Introduction

The puna is an ecosystem of the Central Andes of South America located in the desert plateaux above 3,500 m elevation; it covers parts of north-eastern Chile, north-western Argentina, south-eastern Peru and mid-western Bolivia. In Chile it extends from 17°30’ to 28° S latitude, and westward from the country’s eastern border for a width varying between 20 and 70 km. The puna is composed of sedimentary, volcanic and intrusive rocks, dating from the Palaeozoic to the Quaternary.

The precipitations which fall on the Andean plateau are collected by drainage systems, characterised by an absence of perennial watercourses reaching the more depressed areas. Superficial water run-off infiltrates into fractures in the rock or clastic sedimentary material to form phreatic aquifers. Water is commonly found welling up in the form of springs (Risacher et al., 1999). At the lowest points of these basins small lakes and salt flats are formed. Paleoclimate studies show very limited recharging of the aquifers; the subterranean waters present today would be fossil waters generated at a time when the precipitation in the area was 2.5 times higher than present (^{Messerli et al., 1997}).

^{Gajardo (1995}) places the area of Laguna Lejía in the high-Andean steppe region, high plateau and puna sub-region, which extends from the border with Peru and Bolivia to the Andean mountains of the Maule Region, at altitudes between 4,000 and 5,000 m. Seven plant formations are recognised in the extensive territory of this sub-region: high-Andean plateau steppe, high-Andean sub-desert steppe, pre-plateau scrub steppe, pre-puna scrub steppe, sub-desert steppe of the Atacama puna, desert steppe of the Andean salt flats and high-Andean desert of the Ojos del Salado, each with various plant communities or associations. Two large areas of endemism are recognised in the far north of Chile: one associated with the coast and the other with the Andes Range. The latter contains an endemism of 13.9% for Chile and 2.7% for the region (^{Squeo et al., 1998}; ^{Cavieres et al., 2002}).

The flora and vegetation of the mountains of northern Chile are relatively well documented (e.g. ^{Villagrán et al., 1981}; ^{Arroyo et al., 1988}; ^{Teillier 1998}, 2004; Teillier and Becerra, 2003); phytosociological studies have also been done (e.g., ^{Gajardo, 1995}; ^{Luebert and Gajardo, 2005}; Teillier and Becerra, 2003; ^{Navarro and Rivas-Martínez, 2005}). The highland is one of the most fragile and harsh environments of the Andean ecosystems, due to the combined effects of low temperatures and extreme aridity (^{Gutiérrez et al., 1998}). Wetlands of the highlands of northern Chile are under threat due to human activity, especially mining. The Chilean government has selected a priori several priority sites for conservation of biodiversity, including Laguna Lejía, so the aim of this study was to characterize the flora and vegetation associations present to assess, together with other components of biological diversity, its importance as a priority site.

Materials and methods

Methodology

Collecting and surveying was carried out in January 2008, obtaining the catalogue of flora and the phytosociological inventory (Fig. 1). Each species was identified and classified following APGIII classification (^{Bremer et al., 2009}), and its phytogeographic origin determined from specialised literature (e.g., ^{Zuloaga et al., 2008}). The material collected was prepared as herbarium specimens and deposited in the collection of the Centro de Estudios Agrarios y Ambientales. The life forms were determined as proposed by ^{Ellenberg and Mueller- Dombois (1966}), and the degree of human disturbance to the place as proposed by ^{Hauenstein et al. (1988}), who consider the phytogeographic origin and the life forms (Raunkiaer’s biological forms) as measures of human disturbance. A catalogue of the flora was obtained, containing all the elements mentioned above and the records produced by the present study.

Figure 1 Study area. Numbering of inventory points in Laguna Lejía, northern Chile. A= sub-desert steppe of the Atacama puna. B= Azonal vegetation associated with the Laguna Lejía wetland. 

The phytosociological surveys (inventories) included 12 randomly selected 10x5 m plots (Table 1), using European phytosociological methodology (Braun- Blanquet, 1964). The aquatic and marsh vegetation of the wetlands associated with the area were also considered. The phytosociological tables were processed using the methodology proposed by ^{Braun-Blanquet (1964}). To name each community, generic names of the two species with the highest importance value given in inventories was used.

Table 1 List and characterisation of the inventories of flora and vegetation in Laguna Lejía, northern Chile. 

