A reference database of the pollen representation of the current vegetation in the Dry Puna of Argentina: Contributions to the interpretation of pollen fossil sequences and archeological evidence during the Holocene

Abstract

The present research is framed within an interdisciplinary archeological project that aims to reconstruct the environmental conditions in which human occupations developed in the locality of Barrancas, Dry Puna Argentina, during the Holocene. The aims of this work were to: (1) study the regional vegetation and the modern pollen dispersal-sedimentation process; and (2) generate a reference database for interpretation of the fossil pollen records of the Holocene in the Dry Puna (3) provide information for the study of the relationship between human populations and vegetation in the area during the Late-Holocene. The results show that the main pollen types that characterize the regional vegetation were represented in the surface samples (herbaceous steppe, shrub steppe, mixed steppe, and vegas). Also the environments with evidence of anthropic impact were identified by specific plant species and the corresponding pollen grain. The representation of the vegetation was quantified according to the different pollen types. The study used indices of association to establish relationships between modern pollen and vegetation, and showed a weak association for Solanaceae and Verbenaceae; an over-representation of Ephedrae, Alnus acuminata, Malvaceae, Chenopodiaceae-Amaranthaceae; an association of Asteraceae; the absence of association of Cactaceae and Portulacaceae; and a strong association of Poaceae. These results allow us to specify the interpretation of fossil records and past environments in relation to anthropic modifications on the landscape.

Keywords

archeology anthropic impact Holocenet Puna Argentina vegetation pollen analysis

Introduction to the research problem

The present article is part of the results of two important archeological projects that have been conducted for some decades in the area of Susques and Barrancas, with the aim of exploring the environmental scenarios where human groups developed during the Holocene (Morales, 2011; Morales et al., 2018; Oxman, 2015; Oxman et al., 2013, 2015, 2020; Pirola et al., 2018; Tchilinguirian and Morales, 2013; Yacobaccio and Morales, 2011).

The aims of this work were to contribute to the construction of a database of the pollen representation of the current vegetation for the interpretation of Holocene fossil pollen records in the Dry Puna of Argentina. The Holocene Series/Epoch is the most recent series/epoch in the geological timescale, spanning the interval from 11,700 years to the present day. The new stages are the Lower/Early Holocene Subseries/Subepoch dated at 11,700–8200; the Middle Holocene Subseries/Subepoch dated at 8200 a 4250; and the Upper/Late-Holocene Subseries/Subepoch with a date of 4250 a before 2000 CE (Walker et al., 2012). Especially, the Late-Holocene Late Holoceceneis an important period in archeological terms because it is known as a period the consolidation of a group of cultural traits locally known as “the Formative Period” in the south-central Andes, such as village settlements, pottery, agriculture and/or pastoralism, which may have been elements of a sociocultural strategy to cope with resource uncertainty and economic risk brought on by Late-Holocene environmental instability from ca. 3500 years BP on (Aschero and Yacobaccio, 1998/1999; Yacobaccio, 2001; Yacobaccio and Madero, 1992). The paleoenvironmental studies also distinguish a period during the last part of the Late-Holocene described as a time of decreased moisture and indications of an increase in the anthropic impact on the landscape between 2500 and 1500 years BP, followed by the establishment of current climate conditions, in 1500 years BP (Latorre et al., 2002; Thompson et al., 1995; Vuille and Keimig, 2004). Among the different lines of evidence used for paleoenvironmental studies, fossil pollen is a good indicator of plant communities, since it is produced by plants in considerable amounts, can be easily transported for long distances, and can be preserved in an important variety of depositional environments (Faegri and Iversen, 1989; Seppa, 2007). In this sense, and according to the principle of methodological uniformitarianism or actualism. Therefore, to modern geologists or actualists, uniformitarianism states that; The principle of uniformitarianism states natural laws and processes that happen today also happened in the past but not necessarily at the same rate or intensity. Therefore, the modern geological processes we observe are key to understanding and interpreting the ancient geological processes and features. In this sense and In order to reconstruct the past variations in vegetation and environment from fossil pollen records, it is necessary to know the modern complex relationships among plant communities (their distribution relative to environmental variables) and their representativeness in the pollen record (Jackson and Williams, 2004; Overpeck et al., 1985; Seppä and Bennett, 2003).

