Shrub discriminant traits of the Mediterranean maquis

Mediterranean maquis is largely distributed in the Mediterranean Basin; it is dominated by evergreen sclerophyllous and drought-tolerant semi-deciduous species. Mediterranean maquis structure results from a mixture of different shrub species making dense aggregation. Shrub composition reflects different species adaptive strategies to cope with stress factors, in particular with high air temperature and low water availability. Nevertheless, the structure of shrub species affects the microclimate beneath and around them, and it determines a heterogeneous light environment within the shrub crown affecting leaf morphology of the co-occurring species. Thus, the species aggregation and their position in a shrub depend on their light level adaptability and size. The main objective of this study was to analyse shrub structure of the Mediterranean maquis, developing along the Latium coast near Rome. Species aggregation pattern was also considered. The following parameters were analysed: total shrub and crown height, shrub crown volume, and LAI. Species measurements included: height, total leaf area per plant, specific leaf area (SLA), leaf area mass (LMA), leaf tissue density (LTD), and leaf longevity. Microclimate either within or around shrubs was measured. The results on the whole underlined the impact of shrub size on microclimate, determining a patchiness of microclimatic variations. Shrub volume defined three different shrub sizes: small (1.9±1.5 m3), medium (13.1±4.8 m3) and large (34.9±8.8 m3). Most of the shrubs (86%) were formed by many species (up to a maximum of ten) and the other shrubs by one species. Among the most frequent species co-occurring in shrubs formation, Cistus incanus L. had the highest frequency, occurring mainly at the outermost part of the small shrubs. On the contrary, Erica arborea had the lowest frequency occurring mainly in the large shrubs. Moreover, considering leaf morphological traits, the results underlined a low shade tolerance of C. incanus and a high drought tolerance of Phillyrea latifolia L. and Quercus ilex, characterised by the highest LMA, LTD and leaf longevity. Thus, considering the structural and morphological trait combination, associated also to a short leaf longevity, C. incanus should not be competitive in response to air temperature increase in the Mediterranean Basin. Variations in shrub structure might be the first response to global change affecting Mediterranean maquis species composition. Because of this understanding, Mediterranean maquis shrub structure and species co-occurrence might help to forecast the effects of new climatic conditions on the Mediterranean-type ecosystems