The table includes the frequency of each species, i.e. the number of inventories in which it is present. This frequency is indicated in absolute terms (F) and in terms of relative frequency (Fr), which indicates the percentage frequency of each species, taking the sum of all the frequencies as 100%. We also incorporated the total cover (C) and relative cover (Cr) of each species, the latter being the percentage of the total cover of the species, using the sum of all the covers as 100%. Species with little cover or only one individual are designated with the symbols + and r respectively. These symbols were replaced by the value 1 to calculate the Importance Value (IV) when the information was processed. This was determined for each species using the sums of the relative frequencies and covers (^{Wikum and Shanholtzer, 1978}), thus reflecting the abundance and importance of each species at the study site.

The intra-environment diversity a was determined according to the Shannon-Wiener diversity index, which quantifies the total diversity of a sample and has two basic components: richness and evenness. It thus considers the importance value of each species and expresses the uniformity of the importance values across all the species in the sample. The formula for this function is: H’= -Σ ( ^_pi x log_{2 ^pi} ), where ^_pi is the proportion of the total number of individuals of the species in question in the sample. Its value ranges from zero, when there is only one species, to the maximum (H’max) which corresponds to log₂ S, where S is the number of species. Pielou’s evenness index (J) was also calculated according to the equation: J= H’/H’max. This index quantifies the contribution of the evenness to the total diversity observed. Its value fluctuates between 0 (minimum heterogeneity) and 1 (maximum heterogeneity, i.e. the species are equally abundant) (^{Magurran, 1998}). The inter-environment diversity b was calculated using the ^{Bray-Curtis Index (1957}), using the BioDiversity Professional programme.

Results

Flora

The catalogue of flora is shown in Table 2, in which the 30 species recorded are characterised (two taxa were identified only to genus). The species are distributed taxonomically into 20 Eudicotyledoneae (66.7%) and 10 Monocotyledoneae (33.3%).

Table 2 Catalogue and life forms of the zonal and azonal flora of Laguna Lejía. 

¹Life form, ²Phytogeographic origin, ³Cryptophyte, ⁴Chamaephyte, ⁵Therophyte, ⁶Hemicryptophyte, ⁷Native, ⁸Endemic, ⁹No common name.

The best represented families are Poaceae (six genera - nine species) and Asteraceae (four genera - four species). The biological spectrum (Table 2) shows the presence of 18 hemicryptophytes (perennial herbaceous plants) (60.0%); 8 chamaephytes (sub-shrubs) (26.6%); 2 cryptophytes (geophytes and hydrophytes) (6.7%) and 2 therophytes (6.7%), including annual and biannual plants. The phytogeographic origins are shown in Table 2, which indicates that 27 species are native (90.0%) and 3 are endemic (10.0%). No allochthonous species were recorded for the study area, which is therefore categorised as “without intervention” and pristine.

Phytosociology

The conglomerates analysis distinguished two groups, with no species in common. Table 3 shows the phytosociological results which confirm these groupings, identifying two plant communities: Puccinellia- Calandrinia (A) and Pappostipa-Deyeuxia (B).

Table 3 Phytosociological table with importance values and flora structure in Laguna Lejía, Chile. 

¹Life form, ²Phytogeographic origin, ³Cryptophyte, ⁴Chamaephyte, ⁵Therophyte, ⁶Hemicryptophyte, ⁷Native, ⁸Endemic, ⁹No common name.

Puccinellia-Calandrinia is an herbaceous community (inventories 3 and 10). It is poor in species (only six); the principal ones are Puccinellia frigida, Calandrinia compacta, Xenophyllum incisum and Arenaria rivularis. The community is hygrophilous in type, since its component species are typical of marshland or the verge zone of water bodies, representing the wetland vegetation of Laguna Lejía.

Pappostipa-Deyeuxia is an herbaceous and low shrub community (inventories 1, 2, 4 to 9, 11 and 12), with 24 species, notably Pappostipa frigida, Nassella nardoides, Deyeuxia cabrerae, D. antoniana, Junellia pappigera, Mulinum crassifolium, Pycnophyllum bryoides and P. macropetalum. The importance values of the species, in decreasing order, were: Pappostipa frigida, Deyeuxia cabrerae, Junelliapappigera, Puccinellia frigida and Mulinum crassifolium.

Diversity

Table 4 shows the alpha diversity analysis. The high Andean scrub Pappostipa-Deyeuxia (S= 24) presents greater species richness than the azonal hygrophilous community Puccinellia-Calandrinia (S= 6); the Shannon- Wiener evenness index of the latter is higher, in other words its species, however, few in number, are better represented than those of the high Andean scrub, where a small number of species predominate. Comparison of the two communities shows that they are completely dissimilar (100%), and therefore present maximum beta diversity.

