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Discrimination of Scots pine forests in the Iberian Central System (Pinus sylvestris var. iberica) by means of pollen analysis. Phytosociological considerations/Discriminacion de los bosques de pino albar en el Sistema Central iberico (Pinus sylvestris var. iberica) mediante analisis polinico. Consideraciones fitosociologicas.

INTRODUCTION

Pollen analysis is one of the main methods used to reconstruct vegetation patterns and landscapes of the past. However, the interpretation of the composition and structure of forest communities as well as treeless vegetation from fossil pollen assemblages is complex and sometimes difficult. Pollen production and preservation, dispersal and surface deposition differ distinctively, depending on plant species and climatic conditions (Sugita, 1994; HICKS, 2001; BUNTING & al., 2004). In addition, pollen records vary with vegetation types, size of the depositional basin and other characteristics of the study area (JACOBSON & BRADSHAW, 1981). These facts are especially significant in mountainous environments, where climate varies strongly with altitude, largely determining the zonation of vegetation (RIVAS-MARTINEZ, 2005), reflected in turn by the pollen record at different elevations (CASELDINE & PARDOE, 1994; PARDOE, 2001; CANELLAS-BOLTA & al., 2009).

To date few studies of modern pollen rain have been attempted on mountain environments in central Spain (VAZQUEZ & PEINADO, 1993; ANDRADE & al., 1994; Dorado & RUIZ-ZAPATA, 1994). However, these investigations were generally quite local in extent and tended to include only a limited number of samples. Thus any ecological interpretation of their findings had to be confined to the local scale. Consequently, whilst pollen-based reconstructions of Holocene vegetation and climate yield good results when applied to pollen sequences from low to mid elevation sites (CARRION & al., 2010; GIL-ROMERA & al., 2010), the application of current methods to high-altitude pollen sequences often gives unreliable or hardly testable results. Ultimately, analyses of modern pollen rain are essential for the understanding of fossil pollen sequences in a particular mountain area, and therefore for pollen-based palaeovegetation and palaeoclimate reconstructions (LOPEZ-SAEZ & al., 2010a). This is particularly marked in the case of large pollen producers and wind-pollinated taxa like pine species. In this sense, CASELDINE & al. (2007) stressed the importance of making realistic assumptions about regional background pollen, especially about high pollen producers, such as Pinus sylvestris s. l., in order to obtain reliable simulations in landscape modelling.

Pinus species cover large areas of the Northern Hemisphere and their forests have an ancient history of human impact that has shaped their current structure, composition and distribution (RICHARDSON & al., 2007). In the Mediterranean Basin, the distribution of pines, especially the most abundant and widespread one such as Pinus sylvestris s. l., has been greatly affected by human activities for thousands of years (BARBERO & al., 1998; TAPIAS & al., 2004). The human role in structuring Scots pine forests in the Iberian Central System shows how they have declined considerably as a result of livestock and agriculture activities, land abandonment, forestry, and extensive afforestation (MARTINEZ-GARCIA & MONTERO, 2000), especially in the last five thousand years (FRANCO-MUGICA & al., 2001a). The fact that wildfires in the Iberian Central System have mostly affected Pinus sylvestris var. iberica Sbovoda forests located in dry and subhumid areas implies that climate contributes to limit fire occurrence (PAUSAS & al., 2008) and, therefore, changes in future climate will be likely to modify the fire regime, and, consequently, the vulnerability to fire of Scots pine forests in the study area.

Here, we study for the first time modern pollen samples from the Iberian Central System to discriminate Pinus sylvestris var. iberica forest communities, as modern pollen studies can aid in the interpretation of fossil pollen data in terms of vegetation patterns. Pinus sylvestris s. l. is a widespread species in Europe (MASON & ALIA, 2000) that has left a useful record of its distribution in central Spain during the Holocene in the form of pollen grains and macrofossils preserved in sediments (FRANCO-MUGICA & al., 2001; RUBIALES & al., 2007, 2012; LOPEZ-MERINO & al., 2009). Furthermore, these studies may help to disentangle the factors that triggered vegetation changes. This analysis aims to serve as a basis for further historical reconstruction of vegetation changes during the Holocene in high-mountain environments based on fossil pollen data.

MATERIAL AND METHODS

POLLEN DATA

Fifty-eight modern pollen surface samples (moss polsters) were collected in natural Pinus sylvestris var. iberica forests from the Iberian Central System (Figure 1), with positional and altitudinal data recorded using a portable Garmin Ltd. Global Positioning System (GPS) device. Moss samples were collected over an area of approximately 100 [m.sup.2] by taking multiple moss polsters from the concerned site to ensure an even representation (Gaillard & al., 1992, 1994). The subsamples were sealed in plastic bags and mixed into one sample per site. Moss polsters are commonly used as surface samples for local modern pollen rain as it is assumed that they record an average of several years of pollen deposition and are a good analogue of fossil pollen assemblages.

Table 1 list the locations and gives a short description about each recorded site in the study region. A releve of vegetation was made at each sampling site.

Palynomorphs were extracted from the moss samples following the standard protocol developed by FAEGRI & IVERSEN (1989) and mounted on microscope slides in water-free glycerol. Pollen grains and non-pollen palynomorphs were identified according to MOORE & al. (1991), RAMIL & al. (1992) and LOPEZ-SAEZ & LOPEZ-MERINO (2007) at the lowest currently possible taxonomical level. Ononis type was palynologically identified by its grain larger than 27 [micro]m and its visible columellae (under phase contrast); and Viscum album according to LOPEZ-SAEZ (1999). Unfortunately it was impossible to differentiate pollen morphology of Genisteae species or genera (PRADOS & al., 1985).

A Nikon Eclipse 50i light-microscope (Melville, NY, U.S.A.) was used to identify and count pollen. Routine counting was carried out at 400x magnification. A minimum of 500 pollen grains were counted from each sample. Pollen percentages were calculated using a pollen sum excluding spores and hydro-hygrophytes, and presented as bars in a pollen percentage diagram. Tilia and TGView (GRIMM, 1992) and CorelDraw software were used to plot the pollen diagram (Figure 2).

