1. ÔØ Å ÒÙ× Ö ÔØ
Landscape dynamics of Abies and Fagus in the southern Pyrenees during the
last 2200 years as a result of anthropogenic impacts
Albert P` lachs, Ramon P´ rez-Obiol, Miquel Ninyerola, Jordi Nadal
e e
PII: S0034-6667(09)00048-7
DOI: doi: 10.1016/j.revpalbo.2009.04.005
Reference: PALBO 3026
To appear in: Review of Palaeobotany and Palynology
Received date: 26 September 2008
Revised date: 24 March 2009
Accepted date: 1 April 2009
Please cite this article as: P`lachs, Albert, P´rez-Obiol, Ramon, Ninyerola, Miquel,
e e
Nadal, Jordi, Landscape dynamics of Abies and Fagus in the southern Pyrenees during
the last 2200 years as a result of anthropogenic impacts, Review of Palaeobotany and
Palynology (2009), doi: 10.1016/j.revpalbo.2009.04.005
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1 LANDSCAPE DYNAMICS OF ABIES AND FAGUS IN THE SOUTHERN
2 PYRENEES DURING THE LAST 2200 YEARS AS A RESULT OF
3 ANTHROPOGENIC IMPACTS
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5 Albert Pèlachs a,*, Ramon Pérez-Obiol b, Miquel Ninyerola b, Jordi Nadal a
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7 a GRAMP, Departament de Geografia, Universitat Autònoma de Barcelona. 08193 Bellaterra
8 (Cerdanyola del Vallès). Spain.
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10 b Unitatde Botànica, Facultat de Biociències, Universitat Autònoma de Barcelona, 08193
11 Bellaterra (Cerdanyola del Vallès). Spain.
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13 * correspondingauthor. Tel.: +34 93 5868057; fax: +34 93 5812001.
14 E-mail address: albert.pelachs@uab.cat (A. Pèlachs).
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15 LANDSCAPE DYNAMICS OF ABIES AND FAGUS IN THE SOUTHERN
16 PYRENEES DURING THE LAST 2200 YEARS AS A RESULT OF
17 ANTHROPOGENIC IMPACTS
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19 Abstract
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20 The vegetation landscape dynamic is derived from the relationship established between
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21 a society and its environment through time, and the current landscape has never been
22 seen in the previous 2000 years. The pollen study of a core from a peat bog in València
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d'Àneu (Lleida, NE Iberian Peninsula) shows a maximum extension of Abies alba forest
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about 2200-2000 cal. yr BP. Later on, there is evidence of selective actions affecting
25 this forest and the expansion of Fagus sylvatica at about 2000-1300 cal. yr BP.
26 Beginning in 1300 cal. yr BP, deforestation due to agricultural activities expanded and
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27 beech definitively disappeared at 800 cal. yr BP. Natural and human disturbances
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28 affected the dynamics of Abies alba and Fagus sylvatica from their first appearance to
29 the current vegetation landscape. Human impact on the silver fir forest, which reached
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30 its maximum in the last millennium, favoured the beech population. Pollen data from
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31 this region support our finding that human impact, not climate, is the most important
32 influential factor in the development of beech forests.
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34 Keywords: Pyrenees, Holocene, palynology, GIS suitability mapping, Abies alba,
35 Fagus sylvatica.
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37 Introduction (A)
38 The current discussion concerning the dynamics of the vegetation landscape is rooted in
39 the reasons for change over time and in the weighting of natural and human factors in

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40 its evolution (Galop and Jalut, 1994; Esteban et al., 2003; Riera et al., 2004; Beaulieu et
41 al., 2005; Riera et al., 2006; Pèlachs et al., 2007). Although climatic factors have a very
42 important role in the development of vegetation, palaeobotanic studies have
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43 demonstrated the importance of taking into account the role played by human society.
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44 Therefore, the primary objective of this study is to determine the extent to which the
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45 human imprint has affected the current vegetation landscape, focussing on the dynamics
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46 of Abies and Fagus forests in the Pyrenees.
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Colonization of Abies alba and Fagus sylvatica: the current state of affairs (B)
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An explanation of the plant colonization of the Pyrenees from the beginning of the
50 Holocene can be undertaken on the basis of pollen analyses available from the Pyrenees
51 mountain range (Jalut et al., 1998). It is impossible to interpret which factors affect this
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52 evolution without taking into account at least three variables: the location of refuge
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53 zones, the development of climatic factors and the edaphic dynamics of the soils
54 (Pèlachs, 2005).
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55 In recent years, the study of Abies alba dynamics in Europe (Terhürne-Berson et al.,
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56 2004; Liepelt et al., 2009) has been associated with other species, such as Fagus
57 sylvatica (Tinner and Lotter, 2006). This area of study has developed from a series of
58 interpretations based on the study of climate change, migratory change, unequal growth
59 of species, and the effects of human disturbances and forest fires (Tinner and Lotter,
60 2006).
61 In this sense, phylogenetic studies reveal how the Abies populations in the Pyrenees
62 were isolated from the rest of Europe (Konnert and Bergmann, 1995). This argument
63 was definitive in defending the proximity of the Pyrenees to Abies alba refuge zones,
64 based on plant macroremains and pollen data (Terhürne-Berson et al., 2004; Liepelt et