The relationships between prehistoric societies and their environment is one of the most exciting problems facing archeology (Almquist-Jacobson and Sanger, 1995; Mc Donnell and Picket, 1993 [2007]). In this context, the human groups are understood as another element within the ecosystem, exposed to the modifications produced in his environment, although with a particular attribute: culture, understood as an extrasomatic adaptive system that serves for the integration of a society with its environment. environment and with other sociocultural systems (Binford, 1967, 1980). This definition indicates that the resource structure of a habitat plays a central role in the different organizational spheres of societies, in economic, social and ideological aspects (Morales, 2011). Likewise, human activity can also modify its environment, affecting the original composition of the vegetation (López García et al., 1997; López Sáez and López García, 1992). The most widely used formula to detect anthropogenic activities is the use of the so-called “pollen indicators of anthropogenic disturbance” (Behre, 1981, 1986; Iversen, 1949). This methodology is still delicate (Richard, 1994), because it is based on pollen indicators that are sometimes very discrete or specific at a percentage level, which could reveal weak anthropic pressure or intense activity in distant areas, so it is recommends performing the interpretation based on the convergence of several anthropogenic signals (Barbier et al., 2001). It also occurs with certain pollen types, such as weeds or certain cultigens, which can signal both clearly anthropogenic activities and changes in native vegetation as a result of small-scale environmental changes. In a similar way, the problem of the development of pastoral activities has been addressed, easily verifiable at the palynological level, thanks to the appearance of specific pollen associations (Chenopodiaceae-amaranthaceae, Urtica dioica, Rumex acetosa, Rumex acetosella, Plantago lanceolata, Astragalus sp., among others) (Galop, 1998, 2000; López Sáez et al., 2000).

Archeological evidence is essential for understanding the evolution of vegetation over time and vice versa. Several authors, such as Ruthsatz and Movia (1975), Werner (1976), Braun Wilke (1991), and Lupo (1998), have discussed the influence of the successive human occupations in the Puna, especially of the pastoral activity, on the Puna landscape. The various approaches address both the way in which the plant landscape and the availability of resources conditioned the development of socio-economic strategies developed by human groups as well as human occupations modified and impacted the composition of plants (Lupo, 1998; Yacobaccio et al., 1997–1998).

Ongoing research is focused on elucidating changes in vegetation and land use history during the Holocene in the Puna region using a pollen analysis approach (Albeck et al., 2017; Lupo et al., 2017). However, in northwestern (NW) Argentina, the relationship between fossil pollen records and modern vegetation of steppes and grasslands in semiarid environments of the Central Andes is often poorly understood due to the lack of studies (Torres et al., 2019). These conditions highlight the importance of studying the modern pollen-vegetation relationship, considering the different spatial-temporal scales, with the aim of better interpreting fossil records along with archeological evidence and, therefore, understanding the evolution of vegetation over time in close relationship with human occupations and the use and management of natural resources. Specifically, in the Argentine Puna, several researchers have focused on the study of changes in vegetation using pollen as the main line of evidence related to the history of land use since the earliest hunter-gatherer occupations recorded from the Early Holocene (10,000 years BP) up to the Late-Holocene, when a predominantly pastoral economy began to develop (ca. 2500 years BP) (Albeck et al., 2017; Lupo et al., 2017; Yacobaccio et al., 1997–1998).

Research carried out on pollen fossil records shows evidence of the first pollen indicators of anthropogenic disturbance toward the Mid-Holocene, which might be related to changes in the prevailing economic strategy and the use of space by human groups (the presence of plant associations from disturbed environments and the introduction of species related to pastoral activity) (Graf, 1992; Hansen et al., 1994; Kulemeyer and Lupo, 1998; Lupo et al., 2018; Schittek et al., 2012). In this context, it is of utmost importance to advance in the studies about modern pollen and its relationship with vegetation in order to improve the interpretation of the changes in landscape and human interventions over time.