ENVIRONMENTAL DATA

Twelve land-use and environmental variables were available for 58 sites (Table 1). Arboreal cover was graded on an ordinal scale from 0 to 5 as follows: 5 (75-100%), 4 (50-75%), 3 (25-50%), 2 (5-25%), 1 (1-5%), 0 (0%). In situ observation and the Forest Map of Spain (1:200.000) (RUIZ DE LA TORRE, 2002) were the tools used for estimating the current vegetation cover. Grazing pressure was calculated taking a 0 to 4 index into account (COURT-PICON & al., 2006). The climatic information was taken from the Digital Climatic Atlas of the Iberian Peninsula (NINYEROLA & al., 2006, 2007; PONS & NINYEROLA, 2007). Bioclimatical concepts and nomenclature follow the recent published proposals of RIVAS-MARTINEZ & al. (2007, 2011b). The topographic data came from the Shuttle Radar Topography Mission (FARR & al., 2007), resampled from 90 m to 200 m [(5810 x 4600 cells, Universal Transverse Mercator (UTM) projection, European datum 1950 (ED50)].

CLASSIFICATION

To identify clusters of samples based on their pollen content and hence to define specific Pinus sylvestris var. iberica forest communities, we used multivariate analysis. Although 87 pollen and spore taxa were identified in the surface samples, only palynomorph taxa present at > 1% were included (44). The analyses were performed on recalculated percentages after all modifications had been made. Hierarchical cluster analysis (HCA) was performed using the matrix of the euclidean distances and Ward's minimum variance method (Ward, 1963) with the program IBM SPSS Statistics 21. The percentage values of each taxa were standardized. The hierarchical relationships between clusters are illustrated by the dendrogram in Figure 3.

ORDINATIONS

Data were processed (modern surface pollen samples) by ordination analysis to obtain more information about the data structure. Principal component analysis (PCA) was used as a linear interpretation method because a previously applied detrended canonical correspondence analysis (DCCA) pointing to a linear response of pollen types (variables) to environmental gradients (Escudero & al., 1994; Birks & al., 1998). PCA is an indirect ordination procedure that reduces the multidimensional nature of a data set to a few dimensions (defined by principal components), with minimal loss of information. PCA was used to study the dominant features of the data set in terms of variance. Samples were square-root transformed for a better comparability (AUSTIN, 2013). PCA analysis was carried out on the correlation matrix of the pollen data; principal component scores of the pollen spectra (samples) and loadings for the variables (pollen types) were positioned on the main principal components in a biplot (Figures 4 and 5).

To extract more information from the modern pollen record, supplementary environmental gradients in the ordination project were included (Table 1). These gradients were gained from the interpolated climatic information from the Iberian Peninsula or from our own observation on human impact. We included TA (annual temperature), TM (maximum temperature in the hottest month), Tm (minimum temperature in the coldest month), PA (annual precipitation), PM (precipitation in the wettest month), Pm (precipitation in the driest month) and the measure of human activity (grazing) as passive (supplementary) environmental gradients. Partial redundancy analysis (RDA) was conducted to see which environmental gradient explains better the dataset (Table 2).

The analyses were run using the C2 1.5 software (JUGGINS, 2007). Graphics of the ordination biplots were achieved by using CorelDraw. Analyses were processed with palynomorph taxa present at > 1%.

NOMENCLATURE

Taxonomic nomenclature and authorities follow the published volumes of Flora iberica (CASTROVIEJO & al., 1986-2012) and the compilations of Flora Eu ropaea (TUTIN & al., 1964-1980); the exceptions are specifically mentioned in the floristic appendix Syntaxonomical scheme, nomenclature, and syntaxa authorities follow the compilations and proposals of RIVAS-MARTINEZ & al. (2001, 2002, 2011a).

RESULTS AND DISCUSSION

The pollen and non-pollen palynomorph percentage data for selected taxa are presented in Figure 2. Pinus sylvestris/nigra type pollen percentage in surface samples range from 22% to 89%. It is clearly evident from the results that Pinus sylvestris has, due to high pollen production and good dispersal ability, a larger pollen dispersal area that the other studied species (POSKA & PIDEK, 2010). In the study region Pinus nigra could also contribute to the total Pinus sylvestris/nigra type pollen deposition but it is likely of minor importance in comparison to the one of P. sylvestris.

On the first division level, the dendrogram of the HCA performed on pollen data (Figure 3) shows a clear discrimination between xerophilous Pinus sylvestris var. iberica forest communities (cluster 1; groups 1 to 6) and mesophilous ones (cluster 2; group 7). The following threshold of cluster 1 clearly separates samples from central-western orotemperate submediterranean (orosubmediterranean) communities (cluster [1.sup.1]) from those of the eastern supratemperate (suprasubmediterranean) and supramediterranean belts (cluster The division of cluster [1.sup.1] provides two groups (1 and 2) while cluster [1.sup.2] is divided into four groups (3 to 6).

Groups 1 and 2 represent xerophilous and orophilous (> 1600 m) forest communities from the orosubmediterranean belt of the Guadarrama and the Gredos ranges respectively (Table 1). Although the average annual precipitation (PA) values are high (usually > 1200 m), these forests are considered as xerophilous because they are covered by winter snow for at least 4-5 months and grow on moderate to highly stony soils with low edaphic development (GAVILAN & al., 1998; MARTINEZ-GARCIA & MONTERO, 2000; Gavilan, 2005; LOPEZ-LEIVA & al., 2009). They are characterized by noticeable percentages of Pinus sylvestris (> 20%) and significant frequencies of Poaceae, Genisteae and Juniperus (Figure 2). They are individualized by (i) higher Pinus sylvestris (68-89%) and Juniperus (3-8%) values in group 1 and lower ones in group 2 (22-51% and 2-4% respectively), (ii) lower percentages of Poaceae (3-7%), Cardueae (< 1%) and Genisteae (3-7%) in group 1 and relatively high values in group 2 (16-36%, 2-4% and 13-22%), (iii) the presence of Pteridium (< 1%) and Rumex acetosella s. l. only in group 2 while Cyperaceae, Apiaceae and Fabaceae undiff. are only present in group 1.

