The “Mediterranean Forest”: A Perspective for Vegetation History Reconstruction

Starting from the multifaceted meaning of “Mediterranean”, this thematic review wishes to reconnect the palaeobotanical with the phytogeographical approach in the reconstruction of the Mediterranean Forest of the past. The use of the term “Mediterranean” is somewhat ambiguous in its common use, and has not an unequivocal meaning in different research fields. In botany, geographical-floristic studies produce maps based on the distribution of the plant species; floristic-ecological studies, produce maps that deal with the distribution of the plant communities and their relationships with different habitats. This review reports on the different use of the term “Mediterranean” in geographical or floristic studies, and on the way climate and plant distributions are used to define the Mediterranean area. The Mediterranean Forest through the palynological records is then shortly reported on. Pollen analysis may be employed to reconstruct the Mediterranean Forest of the past but a number of problems make this a difficult task: low pollen preservation, lack of diagnostic features at low taxonomical level, and low pollen production of species which form the Mediterranean Forests. Variable images of this vegetation are visible in different landscapes, but the Mediterranean Forest often remains a sort of “ghost forest” in pollen spectra from the Mediterranean Region. IANSA 2018 ● IX/2 ● 207–218 Marta Mariotti Lippi, Anna Maria Mercuri, Bruno Foggi: The “Mediterranean Forest”: A Perspective for Vegetation History Reconstruction 208 a remarkable variety of topographical features, edaphic conditions, and plant communities. With regard to vegetation history, the palaeoand archaeo-botanical studies deal with the flora and vegetation changes as evidenced in long-term chronological records. Analyses of pollen and plant macroremains from sediment strata and archaeological layers provide lists of plants that better attends to the flora rather than the vegetation, but references to plant communities are highly informative for reconstructing landscapes. Single-case studies are often limited in time and in space, whereas syntheses of several sites allow for wide-ranging reconstructions that overcome specific local events (see, for example, Mercuri, 2014, for cultural landscapes reconstructed through pollen analyses). Local and regional studies can improve our knowledge on the cause-and-effect patterns which have determined broad palaeoenvironmental changes (sharp events or gradual transformations) under the various climate and anthropic influences. Synthesis of the data in a coherent scheme is needed for reconstruction of the vegetation history of each region, but the many inhomogeneities in the terminology concerning various vegetation types, often being referred to in a generic or ambiguous way, is a major difficulty in this task. In papers on palaeoand archaeo-botany, the authors rarely explain to which plant community their results refer to, even if important exceptions exist (e.g. Colombaroli et al., 2009, focusing on the dynamics and history of fires; Piovesan et al., 2018, studying an application for the restoration of forest ecosystems). Certainly we can say that reaching an unequivocal, conclusive definition of the term “Mediterranean” is a hard task and is outside and not the aim of this paper. According to “Conservation International: Biodiversity Hotspots”1, the Mediterranean Basin is one of the hotspots of plant biodiversity (22,500 species with 52% of endemic species against more then 6000 species in other parts of Europe). Due to this wealth of biodiversity, defining the limits of the Mediterranean biogeographical area is a topic that is deeply under discussion among bio-geographers. Therefore, our main purpose is to make the reader aware of the level of this difficulty and try to make less ambiguous the terminology referring to plant communities, and in particular the “Mediterranean Forest”. 2. The geographical use of “Mediterranean” referring to plant communities Recently, a catastrophic event made it quite clear that in layman’s terms “Mediterranean Forest” is used to indicate a forest of the Mediterranean Region in a very generic way. On March 2015, a terrific storm scourged the coast of northern Tuscany. The fall of numerous trees changed the face of the Versilia coast. After this disaster, the local government officials decided to restore the “natural vegetation”. In their 1 Mediterranean Basin September, 2011: http://www.biodiversityhotspots. org/xp/hotspots/mediterranean/Pages/default.aspx. view, the natural, Mediterranean vegetation of the area consisted of woods dominated by umbrella pine often mixed with holly oak. The media were speaking about the “wild Mediterranean Forest”, meaning the woods that people are used to seeing in the territory. They believed those woods to be the natural vegetation of the area and in naming them used a geographical term (Mediterranean) derived