 km/h, and snow accumulation is 33 cm in May, 27 cm in June, 33 cm in July, 47 cm in August and 37 cm in September (Salvioli, 2007). Data recorded in the Zancarron area (28°36′31.89″S – 69°14′55.16″W, 3700 m) during the period 1987–1989 are shown in Table 2.
Solar radiation is the main variable controlling the daily and seasonal temperatures. Mean annual temperature in the studied area is 0° C, and the mean maximum and minimum temperatures are 7° C and -6°C, respectively. Rainfall varies along the altitudinal gradient, from 40 mm, in the Rodeo valley (30°12′55.28″S - 69°07′03.27″W, 1700 m) increasing to the West and Southwest. Snowfalls decrease from South to North, from 300 mm to 200 mm in the Blanco river (in San Guillermo). Between 3000 and 6000 m, precipitations occur mostly as snow, hailstones and hoarfrost, associated with wet winds from the Pacific Ocean (Salvioli, 2007). According to Minetti & al. (1986) mean annual rainfall in the high Andean sector varies from 300 mm in the southern part of the area to 50 mm in the North. According to the Koeppen index, the climate belongs to the high desert arid type (Quintela, 1977). The boundary between different rainfall regimes is the Frontal Cordillera; Atlantic Subtropical continental rainfall (summer rainfall) dominates to the East and a Pacific Subtropical regime (winter precipitations, mostly snow and hailstorm) to the West.
Methods
For each physiographic unit, determined by both satellite image analysis (LANDSAT TM, 1: 250'000) and topographic maps (1: 100'000), 117 floristic surveys were performed during the field work. All collected plants were determined. For taxon names, the contributions of Zuloaga & Morrone (1999) and Peñailillo (2002) were followed. For syntaxa names, the International Code of Phytosociological Nomenclature was followed (Weber & al., 2000).
The phytogeographical units present in the area and their distribution were established based on the floristic-geomorphological analysis of plant communities and on plant species distribution. A data matrix was constructed from the floristic data and the specific plant cover (Table 1). This matrix was analyzed using classification and ordination methods (Mueller Dumbois & Ellenberg, 1974; Orloci, 1978). Data on plant cover were transformed according to: +: 2.5, 1: 5, 2: 17.5, 3: 37.5, 4: 64.5, 5: 84.5. Pearson's correlation was used as a distance algorithm, using complete linkage for clustering, and in the Principal components analysis for ordination.
Results
Dominant geomorphologic processes are: cryoturbation, gelivation, water erosion, debris flow and thermoclastism (Suvires, 2007). The Llanos de San Guillermo region is formed from sediments originating from the uplift of the ancient foothill, up to a constant 3500 m level.
Plant communities
From the floristic matrix data (Table 1) four groups of communities were obtained using cluster analysis (Fig. 1):
Fig. 1.
Cluster of plant communities.
Puna shrublands : 1. Artemisia echegarayi Roig & Martínez Carretero 1998; 2. Artemisietum paramilloensisi ass. nov.; 3. Larrea divaricata community ; 4. Lycio-Ephedretum rupestri ass. nov.; 5. Jaravetum chrysophyllae ass. nov. Saxicolous shrublands : 6. Trycicla spinosa community ; 7. Adesmia pinifolia community.
High Andean vegetation: 8. Jaravetum absconditae ass. nov.; 9. Adesmia subtrraneacommunity; 10. Stipa frigida community.
11. Wetlands communities.
Puna shrublands on sandy soils (Artemisia echegarayi, Artemisia mendozana var. paramilloensis, Larrea divaricata, Lycium chanar-Ephedra rupestris);
Saxicolous shrublands (Adesmia pinifolia and Trycicla spinosa communities);
High Andean vegetation (Jarava speciosa var. abscondita, Adesmia subterranea, and Stipa frigida communities);
Wetland vegetation.
The ordination analysis highlights the same phytogeographical relationships. Axis I distinguishes Puna shrublands on sandy soils from those on rocky outcrops; whereas axis II follows a xericity gradient, from wetlands to communities on sandy and deflated soils such as the Artemisia mendozana var. paramilloensis community (Fig. 2).
Puna communities
The distribution of plant communities in the northwest of San Juan is shown in the vegetation map on a 1: 350'000 scale (Fig. 3).