The first two axes of the PCA biplot (Figure 4, Table 2) explain 51% of variance in the pollen surface dataset. On the first axis (PCA-1) orosubmediterranean silicicolous Pinus sylvestris var. iberica forest communities (groups 1 to 4) are also separated from supratemperate submediterranean (suprasubmediterranean) and supramediterranean ones (groups 5 to 7). The PCA-1 explains 37% of the variance in the dataset and is positively correlated with altitude (r: 0.80), PA (r: 0.66), PM (r: 0.69) and Pm (r: 0.61) and negatively with TA (r: -0.80), TM (r: -0.64) and Tm (r: -0.75). On the first PCA axis (PCA-1) orophilous shrub vegetation (Genisteae, Juniperus) are separated from low-elevation mesophilous taxa (Pteridium, Prunus/Rubus, Cistus type, Veronica, Apiaceae, Rumex acetosella s. l.) located at the negative side of the axis (Figure 5). On the second PCA axis (PCA-2) pollen taxa from tree species (Pinus sylvestris/nigra) are located on the negative side with very high values, while high-mountain meadows (Poaceae) and shrubs (Genisteae, Erica australis s. l., E. arborea, Arctostaphylos uva-ursi, Ononis) are located on the positive side of the PCA-2. The axis explains 14% of the variance in the dataset and is most highly negative correlated with arboreal cover (r: -0.75) (Figure 4, Table 2).

A combined modern distribution range of Pinus sylvestris s.l. with gridded annual precipitation and January temperature (New & al., 1999) shows that its modern range in Europe lies between 400 and 1500 mm [year.sup.-1] and -18[degrees]C to +8[degrees]C respectively. These values are reflected in the populations of central Spain (Table 1). In fact, Pinus sylvestris s.l. has a wider climatic range that the broadleaved deciduous trees in terms of both temperature and precipitation, and their natural populations may inhabit climates that are suboptimal for their growth and development (REHFELDT & al., 2002; GAVILAN, 2005). In short, the PCA plot underscores the importance of thermotype (bioclimatic belts) for the arrangement of Pinus sylvestris var. iberica forest communities in the Iberian Central System. PCA-1 separates orosubmediterranean communities (Tm [less than or equal to] 0[degrees]C, TA < 9[degrees]C, groups 1 to 4) from suprasubmediterranean and supramediterranean ones (Tm [greater than or equal to] 1[degrees]C, TA > 9[degrees]C, groups 5 to 7) (Table 1).

Group 1 (samples 5 to 20) represents orotemperate submediterranean (orosubmediterranean) humid and hyperhumid Pinus sylvestris var. iberica microforests (mesoforests on deep soils at lower altitudes) from the Guadarrama and surrounding mountains, corresponding to the Avenello ibericae-Pinetum ibericae association (RIVAS-MARTINEZ & al., 2001, 2002). They grow between 1,632-1,921 m asl (Table 1) in siliceous soils in the Guadarrama Range (Navacerrada, Canencia and Navafria mountain passes, Figure 1). Although most samples from group 1 are well grouped, some of the pollen assemblages were difficult to interpret in the corresponding vegetation type. This is the case of sample 20, which on the PCA-2 is separated from the remaining samples from group 1, but grouping close with those of group 2 (Figure 4). This is due to its low arboreal cover (1). Samples from group 2 have an arboreal cover of 3 or 4, except sample 4 with only 1 (Table 1), but these pine forests from the Gredos Range correspond to small and isolated nuclei or scattered trees. Instead, pine forests communities from the Guadarrama Range are very dense and extensive. This may suggest that the second axis of the PCA (PCA-2) reflects not only the tree cover but rather forest density in a regional sense.

As a result of multivariate analyses (HCA and PCA), orosubmediterranean Pinus sylvestris var. iberica forest communities from the Gredos Range (group 2, samples 1 to 4) are very well discriminated from other pine forests of the Iberian Central System (Figures 3 and 4). This fact allows us to propose a new pinewood association: Echinosparto barnadesii-Pinetum ibericae SanchezMata, Gavilan & Lopez-Saez ass. nova hoc loco (Table 3, holotypus, rel. 1). It represents orotemperate submediterranean (orosubmediterranean) hyperhumid relict mesoforests growing on ranker soils at an altitudinal level ranging from 1,635 to 1,770 m asl throughout Gredos Mountains (Carpetan-Leonese biogeographical subprovince, Iberian Western Mediterranean province, Western Mediterranean subregion, Mediterranean region (RIVAS-MARTINEZ & al., 2007; Figure 1, Table 1). Floristically and biogeographically it is differentiated from the eastern above mentioned Avenello ibericae-Pinetum ibericae, from the Guadarrama and surrounding ranges, by the presence of western endemic elements such as Echinospartum barnadesii subsp. barnadesii and Festuca elegans subsp. merinoi (SANCHEZ-MATA, 1989, 1999; DE LA FUENTE & ORTUNEZ, 2001) and the absence of essentially eastern species such as Juniperus communis subsp. hemisphaerica and Festuca braunblanquetii (RIVAS-MARTINEZ & al., 2001, 2002). So far we have only been able to inventory these forests in the surrounding summits of Puerto del Pico Pass, as in the rest of the Gredos Range only isolated and scattered trees remain today (GENOCVA & al., 1992; LOPEZ-SAEZ & LOPEZ-GARCIA, 1994; LOPEZ-LEIVA & al., 2009).

The division of cluster 12 provides four main groups (3-6, Figure 3). First, it separates eastern orosubmediterranean forests (groups 3 and 4) from samples from xerophilous suprasubmediterranean and supramediterranean forests (groups 5 and 6). Then, the following threshold discriminates between basiphilous (group 4) and silicicolous forests (group 3). The first principal component axis (PCA-1) separates samples from groups 3 and 4 with low positive values from those of groups 5 and 6 with negative values (Figure 4). Groups 3 and 4 represent easternmost Pinus sylvestris var. iberica forest communities from the Ayllon and Pela ranges respectively. They are placed together on PCA-1 because they have less Tm ([less than or equal to] 0 C) and TA (< 9[degrees]C) but also because their PA (< 700 mm) and Pm (< 83 mm) values are lower; and along PCA-2 (positive values) by their low arboreal cover (3 or 4) (Figure 4, Table 1).