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65 al., 2009). The hypotheses about distribution from the glacial refuges based on
66 isoenzyme studies and other genetic markers (El Mousadik and Petit, 1996) seem to
67 substantiate the existence of five areas of Abies alba refuge and recolonization: the
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68 Pyrenees, central and eastern France, central Italy and the southern Balkans. Pollen and
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69 genetic data indicate clearly that the Abies alba and Fagus sylvatica refuges in the
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70 Pyrenees have suffered the “bottleneck” phenomenon during their history and that
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71 recolonization was not produced exclusively from refuge populations. This theory is
72 well supported because of the low allelic levels, which can be correlated to the current
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distribution of silver fir in the Pyrenees, with populations that are not extensive in
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comparison with the rest of Europe.
75 Palaeobotanical and genetic data for Fagus sylvatica (Magri et al., 2006) have been
76 used to evaluate the genetic consequences in Europe of long-term survival in refuge
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77 areas and postglacial spread. The largely complementary palaeobotanical and genetic
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78 data indicate that Fagus sylvatica survived the last glacial period in multiple refuge
79 areas. The central European refuges were separated from the Mediterranean refuges,
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80 which did not contribute to the colonization of central and northern Europe. Likewise,
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81 some populations expanded considerably during the postglacial period (Magri, 2008),
82 while others experienced only limited expansion. According to Ninyerola et al. (2007a),
83 inferences from more than a few studies lend credibility to the presence in the
84 Mediterranean of deciduous taxa such as Fagus during the early and mid-Holocene. The
85 climatic suitability of Fagus during the early Holocene has been shown by Lozano et al.
86 (2002), who identified Fagus and dated it at c. 17,895 cal. yr BP in Urdaibai (Basque
87 County) or López-Merino et al. (2008) in Sierra de Neila at c. 15,600-13,700 cal. yr BP.
88 This led them to suggest the northern Iberian Peninsula as a possible refuge zone
89 (Hewitt, 1999). In the Balearic Islands, the available data (Ninyerola et al., 2007a;

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90 Pérez-Obiol and Sadori, 2007) seem to indicate that Fagus had refuge in some concave
91 areas during the upper Pleistocene and the Holocene. The presence of small stands of
92 Fagus in Majorca, before the colonization from the Pyrenees took place, makes this a
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93 credible hypothesis. Similarly, examining the Iberian Peninsula, Pott (2000) indicates
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94 that over the last 9000 years Fagus has colonized northern areas from diverse
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95 Pleistocene Mediterranean refuges.
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96 In the Iberian Peninsula, evidence exists (Costa et al., 1998) of the presence of Fagus
97 sylvatica in the Basque Country (Saldropo) and Tramacastilla more than 4000 and 7000
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years ago, respectively, which would confirm the presence of various refuge zones in
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the southern slope of the Pyrenees (Montserrat, 1992). This pattern of colonization is
100 supported by pollen records from the northeast Iberian Peninsula (Pérez-Obiol, 1988),
101 showing that Fagus colonization began between 8800 and 7850 cal. yr BP.
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102 The difficulty comes from site differences that enormously complicate the interpretation
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103 of local pollen and charcoal records, as at Burg Lake in the Pyrenees, close to the study
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area, where Fagus sylvatica does not appear until 3000 cal. yr BP (1050 BC) (Pèlachs,
105 2005).
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106 On the other hand, regional data support the introduction of Fagus sylvatica at Redó
107 Lake at about 4900 cal. yr BP (Catalan et al., 2001), and a little later at Redon Lake
108 (Catalan and Pla, 1998), where it arrives in about 4500 cal. yr BP, probably as a
109 consequence of the difference in altitude (Esteban et al., 2003). Miras et al. (2007)
110 implicate both anthropic participation and onset of new climate conditions (lower
111 summer temperatures and higher annual precipitation) in the timing of the first regular
112 observations of Fagus sylvatica in the Andorran valley of Madriu, at about 4800 cal. yr
113 BP.

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114 Similarly, much farther west of the Pyrenees, Montserrat (1992) explains that, although
115 beech appears intermittently at Ibon de Tramacastilla after 7859 cal. yr BP, its curve
116 does not become continuous until c. 5760 – 4476 cal. yr BP, making its appearance
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117 contemporaneous with the other Pyrenees sites.
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118 No one disputes that the Abies alba dynamics in the Pyrenees during the Holocene
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119 indicate colonization followed by expansion from east to west (Jalut et al., 1998;
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120 Esteban et al., 2003; Pèlachs, 2005; Le Flao, 2005), which would confirm the existence
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of refuges located in the Mediterranean basin. In fact, analysis of the current western
122 boundaries of Abies alba in the Pyrenees shows a progressive lag between the western
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123 and eastern half of the mountain chain, which could be attributed to the progressive
124 distancing of this conifer from its refuge areas (Reille and Andrieu, 1991). Similarly,
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125 some authors have reported that this species first developed on the north slope of the
126 Mediterranean Pyrenees at 11,224 cal. yr BP, specifically in the area of Nohèdes (Jalut,
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127 1974; Reille and Lowe, 1993); this is consistent with the very first appearance of Abies
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alba in the Garrotxa at about 10,204 cal. yr BP (Pérez-Obiol, 1988). Other registries of
129 long-term silver fir presence in the eastern Mediterranean also concur, e.g., Pla de
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130 l’Estany (Burjachs, 1994), Banyoles (Pérez-Obiol and Julià, 1994), and Abric Romaní
131 (Burjachs and Julià, 1994), confirming the presence of refuges in coastal zones and in
132 intramountain valleys of the Iberian Peninsula (Carrión-García et al., 2000). Therefore,
133 colonization of Abies alba and Fagus sylvatica in the meridional slope of the Pyrenees
134 could be due, in part, to refuge zones located to the south and east of the Pyrenees (Fig.
135 1).
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137 [FIGURE 1]
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139 Present day distribution of Fagus and Abies in the Iberian Peninsula related to
140 anthropogenically forced landscape changes (B)
141 Although climate has been regarded as the determining factor in the development of
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142 Fagus sylvatica forests at c. 4500 cal. yr BP (Jalut, 1974; Giesecke et al., 2007), it has
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143 also been demonstrated that human influence may be responsible for its strong
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144 expansion at that time (Kenla and Jalut 1979; Jalut 1984; López-Merino et al., 2008).
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145 According to Tinner and Lotter (2006), beech survived human pressure, while other
146 deciduous trees (e.g. Tilia, Ulmus, Fraxinus excelsior) and silver fir (Abies alba) were
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strongly disadvantaged. The authors hypothesize that in the absence of human impact,
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silver fir would have expanded to areas in Europe where the species is absent today.
149 According to Peñalba (1994), the western and southernmost parts of the peninsula have
150 not been colonized by Fagus. The absence of Fagus in northwestern Spain is striking,
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151 given the importance of this genus in similar climatic conditions in the other Cantabrian
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152 regions. It is unlikely that the spread of Fagus was stopped in Galicia by natural causes
153 at 1390 cal. yr BP. At that time, humans exerted strong influence on the vegetation in
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154 this region; their presence there is recorded since 5760 cal. yr BP. Anthropogenic
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155 disturbance has proved responsible for the final, abrupt decline of Fagus populations in
156 the Cantabrian region. It is likely that severe anthropic pressure on populations of Fagus
157 at their range limit stopped the spread to the west. A similar situation could be inferred
158 for Abies, confined today to the eastern part of the Pyrenees although it had a wider
159 distribution in the Iberian Peninsula during previous interglacial periods. Two facts
160 must be considered: first, man favoured Fagus to the detriment of Abies at the
161 beginning of its extension to the northern side of the Pyrenees (Jalut 1984), and second,
162 Abies grows today in Italy under climatic conditions also found in Spain (Terhürne-
163 Berson et al., 2004; Liepelt et al., 2009), suggesting that the spread of the species into