from the proximity to the coast: But, are those woods the wild Mediterranean vegetation? Is merely growing near the Mediterranean Sea in itself sufficient to be some part of the “Mediterranean vegetation”? The reality is more a mosaic of several vegetation types that form parts of this so-called “wild forest”, including pine plantations dominated by Pinus pinea2 and Pinus pinaster, that have been planted as several reforestation events since Roman times, and were then intensified between the “600 and 800” ies (Giacomini, 1968; Mondino and Bernetti, 1998; Arrigoni, 1998), with an undergrowth of Quercus ilex, and a European vegetation consisting of deciduous trees such as Quercus robur, Alnus glutinosa, and Carpinus betulus. The geographical use of the term “Mediterranean Forest” is also present in scientific papers belonging to research fields other than botany but concerning woodlands or bushlands of the countries facing the Mediterranean Sea (e.g. Cosandey et al., 2005, on experimental studies on forest hydrology). In such papers, the term “Mediterranean Forest” and “macchia” are often reported as synonyms. Indeed, they are both vegetation types dominated by evergreen and sclerophyllous species, but they largely differ in their dominating habitus/ growth forms: there is a prevalence of trees in the forest, and shrubs in the macchia (Arrigoni, 1996). The name “macchia” more properly refers to a very intricate, impenetrable plant community characterized by densely-branched, evergreen, sclerophyllous shrubs and climbing plants. 3. The use of the term “Mediterranean” in floristic studies Narrowing to botany, the specific literature reveals great difficulty in finding an unambiguous definition/use of the adjective “Mediterranean”. In general, two approaches can be used to describe the plant resources of a territory: the former is the geographical-floristic approach based on the local flora leading to the identification of phytochoria, i.e. areas with similar compositions of plant species (Takhtajan, 1986); the latter is the floristic-ecological approach based on the study of the distribution of plant communities and their relationships (Kent, 2012). Numerous maps of Italy based on the geographicalfloristic approach were published during the last century (Fiori, 1923; Arrigoni, 1980, Romagnoli, 2003). They are syntheses useful for the regionalization of areas on a geographical (i.e. large) scale. In this type of map (Figure 1), 2 Species names according to Euro+Med PlantBase (http://www. emplantbase.org/). IANSA 2018 ● IX/2 ● 207–218 Marta Mariotti Lippi, Anna Maria Mercuri, Bruno Foggi: The “Mediterranean Forest”: A Perspective for Vegetation History Reconstruction 209 the largest part of the Italian peninsula is included in the Euro-Siberian Region while only a narrow strip along the coastline, in addition to the whole of Sicily and Sardinia, is attributed to the Mediterranean Region. The floristic-ecological approach focuses on the species that use the same local resources with different type of interactions, from independence to full interdependence (Kent, 2012). In Europe, phytosociological schools often employed this type of study (Géhu and Rivas-Martínez, 1981; Blasi, 2010; Biondi, 2011). It is particularly useful for studying plant communities on a local scale. The maps based on the floristic-ecological approach (Rivas-Martinez et al., 2004, modified for Italy by Blasi and Biondi, 2017) also limited the Mediterranean Region to the coast of the Italian peninsula, and included the hills and mountains of Calabria, Puglia, Sardinia and Sicily. The integration of both the geographical-floristic and floristic-ecological maps constitutes a valuable tool for the study of the past flora and vegetation history at the local scale (see, for example, Mariotti Lippi et al., 2015, for the reconstruction of the vegetation surrounding Grotta Paglicci-Apulia). 4. Climate and plant distribution to define the Mediterranean area The Mediterranean climate is a typical, temperate, biseasonal climate with the dry period – summer – coincident with the season of highest temperatures, and with mild, wet winters (Koppen, 1936). Climate has been used to define the borders of the Mediterranean area. Gaussen (1954) used temperature as a single parameter; more specifically, he considered the average temperature of the coldest month of the year – January or February – as one of the most Figure 1. Geographical-floristic map of Italy (Arrigoni, 1980; Romagnoli, 2003). IANSA 2018 ● IX/2 ● 207–218 Marta Mariotti Lippi, Anna Maria Mercuri, Bruno Foggi: The “Mediterranean Forest”: A Perspective for Vegetation History Reconstruction 210 Ta bl e 1. M os t i m po rta nt tr ee s an d sh ru bs a nd th e m ai n sy nt ax a re la te d to th e fo re st s of th e M ed ite rr an ea n ar ea , a rr an ge d ac co rd in g to th e ve ge ta tio n zo na l b el t. Ve ge ta tio n be lt an d th e di st rib ut io n of s pe ci es a re ac co rd in g to Q ué ze l a nd M éd ai l ( 20 03 m od ifi e