Group 3 (samples 38, 55 and 56) represents supramediterraneanm, suprasubmediterranean and orosubmediterranean subcontinental humid and hyperhumid Pinus sylvestris var. iberica mesoforests from the Ayllon Range growing between 1,520-1,800 m asl (Table 1) on siliceous soils (quartzites, slates and sandstones) in the oromediterranean belt of the Ayllon Range (Alto Rey Range, Figure 1). These forests were studied by De la Cruz & Peinado (1996) without assigning any specific association, but pointing out their differences with western communities from the Guadarrama Range (Avenello ibericae-Pinetum ibericae) by the absence of Cytisus oromediterraneus and Juniperus communis subsp. alpina. Floristically they are characterized by Avenella iberica, Juniperus communis subsp. hemisphaerica, Cistus laurifolius, the relative abundance of Ericaceae (Arctostaphylos uva-ursi, Calluna vulgaris, Erica australis subsp. aragonensis, and E. arborea) and the virtual absence of broom species (Genisteae, ABAD-GARRIDO & MARTINEZ-LABARGA, 2009). The pollen diagram (Figure 2) clearly indicates the importance of the above mentioned taxa (Cistus type 2-3%, Calluna vulgaris 1.5-3%, Juniperus 2-4%, Erica arborea 28%, E. australis 2-3%, Arctostaphylos uva-ursi 2-5%) and the sporadic percentages of Genisteae (< 0.5%). Samples from group 3 in the PCA plot (Figure 4) are arranged close to the relevant pollen indicator taxa (Figure 5) and therefore represent quite well the observed vegetation conditions quite well. According to these facts, we propose a new association for these forests: Erico aragonensis-Pinetum ibericae Sanchez-Mata, Gavilan & Lopez-Saez ass. nova hoc loco (DE LA CRUZ & PEINADO 1996: 340, Table 1, holotypus rel. 1).

Group 4 (samples 57 and 58) represents semi-continental subhumid basiphilous relict mesoforests of the Ononido aragonensis-Pinetum ibericae from the oromediterranean belt of the Pela Range (Figure 1). The occurrence of these basiphilous forests can be recognized in the pollen diagram (Figure 2) by relatively high percentages of Ononis t. (3.3-5.6%), Juniperus (6-10%), Arctostaphylos uva-ursi (1-8%) and Labiatae (2%), although Pinus sylvestris/nigra (43-53%) is the dominant pollen type in the dataset. Floristically they are rich in Ononidetea species and they are characterized by Juniperus communis subsp. hemisphaerica, Ononis aragonensis, Bupleurum gramineum, Vicia pyrenaica and Pulsatilla rubra (DE LA CRUZ & PEINADO, 1996; GAVILAN & al., 2012). Although these forests occupy low altitudes (1,370-1,445 m asl, Table 1), the climatic parameters that characterize them, particularly their thermicity index (It 43.4-62.4), leads to define these forests as orophilous, occupying the lower oromediterranean belt (DE LA CRUZ & PEINADO, 1996; MARTINEZ-GARCIA & MONTERO, 2000). Both samples 57 and 58 are arranged close to Ononis type and other above mentioned pollen taxa in the PCA plot (Figure 5).

Group 5 (samples 39 to 41) included pollen assemblages from xero-mesophilous Pinus sylvestris var. iberica forest communities (TA ~10[degrees]C, Tm > 1[degrees]C, PA ~ 1000 mm) from the northern Gredos Mountains developing at an altitudinal level ranging from 1465 to 1575 m (Figure 1, Table 1) on granite soils. These three samples are individualized in the same cluster (Figure 3), as well as in the PCA biplot (Figure 4), because they produce pollen assemblages with low values of Pinus sylvestris/nigra (53-56%), Poaceae (10-17%), Genisteae (1.5-3%) and Juniperus (< 0.3%)-major differences separating these samples from those of group 2-, and average percentages of mesophilous taxa such as Pteridium (2.3%), Veronica (1-2%) and Prunus/Rubus (0-1%). They are also characterized by the presence of the hemi-parasitic plant Viscum album (1-2%), which currently only parasitizes Pinus sylvestris populations of the northern slopes of the Gredos Range (LOPEZ-SAEZ, 1992, 1993; LOPEZ-SAEZ & SANZ de Bremond, 1992). Groups 5 and 6 are placed close in the cluster 12 and the PCA-1 due to their palynological affinities (Figures 3 and 4), but they are individualized on the PCA-2 by high percentages of Pteridium in group 6 and the absence of Cistus type in group 5 (Figure 2). These two palynomorph taxa are positioned with negative values on PCA-2 (close to samples from group 6) while samples from group 5 show positive values on this axis (Figures 4 and 5).

Floristically, group 5 represents Pinus sylvestris var. iberica relict mesoforests from the supratemperate submediterranean and supramediterranean humid belt of the Gredos Mountains only present in the northern slopes of the Gredos Range in scattered nuclei (Navarredonda de Gredos, Hoyos del Espino). They are characterized by western endemic elements such as Festuca elegans subsp. merinoi, Centaurea amblensis, Ornithogalum concinnum and Genista cinerascens (MARTINEZ-GARCIA & MONTERO, 2000; DE LA FUENTE & ORTUNEZ, 2001), as well as dense broom communities mainly composed by Cytisus scoparius and Genista florida (GAVILAN & al., 2011). This fact allows us to propose a new pinewood association: Festuco merinoi-Pinetum ibericae Sanchez-Mata, Gavilan & Lopez-Saez ass. nova hoc loco (Table 3, holotypus, rel. 5).