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164 the Iberian Peninsula could have been stopped by human interference in the Pyrenees.
165 Nevertheless, climate forcing in the Post-Bronze Iberian Roman Humid Period (2600-
166 1600 cal. yr BP) could be a consideration, as proposed by Martín-Puertas et al. (2008).
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167 Fig. 2 shows the clear decline of Abies alba beginning in the medieval period. When the
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168 human impact was too strong, silver fir totally disappeared (Pérez and Roure, 1990;
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169 Pèlachs, 2005; Tantinyà, 2007).
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170 The potential distribution of Abies alba in the northwest Iberian Peninsula proposed by
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171 Rivas (1987) would result in a much larger region with a much more suitable surface if
172 we consider numerous biotic and abiotic factors that exist at present. To enhance the
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173 potential distribution of these two taxa, a combined spatial suitability surface has been
174 developed through GIS and multivariate statistical methods. This map allows us to
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175 understand the spatial behaviour of Fagus and Abies at regional scale, complementing
176 the palaeopalynological results.
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177
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178 [FIGURE 2]
179
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180 Study Area (A)
181 The Prats de Vila peat bog (longitude 1° 6’ 13” E and latitude 42° 38’ 17” N) is found at
182 1,150 masl and has an estimated area of 2.8 hectares. The lithological substrate
183 corresponds to Cambro-Ordovician slates, even though during the fieldwork we found
184 important granite deposits of glacial remains.
185 The climatic conditions surrounding the peat bog (within a 1 km radius) are humid
186 (Thornthwaite humidity index) with an Autumn-Spring-Summer-Winter precipitation
187 pattern and mean annual values ranging between 652 mm and 887 mm (=736 mm). The
188 mean annual temperature ranges between 6.5 ºC and 10.5 ºC (=8.9 ºC), decreasing in

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189 winter to a mean minimum temperature of around -3.8 ºC. Potential evapotranspiration
190 (computed following the Hargreaves method) shows annual values ranging between 574
191 mm and 850 mm (=716). These values are close to precipitation values, meaning that
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192 this area is free of hydric stress. All the climate data have been extracted from the
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193 Digital Climatic Atlas of the Iberian Peninsula (Ninyerola et al., 2007b and 2007c).
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194 The present vegetation on the peat bog is Subalpine-Montane mesophilous and siliceous
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195 meadows with Agrostis capillaris, Festuca nigrescens, Anthoxanthum odoratum,
196 Galium verum, and Genistella sagittalis. Vegetation surrounding the peat bog in shady
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places includes some deciduous Quercus together with Corylus, Betula and Pinus,
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which in many cases occupy formerly cultivated fields and give way to the most
199 extensive Abies alba stands of the Pyrenees: la Mata de València d’Àneu. In northern
200 Spain, distribution of Quercus petraea (the dominant oak near the study zone) is
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201 typically fragmented. Taking into account its minimal presence in the pollen diagram, it
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202 appears that its distribution area in the study zone has not been of great importance
203 during the last millennia. At the same time, in sunny places, the deciduous Quercus
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204 share their protagonism with Q. Ilex subsp rotundifolia.
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205
206 Materials and Methods (A)
207 The study methodology was based on a combination of pollen data extracted from a
208 peat bog in València d’Àneu (Axial Pyrenees) and fieldwork to identify the main plant
209 communities in the zone.
210 Three core samples were taken with a mechanical sampler and the one with the most
211 consolidated peat was selected for analysis. Two large, clearly differentiated
212 sedimentary units have been described in the register of the peat bog studied (Fig. 3):
213 the upper unit, characterized by the abundance and continuity of the bog, and the lower

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214 level, characterized by a granite conglomerate with very compacted gravel and some
215 pebbles at the transition between the two units. Two samples were selected for dating
216 using 14C-AMS (Beta Analytic Inc.), based on a piece of wood at 59-60 cm depth and a
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217 peat fragment at 165-166 cm depth (Table 1). The resulting sedimentation rate for the
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218 peat section was 0.72 mm/year for the first 60 cm and 0.83 mm/year for the rest. Age
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219 was calibrated to calendar age using the INTCAL04 program (Talma and Vogel, 1993).
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220 For the pollen analysis, we selected only the first two meters of peat from one of the
221 cores (named VAL-III), down to the transition to gravel conglomerate. Chemical
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223
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treatment of the samples was carried out according to the protocol described by Goeury
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and Beaulieu (1979).
224 [FIGURE 3]
225 [TABLE 1]
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226
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227 Suitability mapping (B)
228 The suitability vegetation maps for Fagus and Abies were developed using presence-
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229 absence models adjusted with logistic linking in a General Linear Model (GLM).
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230 Presence data were obtained by choosing plots where these species are dominant from
231 the third National Forest Inventory (a project administered by the Spanish state). The
232 resulting distribution of both species is shown in figures 7-8. This forest inventory
233 regularly samples the territory with a grid density of 1 km. This type of sampling is
234 very interesting because it covers a large area but especially because regular sampling
235 avoids the sampling bias that exists in many other types of chorological data. We would
236 also note that we have access to plots in which the absence of the species studied is
237 ensured, mitigating the problem of pseudo-absences (Chefaoui and Lobo, 2008). To
238 obtain an absence sample, we randomly chose a number of sites equal to the presence

