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Recent Holocene palaeoenvironmental evolution in the central Ebro Basin (NE Spain)
Quaternary International 93-94 (2002) 177–190
Recent Holocene palaeoenvironmental evolution in the central Ebro Basin (NE Spain) P. Gonza! lez-Sampe! riza,*, M.C. Sopena Vicie! nb a b
Instituto Pirenaico de Ecolog!ıa (CSIC), Campus de Aula Dei, Apdo 202, 50.080 Zaragoza, Spain Area de Prehistoria (F.F. y Letras) C/Pedro Cerbuna, 12. 50.009 Universidad de Zaragoza, Spain
Abstract Evolutionary aspects of landscape are analysed from the geomorphological, palynological and archaeological study of a sector in the Central Ebro Basin (NE Spain). In this study we use four representative sites, each of them offering different information about the evolution of the landscape in which they are located. Together, the data allow for the reconstruction of general patterns concerning the Holocene palaeoenvironmental evolution, erosion processes and their genetic interpretation. Climatic factors alone do not explain the key features and profound transformations suffered by this landscape. More likely, they have been the response to the changes activated by human impact. Deforestation since the Neolithic period has given rise to spaces of difficult bio-edaphic recovery. Different erosive agents have been the main source of sediments that currently fill the bottoms of the depressions and plain valleys. Human communities since the Neolithic have modified the landscape sufficiently to be recorded palynologically. Several phases of accumulation and incision stages have been identified (post-Bronze regularisation, Iberian– Roman incision, Medieval accumulative–incisive stage and Actual incision). The importance that the ‘‘climatic factor’’ would have had on the mentioned sites, if without any human intervention in the exploitation of the environment, is still subject to debate. From a climatic point of view, these phases are a consequence of the occurrence of dry and wet periods. Thus, the evolution of the landscape in the Ebro Basin in relation to the human occupation during the Upper Holocene is explained by a succession of dynamic changes. These fluctuations would have been due to a combination of climatic conditions conducive to the triggering of erosive processes, along with the strengthening of them by humans due to their intervention in the environment. r 2002 Elsevier Science Ltd and INQUA. All rights reserved.
1. Introduction Recent geoarchaeological studies on various Bronze ! or Middle Cinca Age sites in the district of Monzon (Sopena, 1998), have demonstrated profound transformations of the semi-arid environment. The sites located on the plains either had been fossilised by Recent Holocene deposits or had been affected by anthropic actions. The sites at the summits of small hills had been practically levelled and those located initially on the hillsides were affected by the active dynamics of the slopes. The results obtained from that study allowed a first estimate of the environmental characteristics in the Bronze Age and their evolution up to the present day, with archaeological data and palynological results of the Tozal de Macarullo site (Gonza! lez-Sampe! riz, 1998).
Interest in understanding the paleoenvironmental evolution of the different geomorphological environments of the Central Ebro Basin led to a complete survey combining geoarchaeological and palynological strategies. The aim sought in this work has been to merge geoarchaeological and palynological data in various sites (Tozal de Macarullo, Tozal de Andres, Civiacas II and El Prao, Huesca, Spain). The goals are to characterise the environment during occupation, to determine their changes and evolution and to analyse the causes that have determined the geomorphological processes. Therefore, our research evaluates the level of environmental change and of landscape modification that human impact as well as the climate could have had since the Bronze Age in the Middle Cinca River area.
2. Geographic setting *Corresponding author. E-mail address: [email protected] (P. Gonz!alez-Samp!eriz).
The area is located in the Central Ebro Basin (Fig. 1) infilled with continental Tertiary materials (Tera! n and
1040-6182/02/$ - see front matter r 2002 Elsevier Science Ltd and INQUA. All rights reserved. PII: S 1 0 4 0 - 6 1 8 2 ( 0 2 ) 0 0 0 1 6 - 2
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Fig. 1. General situation of the study area.
* Sole! Sabaris, 1968; Vinuales and Vericad, 1996). Due to its geographical location, the climate is Mediterranean. However, since it is enclosed by mountain systems, the climate adopts continental traits: aridity, deficit rain (400 mm), drying winds (cierzo), high insolation, elevated nocturnal radiation, and strong annual and daily thermal oscillation. The resulting climate can be defined as semiarid Mediterranean (Biel and Garc!ıa de Pedraza, 1962) with 800–900 mm of potential evapotranspiration (Thornthwaite, 1948). The characteristic soils are calcareous Fluvisoils developed over recent alluvial deposits and without well-differentiated profiles. This zone is located in the chorological province of Aragonese vegetation, the Somontano Aragonese sector, a meso-Mediterranean floor with a dry local climate. The potential vegetation would be a forest of Quercus rotundifolia and Pinus halepensis with sclerophyllous scrub such as Quercus coccifera, Rhamnus alaternus, and Rhamnus lycioides that replace holm oak groves with Juniperus phoenicea, Juniperus oxycedrus, Daphne gnidium, Jasminum fruticans and Retama sphaerocarpa. Greater degradation gives rise to an open underbrush scrubland of heliophytes (Genista scorpius, Teucrium capitanum, Rosmarinus officinalis, Thymus vulgaris, Lavandula latifolia, Helianthemum rubellum, etc.). The most extreme stage is made up of gramineous communities with Brachypodium ramosum, Lygeum spartum or Stipa tenacissima (Braun Blanquet and de Bolos, 1957; Peinado Lorca and Rivas-Mart!ınez, 1987). The riparian vegetation, of great ecological importance and a protector against hastened erosion, has been eliminated for the most part. Today, the surrounding areas of the sites, on the fringes of poor and open scrubland, reflect considerable dry-land agricultural development.
3. Methods The environmental dynamics is a result of physical processes. Study of natural and anthropological deposits allows identification of some of those processes, to associate them with climatic characteristics and/or specific human actions, and to date them. In Mediterranean areas, as there is great topographical, edaphological and climatic heterogeneity, it is difficult to establish valid models of environmental dynamics for extensive areas, so multidisciplinary studies are indispensable. Areas where populations have traditionally concentrated (mainly since the Neolithic period) contain abundant sites. They form part of the landscape, so any modification to the physical features will affect these sites (Burillo et al., 1984; Ru!ız-Zapatero and Burillo, 1988). Additionally, since these are deposits of anthropic origin, they are very appropriate for attempting to establish the magnitude and transcendence of the processes linked to human presence (Dupre! and Renault-Miskovsky, 1990; Gonza! lez-Sampe! riz, 1999). The pollen was extracted in 13 samples (seven in Tozal de Macarullo, three in Tozal de Andre! s, two in El Prao and one in Civiacas II) by the classic chemical method modified, without acetolysis, and concentrated using Thoulet (Dupre! , 1992). Lycopodium spore tablets were added to the samples to calculate the pollen concentration (Stockmarr, 1971). The chronology is constrained by three 14C dates from vegetation charcoals (Miami-USA and Gr.oningen-Holland Laboratories).
4. The archaeological sites In this study we use the same two large palaeoenvironmental units defined by Sopena (1998) (Photo 1).
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* Photo 1. Contact between Peraltilla and Sarinena formations (aerial photo).
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of these morphologies, which can be generalised for the rest of the Ebro Basin, are the dense hydrographic network deeply incised in the terrain and the flat bottom filled in with loamy material, giving them a dugout configuration (Ferrer and Mensua, 1956; Frutos, 1968; Pellicer and Echeverr!ıa, 1989). The majority of these bottoms originally would have had a cradle shape, with a better tie-in to the surrounding hillsides, but they have been modified by human impact. Their contact at the slopes contains large, thick layers of gypsiferous silt with ash horizons. The fossilised remains of human occupation are on the upper part of the hillside accumulations. This is the case at El Prao, an open-air site located in the city limits of Almunia de San Juan (Huesca). The UTM co-ordinates (map n1. 326 of SEG, scale 1:50,000) are 46477.5N and 2716.5E. It was sampled for the palynological study in an existing excavation in settlement, taking only two samples with valid results only at the occupation level. 4.2. Southern units
NORTHERN UNITS
El Prao Tozal de Andrés
SOUTHERN UNITS
Civiacas II Tozal de Macarullo
Fig. 2. Location of settlements in the two palaeoenvironmental units.