Finally, group 6 (samples 21 to 37) and group 7 (samples 42 to 54) represent xero-thermophilous and mesophilous Pinus sylvestris var. iberica forests respectively, from the Guadarrama Range, except sample 42 from the Gredos Range. Their pollen assemblages are characterized by noticeable percentages of Pinus sylvestris/nigra (55-81%), Cistus, Pteridium, Poaceae, and significant frequencies (< 5%) of Scrophulariaceae, Cardueae, Erica arborea, Labiatae, Prunus/Rubus, Crataegus and Viscum album (Figure 2). The PCA axis 1 separates samples from group 6 (score 0 to -0.5) and group 7 (score -0.5 to -1) on the left part of the axis with negative values (Figure 4), in relation to altitude and climatic parameters (Table 1). Our results coincide with those obtained by MARTINEZ-GARCIA & MONTERO (2000). However, some overlap is detected on the PCA-2 (Figure 4). Higher values of anthropogenic pollen taxa (Cichorioideae, Cardueae, Plantago lanceolata) and coprophilous fungi in samples from group 7 (Figure 2) indicates that pine forests at lower altitudes are subjected to greater human impact, especially livestock grazing (LOPEZ-SAEZ & LOPEZ-MERINO, 2007).

Groups 6 and 7 are individualized both in the HCA (clusters 12 and 2) and PCA-1 (Figures 3 and 4) by the following features: (i) higher percentages of Pteridium (7.5-15.7%), Rumex acetosella, Prunus/Rubus, Crataegus, Cichorioideae, Plantago lanceolata, Caryophyllaceae, Apiaceae and coprophilous fungi in mesophilous forests (group 7); (ii) higher values of xerophilous taxa such as Poaceae, Genisteae and Cistus in xerotermophilous pollen assemblages (group 6); and, (iii) the presence of Veronica only in group 7 and Lavandula stoechas in group 6. Sample 21 is included in group 6 although it is placed into a different cluster in the HCA, but in an intermediate position close to group 7. On PCA-1 this sample is also situated between groups 6 and 7. Its pollen assemblage is similar to those from group 6 but with high percentages of coprophilous fungi like samples from group 7.

Groups 6 and 7 represent supratemperate submediterranean and supramediterranean subhumid and humid semicontinental Pinus sylvestris var. iberica mesoforests of the Pteridio aquilini-Pinetum ibericae association from the Guadarrama Range (RIVAS-MARTINEZ & al., 2001, 2002). These forests have been probably extended by human activities and sometimes it is difficult to discriminate between natural and cultivated stands. Floristically, they are characterized by Avenella iberica, Conopodium pyrenaeum, Festuca braun-blanquetii, Galium rotundifolium, Juniperus communis subsp. hemisphaerica and Pteridium aquilinum. In the oromediterranean belt they are replaced by the Avenello ibericaePinetum ibericae microforests. Pollen types for taxa almost exclusively found in groups 6 and 7, such as Pteridium, Prunus/Rubus, Cistus, Veronica and Lavandula stoechas have been found on the negative side of the first axis (Figures 4 and 5), and thus characterize samples from the Pteridio aquilini-Pinetum ibericae.

CONCLUSIONS

Recent years have seen a very controversial discussion among paleoecologists (CARRION & FERNANDEZ, 2009; CARRION, 2010; LOPEZ-SAEZ & al. 2010b) and phytosociologists (FARRIS & al., 2010; LOIDI & al., 2010; MUCINA, 2010; LOIDI & FERNANDEZ-GONZALEZ, 2012) in reference to (i) different interpretations of the 'potential natural vegetation' (PNV) concept, and (ii) the conceptualization of vegetation dynamics from a historical perspective. This debate has even reached to other researchers concerning the possibilities of mapping PVN (CHIARUCCI & al., 2010; LOIDI & FERNANDEZ-GONZALEZ, 2012; SOMODI & al., 2012).

It is not our goal to keep on feeding this absurd misunderstanding and the best evidence is the presented paper demonstrating precisely that both positions should not be so far away but the opposite: the convenience of a multidisciplinary and interdisciplinary approach to an integrated framework for the study of plant communities from a dynamic, temporal and spatial perspective.

It is true that for a long time phytosociological literature obviated Pinus sylvestris var. iberica forests from the Iberian Central System; in some cases they have been considered as vegetation complexes and framed within different geographical races (GALAN DE MERA & al., 1999); the remaining relict forests from the Gredos, Ayllon and Pela ranges, as well as those from the supramediterranean belt of the Guadarrama Range, have been assumed to be derived mainly from afforestation (RIVAS GODAY, 1956; RIVAS-MARTINEZ, 1963, 1964, 1968, 1975, 1982, 1987; IZCO, 1984; RIVAS-MARTINEZ & al., 1987a, 1987b, 1990; PEINADO & MARTINEZ-PARRAS, 1985; RIVAS-MARTINEZ & CANTO, 1987; MONJE-ARENAS, 1988; SANCHEZ-MATA, 1989; FERNANDEZ-GONZALEZ, 1991). However, in some cases it has been recognized the potential character of Pinus sylvestris var. iberica communities in the Gredos Range taking into account fossil pollen records (SANCHEZ-MATA, 1999). RIVAS-MARTINEZ & MOLINA (1997, nom. inval. ICPN, art. 3; in Rivas-Martinez & al., 1999) defined for the first time the silicicolous and climatophilous pinewood communities Avenello ibericae-Pinetum ibericae from the orotemperate submediterranean territory and Pteridio aquilini-Pinetum ibericae (Galio rotundifolii-Pinetum ibericae Rivas- Martinez & Molina 1997, nom. inval. ICPN, art. 3; in Rivas-Martinez & al., 2002) from the supramediterranean and supratemperate submediterranean of the Guadarrama Range, representing both the natural potential vegetation. DE LA CRUZ & PEINADO (1996) proposed simultaneously the Galio idubedae-Pinetum sylvestris association for the basiphilous pinewoods from the Pela Range. Later studies have continued accepting them (PEINADO & al., 2009), although the latter has been corrected as Ononido aragonensis-Pinetum ibericae (RIVAS-MARTINEZ & al., 1999, 2001, 2002).

According to these new phytosociological proposals, modern pollen rain studies and multivariate analyses allow us to discriminate the peculiarities of Pinus sylvestris var. iberica forest communities from the Gredos Range and to propose two new phytosociological associations: Echinosparto barnadesii-Pinetum ibericae and Festuco merinoi-Pinetum ibericae.