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239 sites. In addition, plots that were absence sites for the species we considered were
240 avoided if they were within a 5 km radius of the presence plots and therefore had very
241 similar topoclimatic conditions.
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242 With respect to predictor variables, we incorporated geoclimatic variables obtained by
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243 spatial interpolation methods (Ninyerola et al., 2000), based on a Digital Elevation
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244 Model with 200-m resolution and data from Spain’s National Institute of Meteorology
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245 (INM), which provided readings from 1346 temperature stations and 2519 for
246 precipitation. We would emphasize here that having access to a plot that was
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georeferenced with a high level of precision allowed us to capture the climatology at
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toposcale, minimizing methodological errors. Five variables were analysed: maximum
249 mean temperature for the warmest month, mean annual temperature, minimum mean
250 temperature for the coldest month, accumulated precipitation by season and potential
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251 solar radiation by season. Table 2 shows the ranges for Abies alba and Fagus sylvatica.
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252 We then enriched the databases using vector point files (presence-absence distribution)
253 with the corresponding values from the geoclimatic variables. This enriched database
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254 was submitted to statistical analysis using a GLM with logistic linking, as in other
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255 studies (Felicísimo et al., 2002) of the suitability of forest species. For the process of
256 adjusting the model we used 60% of the plots and saved 40% for validation and to be
257 able to quantify in this way the quality of the resulting maps.
258 Finally, mapping algebra was used to obtain the suitability maps by species using the
259 completed analysis. The regression equations, adjusted by statistical analysis, were
260 reproduced using GIS, replacing each variable with the corresponding topoclimatic
261 map.
262 [TABLE 2]
263 Results and discussion (A)

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264 Pollen diagram from the València d’Àneu peat bog (B)
265 The pollen diagram from the València d’Àneu peat bog permitted us to reconstruct the
266 vegetation changes in the studied zone over the last two millennia (Fig. 4). The diagram
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267 is described using pollen assemblage zones (PAZ).
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268
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269 [FIGURE 4]
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270
271 VAL-III / I (2200-2000 cal. yr BP; 250 BC –50 BC): the decline of the
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“original”Abies alba forest (C)
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At the beginning of this time period, Abies frequency of more than 10% with a peak at
274 approximately 22% can only be explained by the Abies alba in situ occupying a much
275 larger land area than at present. The drop in Abies at the end of this period may be due
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276 to selective human intervention with respect to this species, favouring other species
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277 such as Corylus, which would colonize the space left by silver fir. We must take into
278 account the fact that wood forms part of the Roman social and economic system and is
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279 an indispensable element (Conedera et al., 2004).
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280 Mining is another sector related to exploitation of forest resources. We noted an
281 increase in lead in the sediment of Redon Lake (also in the axial Pyrenees) during the
282 Roman era and a high point in about AD 600 (Catalan and Pla, 1998). The dating of five
283 charcoal kiln sites between the 3rd and 4th VI centuries AD and the identification of
284 charcoals (Pinus and Abies) allows us to relate this first metallurgy with selective acts
285 related to the forest (Pèlachs and Soriano, 2003).
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287 VAL-III / II (2000-1300 cal. yr BP; 50 BC – AD 650): Abies alba forest with Fagus
288 sylvatica (C)

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289 The intervention of the prior phase on the Abies alba forest opens up land that is
290 occupied first by some species that are typical of meadows and clearings (Poaceae,
291 Plantago sp., Asteraceae, etc.) and permit the expansion of plant populations that
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292 compete with the silver fir for space, such as Corylus in the lowest areas and Fagus,
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293 Pinus and Betula in the same zones as the Abies alba.
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294 The occasional presence of Juglans, Juniperus and Artemisia and the start of Cerealia
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295 and Castanea curves denote human management of the landscape, mostly related to
296
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grazing and agricultural activities. Pseudoschizaea (an algal remain indicative of
297 erosive processes) appears. The first occurrences of Juglans are well dated at Ariege
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298 (2000±107 cal. yr BP in Jalut el al. 1982; 1792±59 cal. yr BP, Galop, unpublished).
299 There are regular records from the 10th to the 13th centuries, though the dates may vary
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300 with area and altitude (1048±79 cal. yr BP and 706±28 cal. yr BP, Galop, unpublished;
301 near 643±61 cal. yr BP, Planchais 1985). This cultivated tree is an excellent marker of
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302 the Greco-Roman times. It was introduced in western Mediterranean regions as early as
303
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c. 1952 cal. yr BP (Bottema, 1980) by Greek and Roman settlers. According to the
304 curve of pollen concentration (pollen grains/g), the arboreal biomass does not suffer a
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305 significant decline (Fig. 5). However, forest activities are evident.
306 In any case, the plant dynamics indicate a human pressure that shifts the permanent
307 character of the land. Without technical resources to minimize labour expenditure, mid-
308 slope soils are preferred for agricultural uses (Esteban et al., 2003). This is the reason
309 for disturbances of mid and lower slopes of the forest that affect the dynamics of the
310 silver fir-beech forest.
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312 [FIGURE 5]
313

