Quercus rotundifolia Lam. Woodlands of the Southwestern Iberian Peninsula

: The holm oak woodlands as ecotonic phytocoenoses occur under different ecological conditions, and frequently representing the climax of edaphoxerophilous series of crests and siliceous rocky areas. In this paper we study the ﬂoristic, ecological, and biogeographical differences of the edaphoxerophilous holm oak woodlands of the southwestern Iberian Peninsula, included in the Querco rotundifoliae-Oleenion sylvestris suballiance. Our phytosociological (Braun–Blanquet methodol-ogy) and numerical analysis (hierarchical cluster analysis) of three formerly described association and our own samples lead us to propose a new association: Ulici argentei-Quercetum rotundifoliae , growing mostly on semihyperoceanic Monchique Sierran Biogeographic District, on rocky slopes and outcrops derived from schists and greywackes. Moreover, we present an overview of ecological features and the diversity of plant communities occurring in the serial dynamic of the thermophile holm oak woodlands of the southwest of the Iberian Peninsula.


Introduction
The vegetation geoseries or geosigmetum represents the basic unit of dynamic-catenal phytosociology. These correspond to a catena of edaphoxerophilous, climatophilous, climato-temporihygrophilous, and edaphohygrophilous vegetation series, which is found around a given bioclimatic belt and ascribed to an accurate biogeographical territory [1]. The corresponding topographic geosigmetum, which express the universal crest-slopepiedmont-valley model, comprise the vegetation series or sigmeta (sigmetum) zonation along specific ecological features, resulting from geomorphic systems that interact over time to shape the topography of the landscape unit.
According to Rivas-Martínez et al. [2] and Loidi [3], the climatophilous or zonal series occupy large areas of land (normally, are found in hillslopes) and are located on mature soils according to the mesoclimate, i.e., are conditioned by non-exceptional conditions; the temporihygrophilous series, included among the climatophilous, are those which have

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The Table 1 (Appendix A) reveals the differences in floristic composition among 147 these four groups defined in the dendrogram, based on the presence/absence of diag-148 nostic species as a response to different bioclimatic stages, edaphic conditions, and bio-149 geographic distributions (Appendix A, Table 2; Figure 2). The Quercus rotundifolia 150 woodlands of the Southwestern Iberian Peninsula (in the Querco rotundifoliae-Oleenion 151 sylvestris suballiance) are briefly described below, from a floristic, ecological, and dy-152 namic point of view. 153

Data Collection
Field sampling was carried out from March 2013 to April 2014, following the Zurich-Montpellier phytosociological method [6][7][8][9]. Here, we defined a new woodland association, based on the comparison of phytosociological relevés, performed in Table A1. According to Biondi [9], each relevé is a floristically and ecologically homogeneous plant community that represents the plant association on the ground. Within this definition, for each relevé, all plants that are found in an area whose floristic, structural, and ecological conditions are homogenous, were identified and assigned a quantitative value or index for their coverage, using the conventional abundance-dominance scale of Braun-Blanquet [10].
The Table A1 (Appendix A) reveals the differences in floristic composition among these four groups defined in the dendrogram, based on the presence/absence of diagnostic species as a response to different bioclimatic stages, edaphic conditions, and biogeographic distributions (Appendix A, Table A2; Figure 2). The Quercus rotundifolia woodlands of the Southwestern Iberian Peninsula (in the Querco rotundifoliae-Oleenion sylvestris suballiance) are briefly described below, from a floristic, ecological, and dynamic point of view.