All the species and the plant communities observed may be found in Table 1: the plant communities are ordered following the whole altitudinal gradient studied and considering their phytogeographical position; showing, in addition, the transition between the classes Calamagrostietea vicunarum and the Sipo-Lycietea in the Puna belt:
A phytosociological conspectus follows, with the plant communities described and presented (C: class; O: order; L: alliance; A: association):
C: Mulino-Junellietea scopariae Roig 1989
O: Mulino-Junellietalia scopariae Roig 1989
L: Saturejo-Adesmion uspallatensis Roig 1989
A: 1. Artemisietum echegarayi Roig & Martínez Carretero 1998
C: Stipo-Lycietea fusci Roig & Martínez Carretero 1998
O: Stipo-Lycietalia fusci Roig & Martínez Carretero 1998
L: Chuquirago-Lycion fusci Roig & Martínez Carretero 1998
C: Calamagrostietea vicunarum Rivas Martínez & Tovar 1982
O: Parastrephietalia lepidophyllae Navarro 1993
L: Lobivio-Fabianion densae Ruthsatz 1993
L: Urbanio papigerae-Stipion frigidae Navarro 1993
1. Artemisietum echegarayi (Table 3)
This association belongs to the Saturejo-Adesmion uspallatensis alliance that comprises evergreen pre-Andean shrublands on deep sandy soils (Roig & Martínez Carretero, 1998). In the study area this community occupies lower levels of the Puna between 3200–3300 m, primarily on shady water-eroded slopes. It appears as a low shrubland 0.6–0.8 m in height, and with a total plant cover lower than 20%. Accompanying species are Mulinum ulicinum, Fabiana af. densa, Stipa leptostachya, Lycium chilense var. vergarae, Trycicla spinosa, amongst others. This community extends southwards to 32°S, in the Precordillera of Mendoza with a similar topo - graphy (Martínez Carretero, 2000) (Table 3).
2. Artemisietum paramilloensis, ass. nov. hoc loco (Table 4, survey type no. 16)
This Association is included in the Chuquirago-Lycion fusci alliance that occurs from the South (North of Mendoza province) up to this latitude. It comprises communities of sparse shrubs, with 30–40% cover, generally growing on alluvial fans and at the bottom of slopes covered with Quaternary deposits. In the study area this alliance occurs between 3000– 3500 m.
The Artemisietum paramilloensis appears on local piedmonts with Quaternary cover, intense water erosion and soil disturbed by rodents. On occasions it is found along temporary rivers and in ancient overblown piedmonts. Artemisia mendozana var. paramilloensis is a flashy shrub due to its gray foliage, although it is no more than 0.3–0.4 m high and has a mean plant cover of 25%. Nardophyllum armatum, Atriplex oreophylla and A. mendozana var. are differential species. Accompanying species are Jarava sepciosa var. breviglumis, Argylia uspallatensis, Tarasa antofagastana and Malesherbia lirana, etc.
3. Larrea divaricata community (Table 5)
It occurs on local piedmonts and alluvial fans with laminar erosion, and on slopes of about 3–4% inclination. Rocks show incipient desert varnish. Soils are sandy with clay, debris and gravel. In sectors, such as Quebrada de Alcaparrosa, this community occupies Carbonic clay outcrops with intense water erosion. L. divaricata appears as a shrub 0.4 m in height, with concave profile. Accompanying species are: Acantholippia deserticola, Junellia echegarayi, Ephedra rupestris on long downslopes deeply dissected by water erosion, etc.
4. Lycio-Ephedretum rupestri, ass. nov. hoc loco (Table 6, survey type no. 24)
It is the most extensive community in the study area. It occupies wide sandy flatlands with heterometric gravels, top of sandy downslopes, proximal sectors of alluvial fans, and granitic outcrops covered with sand. Total plant cover is 25– 30%. The lower plant layer is poor or absent.
Lycium chanar is the dominant species with a 10–15% cover, and with 0.8 m tall plants growing 3–5 m apart. Adesmia guttulifera, Glandularia microphylla, Atriplex myriophylla, Ephedra rupestris, among others, are characteristic species. Accompanying species are Fabiana denudata, Chuquiraga erinacea subsp. hystrix, Maihueniopsis ovata, Acantholippia deserticola, Cryptantha diplotricha, Nassella grabripoda, etc. with cover lower than 5%.
5. Jaravetum chrysophyllae, ass. nov. hoc loco (Table 7, survey type no. 40)
This community is of important extent in the protected area. It is located on flatlands (Llano de Los Leones), extensive downslopes and slopes with black and angled material affected by gelifluxion processes. Soils have a sandy matrix. This community commonly occurs at the top of frozen domes in wetlands, where aeolian sand accumulates. J. chrysophylla var. chrysophylla forms grasslands of low cover, between 5–10%, with plants 0.2 m tall. On occasions Adesmia subterranea forms cushions, together with Lepidium nitidum, Muhlenbergia fastigiata, Senecio oreophyton, etc. (Table 7). Characteristic species are: Jaborosa parviflora, J. caulescens var. pinnatifida, Muhlenbergia fastigiata, and Jarava humilis.
6. Trycicla spinosa community (Table 8)
At this latitude many elements belonging to the Lobivio ferocis-Fabianion densae reach their most southern distribution. This alliance is constituted by communities on stony slopes, rocky outcrops, and flatlands with gelifluxion processes, between 3000–3500 m.