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314 VAL-III / III (1300-650 cal. yr BP; AD 650 – AD 1300): the explosion of human
315 activities (C)
316 This entire phase is characterized by a declining AP percentage and an absolute increase
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317 of herbaceous plants (Fig. 5). The massive forest clearance during this period is shown
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318 by the fall in AP values and the greater Poaceae abundance in the studied area. The
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319 decline of Abies and the noticeable extension of Fagus are probable evidence of this
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320 deforestation.
321
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The pollen diagram shows certain peculiarities that led to splitting the zone into three
322 subzones:
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323
324 VAL-III / IIIa (1300-1100 cal. yr BP; AD 650 – AD 850): global disturbance (C)
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325 At the same time that Pinus recedes below 20% and Abies falls below 5%, Fagus,
326 Betula and Corylus take advantage of this by increasing their presence even though,
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327 later on, they will decline just as the rest of the tree population did.
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328 The large increase in Artemisia, Poaceae, Rumex and Polygonum can be explained by
329 the increase in grazing. The strong increment of Cerealia (mostly Secale) and Fabaceae
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330 also indicate the implementation of agricultural practices. This evidence permits us to
331 assume that opening up the landscape led to the arrival of Olea pollen. In that era, olive
332 tree cultivation is documented in the domains of a nearby monastery (Esteban et al.,
333 2003). These facts are clearly evidenced by the drop in pollen concentration. The impact
334 of human disturbance is more noticeable from the Late Medieval period onward.
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336 VAL-III / IIIb (1100-800 cal. yr BP; AD 850 – AD 1150): management of the peat
337 bog (C)

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338 This zone is characterized by the notable presence of Alnus, which together with the
339 dynamics of Cyperaceae and Typha-Sparganium pollen type allows us to connect this
340 period with an increase in the groundwater level of the peat bog and possibly with its
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341 expansion.
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342 Sparganium sp. has great colonizing abilities and may cause a rapid silting in shallow
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343 waters. At this time, its development coincides with the establishment of Alnus. Before
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344 this colonization, Pediastrum was already present, indicating a rise in water level. These
345 percentage increases in taxa are related to a major sedimentary stability (Andrieu et al.,
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347
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2000). Late Medieval period documents explain that during this period it was common
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to plant crops in muddy zones along river banks, which flooded periodically and were
348 called “insules” (Esteban et al., 2003); consequently, it would seem reasonable that a
349 hygrophilous environment was favoured, controlling the flow and the hydric resources
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350 of the area.
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351 The rapidly invading Abies would out-compete Fagus, or substantially slow down its
352 recruitment rate until canopy disturbance created light openings large enough for
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353 successful establishment and growth. According to Doležal et al. (2004), the higher
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354 mortality of Fagus in denser Abies patches and the resulting spatial segregation of the
355 species reflect asymmetric interspecies competition.
356
357 VAL-III / IIIc (800-650 cal. yr BP; AD 1150 – AD 1300): disappearance of the Abies
358 alba-Fagus sylvatica forest (C)
359 The beginning of this phase is characterized by high percentages of Poaceae and
360 Cerealia and the disappearance of Fagus from the study area, a disappearance attributed
361 to the strong human impact on the landscape. From this point on, there will never again
362 be a beech forest or a small mixed Abies alba-Fagus sylvatica forest in the zone. This

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363 drastic change in the forest landscape is also evidenced by the decline in Alnus, Abies
364 and Pinus, which at the end of the sequence permits the return of Corylus.
365
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366 VAL-III / IV (650-350 cal. yr BP; AD 1300 – AD 1600): recovery of the Abies alba
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367 forest (C)
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368 Since 650 cal. yr BP (AD 1300) we have observed a certain recovery of the arboreal
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369 cover, led by the presence of three primary species of trees that are distributed and
370 combined in various stages and habitats: Corylus, Abies and Pinus; Betula is added to
371
372
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the list at the end of this time period. Human pressure on the environment is moderate.
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Therefore, it doesn’t seem that the repercussions of the Little Ice Age were sufficiently
373 important to affect the economic activities of the dominant classes, primarily herders.
374 All the same, documents report major declines in the Pyrenees in some of the species
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375 grown (such as grapevines), which leads us to assume the existence of local differences.
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376
377 VAL-III / V (350-150 cal. yr BP; AD 1600 – AD 1800): a new increase in human
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378 pressure (C)
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379 The slight percentage oscillations in various tree taxa, such as Abies, Corylus, Betula
380 and Pinus, are accompanied by a large increase in Poaceae and Juglans; this denotes a
381 new and different landscape management with the existence of pastures and plantations
382 of trees. It is worth noting that oil was extracted from the walnut trees and had a high
383 food and therapeutic value, equal or superior to that of olive oil, and therefore at
384 particular times could have offered an alternative to the cultivation of olive trees
385 (Esteban et al., 2003). In addition, the appearance of Ericaceae could indicate an
386 increase in ruderal species, given the use of a road network, and that of Glomus would
387 explain the more edaphic conditions of the peat bog.

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388
389 VAL-III / VI (150 cal. yr BP--present; AD 1800 – present): the preamble to the
390 current landscape (C)
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391 The final episode puts the vegetation landscape at the doorstep of the current landscape,
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392 with the percentages of Abies at about 5%, while Pinus recedes significantly and
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393 heliophilous colonizers increase progressively in formerly cultivated zones and open
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394 forest areas, including Corylus –especially at the end of the sequence – or plastic
395 species such as Betula. This occurred in other areas as well.
396
397
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This denotes a decrease in the groundwater of the peat bog as indicated by the curve for
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Cyperaceae and Glomus and suggests the definitive disappearance of Alnus around the
398 bog studied here. Chlamydospores of Glomus cf. fasciculatum would be evidence of
399 erosive phenomena (Van Geel et al., 1989) related to anthropogenic activity and drought
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400 (López-Sáez et al., 2000).
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401
402 [FIGURE 5]
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403
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404 Vegetation dynamics and suitability (B)
405 It is clear from the palynological data presented here that human impact became
406 stronger and reaches its maximum in this last millennium. This stage of the Pyrenean
407 forest history saw the final shaping of the present-day landscape (Kenla and Jalut 1979;
408 Galop, 1998).
409 The pollen diagram is comparable to numerous diagrams of the southern and central
410 Alps, central France and the Pyrenees themselves (Beaulieu, 1978; Clerc, 1988; David,
411 1993; Nakagawa, 1998; Tinner et al., 2005; Finsinger and Tinner, 2006; Pèlachs et al.,
412 2007). In the central Alps, Nakagawa et al. (2000) found a sequence that is