Several representative sites (Fig. 2) were chosen for a palynological survey in order to complete the palaeoclimatic sequences proposed up to now (Sopena, 1998; * 1998). Sopena and Pena, 4.1. Northern units The northern units are associated with a NW/SE anticline. The Eocene gypsum at the core is overlain by the sandstone hills of the Peraltilla Formation (Tera! n and Sole! Sabaris, 1968; Rodr!ıguez-Vidal, 1986). The gypsum is easily eroded by physical and chemical processes, facilitated by the difficulty of sustaining a protective vegetation coverage. The dominant features
To the south of the northern group extends a physical relief of greater amplitude with diverse morphologies, which contains the piedmont terrace area and the high terrace environment of the Cinca valley. The piedmont terrace area constitutes an eroded depression covered by Quaternary accumulations (Pleistocene glacis, Holocene fluvial terraces). The isolated hills of this landscape are * shaped on sandstone and marl of the Sarinena Formation (Quirantes, 1969). The sites of Tozal de Andres and Tozal de Macarullo are located on two of these ridges. The geomorphological processes in this area are determined by the structural and lithological characteristics: the hardness of the sandstone, the thickness of the hard stratum, the gradient with respect to the basal areas, and the frailty of the marl. The dominant processes are fissuring, block fall, shifting, and piping. Tozal de Macarullo is an open-air site located on the city limits of Estiche (Huesca). The UTM co-ordinates (map n1. 357 of SEG, scale 1:50,000) are 46338N and 2584.5E. Palynological sampling (Gonza! lez-Sampe! riz, 1998) was performed on ‘‘core II’’ (square 3/5d0 , e0 and f0 ) between two large blocks of sandstone broken off from the summit. Seven samples were obtained with very uniform spectra, since they record a single moment of occupation around 2810+50 BP (B-59999) (Sopena, 1995, 1998; Sopena and Rodane! s, 1992, 1994a, b; Rodane! s and Sopena, 1998). Tozal de Andre! s is also an open-air site, located in the city limits of Ilche (Huesca). The UTM co-ordinates (map n1. 325 of SEG, scale 1:50,000) are 46461N and 2539E. The palynological study (Sopena and Gonza! lezSampe! riz, in press) was carried out in the cut ‘‘E’’ of an excavation already existing in the town, only taking one sample per level. The representative spectrum recorded
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in this site pertains to a landslide event, immediately after the date obtained at the base of the occupation: 2980+50 BP (GrA-5448). The second differentiated area is the high terrace environment located on the left-hand margin of the Cinca River. In this area, the accumulation of terraces reaches its maximum development with ten levels (Bomer, 1979; Alberto et al., 1983; Sancho, 1988, * 1991). In this area, the erosion of the Sarinena Formation by the Cinca River has led to the formation of gravel terraces. The relief of Civiacas II is located in the city limits of Alfantega (Huesca). The UTM coordinates (map n1. 358 of SEG, scale 1:50,000) are 46351.5N and 2645.5E. Since only a part of the ash level has been preserved, it was difficult to obtain a goad sample. In fact, statistically valid results could not be obtained.
5. Results 5.1. El Prao (Almunia de San Juan, Huesca) The ridge where this site is located presents an asymmetrical profile, as the layers remain vertical. The main processes are linear incision and superficial scarring. The construction of a road at the base of the SE slope allowed a ‘‘stratigraphical cut’’ to be observed, from which the samples were taken for palynological analysis (Fig. 3). On top of the ash level (evidence of occupation), there is also a deposit of slope accumulation with archaeological remains that fossilises the entire lower sector of the slope (Fig. 4). This has contributed to its preservation. According to geoarchaeological data, evolutionary phases have been established that, along with the palynological results, allow palaeoenvironmental reconstruction: 1. At a time before occupation at Recent Final Bronze Age, the hill would have had dimensions that are somewhat larger than the current ones, although with a similar morphology. On the SE hillside, there would be a slope accumulation level with material coming from the cornice as well as from the gypsum and mud slopes. It is very probable that at that time, there was already a certain anthropic influence on the vegetation, inherited from the Neolithic. 2. On top of this slope deposit, the pre-historic occupation occurs on its lower section, judging by the levels of ash and remains found in situ. It is probable that it also existed at higher elevations according to construction remains and the material contained in the upper deposit. Man could alter this smooth slope level in preparation to construct dwellings (levelling, terracing), therefore breaking the
balance in the evolutionary dynamics of these hillsides. The herbaceous layer determined from the pollen analysis seems to record an open environment possibly exploited for and by shepherding/branch cutting (Garc!ıa-Ruiz et al., 2000), with abundant heliophytes, nitrouphyles and taxonomic indicators of aridity in notable percentages: Ephedra t.fragilis (6%), Poaceae (6%), Chenopodiaceae (5%), Urticaceae (6%), Malvaceae (4%), Plantago (3%), Rumex, Cichorioideae, Lygeum spartum, Artemisia, Asteroideae, Helianthemum, and Lamiaceae. The tree–shrub composition is absolutely dominated by pine, which tends to be the norm in NE studies of this period (Iriarte, 1996), with lesser Juniperus. The AP group is completed by the presence of Quercus t.ilex, Pistacia and Tamarix (probably associated with a water course or wet ravine). In this case, it seems probable that there is an important correlation between the edaphic determination (gypsum substrate) and the anthropic action of mainly livestock activity according to palynological and archaeological records (Sopena, 1998). 3. After abandonment or destruction of the settlement, a dynamic stage occurs on the hillsides, coinciding with a more humid climate. These new environmental conditions caused a decrease in the size of the ridge as well as a softening of the cornice profile. As a consequence, the archaeological structures and materials started to undergo small movements towards the basal part of the ridge, and fossilisation and partial burying of the remains initially located in the lower sector of SE slope began. It is possible that during this period the anthropic pressure decreased due to the abandonment or destruction of the settlement, causing a certain increase in the vegetation coverage (mainly herbaceous and shrub ground cover). In any case livestock exploitation would probably continue. 4. Coinciding with a drier period, erosive processes would dominate over the accumulative ones. The hillside with archaeological materials would be impacted by the action of ravines, rain, and wind, causing washing away and dismantling of the deposit towards lower elevations, and as a result accelerating the destruction process of the site. The accentuation of these erosive processes would be favoured by the non-existence of a sufficiently developed vegetation layer in order to prevent or diminish their effects. 5. Due to its location, El Prao has been affected by the recent construction of various access roads into the valleys so that many of the remains that we can find today are out of context. Nevertheless, these recent actions have also facilitated locating some ‘‘cuts’’ in the deposits with ash levels and archaeological
Fig. 3. Pollen histogram of reduced data from settlements.
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Fig. 4. Geomorphology sketch of El Prao site.
remains, allowing the hillside accumulation levels after occupation to be identified, since archaeological soundings had not been carried out in this enclave. 5.2. Tozal de Macarullo (Estiche, Huesca) This is a palaeochannel composed of alternating strata of sandstone and marl, forming a structure in tiers and with a frustum profile (Photo 2). The erosion processes left a large quantity of blocks that blanket the hillsides. The sediment that covered the summit has disappeared, retained at the foot. The observation of these processes and taking an archaeological sounding have allowed an evolutionary sequence to be established, with the following phases (Utrilla and Rodane! s,
Photo 2. General view of Tozal de Macarullo site.
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1997; Rodane! s and Sopena, 1998; Sopena, 1998) (Fig. 5): 1. Before the occupation, the summit would have a diameter at least three times as large, presenting an
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abrupt escarpment and surely with some shelter. We can assume that there was a vegetation layer protecting the summits and the slopes. 2. The Recent Bronze Age installation was made along the hillside, creating excavated steps in the terrain at
Fig. 5. Evolution diagram of Tozal de Macarullo site.