Study area

The study was conducted in the Argentine Puna, located between 19° and 27° S and between 3000 and 4500 masl. It is a high Andean plateau crossed by NE-SW mountain ranges and deﬁned as a highland desert biome, characterized by high solar radiation, low atmospheric pressure, and low mean annual precipitation varying from >300 mm/year in the northwestern sector of the region to <100 mm/year in the southeast; approximately 80% of the total annual rainfall occurs between December and March, governed by the South American Monsoon System (Vuille and Keimig, 2004; Zhou and Lau, 1998). The general hydrological landscape is characterized by a few permanent freshwater basins, salt lakes, pans and playas. The altitudinal variations define three vegetation belts: The Puna, the lower High-Andean belt, and the upper High-Andean belts. The Puna belt occupies the lower altitudinal level (3500–4200 masl). Plant communities are composed of a shrub steppe of Baccharis boliviensis and Fabiana densa. Other typical communities include the scrublands of Parastrephia quadrangularis and isolated woods of Polylepis tomentella (Bonaventura et al., 1995; Ruthsatz, 1983; Ruthsatz and Movia, 1975). The lower High-Andean belt is located between 4200 and 4500 masl, with plant communities characterized by steppes of Tetraglochin cristatum co-dominated with Poaceae clumps, along with xerophytic shrubs, such as Adesmia horrida, and diverse species of Cactaceae. The physiognomy of the grassland is characterized by different Poaceae clumps, with sparse shrubs of Nassauvia axilaris and some Puna shrubs (Schittek, 2014). The upper High-Andean belt is located above 4500 masl, and is dominated by circular and semicircular clumps of Festuca orthophylla. This herbaceous plant has hard and sharp leaves, and is accompanied by perennial herbs, such as Frankenia triandra cushions (Cabrera, 1976). Wetlands, or vegas, are an ecosystem composed of dense and discrete grasslands with high vegetation cover, frequently associated with palustrine water systems. Vegas are essential in the Puna landscape, since they sustain plant communities that concentrate the highest primary productivity and biological diversity at the regional scale (Schittek et al., 2012). Vegas are intensively used by humans for animal grazing and crop irrigation.

At present, the Puna region is home to aboriginal peoples and local communities with deep relationship with nature and the space. The socio-economic family organization is based on grazing by llamas, sheep, and goats. Grazing is an economic system based on the raising of domestic animals owned by producers (Chang and Koster, 1986) in arid areas; the activity typically requires extensive displacement to be productive (Ikeya and Fratkin, 2005; Yacobaccio, 2013). Two types of settlements can be distinguished: residential bases and temporary sites located in different strategic sectors used for grazing. Residential bases are usually located near water sources (vegas), whereas temporary sites are used to avoid overgrazing of the pasturelands (Flores Ochoa, 1968; Göbel, 2002; Tomasi, 2013; Yacobaccio, 2013; Yacobaccio et al., 1998).

Archeological evidence about knowledge and use of plants in the Jujuy Puna

Materials and methods

Field work was conducted in different localities of the Puna region, between 3500 and 4300 masl (Figure 1), from 2012 to 2018. The survey was carried out in the summer and winter seasons, with the collaboration of colleagues from the research team. The survey of modern vegetation and sampling of surface pollen are detailed below. The methods used for the data relational analysis (modern vegetation-pollen)) are also described.

Figure 1.

The five study sites and their geographic position in the map of the study area.

Sampling of vegetation and surface pollen

Surveys of modern flora and surface pollen were conducted in different localities of Pastos Chicos, Barrancas, Susques, Taire, Laguna Ana and Tuzgle, with the aim of identifying the different plant compositions at 3600–4200 masl. Barrancas, Pastos Chicos and Lapao are at the same altitude and represents the typical vegetation of the shrub steppe. These three locations mentioned have been selected for the study because contribute to the study of environmental and archeological research carried out in the area. Likewise, the localities of Tzugle, Laguna Ana and Taire are incorporated since they are located at a higher altitude, which represents the vegetation of the Andean grassland.

The taxa in vegetation were identified at the family, genus and species levels, using the keys (Bridson and Forman, 1992) and descriptions available for the area in the botanic literature (Cabrera, 1976; Ruthsatz and Movia, 1975) and a list of species was performed. Samples were taken for constructing the herbarium. Survey sites were selected according to homogeneity of vegetation. Representative or dominant plant species and individuals were counted in each of the 33 vegetation surveys made in 5 m × 5 m plots in the localities of Pastos Chicos (n = 6), Lapao (Susques) (n = 6), Barrancas (n = 16), Tuzgle (n = 2), Laguna Ana (n = 2), and Taire (n = 1). For the survey of the current vegetation, the dominant species were selected (Matteucci and Colma, 1982).

Counts of plants and pollen per survey are expressed in terms of frequency.