Table 4 Diversity indices of the two plant communities in Laguna Lejía, northern Chile. 

¹Total frequency

Discussion

The vegetation recorded around Laguna Lejía coincides with that expected in ecosystems located in captive salt flat depressions of the pre-plateau, with isolated, intermontane, saline lacustrine basins dominated by a high-altitude steppe climate. The best represented families, Poaceae and Asteraceae, contain species adapted to xeric environments and steppe communities. All these life forms present both structural and physiological adaptations to the climatic conditions of the area (^{Montenegro et al., 1979}). Chamaephytes with their pulviniform shape and small size resist the cold, the strong winds and the weight of the snow; cryptophytes, in this case geophytes - plants with lasting subterranean organs - represent this type of arid climate very well; the survival of therophytes is based on their short life cycles. Hemicryptophytes are well adapted to these environments.

The two plant associations identified- the sub-desert steppe of the Atacama puna and the high Andean wetland vegetation associated with the lake - are completely dissimilar. The Pappostipa-Deyeuxia community is related to that described by ^{Gajardo (1995}) as Stipa chrysophylla, characteristic of the highest sectors of the Andes Range, which generally indicates the highest limit of vegetation. Caespitose plants are the predominant life form. According to ^{Teillier (2004}), who studied the flora and vegetation of the mid-upper basin of the Loa River, this plant community corresponds to high Andean scrub. This unit is classified taxonomically in the Urbanio pappigerae-Stipion frigidae association.

The diversity of vascular plants is that expected for the type of habitat. The wetland verge zone is important for its ecological role in maintaining the assemblage of aquatic birds and invertebrates present in the lake (Muñoz- Pedreros et al. unpubl.).

The plant diversity recorded in Laguna Lejía (30 spp.) is comparable to that documented by ^{Gutiérrez et al. (1998}) for the Salado river (3,108 m with 31 species) and higher than that recorded by Gutiérrez et al. (op. cit.) in the Coya stream (3,782 m with 18 species), and by ^{Teillier and Becerra (2003}) for the Ascotán salt flat (3,800 m with 21 species). This salt flat was explored on several occasions between 1993 and 1998 based on 46 plots in eight patches of vegetation, each associated with a different lake with completely dissimilar azonal and zonal flora as was found in Laguna Lejía. Teillier and Becerra (2003) suggested that the absence of zonal species in the salt flat is probably due to osmotic and/or nutritional problems produced by the high concentrations of salts. Conversely, the low water availability in the surrounding slopes might determine the absence of wetland species (salt flat and Laguna Lejía) in these habitats (^{Schat and Scholten, 1986}; ^{Shumway and Bertness, 1992}).

Our results agree with the findings of ^{Navarro and Rivas-Martínez (2005}) in a transect from Calama (2,260 m) to the south-eastern slopes of Licancabur volcano (5,600 m); although their stations are not geo-referenced, we assume that from their inventory 3 they would be within our study area. Their inventory 20 might be outside, but its inclusion makes sense ecologically and would add only two species to the inventory, Deyeuxia deserticola and D. crispa.

The study area is an extremely fragile ecosystem, like all the puna, highly sensitive to human disturbance like water extraction for use in mining, although there is still no such activity in the study area. Both plant communities are therefore important: the high Andean scrub for its high proportional species richness (S= 25) (e.g. compared to S= 21 of the saltmarsh vascular flora in Ascotán, also in the Antofagasta region at 3,800 m (^{Teillier and Becerra, 2003})) and the azonal hygrophilous community for its high evenness index (all the species are well represented). Its importance also lies in its highly pristine condition and its ecological role in maintaining the assemblage of aquatic birds (e.g. flamingos Phoenicopterus chilensis, Phoenicoparrus spp., piuquén Choephaga melanoptera) and invertebrates (^{Muñoz-Pedreros et al., 2013}).

Conclusions

Both plant communities in Laguna Lejía show highly pristine condition. The conservation of this ecosystem is important given the high proportional species richness of the high Andean scrub and the ecological role of the azonal hygrophilous community associated with the lake in maintaining the assemblage of aquatic birds. This is sufficient justification to consider Laguna Lejía a priority site for the conservation of biodiversity in northern Chile by the government.