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the marl levels and constructing houses arranged in parallel with the contour of the summit. At this time, there already must have existed a deep shelter, possibly enlarged artificially. The results of palynological analysis (see Fig. 3) point to a typically Mediterranean zone with deforested spaces for agricultural–livestock activities (although they are not as clearly shown as the livestock activity in El Prao and the agriculture activity in Tozal de Andre! s). They only seem to record the ‘‘background noise’’ of a few cereals, some Plantago, Chenopodiaceae, Centaurea, Rumex and Artemisia. In any case, it is impossible to estimate the importance of the crops, their extent, and their exact location with respect to the site (Iriarte, 1994). The tree coverage is not as absolutely dominated by Pinus, as at the other sites. Although it is the majority, it shows similar percentage to that of Quercus t.ilex. Greater taxonomic diversity is recorded by the presence of Quercus t.faginea, Oleaceae, Pistacia, Buxus, Viburnum and Juglans. The AP (40%)/NAP (60%) relationship indicates that deforestation is still not devastating, but pine can be overrepresented, and theoretically, if the anthropic action is not measured, the tree–shrub group should be dominant (Gonza! lez-Sampe! riz, 1998). 3. After the Bronze Age, the outermost blocks of the cornice fell, which additionally shifted slightly over the marl base, since slight, basal undulations are observed, indicating spreading or cambering. The outermost block was positioned over one of the excavated houses (‘‘Sondeo II’’). Based on excavation, the house must have been destroyed previously by fire, so it must have already been abandoned. At this time, the summit was very probably occupied, as the ceramics located at the upper part appear younger than those from the houses built in the second phase. With this new occupation, we can assume that the anthropic influence on the environment would continue to increase, making it impossible for the natural development of potential vegetation, which would be more and more restricted. 4. After the Iron Age, the upper part of the site must have been destroyed. The sediments filled the spaces existing between the blocks covering homogeneously the slopes so that the only remains of this late stage are located in sediment ‘‘traps’’ and never in situ. 5. During another period of non-occupation, vegetation expansion occurred on the ridge. The hillsides remained stabilised until very recently, when the incision process began at the base of slopes as well as in the interior of existing sediment traps between the blocks. Fortunately, the position of the shifted blocks, with a slightly pronounced inclination due to the slight incline of a large part of the hillside,
protected the construction remains up to eight rows in situ. Currently, since it is located in a livestock development area, the entire base has been subject to being cut away due to the construction of a road system, which has caused the intensification of the incision and gully formations in the lower part of the ridge so that the remains are subject to a greater level of dispersion. 5.3. Tozal de Andr!es (Ilche, Huesca) Here, the palaeochannel is made up of a single sandstone substrate that forms the summit and rests on a marl-argillaceous base. As at Tozal de Macarullo, the compartmentalisation of the summit has also occurred in blocks shifted towards the slopes due to the mentioned processes (Photo 3). A Recent Bronze Age occupation prior to the shifting has been identified (Rodane! s and Sopena, 1998); afterwards there is an accumulation level with large blocks, with scarce archaeological remains forming a graded hillside. On top of it, there is a second occupation phase, probably from the beginning of the Iron Age (Fig. 6). Most notable from the pollen record (see Fig. 3) of this site (similar to Tozal de Macarullo) are the unusual percentages recorded for Cerealia. Cereal values of around 10–15% indicate a broadly cultivated landscape or the very near presence of crops. The records obtained in Tozal de Macarullo suggest that the crops would be somewhat distant from the place of occupation; nevertheless, the results point to the nearby existence of cereal fields (percentage: 14%) in Tozal de Andres (Iriarte, ! 1994; Lopez Garc!ıa et al., 1997). The accompanying herbaceous layer is typical of agricultural activities and open spaces (Moore and Webb, 1978; Behre, 1981; Dupre! , 1991, 1992; Jalut, 1991) dotted with shrubbery examples in the middle of Mediterranean brushwood: Poaceae, Chenopodiaceae, Cichorioideae, Asphodelus, Artemisia, Centaurea,
Photo 3. View of Tozal de Andr!es site from the top.
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Fig. 6. Stratification cut of Tozal de Andr!es site.
Rumex, Brassicaceae, Plantago and Malvaceae or Pinus, Juniperus, Quercus t.ilex, Pistacia, Rhamnus and Buxus with Lamiaceae, Helianthemum, Rubiacaeae, etc. on the other hand. We want to highlight only the reliable presence of Corylus, logically associated with shaded enclaves and/or edaphic humidity (Valero-Garce! s et al., 1999, 2000).
5.4. Civiacas II (Alfantega, Huesca) Underneath a shifted block of palaeochannel where the site is located (Photo 4), linear incision exposed a natural cut. In its stratigraphy, a home was in situ identified between the natural marls and an occupation level (Photo 5). The results suggest that the climate in the district of ! during the Bronze Age was very similar to the Monzon current one, with arid conditions possibly derived from the seasonal drought that continues to characterise the climate today, where the edaphic substrate and human intervention would have to be added to the intensification of the erosive processes. The palynological analysis of the sites Tozal de Macarullo, Tozal de Andres and El Prao has suggested a landscape similar to what exists today, despite the fact that currently some of the taxonomies are absent within a considerable distance around the settlements.
Photo 4. View of a fossilised ash level (home) at Civiacas site.
6. Landscape evolution Based on the current status of the sites, the palynological analysis, and the geomorphological processes, we can establish a series of fundamental phases that can be correlated to other areas of the Ebro Basin, * et al. (1996a) evolutionary model for following the Pena the Lower Cinca-Segre valley and the Rodane! s and Sopena (1998) model for the Middle Cinca valley.
Photo 5. Details of home at Civiacas.
6.1. Old stages In situ remains prior to the Bronze Age have not been preserved in this area. Neolithic remains have appeared,
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forming part of the material washed away from the ridges occupied during the different chronological stages. It is possible that the Holocene accumulations have fossilised sites prior to the Bronze Age in the lower areas of the hillsides and deep down valleys, so that * 1998). today they are not visible (Sopena and Pena, At some sites, materials have been found from the Ancient Bronze Age, shifted from and included in the base of the debris cone (Sopena, 1998). These are the result of erosional processes, from the same time or a little after the era of these remains, since they contain archaeological materials from the Recent Bronze Age. At a regional level, the information existing on the ancient stages is very scarce, and only deposits between the Neolithic and the Bronze Age have been dated in the * 1996a; basal parts of bottom plain valley fills (Pena, * et al., 1996a, b) without archaeological remains. Pena We cannot compare the pollen record obtained at these sites with others from the time prior to the Bronze Age occupation in this area. However, regional and local studies indicate intense exploitation of the area, although not the first moment of deforestation. In the Middle Cinca valley and Bardenas Reales, for example, it seems that pine was the predominant tree element, accompanied by typical Mediterranean flora. There is evidence for agricultural–livestock activities near the sites. The vegetation throughout the third millennium BP in both areas was a Mediterranean landscape in which the herbaceous stratum predominated as a result of the different economic interests: the need for raw materials, fields and grazing. Iriarte (1994) observed how the installation of a settlement means a reduction in the surrounding tree mass and the consequent increase of open spaces, a part of which would be destined for crops. In Puy Aguila (Bardenas), the vegetation prior to the settlement indicates a landscape dominated by Quercus ilex-coccifera, with Juniperus well represented (Iriarte, 1996). Nevertheless, not even then was the forest fully developed, indicating that there was human intervention in previous periods that resulted in the clearing of the forest mass. Data obtained for the Bronze Age along the Ebro valley, the Cova Punta Farisa (Fraga, Huesca) (Burjachs, 1993); Chaves Cave (Bastara! s, Huesca) and ! Moro’s Cave (Olvena, Huesca) (Lopez Garc!ıa, 1992; ! ! Lopez Garc!ıa and Lopez Sa! ez, 1994); from Majaladares ! Cave (Borja, Zaragoza) (Lopez Garc!ıa, 1992) and from the Aragonese Pyrenees (Montserrat, 1992; Garc!ıa-Ruiz et al., 2000), are in general agreement, in spite of the geographic, topographic, and altitude differences. 6.2. Post-Bronze stage In the two differentiated geomorphologic units, there are common features that suggest the existence of an important slope regularisation stage. They are the
accumulation of fine and coarse detritus, even large blocks, which are the result of strong gravitational activity and sliding processes. Due to the characteristics of the processes and the resulting deposit, we can deduce that this stage is the result of a climatic situation that was more humid than the current one. Starting from the chronologic data obtained, we can place this moment at least during and after the final phases of the Bronze Age, given that the sites from this period are sitting on hillside materials already assignable to the beginnings of this accumulative stage, which were fossilised by the final stages of the accumulation. The resulting morphology is a smooth hillside, with some larger sized blocks protruding. The existence of buildings from the Iron Age located on these regularised hillsides leads us to believe that they were already formed by that time. This regularisation stage is very generalised for the Ebro Basin and Iberian Range as a whole. It is climatically related to the humid phase transitional between the Sub-Boreal to Sub-Atlantic stage, assigning it to the Bronze Age and even post-Iron Age, but always prior to the Iberian (Burillo et al., 1981; Sancho et al., * 1992). 1991; Gutie! rrez and Pena, The vegetation environment reflected in the analyses from some sites of Bardenas, with Iron Age occupations, indicates a strong human impact (Iriarte, 1994, 1996) in the Central Ebro valley. In general terms the situation is the same. The evolution of the different taxonomies testifies to the presence of a degraded arboreal landscape where elements characteristic of an anthropically affected landscape predominate. In Bardenas, the main tree components are Pinus, Quercus t.ilex-coccifera and, to a lesser extent, Juniperus. Along with this type of flora, riparian vegetation is documented, as well as a more or less notable predominance of the herbaceous stratum. It is thus a situation inherited from the Bronze Age and with a more than probable beginning during the Neolithic. 6.3. Iberian–Roman stage Afterwards, a period of strong erosion began, which slowly destroyed the previous accumulations. This degradation process, with some interruptions, has been maintained up to today, and it responds to environmental conditions favouring concentrated over-land flows. It is caused by a combination of a semi-arid climate with concentrated precipitation similar today and hillsides scarcely protected by vegetation due to climatic stress and/or anthropic activity (fire, overgrazing). The eroded materials are dragged down the small ravines to the adjoining lower areas. Logically, the chronological information offered by these remains does not always allow adequate accuracy. Their true age would be indicated by the more recent archaeological material included in them. In the case of Tozal de
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Franche! and Pialfor (in this district), the debris cones contain ceramics from the Bronze and Iberian ages, which give a post-Iberian Age for these accumulative forms (Sopena, 1998). In some sectors, the washed-away material formed bulky accumulations at the bottom of the valleys, giving rise to flat and cradle-bottom morphologies. In other areas of the Ebro basin, debris cones and fill accumulation of valleys have been studied, establishing their chronology as mainly post-Iberian or post-Roman, even reaching dates around the 4th/5th century (Burillo et al., * 1996a, b; Pena * et al., 1996b) for the fill 1981; Pena, accumulation. From a palaeoclimatic point of view, this dry and hot climate stage corresponds to the initial stages of the Sub-Atlantic, although the triggering of the processes must have been caused by the climatic situation as well as the intense degradation of this * 1992, 1998). territory (Gutie! rrez and Pena, The palynological and geomorphological studies * area (playa lakes and Regallo made in the Alcaniz River) (Stevenson et al., 1991) show during the Iberian Period the existence of certain modifications in the vegetation, implying a change towards drier conditions than those observed in previous times. Davis (1994) studied diverse Ebro Basin ‘‘playa lakes’’ * (Alcaniz, Teruel), and also confirmed the existence * during the Iberian period (‘‘Salada Pequena’’ core) of a mild climate with more or less wet winters and dry summers (an increase in the spectra from this analysis of Quercus ilex-coccifera percentages, along with the appearance of other taxonomies of a noticeably Mediterranean nature). This ‘‘climatic improvement’’ with respect to the Bronze Age coincides with an important increase in anthropic activity in this area.