For pollen analysis, sediment samples were taken within each of the 33 plots (Adam and Mehringer, 1975). However, it must be taken into account that association indices have scope limitations (spatial extension) for the study of vegetation, depending on the characteristics of the research design. On the other hand, 30 samples of specific sites in the landscape were taken, including wetlands or vegas, corrals associated with present pastor settlements, and Andean grassland above 3600 masl. At these specific sampling sites, sediment was collected for pollen analysis but vegetation was not surveyed; only the dominant species were recorded. The abundance of each taxon was quantified and a data matrix was constructed for statistical analyses.

Sampling of surface pollen was conducted following the multiple subsample technique of Adam and Mehringer (1975). Five subsamples were taken from the vegetation survey plots. The laboratory work stage consisted of processing of pollen samples according to the conventional techniques for Quaternary sediments (Faegri and Iversen, 1989; Gray, 1965), consisting of filtering through a 250 -µm mesh, addition of Lycopodium clavatum tablets, removal clays and humics acids 10% KOH, removal of silica with HF, acetolysis, washing with acetic acid, and mounting in paraffin. Pollen count was performed under a Zeiss ICS KF2 light microscope with 400 magnifications. A minimum of 300 pollen grains per sample were counted and identification was aided by the reference collection held at the Laboratorio de Palinología, Facultad de Ciencias Agrarias, Universidad Nacional de Jujuy (PAL-JUA) and pollen atlases (Heusser, 1971; Markgraf and D’Antoni, 1978).

Interpretation of the vegetation composition in the pollen graphs (see Figures 2 and 3) was conducted using the literature available for the study area; the following main pollen associations were determined: Forest, shrub steppe, herbaceous steppe, local humidity and anthropogenic impact (Lupo et al., 2018). Likewise, the interpretation is also supported by other observations on the development of the flora related to variables such as geographical location, topography, evidence of anthropic modifications of the landscape and/or archeological evidence present in the place (Table 1).

Figure 2.

Current vegetation survey cluster analysis diagram.

Figure 3.

Photographic sheets of pollen grains from sediment samples taken from the current surface. A, B, C, D, E G, I, J, K, L, M: Poaceae/F: fungal spores N, Ñ, O, P, Q, R, S, T, U, V, W, X, Y: Asteraceae/Z, ZA, ZB, ZC, ZD, ZE: Cyperaceae. ZF, ZG: Amaranthaceae/ZH: unidentified/ZI, ZJ, ZK, ZL: Trilete ZM, ZN, ZO: Chenopodiaceae/ZP: unidentified/ZQ: Eucalyptus-Myrtaceae ZR: unidentified/ZS: fungal spore/ZT: Podocarpus.

Table 1.

Main pollen types of the pollen associations of the analyzed samples.

Pollen associations	Pollen types
Forest	Alnus, Juglans australis, Popdocarpus, Celtis.
Shrub steppe	Adesmia, Chuquiragua, Asteraceae, Opuntia, Cactaceae, Ephedrae, Fabacaee, Mimosaceae, Fabiana, Solanaceae, Verbenaceae.
Herbaceous steppe of the Puna	Poaceae, Ephedrae.
Local humidity	Carex, juncaceae, Myriophillum, Cyperaceae, Pteris, esporas triletes, Polypodium
Anthropic impact	Malvaceae, Gomphrena, Tipo Alternanthera, Chenopodiaceae-Amaranthaceae.

Modern pollen-vegetation relationship: modern analog analysis

The relationship between vegetation and pollen was established using a presence–absence analysis. Results were used to calculate the indices of association (A), under-representation (U) and over-representation (O) with the equations proposed by Davis (1984): Association = B0/(P0 + P1 + B0). Under-representation = P1/(P1 + B0). Over-representation = P0 / (P0 + B0). where B0 is the number of surveys in which the pollen type is present in the sample and the plant is found in the surveyed plot; P0 is the number of surveys in which pollen is present, but the plant is absent; and P1 is the number of surveys in which the plant is present and its corresponding pollen is absent. Index A ranges between 0 and 1, with A = 1 indicating that pollen and plant are always present, and A = 0 indicating that pollen is present and the plant is absent or vice versa. Index U ranges between 0 and 1, with U = 1 being assigned to all pollen types that are absent if the corresponding plant is present and U = 0 being assigned if pollen and plant are present. Index O ranges from 1, corresponding to pollen that is present but the plant is absent, to 0, where both pollen and plant species are absent.