It appears on the upper part of andesitic or very meteorized granitic ranges, with a sandy matrix and intense aeolian erosion. Trycicla spinosa forms facies together with Junellia echegarayi and Phacelia setigera. The extreme environmental conditions of these sites are highlighted through the isolateral growth of the cambium, the stem taking shape of a racquet, with strongly reduced leaves, and with fruits rich in antocians.
7. Adesmia pinifolia community (Table 9)
This community occurs on rocky outcrops, especially with South and Southwest exposure, where snow remains until late summer. The soil is composed of very meteorized granite or black and diaclased schists, as in the El Fierro mine. It is common that the shrubland follows the water courses, marking their way on the rocky slope.
This community is noted for the yellow colour of the branches of A. pinifolia, contrasting with the dark soil materials. A. pinifolia reaches up to 2.5 m in height, and the community achieves a cover of 15–18%. Among accompanying species are: Haploppapus marginalis, Nasella grabifolia, Lecanophora ameghinoi, Descurainia cumingiana, etc.
8. Jaravetum absconditae, ass. nov. hoc loco (Table 10, survey type no. 64)
The Urbanio-pappiegrae alliance reaches its southernmost boundary in the northwest of San Juan and southwest of La Rioja provinces. In general it consists of grasslands with small and sparse pulvinate shrubs, between 4000–4500 m. It extends from south-western Bolivia (Sajama region, 18°l′S ) (Navarro, 1993) to 30°S latitude.
This is a community of small coverage. It occupies the bottom of valleys and sandy soils among very diaclased rocks or on covered glaciers (as the beginning of the Santa Rosa river). It appears in distal parts of local foothills and lower edges of lateral moraines. The grassland of J. speciosa var. abscondita extends up to 4000 m. Mean plant cover is 25%. Differentials species are: Chaptalia similis, Astragalus af. crypticus, Cistanthe frigida, Tetraglochin cristatum, among others. Among accompanying species are: Jarava nicorae, Cajophora coronata and Phacelia setigera.
9. Adesmia subterranea community (Table 11)
It occurs on diverse types of soils: sandy soil among moraine deposits, on loose slopes with clasts in a sandy matrix, on proximal parts of large local foothills (such as the Sapito river). In general, it is present in areas with evidence of intense cryoturbation processes, between 3700–4200 m. Plant cover is lower than 15–18%. Nototriche compacta, Lenzia chamaepitys and Huarpea andina, amongst others, are accompanying species.
10. Stipa frigida community (Table 12)
This community occurs on the upper part of slopes, on runoff edges on long downslopes, and on sandy soils with angled clasts. Plant cover varies between 2–5%. Senecio volckmanii, Kurzamra pulchella, Arenaria serpens, Festuca weberbaueri, Jarava nicorae, Lenzia chamaepitys, etc. are accompanying species.
Wetland vegetation
Wetlands are found in both Puna and High Andean vegetation belts (Table 13). They show different vegetation belts according to the water saturation degree of soils, belonging to the minerothrophic type (Igarzabal, 1984). The following plant communities can be mentioned for wetlands in the study area.
Juncus arcticus community: in soils dry on the surface, with a water table 20–30 cm deep, accompanied by Astragalus af. famatinae, Polypogon interruptus, Puccinelia frigida, Nastanthus caespitosum, Ranunculus cymbalaria f. exilis, etc.
Carex incurva community: in over-saturated soils with water near the surface, with puddles on occasions. This community usually appears as a mosaic on drier soils. Accompanying species are Poa annua, Ranunculus af. flagelliformis, Deyeuxia velutina, etc. Festuca nardifolia is a variant with higher cover on small cryogenic domes (10–15 cm high).
Patosia clandestina community: on over-saturated soils, without free water, and with a 0–15 cm deep water table. Werneria pygmaea, Caltha sagittata, Juncus depauperatus, Triglochin palustris, Carex subantarctica, Oxychloe andina, among others, are accompanying species.
Juncus balticus community: on over-saturated soils with water in puddles. The important moss stratum indicates a water-saturated environment. Other species of the community are Plantago tomentosa, Carex atropicta, Heleocharis sp., etc.
Potamogeton pectinatus communty: in both stagnant and moving water, with Myriophyllum aquaticum and mosses.
Plant species on granitic bedrock covered by organic matter 5–15 cm deep; where water runs very slowly on the rocky outcrop keeping the soil over-saturated, where Urtica buchtienii, Deschampsia caespitosa, Calceolaria glacialis, amongst other species, occur.
Some species from contact communities tend to occupy habitats where aeolian sand is deposited, indicating more xeric conditions, such as Stirpa frigida and Festuca weberbaueri in the upper part of cryogenic domes inside wetlands (Martínez Carretero, 1997).