* et al., 1996a; In the Zaragoza plain valleys (Pena * 1996b), and in the Lower Cinca valley (Gutie! rrez Pena, * * and Rodane! s, 1992) hillside and Pena, 1992; Pena formation and filling valley stages are also cited corresponding to the last centuries. Some debris cones such as those situated at the east foot of Morilla Castle (near Tozal de Andres) that contain medieval material (pottery) as well as Bronze Age material also belong to this stage. Likewise, a large part of the fills in the broad piedmont valleys—south units—must belong to this evolutionary moment, also indicated in Hoya de Huesca (Rodr!ıguez Vidal, 1986). In spite of this chronological assignment, some of these accumulations can present an older accumulative base, fossilised by these recent deposits.
6.4. Post-medieval stage
7. Discussion: regional significance
Between this last phase of erosion–accumulation that culminates in the Iberian–Roman era and the present day, when another strong period of erosion favoured for human impact develops, there were stages with alternating geomorphological processes that in general terms had a lesser impact on the landscape but that in some places had considerable importance. Hillside accumulations appear that occupy areas normally oriented towards the south and that have suffered from the intense erosion of the previous stage. The most significant case is Monte Gil II (Sopena, 1998), where two perfectly individualised accumulation stages have been differentiated, with an incision phase between them. Given that they are very recent accumulations, medieval or post-medieval, they inform us about climatic variability at century scale. Although it is difficult to assign a specific origin to them, due to their coincidence with the Little Ice Age (15th–19th centuries), a climatic influence could be significant.
Landscape is the result of the inter-relationship of various factors. Due to their intensity, climatic and anthropic actions can be highlighted. In semi-arid environments, pressure by human beings accentuates the erosive processes resulting from the Mediterranean climate. This human pressure has been growing throughout history. During the Pleistocene, harvesters already formed an active part of the ecosystem (Braidwood, 1960), but exploitation of the environment was so light that it is not evident in pollen records. For this reason, important alterations in the vegetation dynamics in this period are attributed to Quaternary climatic oscillations. Nevertheless, starting from the Neolithic, it is not very clear, fundamentally due to the growing anthropic action. In a broad environment such as the Central-Eastern Mediterranean, some authors (Neboit, 1979; Bruckner, 1986; Van Andel et al., 1986) consider humans the principal protagonist of palaeoenvironmental changes. It seems that the first farmers quickly
6.5. Modern stage The current dynamics are characterised by climatic conditions and human environmental impact conducive to erosive processes (incision, washing away, concentrated over-land flows). They add to the indicated prior incisive stages. The good qualities of the soils and the topography have favoured the construction of irrigation canals, the intensification of technology-enhanced agricultural development, and the construction of a road system. The result is that the base of hills where sites are located has been subject to undercutting and the reduction of its original extent and the increase of the lack of vegetable protection, favouring site erosion, accelerating the concentrated over-land flow and piping processes for the weaker materials and the collapsing of soft blocks by harder ones.
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modified the natural vegetation on the plains and in the mountains, in Northern Europe as well as in the Mediterranean region. So more than climate, agriculture since its appearance is affirmed as the determining factor in the evolution of the vegetational landscape (Jalut, 1991). Other authors consider the supremacy of climatic action over any important change produced to vegetation (Burjachs et al., 1994; Yll et al., 1999) and to the landscape in general (Vita-Finzi, 1969), including Holocene aluvial bottoms (Burillo et al., 1985, * 1992) and slopes (Sancho 1986; Gutie! rrez and Pena, * and Gonza! lez, 1992). Others advocate et al., 1988; Pena the interrelationship of both factors (Neboit, 1983), but without overestimating anthropic action that could ! be considered minimal up until recently (Pantaleon* Cano et al., 1999). The controversy is derived, as Pena (1996a) recently showed, from the similarity between the processes of erosive degradation of the environment due to natural causes (torrential rains and scarce vegetable protection on hillsides) and those generated after human intervention eliminating that protection (fields, grazing, deforestation, raw materials and others). The protagonist role that the climate seems to acquire over the landscape evolution has also been detected on reduced scales, specifically on the areas where the sites are established. As a consequence accumulative deposits form on the hillsides (gravity movements, rotation, solifluction), on bottom areas (debris cores) or in the surrounding valleys (fills, flows), and as erosive features (carcaves, incisions, piping), occur contributing to the deterioration and decontextualisation of archaeological remains. The climatic factors by themselves do not seem to explain the key features and profound transformations suffered by this landscape. More likely, they have been the response to the changes activated by human impact as has been pointed out for the entire Mediterranean environment (Bintliff, 1992). It seems clear that deforestation since the Neolithic period has given rise to spaces of difficult bio-edaphic recovery. Different erosive agents have dismantled the soils, and they have been the main source of sediments that currently fill the bottoms of the depressions and plain valleys. These areas have become irrigated, cleared, deforested, and burned for logging. These main agents of environmental degradation have produced impoverished soils, the alteration of hydraulic routes, and decreased vegetation. What we can point out is that human communities since the Neolithic have taken much advantage of the environment. The natural vegetation has been harvested in order to collect acorns and other fruits, the fields for grazing; the plains of the most fertile soils, for crops; perhaps around ravines or rivers to plant orchards or other products more demanding of water, reserving the
drier areas for cereals and dry-farming trees (Dupre! , 1988). All of this would modify the landscape in a sufficiently considerable way to be recorded in the pollen rains of the time. Consequently, some of the observed changes in pollen should not be attributed (at least exclusively) to climatic action. Chronologically, in the entire Ebro Basin environment, several phases of accumulation and incision stages have been identified (post-Bronze regularisation, Iberian–Roman incision, Medieval accumulative–incisive stage and Actual incision). The importance that the ‘‘climatic factor’’ would have had on the mentioned sites, if without any human intervention in the exploitation of the environment, is still subject to debate. From a climatic point of view, these phases are a consequence of the occurrence of dry and wet periods. Thus, the evolution of the landscape in the Ebro Basin in relation to the human occupation during the Upper Holocene is explained by a succession of dynamic changes. These fluctuations would have been due to a combination of climatic conditions conducive to the triggering of erosive processes, along with the strengthening of them by humans due to their intervention in the environment. This study has verified a landscape transformation, and analysed the processes and their evolution, particularly the climate and the impact of the human factor throughout history on the environment. The human presence at different times has not only served to ‘‘date’’ such processes, but also to evaluate their impact on the sites and their environment. The climatic conclusions that have been made according to the resulting morphologies of the processes have allowed the archaeological contexts to be more accurately evaluated.
Acknowledgements We have to state our acknowledgements to persons and institutions that have collaborated in development of this study: Instituto de Estudios Altoaragoneses ! (IEA) for projects ‘‘Estudio geoarqueologico de los yacimientos de la Edad del Bronce de la Comarca de ! Monzon’’ and ‘‘Estudio paleoambiental aplicado a la ! paleoclimatica ! ! reconstruccion en medios mediterraneos’’ and also to the Diputacion General de Aragon (DGA) for financial support to Laboratorio de Ciencias ! Historico-Geogr a! ficas (University of Zaragoza) and to Instituto Pirenaico de Ecolog!ıa (CSIC) for palynological * analysis. We are grateful to Jose! Luis Pena-Monn e! , Catedra! tico of Physical Geography (University of Zaragoza) and to Blas Valero-Garce! s, research of IPE-CSIC (Pyrenean Institute of Ecology), for their very thoughtful ideas and opinions.