Results

Vegetation survey

The pollen analysis identified 29 taxa and the Cluster Analysis performed with percentages of modern vegetation recorded in the 33 survey plots showed two large pollen groups (Figure 2). This grouping is based on the dominance of the taxa Poaceae (1A), Aristida adscensionis (Poaceae) (1B) and Asteraceae (2) in the samples. Surveys of group 1 A include vegetationgroups located above 4000 masl, where herbaceous steppe or High-Andean grassland dominates (Cabrera, 1976). Surveys of group 1 B were performed at the end of March, when perennial herbaceous species dominate and shrubs are no longer at the flowering stage. Aristida adscensionis is a dominant Poaceae in samples taken from the shrub steppe (between 3600 and 3800 masl) after the rainy season (early April). If this species is removed from the analysis, the program automatically incorporates these samples to the shrub steppe group. Finally, group 2 includes the surveys dominated by Asteraceae, all of them located in the shrub steppe of the Puna, between 3600 and 3900 masl. (Figure 3). Survey 20, which was conducted in a hill near the locality of Susques, stands out for the high values of an anthropogenic indicator (Gutierrezia sp.). Sampling revealed that this sector of the ravine was used for the extraction of material for making building bricks.

Pollen survey

The pollen analysis identified 20 taxa (Figure 3) and the surface pollen samples were statistically analyzed using the constrained cluster analysis, including 27 of the 63 surveys that were statistically significant for the analysis (the pollen samples that had the absolute minimum number of pollen grains to be incorporated into the statistical analysis); values are expressed in percentages and Euclidean distances were applied (Figure 4).

Figure 4.

Pollen diagram of the surface samples. P: Specific surface pollen sampling sites; S: surface pollen and vegetation plots.

The analysis of modern vegetation and surface pollen rain show that the main pollen types characterizing the elevation gradient of regional vegetation are represented in the pollen groups of surface samples (herbaceous and shrub steppe). The CONISS analysis discriminated three main groups and two subgroups. Group 1A is characterized by a high proportion of Poaceae, with plot S6 standing out for its high proportion of Chenopoidiaceae-amaranthaceae. Group 1B is characterized by having a similar value of Poaceae and Asteraceae, followed by Cyperaceae, Chenopodiaceae Amaranthaceae. Group 2 includes the samples with high values of Cyperaceae (45%), with the lack of Alnus sp standing out. Group 3 differs in the dominance of Asteraceae, accompanied by other shrub species and a low proportion of Poaceae.

Modern pollen–vegetation relationship

The analysis of modern pollen–vegetation relationship It was based on work with the 11 taxa that were identified in pollen and vegetation. The analysis allowed us to assign a value to each taxon and order them in the following groups (Table 2).

Table 2.

Indices of association (A), under representation (U) and over representation (O).

TAXA	A	U	O
STRONGLY ASSOCIATED TYPES
Poaceae	1	0	0
ASSOCIATED TYPES
Asteraceae	0.7	0.1	0.2
WEAKLY ASSOCIATED TYPES
Solanaceae	0.4	0.6	0.2
Verbenaceae	0.3	0.3	0
UNDER REPRESENTED TYPES
Portulacaceae	0	1	0
Cactaceae	0.1	0.8	0.5
OVER REPRESENTED TYPES
Malvaceae	0	0	1
Alnus acuminata	0	0	1
Chenopodiaceae-Amaranthaceae	0.05	0	1
Ephedraceae	0.1	0.0	0.9

Strongly associated types: Poaceae

This family is anemophilous, with pollen dispersal depending on wind, and therefore being highly represented. These grains are small and therefore can remain suspended for a long time (Poaceae 20–40 µm).

Associated types: Asteraceae

The family Asteraceae has entomophilous dispersal (e.g. Baccharis spp. and Nardophyllum spp.). Individuals produce large amounts of pollen; however, pollen is not dispersed over long distances.

Weakly represented types: Verbenaceae and Solanaceae

In general, these families are entomophilous, which supports the weak association observed. Species of the family Verbenaceae are entomophilous; therefore, they have low dispersal and pollen representation. Within this family, the species Acantholippia salsoloide and Junellia seriphioides were detected.