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413 chronologically similar and has three stages of impact, each of which is followed by a
414 different pattern of forest restoration. The first deforestation occurs at about 2060 cal. yr
415 BP, during the Roman era, and a selective exploitation of Abies alba forest is evidenced.
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416 The silver fir forests formed part of a very active economy near the Rhine river. Küster
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417 (1994) compiles various pollen diagrams for the Rhine, Elbe, and Danube and
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418 demonstrates that the use during Roman times was not totally destructive. Various
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419 zones of silver fir forest were left untouched. The author concludes that the concept and
420 practice of “forest management” was common in Roman times. The second
421
422
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deforestation, around 1520 cal. yr BP (or during the 5th and 6th centuries), denotes
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substantial evidence of agricultural activity. The third, around 810 cal. yr BP or right in
423 the middle of the 12th century, is similar to its predecessor but much longer and not at
424 all selective, so that the forest had no chance to recover.
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425 These facts coincide quite well with the changes in percentages and pollen
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426 concentration for Abies (Fig. 5). This dynamic also coincides with those found in other
427 localities close to the studied zone (Esteban et al., 2003; Pèlachs et al., 2007). The peat
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428 bog studied demonstrates much more clearly a possible selective action involving Abies
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429 alba forests during the Roman era and confirms the indices that explain how some
430 dynamics began in the medieval period, continued during the Modern Age and the 20th
431 century, and brought us to the current landscape.
432 In other areas of the Pyrenees, Abies alba was the primary species of trees between
433 6200 and 2800 cal. yr BP (4250-850 BC), a time when the stable Abies alba presence
434 gave way to red pine forest in the subalpine stage. At the same time this was happening,
435 a mixture of oak (Quercus sp., Tilia sp., Ulmus sp. etc.) also experienced a sharp
436 decrease. This strong disturbance of the subalpine and mountain area would permit the
437 pine forest to expand as a rapid colonizer and populate the space that had been occupied

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438 by silver fir; this was the product of accumulating circumstances where climate change
439 and human actions intersected (Pèlachs et al., 2007). In the studied zone this didn’t
440 happen and the silver fir, despite the strong disturbance they suffered, recovered again
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441 and again, even though the population would never reach the levels of 2000 years
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442 earlier (Fig. 4). Abies forests remained important during a large part of the Holocene,
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443 which could be explained by the topography of the valley and slopes.
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444 The current pollen spectrum had never been seen in the previous 2000 years. This fact
445
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led us to deduce that models such as Modern Analogue Technique (MAT) could be
446 difficult to apply in this zone of the Pyrenees, at least during the last 2000 years.
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447 Establishing detailed comparisons, we observe notable differences between two data
448 groups of interest: pollen and vegetation cover; this means that we must explore models
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449 that work for mountain regions in particular. Calibrating the mountain vegetation and
450 pollen spectra is key to this type of research if we are to understand certain evolutionary
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451 patterns. The hypotheses of authors such as Muller et al. (2005), which postulate that
452
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there is an increase in regional and distant pollen in sediment at high altitude, is only
453 valid for certain taxa. In sedimentary samples of lake surfaces, we see that the presence
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454 in the pollen spectra of taxa such as Tilia, Abies, Ulmus and Fagus almost always
455 represents a local or nearby presence in mountain regions. Many calibrations have used
456 correction factors or R-values (the ratio between the pollen group and the vegetation
457 community it represents). At present, different models are grouped within the Extended
458 R-value (ERV). With respect to Abies, a taxon that has had a strong impact on the
459 evolution of the vegetation landscape in this zone during the last 2000 years, it must be
460 said that it is very sensitive to the described method of weighing distance. For example,
461 according to Eisenhut (1961) Abies alba presents a falling speed of 0.12m.s-1, while
462 other similar plants such as Pinus sylvestris have values of 0.056 m.s-1. We must always

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463 think in terms of intertaxonomic differences if we are able to properly interpret pollen
464 dispersal and deposition patterns.
465 The pollen analysis presented advocates the possibility of an anthropogenic trigger for
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466 Fagus sylvatica expansion. Many other studies suggest that human disturbance
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467 facilitated the expansion of this tree where climatic conditions were favourable (Küster,
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468 1997). This hypothesis has its origin in northern and north-western Europe (e.g.
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469 Andersen, 1973; Iversen, 1973), where Fagus sylvatica expanded only after the
470 beginning of the Neolithic (Lang, 1994). According to Tinner and Lotter (2006: 541):
471
472
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“human activities as one (if not the most important) cause for the invasion of Fagus
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sylvatica into Central Europe (e.g., Küster, 1997, 1999; Ralska-Jasiewiczowa et al.,
473 2003) has repeatedly been questioned and is still debated (e.g., Huntley et al., 1989;
474 Lang, 1994; Huntley, 1996; Gardner and Willis, 1999; Pott, 2000)”. In locations where
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475 Fagus is found forming monospecific communities, it is because in the middle of its
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476 distribution area young beech has behaved like an eurioic species with a broad
477 ecological valence, capable of shaping itself to edaphic and climatic conditions that are
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478 relatively diverse (Costa et al., 1998), which gives a certain advantage in confronting
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479 Abies alba and other colonizers. From this point on it seems logical to think that Fagus
480 sylvatica was occupying the lower part of the Abies alba forest, exactly in the place that
481 was cut and burned to convert the land to cultivated fields. For this reason it did not
482 repopulate and was replaced by hazelnut. This process could only begin in the Middle
483 Ages, with the availability of technologies to occupy the valley floor, the experience
484 necessary to manage the drainage of peat bogs, and the consolidation of fluvial
485 boundaries, in addition to the political capacity to carry out the appropriation of these
486 spaces. In this moment in the history of “slash and burn” agriculture, which means that
487 itinerant agriculture was replaced by the permanent roturation of valley floors, a fact