Description of Holm Oak Communities
I-Ulici argentei-Quercetum rotundifoliae ass. nova hoc loco (Appendix A, Table A3; clusters 1-10) The relevés of the new association Ulici argentei-Quercetum rotundifoliae (holotypus Appendix A, Table A3, relevé 7) have a high dissimilarity in relation to the other associations. These holm oak woodlands are exclusive to the southern territories of the Monchique Sierran District, particularly in the sub-coastal siliceous areas of the Caldeirão Mountains [24]. They form edaphoxerophilous micro-forests on incipient lithosols, rocky slopes and outcrops derived from schists and greywackes, and are found in the thermomediterranean sub-humid belt, where it appears to have its optimum.
Of particular interest is the frequent presence of Ulex argenteus, an acidic gorse, exclusively found in the oceanic biogeographic areas of the Algarve and Monchique Sector. Of the various species represented here, we also highlight the presence of other oceanic species, such as: Scilla monophyllos, Avenella stricta, Lavandula viridis, Osyris lanceolata, Cynara algarbiensis. As shown in Table A3 (Appendix A), the floristic composition of these woods also contains other characteristic species from the Quercetea ilicis species, like Erica arborea, Quercus coccifera, Pistacia lentiscus, Arbutus unedo, all occur frequently and Rhamnus alaternus, Phillyrea angustifolia, Olea europaea var. sylvestris, more occasionally. The canopy is further enriched by Smilax aspera var. altissima, Lonicera implexa, Rubia peregrina. Regarding the xerophilous position, the flora of the Ulici argentei-Quercetum rotundifoliae is characteristic with its much more obvious rupicolous elements: Umbilicus rupestris, Phagnalon saxatile, Rumex induratus, Saxifraga granulata, Cheilanthes guanchica, Sanguisorba rupicola, among others. The degradation of the Ulici argentei-Quercetum rotundifoliae woodland lead us to the formations dominated by We place the Ulici argentei-Quercetum rotundifoliae ass. nova hoc loco, at the syntaxonomic level, in the Querco rotundifoliae-Oleenion sylvestris suballiance (Oleo sylvestris-Quercion rotundifoliae, Quercetalia ilicis, Quercetea ilicis).

II-Myrto communis-Quercetum rotundifoliae Rivas Goday in Rivas Goday, Borja, Esteve, Galiano, Rigual & Rivas-Martínez 1959 (clusters 11-20, Figure 2)
This holm oak association occurs through the southern and southwestern part of the Iberian Peninsula, where represents the climax vegetation over siliceous substrates. Despite the wide distribution, it is in the thermomediterranean sites with dry ombrotype of the Mediterranean-Iberoatlantic biogeographic territories that this community constitutes the mature climatic stage, and therefore is not present in Monchique Sierran District, where it is substituted by the association Ulici argentei-Quercetum rotundifoliae. As evidenced by Rivas-Martínez et al. [13], the characteristic species of the Myrto communis-Quercetum rotundifoliae are Quercus rotundifolia, Myrtus communis, Chamaerops humilis and Lavandula sampaioana. Furthermore, at later stage in succession, zonation involves the annual grasslands of Trifolio cherleri-Plantaginetum bellardii, usually dominated by therophitic species, such as Plantago bellardii, Trifolium cherleri, Aira cupaniana, Tolpis barbata, Hymenocarpos lotoides, Leontodon taraxacoides subsp. longirostris, among others. In areas subject to moderate disturbance, often grazing-related, this community is replaced by the subnitrophilous grasslands, represented by the Trifolio cherleri- Taeniatheretum [24]. This perennial grassland presents a high-value to livestock grazing and appears as part of managed, cultural silvopastoral or agro-silvopastoral systems known as montados in Portugal and dehesas in Spain. Furthermore, the intensive overgrazing increases in the abundance of nitrophilous species from Artemisietea vulgaris Lohmeyer et al. The holm oak woodlands of the southwest of the Iberian Peninsula (Bética and Cádiz and Sado biogeographic territories) typically associated to limestone and calco-dolomitic substrates corresponds to the Rhamno oleoidis-Quercetum rotundifoliae. This woodland has its optimum development in the thermomediterranean, dry to subhumid, bioclimatic belt, and can be differentiated by the presence of typical basophilous species, such as Ulex baeticus subsp. scaber, Thymbra capitata, Cistus albidus, Ptilostemon hispanicus. These Quercus rotundifolia woods can develop dense canopy, with a high presence of climbing species, such as Aristolochia baetica, Clematis flammula, Smilax aspera var. altissima, Rubia peregrina, Lonicera implexa. Other thermophile species, occurring throughout the community or more frequently in its preforest community (ascribed to the calcicolous variant of the association Asparago albi-Rhamnetum oleoidis), including Pistacia lentiscus, Phillyrea latifolia, Olea europaea var. sylvestris, Rhamnus oleoides, Rhamnus alaternus, Chamaerops humilis, Phlomis purpurea, Ceratonia siliqua, Asparagus aphyllus, among others. In open areas of woodlands and their pre-forestry mantles, occur perennial xerophytic grasslands, dominated by Brachypodium phoenicoides, Brachypodium retusum, Stipa tenacissima, Hyparrhenia hirta and Hyparrhenia sinaica.