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Recent Holocene palaeoenvironmental evolution in the central Ebro Basin (NE Spain) P. Gonza! lez-Sampe! riza,*, M.C. Sopena Vicie! nb a b
Instituto Pirenaico de Ecolog!ıa (CSIC), Campus de Aula Dei, Apdo 202, 50.080 Zaragoza, Spain Area de Prehistoria (F.F. y Letras) C/Pedro Cerbuna, 12. 50.009 Universidad de Zaragoza, Spain
Abstract Evolutionary aspects of landscape are analysed from the geomorphological, palynological and archaeological study of a sector in the Central Ebro Basin (NE Spain). In this study we use four representative sites, each of them offering different information about the evolution of the landscape in which they are located. Together, the data allow for the reconstruction of general patterns concerning the Holocene palaeoenvironmental evolution, erosion processes and their genetic interpretation. Climatic factors alone do not explain the key features and profound transformations suffered by this landscape. More likely, they have been the response to the changes activated by human impact. Deforestation since the Neolithic period has given rise to spaces of difficult bio-edaphic recovery. Different erosive agents have been the main source of sediments that currently fill the bottoms of the depressions and plain valleys. Human communities since the Neolithic have modified the landscape sufficiently to be recorded palynologically. Several phases of accumulation and incision stages have been identified (post-Bronze regularisation, Iberian– Roman incision, Medieval accumulative–incisive stage and Actual incision). The importance that the ‘‘climatic factor’’ would have had on the mentioned sites, if without any human intervention in the exploitation of the environment, is still subject to debate. From a climatic point of view, these phases are a consequence of the occurrence of dry and wet periods. Thus, the evolution of the landscape in the Ebro Basin in relation to the human occupation during the Upper Holocene is explained by a succession of dynamic changes. These fluctuations would have been due to a combination of climatic conditions conducive to the triggering of erosive processes, along with the strengthening of them by humans due to their intervention in the environment. r 2002 Elsevier Science Ltd and INQUA. All rights reserved.
1. Introduction Recent geoarchaeological studies on various Bronze ! or Middle Cinca Age sites in the district of Monzon (Sopena, 1998), have demonstrated profound transformations of the semi-arid environment. The sites located on the plains either had been fossilised by Recent Holocene deposits or had been affected by anthropic actions. The sites at the summits of small hills had been practically levelled and those located initially on the hillsides were affected by the active dynamics of the slopes. The results obtained from that study allowed a first estimate of the environmental characteristics in the Bronze Age and their evolution up to the present day, with archaeological data and palynological results of the Tozal de Macarullo site (Gonza! lez-Sampe! riz, 1998).
Interest in understanding the paleoenvironmental evolution of the different geomorphological environments of the Central Ebro Basin led to a complete survey combining geoarchaeological and palynological strategies. The aim sought in this work has been to merge geoarchaeological and palynological data in various sites (Tozal de Macarullo, Tozal de Andres, Civiacas II and El Prao, Huesca, Spain). The goals are to characterise the environment during occupation, to determine their changes and evolution and to analyse the causes that have determined the geomorphological processes. Therefore, our research evaluates the level of environmental change and of landscape modification that human impact as well as the climate could have had since the Bronze Age in the Middle Cinca River area.
2. Geographic setting *Corresponding author. E-mail address: [email protected] (P. Gonz!alez-Samp!eriz).
The area is located in the Central Ebro Basin (Fig. 1) infilled with continental Tertiary materials (Tera! n and
1040-6182/02/$ - see front matter r 2002 Elsevier Science Ltd and INQUA. All rights reserved. PII: S 1 0 4 0 - 6 1 8 2 ( 0 2 ) 0 0 0 1 6 - 2
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Fig. 1. General situation of the study area.
* Sole! Sabaris, 1968; Vinuales and Vericad, 1996). Due to its geographical location, the climate is Mediterranean. However, since it is enclosed by mountain systems, the climate adopts continental traits: aridity, deficit rain (400 mm), drying winds (cierzo), high insolation, elevated nocturnal radiation, and strong annual and daily thermal oscillation. The resulting climate can be defined as semiarid Mediterranean (Biel and Garc!ıa de Pedraza, 1962) with 800–900 mm of potential evapotranspiration (Thornthwaite, 1948). The characteristic soils are calcareous Fluvisoils developed over recent alluvial deposits and without well-differentiated profiles. This zone is located in the chorological province of Aragonese vegetation, the Somontano Aragonese sector, a meso-Mediterranean floor with a dry local climate. The potential vegetation would be a forest of Quercus rotundifolia and Pinus halepensis with sclerophyllous scrub such as Quercus coccifera, Rhamnus alaternus, and Rhamnus lycioides that replace holm oak groves with Juniperus phoenicea, Juniperus oxycedrus, Daphne gnidium, Jasminum fruticans and Retama sphaerocarpa. Greater degradation gives rise to an open underbrush scrubland of heliophytes (Genista scorpius, Teucrium capitanum, Rosmarinus officinalis, Thymus vulgaris, Lavandula latifolia, Helianthemum rubellum, etc.). The most extreme stage is made up of gramineous communities with Brachypodium ramosum, Lygeum spartum or Stipa tenacissima (Braun Blanquet and de Bolos, 1957; Peinado Lorca and Rivas-Mart!ınez, 1987). The riparian vegetation, of great ecological importance and a protector against hastened erosion, has been eliminated for the most part. Today, the surrounding areas of the sites, on the fringes of poor and open scrubland, reflect considerable dry-land agricultural development.
3. Methods The environmental dynamics is a result of physical processes. Study of natural and anthropological deposits allows identification of some of those processes, to associate them with climatic characteristics and/or specific human actions, and to date them. In Mediterranean areas, as there is great topographical, edaphological and climatic heterogeneity, it is difficult to establish valid models of environmental dynamics for extensive areas, so multidisciplinary studies are indispensable. Areas where populations have traditionally concentrated (mainly since the Neolithic period) contain abundant sites. They form part of the landscape, so any modification to the physical features will affect these sites (Burillo et al., 1984; Ru!ız-Zapatero and Burillo, 1988). Additionally, since these are deposits of anthropic origin, they are very appropriate for attempting to establish the magnitude and transcendence of the processes linked to human presence (Dupre! and Renault-Miskovsky, 1990; Gonza! lez-Sampe! riz, 1999). The pollen was extracted in 13 samples (seven in Tozal de Macarullo, three in Tozal de Andre! s, two in El Prao and one in Civiacas II) by the classic chemical method modified, without acetolysis, and concentrated using Thoulet (Dupre! , 1992). Lycopodium spore tablets were added to the samples to calculate the pollen concentration (Stockmarr, 1971). The chronology is constrained by three 14C dates from vegetation charcoals (Miami-USA and Gr.oningen-Holland Laboratories).
4. The archaeological sites In this study we use the same two large palaeoenvironmental units defined by Sopena (1998) (Photo 1).
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* Photo 1. Contact between Peraltilla and Sarinena formations (aerial photo).
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of these morphologies, which can be generalised for the rest of the Ebro Basin, are the dense hydrographic network deeply incised in the terrain and the flat bottom filled in with loamy material, giving them a dugout configuration (Ferrer and Mensua, 1956; Frutos, 1968; Pellicer and Echeverr!ıa, 1989). The majority of these bottoms originally would have had a cradle shape, with a better tie-in to the surrounding hillsides, but they have been modified by human impact. Their contact at the slopes contains large, thick layers of gypsiferous silt with ash horizons. The fossilised remains of human occupation are on the upper part of the hillside accumulations. This is the case at El Prao, an open-air site located in the city limits of Almunia de San Juan (Huesca). The UTM co-ordinates (map n1. 326 of SEG, scale 1:50,000) are 46477.5N and 2716.5E. It was sampled for the palynological study in an existing excavation in settlement, taking only two samples with valid results only at the occupation level. 4.2. Southern units
NORTHERN UNITS
El Prao Tozal de Andrés
SOUTHERN UNITS
Civiacas II Tozal de Macarullo
Fig. 2. Location of settlements in the two palaeoenvironmental units.