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488 that required limiting the diversity of resources available to peasants, who had to
489 specialize in specific products selected not for their productivity but rather for their
490 adaptability to feudal uses (Esteban et al., 2003).
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491 According to the ecological literature, Tinner and Lotter (2006) affirm that Fagus
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492 sylvatica and Abies alba have similar environmental requirements. These authors have
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493 put on record that 1) today, Abies alba is more competitive than Fagus sylvatica where
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494 summer precipitation is higher and temperature is lower (Ellenberg, 1996) and 2)
495 palaeobotanical evidence suggests that high summer precipitation is more important for
496
497
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Abies alba than low temperatures. If we analyse the distribution of Abies alba in the
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Spanish National Forest Inventory, we see how the silver fir on the Iberian Peninsula
498 today live with a mean annual precipitation of about 1100 mm/year and an estimated
499 mean annual temperature between 3.5ºC and 10.5ºC (Ninyerola, 2001). In the Iberian
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500 Peninsula, young beech stands are found in zones in which the monthly average
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501 temperatures fluctuate very little between the coldest and warmest month. Normally this
502 change does not exceed 15 ºC, although it might reach 25 ºC in the middle of the
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503 peninsula. Young beech has great resistance to cold during the fallow times.
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504 The present-day suitability maps of Abies, Fagus and Abies-Fagus mixed forest can be
505 observed in Fig. 6 and Fig. 7. If we focus on the area closest to the studied peat bog, we
506 find low (<0.3) and intermediate (0.3-0.7) Fagus suitability values. The closest nucleus
507 with high suitability (>0.7) is found about 10 km east of the bog. In contrast, with
508 respect to Abies we can see that cells with intermediate values dominate and, most of
509 all, less than 2 km away we find abundant areas that are highly appropriate for this
510 species. This makes one think that the studied area, and nearby zones, have topoclimatic
511 characteristics that are more favourable to the development of Abies. This situation is in
512 accord with the interpretation of the pollen diagram (Fig. 5), which makes us think that

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513 Abies recovers more readily when topoclimatic factors outweigh anthropic ones. From
514 the point of view of plant suitability, we can consider the València d’Àneu peat bog as
515 located in an area where the influence of ideal zones for Abies is clearly higher than for
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516 Fagus. Statistical details of the model (adjustment and validation) underlying this
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517 cartography can be found in table 3.
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518 [FIGURE 6]
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519 [FIGURE 7]
520 [TABLE 3]
521
522
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5. Conclusions (A)
523 The València d’Àneu peat bog has been shown to be a good palaeoenvironmental
524 record, giving us an image of the short-term changes that make possible a study of the
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525 abrupt anthropic effects. The pollen analysis has made evident, in no uncertain terms, a
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526 possible selective action affecting Abies alba forest in the Roman period and confirmed
527 the indicators that explain how during the medieval period some dynamics began that
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528 would evolve during the Modern Age and the 20th century to produce the current
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529 landscape in this area. The current vegetation landscape of this region of the Pyrenees
530 has never before existed over the course of the last 2000 years and the climatic frame is
531 not well represented due to human disturbance of the landscape during this period.
532 The surroundings of the peat bog provided good conditions for human settlement and
533 pastures by removing forest. The palynological data support that human impact became
534 stronger and reached its maximum in the last millennium.
535 A direct climatic inference cannot be made. It is not possible to isolate the human
536 presence from the plant dynamics and therefore there can be no clear correlation during
537 this period between climate and original vegetation.

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538 Silver fir shows a decline in this area due to factors much more related to human
539 intervention than to climate. Likewise, Abies recovers with a certain ease, in contrast to
540 what happens in other parts of the Pyrenees and pre-Pyrenees; a higher suitability with
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541 respect to its current habitat is evidenced.
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542 During the first millennium of our era, we note the presence of beech woods, most
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543 likely coexisting with Abies alba as a product of continual and selective actions in the
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544 forest. Fagus sylvatica acts as a colonizer of open space and can be? directly related
545 with human activity, especially since the Middle Ages, provoking a change in the
546
547
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altitude limits of forest and other ecotonic zones. In the same way, the maximum levels
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of Corylus avellana currently present are due to the colonization of humid lowlands
548 previously used for crops and pasture.
549 In summary, then, plant succession over the past two millennia in the studied area can
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550 be described as a maximum extension of Abies alba forest (2200-2000 cal. yr BP);
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551 selective actions affecting the silver fir forest and arrival of beech (2000-1300 cal. yr
552 BP); deforestation as the agricultural zone expanded, with a reduction in the upper
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553 altitude limit of the forest and definitive disappearance of Fagus sylvatica (1300-800
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554 cal. yr BP); total Abies alba deforestation (800-650 cal. yr BP) and the recovery of
555 silver fir forest (without Fagus sylvatica presence) that, with various fluctuations,
556 persists into the present.
557
558 Acknowledgments (A)
559 This research would not have been possible without the support received from those
560 responsible for the High Pyrenees Natural Park; we especially want to acknowledge
561 Agustí Esteban Amat for his sensitivity to environmental research and his knowledge of
562 the area. Sampling of the peat bog was possible thanks to the efforts of Aureli Carnicer

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563 and also of COPCISA, which authorized access under the supervision of María Álvarez,
564 to whom we are especially grateful for the assistance she provided. We also wish to
565 gratefully acknowledge the unselfish collaboration in the field that we received from
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566 Riker Yll and Jordi Llorens. Finally, the authors thank Elaine Lilly, Ph.D., of Writer’s
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567 First Aid for English translation and revision.
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568
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569 References (A)
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706 holocène de la végétation et occupation des Pyrénées andorranes depuis le