Under-represented types: Portulaca and Cactaceae

The families Cactaceae and Portulacaceae have zoophilous dispersal, depending mostly on agents such as insects and birds. Pollination is ensured in these species, since despite their low production of pollen, their grains are big (between 80 and 100 µm) and are generally transported a short distance from the source.

Over-represented types: Ephedra, Chenopoideae-Amaranthaceae, Malvaceae and Alnus acuminata

The recorded over-represented taxa are all anemophilous and, therefore, are highly represented. These grains are small and, therefore, can remain suspended for a long time (Ephedrae ca. 20 µm, Chenopodioideae-Amaranthaceae 13–23 µm, Malvaceae 30–40 µm and Alnus acuminata 20 µm) (Cuadrado, 1989; Erdtman, 1957). A clear example of this phenomenon is observed in Alnus acuminata, a pollen type that is usually found in the pollen records of the Puna, obtained in the upper or montane forests of the Yungas, ca. 80 km to the east of the Eastern Cordillera (outside the limit of the study region). The weak association of the species of the family Solanaceae might be attributed to the flower morphology. Flowers are perfect, actinomorphic or slightly zygomorphic, are arranged in clusters; they can be solitary and usually have free stamens. The latter characteristic might explain the short dispersal.

Discussion

The results of the modern pollen rain show a clear relationship with the assemblage of vegetation; thus, from the pollen rain the two principal vegetation belts characterizing the altitudinal gradient of the Puna region can be differentiated: The Andean grassland, marked by the high percentages of Poaceae and the shrub steppe by Asteraceae. Since the differences cannot be established in the other samples, which include the grassland with shrubs and mixed steppe, it can be said that they represent an ecotone (mixed steppe), since they present equivalent percentages between herbaceous plants from the high Andean province and Puno shrubs. Fortunately, the results of the analysis of modern analogs indicate such as strongly associated types Poaceae and associated Asteraceae. Also, these results agree with previous findings of studies conducted in other localities of the Argentine Puna and northern Chile (Collao-Alvarado et al., 2015; Kuentz et al., 2007, 2011; Lupo, 1998; Torres et al., 2019; Villagrán et al., 1981), where the pollen spectra reflect the altitudinal variations and the associated humidity, temperature conditions and hydric balance, which are the basis for macroscale paleoecological and paleoclimatic interpretations. Thus, firstly the shrub and secondly the herbaceous steppes from the Puna represent drier conditions than grasslands and high Andean herbaceous steppes (Lupo et al., 2018). Also, the development of vegas can be detected based on the pollen types that develop exclusively in these ecosystems, such as Carex, Myriophyllum, Juncaceae, Cyperaceae, Urticaceae, Anemia tomentosa, Polypodium, and Pteris. Finally, it was detected an association of pollen indicators of anthropogenic impact, such as Chenopodiaceae, Amaranthacea, and Malvaceae.

The pollen components that appear under represented (portulaca and cactaceae) due to low pollen production and large size and overrepresented due to their small size and wide dispersion transport (malva, chenopodiaceae-amaranthaceae and ephedra). The pollen type Alnus is overrepresented since it corresponds to the vegetation of the Yunga and is transportable over long distances.

The results of the application of the analog technique allows adjusting the paleoenvironmental reconstructions, based on the actualist palynological model implemented. This represents a contribution to the search for modern analogs for high mountain plant communities in the NOA region, to interpret the relationship between fossil assemblages and their respective emission sources.