Several representative sites (Fig. 2) were chosen for a palynological survey in order to complete the palaeoclimatic sequences proposed up to now (Sopena, 1998; * 1998). Sopena and Pena, 4.1. Northern units The northern units are associated with a NW/SE anticline. The Eocene gypsum at the core is overlain by the sandstone hills of the Peraltilla Formation (Tera! n and Sole! Sabaris, 1968; Rodr!ıguez-Vidal, 1986). The gypsum is easily eroded by physical and chemical processes, facilitated by the difficulty of sustaining a protective vegetation coverage. The dominant features
To the south of the northern group extends a physical relief of greater amplitude with diverse morphologies, which contains the piedmont terrace area and the high terrace environment of the Cinca valley. The piedmont terrace area constitutes an eroded depression covered by Quaternary accumulations (Pleistocene glacis, Holocene fluvial terraces). The isolated hills of this landscape are * shaped on sandstone and marl of the Sarinena Formation (Quirantes, 1969). The sites of Tozal de Andres and Tozal de Macarullo are located on two of these ridges. The geomorphological processes in this area are determined by the structural and lithological characteristics: the hardness of the sandstone, the thickness of the hard stratum, the gradient with respect to the basal areas, and the frailty of the marl. The dominant processes are fissuring, block fall, shifting, and piping. Tozal de Macarullo is an open-air site located on the city limits of Estiche (Huesca). The UTM co-ordinates (map n1. 357 of SEG, scale 1:50,000) are 46338N and 2584.5E. Palynological sampling (Gonza! lez-Sampe! riz, 1998) was performed on ‘‘core II’’ (square 3/5d0 , e0 and f0 ) between two large blocks of sandstone broken off from the summit. Seven samples were obtained with very uniform spectra, since they record a single moment of occupation around 2810+50 BP (B-59999) (Sopena, 1995, 1998; Sopena and Rodane! s, 1992, 1994a, b; Rodane! s and Sopena, 1998). Tozal de Andre! s is also an open-air site, located in the city limits of Ilche (Huesca). The UTM co-ordinates (map n1. 325 of SEG, scale 1:50,000) are 46461N and 2539E. The palynological study (Sopena and Gonza! lezSampe! riz, in press) was carried out in the cut ‘‘E’’ of an excavation already existing in the town, only taking one sample per level. The representative spectrum recorded
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in this site pertains to a landslide event, immediately after the date obtained at the base of the occupation: 2980+50 BP (GrA-5448). The second differentiated area is the high terrace environment located on the left-hand margin of the Cinca River. In this area, the accumulation of terraces reaches its maximum development with ten levels (Bomer, 1979; Alberto et al., 1983; Sancho, 1988, * 1991). In this area, the erosion of the Sarinena Formation by the Cinca River has led to the formation of gravel terraces. The relief of Civiacas II is located in the city limits of Alfantega (Huesca). The UTM coordinates (map n1. 358 of SEG, scale 1:50,000) are 46351.5N and 2645.5E. Since only a part of the ash level has been preserved, it was difficult to obtain a goad sample. In fact, statistically valid results could not be obtained.
5. Results 5.1. El Prao (Almunia de San Juan, Huesca) The ridge where this site is located presents an asymmetrical profile, as the layers remain vertical. The main processes are linear incision and superficial scarring. The construction of a road at the base of the SE slope allowed a ‘‘stratigraphical cut’’ to be observed, from which the samples were taken for palynological analysis (Fig. 3). On top of the ash level (evidence of occupation), there is also a deposit of slope accumulation with archaeological remains that fossilises the entire lower sector of the slope (Fig. 4). This has contributed to its preservation. According to geoarchaeological data, evolutionary phases have been established that, along with the palynological results, allow palaeoenvironmental reconstruction: 1. At a time before occupation at Recent Final Bronze Age, the hill would have had dimensions that are somewhat larger than the current ones, although with a similar morphology. On the SE hillside, there would be a slope accumulation level with material coming from the cornice as well as from the gypsum and mud slopes. It is very probable that at that time, there was already a certain anthropic influence on the vegetation, inherited from the Neolithic. 2. On top of this slope deposit, the pre-historic occupation occurs on its lower section, judging by the levels of ash and remains found in situ. It is probable that it also existed at higher elevations according to construction remains and the material contained in the upper deposit. Man could alter this smooth slope level in preparation to construct dwellings (levelling, terracing), therefore breaking the
balance in the evolutionary dynamics of these hillsides. The herbaceous layer determined from the pollen analysis seems to record an open environment possibly exploited for and by shepherding/branch cutting (Garc!ıa-Ruiz et al., 2000), with abundant heliophytes, nitrouphyles and taxonomic indicators of aridity in notable percentages: Ephedra t.fragilis (6%), Poaceae (6%), Chenopodiaceae (5%), Urticaceae (6%), Malvaceae (4%), Plantago (3%), Rumex, Cichorioideae, Lygeum spartum, Artemisia, Asteroideae, Helianthemum, and Lamiaceae. The tree–shrub composition is absolutely dominated by pine, which tends to be the norm in NE studies of this period (Iriarte, 1996), with lesser Juniperus. The AP group is completed by the presence of Quercus t.ilex, Pistacia and Tamarix (probably associated with a water course or wet ravine). In this case, it seems probable that there is an important correlation between the edaphic determination (gypsum substrate) and the anthropic action of mainly livestock activity according to palynological and archaeological records (Sopena, 1998). 3. After abandonment or destruction of the settlement, a dynamic stage occurs on the hillsides, coinciding with a more humid climate. These new environmental conditions caused a decrease in the size of the ridge as well as a softening of the cornice profile. As a consequence, the archaeological structures and materials started to undergo small movements towards the basal part of the ridge, and fossilisation and partial burying of the remains initially located in the lower sector of SE slope began. It is possible that during this period the anthropic pressure decreased due to the abandonment or destruction of the settlement, causing a certain increase in the vegetation coverage (mainly herbaceous and shrub ground cover). In any case livestock exploitation would probably continue. 4. Coinciding with a drier period, erosive processes would dominate over the accumulative ones. The hillside with archaeological materials would be impacted by the action of ravines, rain, and wind, causing washing away and dismantling of the deposit towards lower elevations, and as a result accelerating the destruction process of the site. The accentuation of these erosive processes would be favoured by the non-existence of a sufficiently developed vegetation layer in order to prevent or diminish their effects. 5. Due to its location, El Prao has been affected by the recent construction of various access roads into the valleys so that many of the remains that we can find today are out of context. Nevertheless, these recent actions have also facilitated locating some ‘‘cuts’’ in the deposits with ash levels and archaeological
Fig. 3. Pollen histogram of reduced data from settlements.
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Fig. 4. Geomorphology sketch of El Prao site.
remains, allowing the hillside accumulation levels after occupation to be identified, since archaeological soundings had not been carried out in this enclave. 5.2. Tozal de Macarullo (Estiche, Huesca) This is a palaeochannel composed of alternating strata of sandstone and marl, forming a structure in tiers and with a frustum profile (Photo 2). The erosion processes left a large quantity of blocks that blanket the hillsides. The sediment that covered the summit has disappeared, retained at the foot. The observation of these processes and taking an archaeological sounding have allowed an evolutionary sequence to be established, with the following phases (Utrilla and Rodane! s,
Photo 2. General view of Tozal de Macarullo site.
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1997; Rodane! s and Sopena, 1998; Sopena, 1998) (Fig. 5): 1. Before the occupation, the summit would have a diameter at least three times as large, presenting an
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abrupt escarpment and surely with some shelter. We can assume that there was a vegetation layer protecting the summits and the slopes. 2. The Recent Bronze Age installation was made along the hillside, creating excavated steps in the terrain at
Fig. 5. Evolution diagram of Tozal de Macarullo site.