In fact, fossil pollen data have revealed the existence of a continuous band of Scots pine forests on both orosubmediterranean and suprasubmediterranean areas (reaching some supramediterranean sites) of this range during at least the last seven thousand years. Pollen records from Puerto de la Pena Negra (1,909 m asl), Puerto de Chia (1,701 m asl), Puerto de Serranillos (1,700 m asl), Narrillos del Rebollar (1,560 m asl), Hoyos del Espino (1,450 m), Navarredonda de Gredos (1,550 m asl), Garganta de los Caballeros (1,365 m asl), Hoyocasero (1,250 m asl), Baterna (1,140 m asl), and Riatas (1,120 m asl) peat bogs provide clear evidence of these facts (FRANCO-MUGICA, 1995; ANDRADE & al., 1996; FRANCO-MUGICA & al., 1997; DORADO & al., 2001; ANDRADE & GONZALEZ-JONTE, 2007; LOPEZ-MERINO & al., 2009; LOPEZ-SAEZ & al., 2009a, 2009b; RUIZ-ZAPATA & al., 2011).

The development of La Mesta system, the organization of high-mountain pastoral spaces with the use of montane areas as summer pasturelands, as well as the repeated use of fire, since 13th century, but more particularly after its dissolution in 1836, were the main reasons of the abrupt disappearance of most Pinus sylvestris forests from the Gredos Range (LOPEZ-SAEZ & al., 2009b), where only small groups are currently represented on the northern slope and scattered trees on both northern and southern slopes (GENOVA & al., 1992; MARTINEZ-GARCIA & MONTERO, 2000). A similar picture is observed in other mountains such as Guadarrama and Ayllon ranges (FRANCO-MUGICA, 1995; FRANCO-MUGICA & al., 1998, 2001b; GOMEZ-GONZALEZ & al., 2009) although with much lesser intensity allowing the current existence of wide forests; and even in the Pela Range where pinewoods deforestation occurred since the Roman period (CURRAS & al., 2012). It is particularly noteworthy that the fossil pollen record also demonstrates the existence of Pinus sylvestris forests in western areas of the Iberian Central System where they have currently disappeared, such as the Bejar and Francia ranges for most of the Holocene (ATIENZA & al., 1996; LOPEZ-JIMENEZ & LOPEZ-SAEZ, 2005; RUIZ-ZAPATA & al., 2011; ABEL-SCHAAD, 2012; ABEL-SCHAAD & LOPEZ-SAEZ, 2013; MORALES-MOLINO & al., 2013).

SYNTAXONOMICAL SCHEME

JUNIPERO SABINAE-PINETEA SYLVESTRIS Rivas-Martinez 1965 nom. inv.
propos.
  Junipero sabinae-Pinetalia sylvestris Rivas-Martinez 1965 nom. inv.
  propos.
    Junipero sabinae-Pinion ibericae Rivas Goday ex Rivas Goday &
    Borja 1961 corr. Rivas-Martinez & J.A. Molina in Rivas-Martinez,
    Fernandez-Gonzalez & Loidi 1999
      Ononido aragonensis-Pinetum ibericae (Rivas Goday & Borja
      1961) Rivas-Martinez 1969 corr.
      Rivas-Martinez, T.E. Diaz, Fernandez-Gonzalez, Izco, Loidi,
      Lousa & Penas 2002
    Avenello ibericae-Pinion ibericae Rivas-Martinez & J.A. Molina in
    Rivas-Martinez, Fernandez-Gonzalez & Loidi 1999
      Avenello ibericae-Pinetum ibericae Rivas-Martinez & J.A. Molina
      in Rivas-Martinez, Fernandez-Gonzalez & Loidi 1999
      Pteridio aquilini-Pinetum ibericae Rivas-Martinez & J.A. Molina
      in Rivas-Martinez & al. 2002
      Echinosparto barnadesii-Pinetum ibericae Sanchez-Mata, Gavilan &
      Lopez-Saez ass. nova
      Festuco merinoi-Pinetum ibericae Sanchez-Mata, Gavilan &
      Lopez-Saez ass. nova
      Erico aragonensis-Pinetum ibericae Sanchez-Mata, Gavilan &
      Lopez-Saez ass. nova

FLORISTIC APPENDIX

Avenella iberica (Rivas Mart., Izco & Costa) Rivas Mart.
Cytisus striatus subsp. eriocarpus (Boiss. & Reut.) Rivas Mart.
Erica australis subsp. aragonensis (Willk.) Cout.
Festuca braun-blaunquetii (Fuente, Ortunez & Ferrero) Rivas Mart.,
  Fern. Gonz. & Loidi
Festuca durandoi Clauson
Festuca elegans subsp. merinoi (Pau) Fuente et Ortunez
Festuca gredensis Fuente & ortunez
Jasione montana subsp. echinata (Boiss. & Reut.) Rivas Mart.
Festuca paniculata subsp. multispiculata Rivas Ponce & Cebolla
Leucanthemopsispallida subsp. alpina (Boiss. & Reut.) Rivas Mart.,
  Fern. Gonz. & Sanchez-Mata
Pinus sylvestris var. iberica Svoboda


doi: 10.5209/rev_LAZA.2013.v34.n1.43599

Received: 30 April 2013

Accepted: 13 November 2013

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Jose Antonio Lopez-Saez (*), Daniel Sanchez-Mata (**), Francisca Alba-Sanchez (***), Daniel Abel-Schaad (*), Rosario G. Gavilan (**) & Sebastian Perez-Diaz (*)

(*) Grupo de Investigacion Arqueobiologia. Instituto de Historia. CCHS. CSIC. Albasanz 26-28. E-28037 Madrid. Espana- Spain. E-mail: joseantonio.lopez@cchs.csic.es, dabel222@hotmail.com, sebas.perezdiaz@gmail.com

(**) Departamento de Biologia Vegetal II. Facultad de Farmacia. Universidad Complutense. E-28040 Madrid. Espana-Spain. E-mail: dsmata@ucm.es, rgavilan@ucm.es

(***) Departamento de Biologia Vegetal. Facultad de Ciencias. Universidad de Granada. E-18001 Granada. Espana-Spain. Email: falba@ugr.es

Table 1
Study sites and site characteristics for the 58 modern pollen surface
samples from the Iberian Central System. Parameters: Tm: minimum
temperature in the coldest month, TM: maximum temperature in the
hottest month, TA: annual temperature, Pm: precipitation in the driest
month, PM: precipitation in the wettest month, PA: annual
precipitation.