The environmental history studies in the central-southern Andes evidence important changes in the vegetation composition occurred during the Holocene, related to variations in precipitation and temperatures. Particularly, in the studies of the fossil pollen records from 3600 masl in the Argentine Puna (where there is a shrub or mixed steppe at present), samples dominated by Poaceae are typically interpreted as the result of an extension of the Andean grassland due to an increase in the regional humidity conditions. The results obtained from the analysis of the surface samples indicate that samples taken from areas with grassland patches and/or vegas in humid areas can also be dominated by Poaceae; nevertheless, this inference does not mean an extension of the Andean grassland. In both cases, the presence of an environment dominated by Poaceae represents conditions of greater humidity, although they would vary in the extension of the area of vegetation that they would represent. Generally, the dominance of Poaceas in the paleoenvironmental records of the area occurs toward the early Holocene (Lupo, 1998; Markgraf, 1985; Oxman, 2015). The archeological implications are modeled at the end of the availability of resources for the subsistence of hunter-gatherer groups. The humther gatherer groups characterized by high mobility (Lee and DeVore, 1968). In this regard, Kelly (1995) has highlighted that the environment is a fundamental factor for understanding mobility within hunter-gatherer groups (Smith and Wintherhalder, 1992). The patch choice model explains the choice of the patch of resources to exploit within a given environment to maximize the energy obtained at each site (Bettinger, 1991). At the same time, the patches are not distributed constantly over time nor homogeneously distributed in space. In environmental terms, as humidity conditions increase, primary productivity increases and the distance between patches decreases. By decreasing the distance between patches, the risk in obtaining food for human groups also decreases (Binford, 1980; Kelly, 1995). Therefore, by decreasing the risk of moving between patches in search of food, hunter-gatherer groups move more. In turn, high mobility has consequences in the archeological record such as the low density of materials and the consequent difficulty in finding traces of anthropic activity in the landscape.

Specifically, during the Late-Holocene, variations known as recent climatic oscillations and the intensification of the land use are detected (Flantua et al., 2016; Liu et al., 2005; Schittek et al., 2015). In the Argentine Puna, the indicators of the anthropogenic impact can be inferred from ca. 4000 cal. years BP (Pearsall, 1989; Silverman and Isbell, 2008) and an increase is observed mainly when human populations developed a pastoral economy, after 2080 BP. Moreover, the intensive grazing in the entire area can be observed in soil physical and chemical alterations, erosion processes and the degradation of the current plant cover (Flantua et al., 2016; Lupo et al., 2006; Ruthsatz, 1983; Schittek et al., 2015). Especially during the last 2000 years, this period is marked by the presence of anthropic disturbance (indicators of grazing, fires, crops and weeds), as well as changes in pre-Hispanic-Hispanic cultural patterns that, in some sectors with intensification of human occupation, can make paleoclimatic reconstructions difficult (Lupo et al., 2018). The anthropic impact associations are well documented, for example in Yavi from approximately 4500 years cal. BP with incipient livestock and agriculture production in the Puna (Lupo, 1998). Grazing in the highland Puna is considered to have led to a reduction in grassland (Poaceae family) density and consequently to a process of generalized erosion and deepening of the water courses in the valleys as of ca. 2000 years cal. BP (Kulemeyer, 2005; Kulemeyer and Lupo, 1998). Moreover, Santa Victoria Core shows the prevalence of arid conditions across the Puna-Highland ca. 2600 years cal. BP (De Porras and Maldonado, 2018; Hooper et al., 2020; Lupo et al., 2018).

Final remarks

Our results allowed us to build a reference data base to recognize the regional flora, the dominant species describing the major communities and the general ecological aspects that influence the plant distribution in the study region.

The relationship between vegetation assemblages and modern pollen detected in the study area indicates that the pollen spectra reflect both altitudinal variations and environmental conditions.

As can be seen, this analysis provides detailed information on surface pollen rainfall at a local scale, achieving good results in the separation of plant units, such as those obtained in surrounding areas and other sectors of the Central Andes (Lupo, 1998; Ortuño, 2000).

In turn, the study of the surface pollen spectra allowed us to establish the main modern analogs. The techniques to analyze the pollen-vegetation relationships were adequate. The association index was useful to describe the presence of a plant when its pollen type was found. Our results confirm that Asteraceae and Poaceae pollen records are the ones that represent the past vegetation in the region. However, it is difficult to differentiate between pollen association of the family Poaceae and both the High-Andean grassland and grassland areas below 4000 masl. In these cases, pollen analysis along with other lines of evidence (sediments, diatoms and geochemistry, among others) are necessary to differentiate these two types of environments.

Footnotes

Acknowledgements

We are grateful to the Susques, Huancar and Barrancas community for allowing us to work in their lands. Also, we are thankful to Sarita Brown Wilke and Francisco Ratto for identifying the plants. Thanks are also due to Hugo Yacobaccio for the support and direction of the archeological Project and your team.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad de Buenos Aires (UBACyT230B), Agencia de Promoción Científica y Tecnología (PICT 4376-2016 and PICT 2015-3047), Secretaria de Ciencia y Técnica y Estudios Regionales and Universidad Nacionald e Jujuy (SeCTER-UNJu).

ORCID iD

Brenda Irene Oxman

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