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the marl levels and constructing houses arranged in parallel with the contour of the summit. At this time, there already must have existed a deep shelter, possibly enlarged artificially. The results of palynological analysis (see Fig. 3) point to a typically Mediterranean zone with deforested spaces for agricultural–livestock activities (although they are not as clearly shown as the livestock activity in El Prao and the agriculture activity in Tozal de Andre! s). They only seem to record the ‘‘background noise’’ of a few cereals, some Plantago, Chenopodiaceae, Centaurea, Rumex and Artemisia. In any case, it is impossible to estimate the importance of the crops, their extent, and their exact location with respect to the site (Iriarte, 1994). The tree coverage is not as absolutely dominated by Pinus, as at the other sites. Although it is the majority, it shows similar percentage to that of Quercus t.ilex. Greater taxonomic diversity is recorded by the presence of Quercus t.faginea, Oleaceae, Pistacia, Buxus, Viburnum and Juglans. The AP (40%)/NAP (60%) relationship indicates that deforestation is still not devastating, but pine can be overrepresented, and theoretically, if the anthropic action is not measured, the tree–shrub group should be dominant (Gonza! lez-Sampe! riz, 1998). 3. After the Bronze Age, the outermost blocks of the cornice fell, which additionally shifted slightly over the marl base, since slight, basal undulations are observed, indicating spreading or cambering. The outermost block was positioned over one of the excavated houses (‘‘Sondeo II’’). Based on excavation, the house must have been destroyed previously by fire, so it must have already been abandoned. At this time, the summit was very probably occupied, as the ceramics located at the upper part appear younger than those from the houses built in the second phase. With this new occupation, we can assume that the anthropic influence on the environment would continue to increase, making it impossible for the natural development of potential vegetation, which would be more and more restricted. 4. After the Iron Age, the upper part of the site must have been destroyed. The sediments filled the spaces existing between the blocks covering homogeneously the slopes so that the only remains of this late stage are located in sediment ‘‘traps’’ and never in situ. 5. During another period of non-occupation, vegetation expansion occurred on the ridge. The hillsides remained stabilised until very recently, when the incision process began at the base of slopes as well as in the interior of existing sediment traps between the blocks. Fortunately, the position of the shifted blocks, with a slightly pronounced inclination due to the slight incline of a large part of the hillside,
protected the construction remains up to eight rows in situ. Currently, since it is located in a livestock development area, the entire base has been subject to being cut away due to the construction of a road system, which has caused the intensification of the incision and gully formations in the lower part of the ridge so that the remains are subject to a greater level of dispersion. 5.3. Tozal de Andr!es (Ilche, Huesca) Here, the palaeochannel is made up of a single sandstone substrate that forms the summit and rests on a marl-argillaceous base. As at Tozal de Macarullo, the compartmentalisation of the summit has also occurred in blocks shifted towards the slopes due to the mentioned processes (Photo 3). A Recent Bronze Age occupation prior to the shifting has been identified (Rodane! s and Sopena, 1998); afterwards there is an accumulation level with large blocks, with scarce archaeological remains forming a graded hillside. On top of it, there is a second occupation phase, probably from the beginning of the Iron Age (Fig. 6). Most notable from the pollen record (see Fig. 3) of this site (similar to Tozal de Macarullo) are the unusual percentages recorded for Cerealia. Cereal values of around 10–15% indicate a broadly cultivated landscape or the very near presence of crops. The records obtained in Tozal de Macarullo suggest that the crops would be somewhat distant from the place of occupation; nevertheless, the results point to the nearby existence of cereal fields (percentage: 14%) in Tozal de Andres (Iriarte, ! 1994; Lopez Garc!ıa et al., 1997). The accompanying herbaceous layer is typical of agricultural activities and open spaces (Moore and Webb, 1978; Behre, 1981; Dupre! , 1991, 1992; Jalut, 1991) dotted with shrubbery examples in the middle of Mediterranean brushwood: Poaceae, Chenopodiaceae, Cichorioideae, Asphodelus, Artemisia, Centaurea,
Photo 3. View of Tozal de Andr!es site from the top.
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Fig. 6. Stratification cut of Tozal de Andr!es site.
Rumex, Brassicaceae, Plantago and Malvaceae or Pinus, Juniperus, Quercus t.ilex, Pistacia, Rhamnus and Buxus with Lamiaceae, Helianthemum, Rubiacaeae, etc. on the other hand. We want to highlight only the reliable presence of Corylus, logically associated with shaded enclaves and/or edaphic humidity (Valero-Garce! s et al., 1999, 2000).
5.4. Civiacas II (Alfantega, Huesca) Underneath a shifted block of palaeochannel where the site is located (Photo 4), linear incision exposed a natural cut. In its stratigraphy, a home was in situ identified between the natural marls and an occupation level (Photo 5). The results suggest that the climate in the district of ! during the Bronze Age was very similar to the Monzon current one, with arid conditions possibly derived from the seasonal drought that continues to characterise the climate today, where the edaphic substrate and human intervention would have to be added to the intensification of the erosive processes. The palynological analysis of the sites Tozal de Macarullo, Tozal de Andres and El Prao has suggested a landscape similar to what exists today, despite the fact that currently some of the taxonomies are absent within a considerable distance around the settlements.
Photo 4. View of a fossilised ash level (home) at Civiacas site.
6. Landscape evolution Based on the current status of the sites, the palynological analysis, and the geomorphological processes, we can establish a series of fundamental phases that can be correlated to other areas of the Ebro Basin, * et al. (1996a) evolutionary model for following the Pena the Lower Cinca-Segre valley and the Rodane! s and Sopena (1998) model for the Middle Cinca valley.
Photo 5. Details of home at Civiacas.
6.1. Old stages In situ remains prior to the Bronze Age have not been preserved in this area. Neolithic remains have appeared,
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forming part of the material washed away from the ridges occupied during the different chronological stages. It is possible that the Holocene accumulations have fossilised sites prior to the Bronze Age in the lower areas of the hillsides and deep down valleys, so that * 1998). today they are not visible (Sopena and Pena, At some sites, materials have been found from the Ancient Bronze Age, shifted from and included in the base of the debris cone (Sopena, 1998). These are the result of erosional processes, from the same time or a little after the era of these remains, since they contain archaeological materials from the Recent Bronze Age. At a regional level, the information existing on the ancient stages is very scarce, and only deposits between the Neolithic and the Bronze Age have been dated in the * 1996a; basal parts of bottom plain valley fills (Pena, * et al., 1996a, b) without archaeological remains. Pena We cannot compare the pollen record obtained at these sites with others from the time prior to the Bronze Age occupation in this area. However, regional and local studies indicate intense exploitation of the area, although not the first moment of deforestation. In the Middle Cinca valley and Bardenas Reales, for example, it seems that pine was the predominant tree element, accompanied by typical Mediterranean flora. There is evidence for agricultural–livestock activities near the sites. The vegetation throughout the third millennium BP in both areas was a Mediterranean landscape in which the herbaceous stratum predominated as a result of the different economic interests: the need for raw materials, fields and grazing. Iriarte (1994) observed how the installation of a settlement means a reduction in the surrounding tree mass and the consequent increase of open spaces, a part of which would be destined for crops. In Puy Aguila (Bardenas), the vegetation prior to the settlement indicates a landscape dominated by Quercus ilex-coccifera, with Juniperus well represented (Iriarte, 1996). Nevertheless, not even then was the forest fully developed, indicating that there was human intervention in previous periods that resulted in the clearing of the forest mass. Data obtained for the Bronze Age along the Ebro valley, the Cova Punta Farisa (Fraga, Huesca) (Burjachs, 1993); Chaves Cave (Bastara! s, Huesca) and ! Moro’s Cave (Olvena, Huesca) (Lopez Garc!ıa, 1992; ! ! Lopez Garc!ıa and Lopez Sa! ez, 1994); from Majaladares ! Cave (Borja, Zaragoza) (Lopez Garc!ıa, 1992) and from the Aragonese Pyrenees (Montserrat, 1992; Garc!ıa-Ruiz et al., 2000), are in general agreement, in spite of the geographic, topographic, and altitude differences. 6.2. Post-Bronze stage In the two differentiated geomorphologic units, there are common features that suggest the existence of an important slope regularisation stage. They are the
accumulation of fine and coarse detritus, even large blocks, which are the result of strong gravitational activity and sliding processes. Due to the characteristics of the processes and the resulting deposit, we can deduce that this stage is the result of a climatic situation that was more humid than the current one. Starting from the chronologic data obtained, we can place this moment at least during and after the final phases of the Bronze Age, given that the sites from this period are sitting on hillside materials already assignable to the beginnings of this accumulative stage, which were fossilised by the final stages of the accumulation. The resulting morphology is a smooth hillside, with some larger sized blocks protruding. The existence of buildings from the Iron Age located on these regularised hillsides leads us to believe that they were already formed by that time. This regularisation stage is very generalised for the Ebro Basin and Iberian Range as a whole. It is climatically related to the humid phase transitional between the Sub-Boreal to Sub-Atlantic stage, assigning it to the Bronze Age and even post-Iron Age, but always prior to the Iberian (Burillo et al., 1981; Sancho et al., * 1992). 1991; Gutie! rrez and Pena, The vegetation environment reflected in the analyses from some sites of Bardenas, with Iron Age occupations, indicates a strong human impact (Iriarte, 1994, 1996) in the Central Ebro valley. In general terms the situation is the same. The evolution of the different taxonomies testifies to the presence of a degraded arboreal landscape where elements characteristic of an anthropically affected landscape predominate. In Bardenas, the main tree components are Pinus, Quercus t.ilex-coccifera and, to a lesser extent, Juniperus. Along with this type of flora, riparian vegetation is documented, as well as a more or less notable predominance of the herbaceous stratum. It is thus a situation inherited from the Bronze Age and with a more than probable beginning during the Neolithic. 6.3. Iberian–Roman stage Afterwards, a period of strong erosion began, which slowly destroyed the previous accumulations. This degradation process, with some interruptions, has been maintained up to today, and it responds to environmental conditions favouring concentrated over-land flows. It is caused by a combination of a semi-arid climate with concentrated precipitation similar today and hillsides scarcely protected by vegetation due to climatic stress and/or anthropic activity (fire, overgrazing). The eroded materials are dragged down the small ravines to the adjoining lower areas. Logically, the chronological information offered by these remains does not always allow adequate accuracy. Their true age would be indicated by the more recent archaeological material included in them. In the case of Tozal de
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Franche! and Pialfor (in this district), the debris cones contain ceramics from the Bronze and Iberian ages, which give a post-Iberian Age for these accumulative forms (Sopena, 1998). In some sectors, the washed-away material formed bulky accumulations at the bottom of the valleys, giving rise to flat and cradle-bottom morphologies. In other areas of the Ebro basin, debris cones and fill accumulation of valleys have been studied, establishing their chronology as mainly post-Iberian or post-Roman, even reaching dates around the 4th/5th century (Burillo et al., * 1996a, b; Pena * et al., 1996b) for the fill 1981; Pena, accumulation. From a palaeoclimatic point of view, this dry and hot climate stage corresponds to the initial stages of the Sub-Atlantic, although the triggering of the processes must have been caused by the climatic situation as well as the intense degradation of this * 1992, 1998). territory (Gutie! rrez and Pena, The palynological and geomorphological studies * area (playa lakes and Regallo made in the Alcaniz River) (Stevenson et al., 1991) show during the Iberian Period the existence of certain modifications in the vegetation, implying a change towards drier conditions than those observed in previous times. Davis (1994) studied diverse Ebro Basin ‘‘playa lakes’’ * (Alcaniz, Teruel), and also confirmed the existence * during the Iberian period (‘‘Salada Pequena’’ core) of a mild climate with more or less wet winters and dry summers (an increase in the spectra from this analysis of Quercus ilex-coccifera percentages, along with the appearance of other taxonomies of a noticeably Mediterranean nature). This ‘‘climatic improvement’’ with respect to the Bronze Age coincides with an important increase in anthropic activity in this area.