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708 Estanyons (2180 m, Vall del Madriu, Andorre). C.R. Palevol 6, 291-300.
709 Montserrat, J.M., 1992. Evolución glaciar y postglaciar del clima y la vegetación en la
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713 fluctuations during the last interglacial in central Europe. Geology 33, 449-452.
714 Nakagawa, T., 1998. Etudes palynologiques dans les Alpes françaises centrales et
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717 Nakagawa, T., Beaulieu, J.L. De, Kitagawa, H., 2000. Pollen-derived history of timber
718 exploitation from the Roman period onwards in the Romanche valley, central French
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719 Alps. Vegetation History and Archaeobotany 9, 85-89.
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720 Ninyerola, M., 2001. Modelització climàtica mitjançant tècniques SIG i la seva
721 aplicació a l’anàlisi quantitativa de la distribució d’espècies vegetals a l’Espanya
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722 Peninsular. Ph D. Thesis. Universitat Autònoma de Barcelona,
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723 http.//www.tesisenxarxa.net/TDX-0618101-111736.
724 Ninyerola, M., Pons, X., Roure, J.M., 2000. A methodological approach of
725 climatological modelling of air temperature and precipitation through GIS
726 techniques. International Journal of Climatology 20, 1823-1841.
727 Ninyerola, M., Sáez, L., Pérez-Obiol, R., 2007a. Relating postglacial relict plants and
728 Holocene vegetation dynamics in the Balearic Islands through field surveys, pollen
729 analysis and GIS modelling. Plant Biosystems 141 (3), 292-304.

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730 Ninyerola, M., Pons, X., Roure, JM., 2007b. Objective air temperature mapping for the
731 Iberian Peninsula using spatial interpolation and GIS. International Journal of
732 Climatology 27: 1231-1242.
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733 Ninyerola M, Pons X and Roure JM., 2007c. Monthly precipitation mapping of the
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734 Iberian Peninsula using spatial interpolation tools implemented in a Geographic
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735 Information System. Theoretical and Applied Climatology 89: 195-209. DOI:
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737 Pèlachs, A., 2005. Deu mil anys de geohistòria ambiental al Pirineu Central Català.
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739 Coma de Burg i a la Vallferrera. Ph D Thesis. Universitat Autònoma de Barcelona.
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741 Pèlachs, A., Soriano, J.M., 2003. Las fuentes paleobotánicas y la historia forestal. el
742 ejemplo de los valles de la Coma de Burg y Vallferrera (Pallars Sobirà-Lleida).
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743 Cuadernos de la Sociedad Española de Ciencias Forestales 16, 155-160.
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744 Pèlachs, A., Soriano, J.M., Nadal, J., Esteban, A., 2007. Holocene environmental
745 history and human impact in the Pyrenees. Contributions to Science 3 (3), 423–431.
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746 Peñalba, M. C., 1994. The history of the Holocene vegetation in northern Spain from
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792 of the lateglacial type section at Usselo (The Netherlands). Review of Palaeobotany
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794 Fig. 1. Location of the València d’Àneu (VAL-III) peatbog (star) and fir forest (in grey)
795 in the Pyrenees.
796
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797 Fig. 2. Current distribution of Abies alba (white dots) in the Pyrenees and first
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798 occurrences and dynamics during the Holocene (Pérez-Obiol, 1988; Pèlachs et al.,
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799 2007).
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800 Fig. 3. Lithologic column and sediment structure of the peat bog.
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803 III).
804
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805 Fig. 5.
806 Left: Non Arboreal Pollen Concentration vs. Arboreal Pollen Concentration (pol/g).
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807 Right: Arboreal Pollen Concentration of Abies alba and Fagus sylvatica. Peat bog of
808
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València d’Àneu (VAL-III)
809
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811 Fig. 6. Suitability maps of Abies alba (a) and Fagus sylvatica (b). Dots represent the
812 present observed distribution (National Forest Inventory). High, medium and low
813 suitability are denoted by black, grey and white tones, respectively.
814
815 Fig. 7. Suitability map of mixed Abies-Fagus. This map is based on the layered
816 combination of suitability maps of each species. Black colours represent areas where
817 both species have high suitability, grey tones where only one has high suitability and
818 white colour where there is no suitability.

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819 Fig 1
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821 Fig 2
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822

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823 Fig 3
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825 Fig 4
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826

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827 Fig 5
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829 Fig 6
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831 Fig 7
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833
Sample Laboratory Material Conventional Dating calibrated to Intercept calibration
(cm) Code dating BP 2σ (95% curve
probability)
59-60 Beta- Wood 780±40 cal BP (730-680) cal BP 690
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240388
165- Beta- Peat 1990±50 cal BP (1990-1880) cal BP 1940
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166 240387
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834
835 Table 1. 14C dating of peat bog VAL-III
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836
MX_HOT MT_AN MN_COL PR_WIN PR_SPR PR_SUM PR_AUT RAD_WIN RAD_SPR RAD_SUM RAD_AUT N
Fagus
20.6-27.6 6.0-12.9 -5.9-3.1 121-509 166-449 94-330 139-436 338-1310 1978-2804 2656-3137 909-1935 3681
sylvatica
Abies
18.2- 26.4 3.5-10.4 -8.1, -1.1 139-385 212-395 186- 369 201-380 159-1345 1734-2799 2457-3133 652- 1968 614
alba
837
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838 Table 2. Ranging values from the predictors used in the GLM suitability models. The values
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839 presented avoid the lowest and highest 2.5% of values.
840
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841
R2 Cut-off Predicted CCR fpos fneg
Species
Nagelkerke point Observed absence presence (a+d)/N b/(b+d) c((a+c)
Fagus absence 669 (a) 65 (b)
0.30
sylvatica 0.84 presence 53 (c) 685 (d) 92% 0.09% 0.07%
0.91 absence 105 (a) 12 (b)
Abies alba 0.55
presence 7 (c) 121 (d) 92% 0.09% 0.06%
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842
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843 Table 3. Fitting and validation results from the Abies and Fagus suitability GLM models. CCR
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844 (Correct classification rate) represents the general performance of the model. Fpos (False
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845 positive rate) shows the percentage of suitability areas that do not match with present-day
846 distribution. This cannot be considered an error because exists suitability for both species. Fneg
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847 (false negative rate) is the measure that can be considered as the error.
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