Sample     UTM X     UTM Y      Altitude     Canopy    Grazing
                      (m)        Cover      pressure
1         327709    4464812       1770         4          0
2         327848    4464725       1715         4          0
3         327867    4464350       1590         3          0
4         326597    4464082       1635         1          1
5         416931    4517116       1800         5          0
6         416672    4516225       1880         5          1
7         418093    4519516       1780         5          0
8         416618    4516525       1816         5          0
9         413883    4515273       1888         5          0
10        415407    4515938       1860         5          0
11        415337    4514482       1750         5          0
12        414783    4513166       1650         4          0
13        419149    4519056       1830         5          0
14        416604    4516342       1874         5          0
15        419040    4519753       1840         4          0
16        420360    4520139       1700         5          0
17        429870    4519977       1785         5          0
18        430590    4519855       1632         5          0
19        431758    4537645       1816         5          0
20        430462    4537131       1921         1          0
21        398281    4500981       1458         4          3
22        397621    4500359       1473         5          2
23        402525    4506945       1425         4          0
24        402768    4506096       1572         5          0
25        399226    4506837       1350         5          0
26        403764    4502750       1510         5          0
27        404179    4505126       1400         5          0
28        405427    4504572       1350         4          0
29        402585    4506997       1487         5          0
30        401615    4506304       1425         4          0
31        399328    4507690       1350         5          0
32        414113    4517053       1692         5          0
33        417166    4523212       1725         4          0
34        431401    4519460       1533         5          0
35        432348    4518261       1457         5          0
36        432267    4516523       1305         5          0
37        431047    4536158       1654         4          0
38        489594    4557566       1800         4          0
39        321560    4468930       1572         5          0
40        320378    4469216       1575         4          0
41        316024    4467375       1465         4          0
42        330826    4472781       1340         5          1
43        423550    4520940       1400         5          0
44        424949    4521863       1320         5          0
45        425284    4522320       1300         4          0
46        424945    4523467       1325         5          1
47        422678    4520646       1500         5          0
48        434957    4518806       1305         5          1
49        434826    4518377       1215         4          1
50        413441    4520519       1320         5          1
51        415464    4518224       1564         5          1
52        413445    4520865       1293         5          1
53        413321    4522269       1254         5          1
54        413264    4523988       1215         5          2
55        491756    4560145       1685         3          0
56        484031    4561244       1520         4          0
57        493275    4566455       1445         3          0
58        485912    4569044       1370         3          1

Sample     Tm      TM      TA      Pm      PM      PA

1         -0.1    19.8     8.3    21.9    171.6   1205
2          0.6    20.1     8.8     21     173.6   1211
3          1.3    20.6     9.5    20.5    175.9   1220
4          0.7    20.1     8.8    19.1     174    1214
5         -1.5    17.1     6.5    33.8    155.1   1207
6         -2.3    16.6      6     38.2    165.3   1303
7         -0.1    18.2     7.6    27.6     138    1049
8         -1.8    16.9     6.3    38.6    166.5   1308
9         -2.6    15.7     5.3    33.1    183.5   1381
10        -1.7    16.2     5.9    30.7    177.7   1330
11        -1.3    16.4     6.3    31.4    186.5   1380
12        -0.3    17.7     7.6    30.5    174.2   1273
13        -1.1    17.7     6.9    27.1     133    1018
14        -2.3    16.6      6     38.2    165.3   1303
15         -1     17.7      7     25.4     132    1001
16        -0.4    18.1     7.5    23.9    126.5    957
17        -0.8    18.5     7.6    27.4    106.8    862
18         -1     18.5     7.6    29.4    106.2    876
19        -0.1    18.5     7.8    23.4    91.2     732
20        -0.4     18      7.2    22.4    95.3     751
21         1.3    19.9     9.2    19.8    107.2    794
22         1.7    20.1     9.6    19.3    107.3    789
23         1.4    19.4     9.1    23.7    112.5    851
24          1     19.3     8.9    25.2    118.4    885
25         1.9    19.3     9.4    27.5     103     815
26         2.7    20.9    10.6     19      130     860
27         2.2    20.1     9.7    17.8    125.2    852
28         2.7    20.9    10.6    18.5    128.3    859
29         1.4    19.4     9.1    23.7    112.5    851
30         1.5    19.3     9.1    25.6    112.2    859
31         2.8    19.7     9.8    20.9    99.9     743
32        -0.4    17.4     7.3    31.4    166.9   1253
33        -0.2    18.6      8     29.6    116.4    946
34        -0.1    19.3     8.6    31.9    104.8    883
35         1.2    19.7     9.2    21.6    100.8    778
36         2.9    20.6    10.7    18.3    99.6     735
37         0.8     19      8.4    21.3    92.2     726
38        -0.9    17.2     6.7    20.6    80.9     645
39         1.2    20.6     9.5    18.7    144.5   1006
40         1.3    20.5     9.6     18     139.3    966
41         1.6     21     10.1    21.1    138.3    967
42         1.8    21.1    10.2    17.4    141.1    986
43         1.7    19.5     9.5    25.9    119.5    917
44         1.9    19.3     9.5    23.8    113.4    868
45         2.3    19.5     9.9    24.7     113     870
46         2.2    19.2     9.8    23.2    109.4    843
47         1.2    19.2      9     25.8    120.1    922
48         2.9    20.8    10.7    16.4    94.6     695
49         3.2    21.1     11      17     94.9     700
50         1.7    19.6     9.6    24.9    129.6    975
51        -0.2    18.1     7.9    31.1    148.6   1141
52         1.8    19.8     9.7    24.4    126.6    955
53          2     20.1     10     26.1    118.6    917
54         2.4    20.5    10.4    23.1     108     836
55        -0.1    17.6     7.7    25.5    82.6     663
56         0.1    18.1     7.9    24.5    82.9     685
57         0.1    18.2     8.1    25.5    78.4     627
58         0.7    18.9     8.6    24.2    76.5     636

Table 2
Results of partial RDA and PCA for pollen data of surface samples All
gradients are significant at the 5% significance level
(p [less than or equal to] 0.05)