* et al., 1996a; In the Zaragoza plain valleys (Pena * 1996b), and in the Lower Cinca valley (Gutie! rrez Pena, * * and Rodane! s, 1992) hillside and Pena, 1992; Pena formation and filling valley stages are also cited corresponding to the last centuries. Some debris cones such as those situated at the east foot of Morilla Castle (near Tozal de Andres) that contain medieval material (pottery) as well as Bronze Age material also belong to this stage. Likewise, a large part of the fills in the broad piedmont valleys—south units—must belong to this evolutionary moment, also indicated in Hoya de Huesca (Rodr!ıguez Vidal, 1986). In spite of this chronological assignment, some of these accumulations can present an older accumulative base, fossilised by these recent deposits.
6.4. Post-medieval stage
7. Discussion: regional significance
Between this last phase of erosion–accumulation that culminates in the Iberian–Roman era and the present day, when another strong period of erosion favoured for human impact develops, there were stages with alternating geomorphological processes that in general terms had a lesser impact on the landscape but that in some places had considerable importance. Hillside accumulations appear that occupy areas normally oriented towards the south and that have suffered from the intense erosion of the previous stage. The most significant case is Monte Gil II (Sopena, 1998), where two perfectly individualised accumulation stages have been differentiated, with an incision phase between them. Given that they are very recent accumulations, medieval or post-medieval, they inform us about climatic variability at century scale. Although it is difficult to assign a specific origin to them, due to their coincidence with the Little Ice Age (15th–19th centuries), a climatic influence could be significant.
Landscape is the result of the inter-relationship of various factors. Due to their intensity, climatic and anthropic actions can be highlighted. In semi-arid environments, pressure by human beings accentuates the erosive processes resulting from the Mediterranean climate. This human pressure has been growing throughout history. During the Pleistocene, harvesters already formed an active part of the ecosystem (Braidwood, 1960), but exploitation of the environment was so light that it is not evident in pollen records. For this reason, important alterations in the vegetation dynamics in this period are attributed to Quaternary climatic oscillations. Nevertheless, starting from the Neolithic, it is not very clear, fundamentally due to the growing anthropic action. In a broad environment such as the Central-Eastern Mediterranean, some authors (Neboit, 1979; Bruckner, 1986; Van Andel et al., 1986) consider humans the principal protagonist of palaeoenvironmental changes. It seems that the first farmers quickly
6.5. Modern stage The current dynamics are characterised by climatic conditions and human environmental impact conducive to erosive processes (incision, washing away, concentrated over-land flows). They add to the indicated prior incisive stages. The good qualities of the soils and the topography have favoured the construction of irrigation canals, the intensification of technology-enhanced agricultural development, and the construction of a road system. The result is that the base of hills where sites are located has been subject to undercutting and the reduction of its original extent and the increase of the lack of vegetable protection, favouring site erosion, accelerating the concentrated over-land flow and piping processes for the weaker materials and the collapsing of soft blocks by harder ones.
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modified the natural vegetation on the plains and in the mountains, in Northern Europe as well as in the Mediterranean region. So more than climate, agriculture since its appearance is affirmed as the determining factor in the evolution of the vegetational landscape (Jalut, 1991). Other authors consider the supremacy of climatic action over any important change produced to vegetation (Burjachs et al., 1994; Yll et al., 1999) and to the landscape in general (Vita-Finzi, 1969), including Holocene aluvial bottoms (Burillo et al., 1985, * 1992) and slopes (Sancho 1986; Gutie! rrez and Pena, * and Gonza! lez, 1992). Others advocate et al., 1988; Pena the interrelationship of both factors (Neboit, 1983), but without overestimating anthropic action that could ! be considered minimal up until recently (Pantaleon* Cano et al., 1999). The controversy is derived, as Pena (1996a) recently showed, from the similarity between the processes of erosive degradation of the environment due to natural causes (torrential rains and scarce vegetable protection on hillsides) and those generated after human intervention eliminating that protection (fields, grazing, deforestation, raw materials and others). The protagonist role that the climate seems to acquire over the landscape evolution has also been detected on reduced scales, specifically on the areas where the sites are established. As a consequence accumulative deposits form on the hillsides (gravity movements, rotation, solifluction), on bottom areas (debris cores) or in the surrounding valleys (fills, flows), and as erosive features (carcaves, incisions, piping), occur contributing to the deterioration and decontextualisation of archaeological remains. The climatic factors by themselves do not seem to explain the key features and profound transformations suffered by this landscape. More likely, they have been the response to the changes activated by human impact as has been pointed out for the entire Mediterranean environment (Bintliff, 1992). It seems clear that deforestation since the Neolithic period has given rise to spaces of difficult bio-edaphic recovery. Different erosive agents have dismantled the soils, and they have been the main source of sediments that currently fill the bottoms of the depressions and plain valleys. These areas have become irrigated, cleared, deforested, and burned for logging. These main agents of environmental degradation have produced impoverished soils, the alteration of hydraulic routes, and decreased vegetation. What we can point out is that human communities since the Neolithic have taken much advantage of the environment. The natural vegetation has been harvested in order to collect acorns and other fruits, the fields for grazing; the plains of the most fertile soils, for crops; perhaps around ravines or rivers to plant orchards or other products more demanding of water, reserving the
drier areas for cereals and dry-farming trees (Dupre! , 1988). All of this would modify the landscape in a sufficiently considerable way to be recorded in the pollen rains of the time. Consequently, some of the observed changes in pollen should not be attributed (at least exclusively) to climatic action. Chronologically, in the entire Ebro Basin environment, several phases of accumulation and incision stages have been identified (post-Bronze regularisation, Iberian–Roman incision, Medieval accumulative–incisive stage and Actual incision). The importance that the ‘‘climatic factor’’ would have had on the mentioned sites, if without any human intervention in the exploitation of the environment, is still subject to debate. From a climatic point of view, these phases are a consequence of the occurrence of dry and wet periods. Thus, the evolution of the landscape in the Ebro Basin in relation to the human occupation during the Upper Holocene is explained by a succession of dynamic changes. These fluctuations would have been due to a combination of climatic conditions conducive to the triggering of erosive processes, along with the strengthening of them by humans due to their intervention in the environment. This study has verified a landscape transformation, and analysed the processes and their evolution, particularly the climate and the impact of the human factor throughout history on the environment. The human presence at different times has not only served to ‘‘date’’ such processes, but also to evaluate their impact on the sites and their environment. The climatic conclusions that have been made according to the resulting morphologies of the processes have allowed the archaeological contexts to be more accurately evaluated.
Acknowledgements We have to state our acknowledgements to persons and institutions that have collaborated in development of this study: Instituto de Estudios Altoaragoneses ! (IEA) for projects ‘‘Estudio geoarqueologico de los yacimientos de la Edad del Bronce de la Comarca de ! Monzon’’ and ‘‘Estudio paleoambiental aplicado a la ! paleoclimatica ! ! reconstruccion en medios mediterraneos’’ and also to the Diputacion General de Aragon (DGA) for financial support to Laboratorio de Ciencias ! Historico-Geogr a! ficas (University of Zaragoza) and to Instituto Pirenaico de Ecolog!ıa (CSIC) for palynological * analysis. We are grateful to Jose! Luis Pena-Monn e! , Catedra! tico of Physical Geography (University of Zaragoza) and to Blas Valero-Garce! s, research of IPE-CSIC (Pyrenean Institute of Ecology), for their very thoughtful ideas and opinions.
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