Phytogeographical units
Three phytogeographical provinces are present in the study area: Monte, Puna and High Andean provinces, with transitions between them that vary according to exposure and inclination. The Cardonal unit appears on North-exposed slopes, close to the area.
Monte
It is located in the South of the area, reaching up to 2800 m. Species such as Larrea divaricata, Bulnesia retama, Bredemeyera colletioides, Atriplex deserticola, among others, are dominant. In the Quebrada de Alcaparrosa, the Monte Formation reaches 2800 m. and shows an ecotone with Puna elements up to 3000 m.
Cardonal
This unit appears on the eastern border of the area, on sunny slopes, between 2500–2800 m in a narrow strip of between 100–150 m wide. Some plant species indicate the extent of the unit from Bolivia southwards (López, 2000). Species indicative of the Cardonal are: Dipyrena glaberrima, Deuterocohnia longipetala, Denmoza rhodacantha, Dolichlasium lagascae, Mentzelia parvifolia, Satureja parviflora, Aphyllocladus san-martinianus, Gymnophyton polycephalum, Caesalpinia pumilio, etc.
Puna
It is the best represented vegetation belt in the study area. It appears between 2900–3800 m with an ecotone with the High Andean belt between 3800–4000 m, depending on the topography. Species such as Lycium chanar, Atriplex myriophylla, Jaravetum chrysophylla var. chrysophylla, among others are indicative of the Puna region.
High Andean region
It lies above 4000 m up to the vegetation boundary (4400 m in the study area). Species adapted to soils with cryogenic processes are Stipa frigida, Chaetanthera spathulifolia, Cistanthe picta, Barneoudia chilensis, etc.
Discussion and conclusions
The Central Andes of Argentina, at 30°S, show an interesting confluence of elements belonging to two vegetation classes: Calamagrostietea vicunarum, from the North (Peru, Chile and Bolivia), and Stipo-Lycietea fusci from the South (Mendoza). The former consists mostly of grasslands on sandy soils, and the latter of shrublands on stony slopes and downslopes, both with scarce plant cover. The Jaravetum chrysophyllae is the main vegetation unit linking both classes. The phytogeographical boundaries of the High Andean (3800- 4400 m), Puna (3800–2900 m) and Monte (< 2800 m) provinces are proposed for the study area.
The Puna belt is in agreement with the altimetry and floristic composition suggested by Martínez Carretero (1995) for Argentina. Within this belt, the study area corresponds to the Cuyano District. On the other hand, both altitudinal zones proposed by Martínez Carretero (1997) for the Puna of Catamarca province are present: the lower shrubby zone, between 3600–3800 m with Acantholippia deserticola, Lycium chanar, etc., and the higher one, with grasslands of Stipa and Jarava species. Syntaxonomically, syntaxa proposed by Roig & Martínez Carretero (1998) for the Puna of Mendoza province fit the study area, especially the Stipo-Lycietalia fusci, which includes shrub and grass associations such as Chuquirago-Lycietum fusci, Baccharidetum incari, Ephe - dretum breanae. A similar floristic coincidence appears in communities proposed by Ruthsatz & Movia (1975) for the Jujuy province. The Puna region shows reduced specific diversity toward the South, from 119 species in Jujuy (Ruthsatz, 1977), to 85 species in northwest San Juan (Table 1) and 89 in Mendoza (Roig & Martínez Carretero, 1998). Similar values between the last two localities justify their being included by Martínez Carretero (1995) in the Cuyano District of the arid Puna, which is characterized by the presence of Lycium fuscum, L. chanar, Stipa frigida, Artemizia mendozana var. paramilloensis, Stipa nicorae, among other common species.
From the syntaxonomical point of view four new associations are described for the Central Andes of Argentina: Artemisietum paramilloensis, Lycio-Ephedretum rupestri, Jaravetum chrysophyllae, and J. absconditae, all of them included in the Puna and High Andean belts.
Table 2.
- Climatic data for Zancarron area : absolute and mean temperatures, period 1987–1989.
Table 3.
- Floristic surveys for the Artemisietum echegarayii Roig & Martínez Carretero 1998.
Table 4.
- Floristic surveys for the Artemisietum paramilloensis ass. nov.
Table 5.
- Floristical surveys for the Larrea divaricata community.
Table 7.
- Floristic surveys of the Jaravetum chrysophyllae ass. nov.
Table 8.
- Floristic surveys for the Trycicla spinosa community.
Table 10.
- Floristic surveys for the Jaravetum absconditae ass. nov.
Table 11.
- Floristic surveys of Adesmia subterranea community.
Table 12.
- Floristic surveys of the Stipa frigida community.
Acknowledgements
We thank U. Eskuche and D. Iriart from Herbarium Humboldtianum, R. Pott from Hannover University, S. Rivas Martínez for their valuable comments, and N. Horak for the English version.