Gradient       Explained   p-value     Correlation       Correlation
               variance                with PCA-1        with PCA-2
                                     ([lambda]=0.37)   ([lambda]=0.14)

Altitude          17%       0.002         0.80              0.33
Canopy cover      10%       0.005         0.12              -0.75
Grazing           3%        0.01         -0.62              0.19
TA                14%       0.002        -0.80              0.05
TM                11%       0.005        -0.64              0.09
Tm                8%        0.005        -0.75              0.02
PA                15%       0.002         0.66              0.17
PM                12%       0.002         0.69              0.12
Pm                9%        0.005         0.61              0.05

Table 3
Echinosparto barnadesii-Pinetum ibericae Sanchez-Mata, Gavilan &
Lopez-Saez ass. nova (1-4) Festuco merinoi-Pinetum ibericae Sanchez-
Mata, Gavilan & Lopez-Saez ass. nova (5-8) (Avenello ibericae-Pinion
ibericae, Junipero sabinae-Pinetalia sylvestris, Junipero sabinae-
Pinetea sylvestris)

Altitude (1=10 m)                            177    180    175    171
Number of species                             15     15     17     20
Releve number                                 1      2      3      4

Characteristics
Pinus sylvestris var. iberica                 5      4      4      4
Cytisus oromediterraneus                      1      2      1      1
Avenella iberica                              1      2      +      +
Festuca elegans subsp. merinoi                .      .      +      +
Genista cinerascens                           .      .
Echinospartum barnadesii                      2      3      3      4
Juniperus communis subsp. alpina              1      +      1      2
Shrubby, forest and perennials companions
Festuca gredensis                             1      1      1      1
Luzula lactea                                 1      1      1      +
Erica arborea                                 .      +      +      +
Pteridium aquilinum                           .      .      +      +
Poa bulbosa                                   .      +      +      .
Agrostis castellana                           1      +      1      1
Cytisus scoparius                             .      .      .      .
Genista florida                               .      .      .      .
Santolina oblongifolia                        .      .      .      .
Cytisus striatus subsp. eriocarpus            1      +      +      +
Festuca paniculata subsp. multispiculata      .      .      .      .
Others
Arrhenatherum elatius s. l.                   1      1      +      +
Cerastium ramosissimum                        .      +      1      +
Rumex acetosella                              +      .      .      +
Carduus carpetanus                            +      .      .      .
Leucanthemopsis pallida subsp. alpina         .      +      +      +
Armeria caespitosa                            1      1      +      +
Hieracium castellanum                         .      .      .      .
Achillea millefolium                          .      .      .      .
Silene nutans                                 .      .      .      .
Hypochoeris radicata                          .      .      .      .
Spergula morisonii                            .      .      .      .
Jasione montana subsp. echinata               .      .      .      .
Lotus corniculatus s. l.                      .      .      .      .
Anthoxanthum odoratum                         .      .      .      .
Arenaria montana                              .      .      .      .
Conopodium pyrenaeum                          .      .      .      .
Viola riviniana                               .      .      .      .
Ornithogalum concinnum                        .      .      .      .

Altitude (1=10 m)                            150    153    146    157
Number of species                             23     27     30     34
Releve number                                 5      6      7      8

Characteristics
Pinus sylvestris var. iberica                 5      4      4      4
Cytisus oromediterraneus                      1      1      +      1
Avenella iberica                              1      1      1      +
Festuca elegans subsp. merinoi                2      2      2      2
Genista cinerascens                           1      2      2      2
Echinospartum barnadesii                      .      .      .      .
Juniperus communis subsp. alpina              .      .      .      .
Shrubby, forest and perennials companions
Festuca gredensis                             1      1      1      1
Luzula lactea                                 +      +      +      +
Erica arborea                                 +      1             +
Pteridium aquilinum                           1      1      1      1
Poa bulbosa                                   +      1      1      +
Agrostis castellana                           .      1      .      .
Cytisus scoparius                             +      +      1      1
Genista florida                               +      +      1      1
Santolina oblongifolia                        +      +      1      +
Cytisus striatus subsp. eriocarpus            .      .      .      .
Festuca paniculata subsp. multispiculata      +      .      +      +
Others
Arrhenatherum elatius s. l.                   +      .      .      +
Cerastium ramosissimum                        .      +      +      +
Rumex acetosella                              .      1      1      1
Carduus carpetanus                            +      +      +      +
Leucanthemopsis pallida subsp. alpina         +      .      .      +
Armeria caespitosa                            .      .      .      .
Hieracium castellanum                         +      +      1      1
Achillea millefolium                          +      +      1      +
Silene nutans                                 +      +      1      +
Hypochoeris radicata                          +      1      1      +
Spergula morisonii                            +      +      +      +
Jasione montana subsp. echinata               +      .      1      +
Lotus corniculatus s. l.                      .      +      1      1
Anthoxanthum odoratum                         .      1      +      +
Arenaria montana                              .      +      +      1
Conopodium pyrenaeum                          .      +      +      +
Viola riviniana                               .      .      1      +
Ornithogalum concinnum                        .      +      .      +

Other species: shrubby, forest and perennials companions: Sorbus
aucuparia + in 4 and Ilex aquifolium + in 7. Others: Thymus mastichina
and Nardus stricta + in 1; Jasione sessiliflora and Urtica dioica + in
4; Senecio adonidifolius and Tanacetum corymbosum + in 7; Arenaria
querioides, Hieracium murorum and Centaurea amblensis + in 8.

Localities: avila, Gredos Range. 1-4: Surrounding summits of Puerto
del Pico, La Rubia, Hoyos del Espino and Navarredonda de Gredos,
holotypus Echinosparto-Pinetum rel. 1; 5,6,8: Navarredonda de Gredos
mountain summits, holotypus Festuco-Pinetum rel. 5; 7: Hoyos del
Espino summits.
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Title Annotation:articulo en ingles
Author:Lopez-Saez, Jose Antonio; Sanchez-Mata, Daniel; Alba-Sanchez, Francisca; Abel-Schaad, Daniel; Gavila
Publication:Lazaroa
Date:Jan 1, 2013
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