Considerations of the Typical Sequence of Vegetation Stages Occurring in the Holm Oak Vegetation Series
The Quercus rotundifolia woodlands constitute unique ecosystems that are recognized for their ecological value, linked to water retention, watershed protection, reducing fire risk and soil erosion, carbon sequestration and key-habitats for rare and endemic species [33]. However, as evidence by Quinto-Canas [24] and Quinto-Canas et al. [32] these oak forests have been transformed throughout history and well-preserved examples are rare, since their extension have been considerably reduced in area due to the cumulative effect of various kind anthropic interference, namely cutting, inappropriate silvicultural management, mechanized shrub clearance, intensive grazing, agricultural intensification, and forest fires (Figure 3).

Conclusions
As a result of this work we have been able to extend the forest communities dominated by Quercus rotundifolia in the south of Portugal. The new association Ulici argentei-Quercetum rotundifoliae, with an edaphoxerophilous character, has an original floristic patterns and specific ecological features that segregate biogeographically this association from the other holm oak woodlands of Querco rotundifoliae-Oleenion sylvestris suballiance in the southwestern Iberian Peninsula. In order to ensure its preservation, this community should be enacted through the Habitats Directive 92/43/EEC, under the Natura 2000 code: 9340 Quercus ilex and Quercus rotundifolia forests habitat, from the Annex I habitat types of the Council Directive 92/43/EEC of 21 May 1992.
Moreover, the Southwestern Iberian Peninsula holm oak woodlands occur in less accessible areas, mostly restricted to small patches and consequently, conservation measure required to achieve favorable conservation status of Quercus rotundifolia woodlands. Hence, strategic policies recommendations include: i) Protect the holm oak woodlands through regulation, environmental planning instruments and assessment, in order to avoid its destruction driven by changes in land use (mainly, forestry planting, agricultural, grazing, soil mobilization); ii) ensure that the protection of rare species is factored into management/monitoring objectives; iii) increase efficiency of forest monitoring to ensure the long-term future of holm oak woodland habitat area; and iv) apply environmental and ecological economics tools to the valuation of biodiversity conservation and ecosystem services of holm oak woodlands.  These practices lead to the degradation of holm oak woodlands and consequently, current vegetation cover (in anthropic modified landscapes) are dominated by lower layers and stages of vegetal dynamics (such as, maquis scrubland, broomland, perennial grassland, gorse and cistaceous scrubland, and annual grasslands) or agricultural and silvopastoral systems.

Conclusions
As a result of this work we have been able to extend the forest communities dominated by Quercus rotundifolia in the south of Portugal. The new association Ulici argentei-Quercetum rotundifoliae, with an edaphoxerophilous character, has an original floristic patterns and specific ecological features that segregate biogeographically this association from the other holm oak woodlands of Querco rotundifoliae-Oleenion sylvestris suballiance in the southwestern Iberian Peninsula. In order to ensure its preservation, this community should be enacted through the Habitats Directive 92/43/EEC, under the Natura 2000 code: 9340 Quercus ilex and Quercus rotundifolia forests habitat, from the Annex I habitat types of the Council Directive 92/43/EEC of 21 May 1992.
Moreover, the Southwestern Iberian Peninsula holm oak woodlands occur in less accessible areas, mostly restricted to small patches and consequently, conservation measure required to achieve favorable conservation status of Quercus rotundifolia woodlands. Hence, strategic policies recommendations include: (i) Protect the holm oak woodlands through regulation, environmental planning instruments and assessment, in order to avoid its destruction driven by changes in land use (mainly, forestry planting, agricultural, grazing, soil mobilization); (ii) ensure that the protection of rare species is factored into management/monitoring objectives; (iii) increase efficiency of forest monitoring to ensure the long-term future of holm oak woodland habitat area; and (iv) apply environmental and ecological economics tools to the valuation of biodiversity conservation and ecosystem services of holm oak woodlands.

Conflicts of Interest:
The authors declare no conflict of interest.
Appendix A Table A1. Synoptic table of the holm oak woodlands linked to the Querco rotundifoliae-Oleenion sylvestris suballiance in the southwest of the Iberian Peninsula.