Assessment of plant species diversity associated with the carob tree (Ceratonia siliqua, Fabaceae) at the Mediterranean scale

Abstract

Background and aims – The thermophilous woodlands of the Mediterranean region constitute reservoirs of genetic resources for several fruit trees. Among them, the carob tree (Ceratonia siliqua) is a key component of traditional Mediterranean agroecosystems but its ecology was never assessed at the scale of its whole distribution area. Fortunately, phytosociological literature shelters invaluable resources for several issues in conservation, among them the possibility to analyse plant biodiversity at regional or continental scale. Here, we present the results of a comprehensive survey of the phytosociological literature associated to carob tree. Methods – We collected 1542 floristic relevés performed in 18 geographical areas distributed around the Mediterranean in which the presence of C. siliqua was recorded. Species composition of the plant communities was analysed by multivariate ordination and hierarchical classification, and species diversity was evaluated by rarefaction and prediction analyses of Hill numbers. Key results – Multivariate analyses revealed that plant communities associated with the carob tree are well differentiated between the Western and Eastern basins. A wider range of floristic differentiation is revealed in the Western basin where the vegetation reaches its maximal heterogeneity. By comparison, in the Eastern basin the plant assemblages associated with the carob tree are more homogeneous and with a lower species richness but a higher Simpson diversity. Conclusions – The large ecological range of the Mediterranean carob trees is potentially an important evolutionary legacy for the conservation of genetic resources and seed sourcing for new uses such as restoration ecology.

A strong east–west Mediterranean divergence supports a new phylogeographic history of the carob tree (Ceratonia siliqua, Leguminosae) and multiple domestications from native populations

“…Leaves of 1,067 carob trees from 78 populations were sampled across the Mediterranean between 2015 and 2017. Localities were selected to cover the geographic and ecological ranges of C. siliqua as described in Baumel et al (2018 ; Table S1.1 in Appendix S1). Although discriminating wild carob trees from abandoned orchards was not always possible, most efforts were done to collect leaves of individuals from natural habitats.…”

“…Among the Mediterranean fruit trees, the carob ( Ceratonia siliqua L., Leguminosae) is an evergreen dioecious tree characteristic of thermophilous vegetation (Baumel et al, ; Quézel & Médail, ; Zohary, ). It has been widely exploited since antiquity, and it is currently used for industrial, agricultural and soil restoration purposes.…”

“…Despite its economic and cultural importance in the Mediterranean and the long‐standing interest of botanists (e.g. de Candolle, ), the status of the carob tree as a native species of the west Mediterranean vegetation is still source of debate (Baumel et al, ; Ramon‐Laca & Mabberley, ) and a phylogeographic study was still pending.…”

“…In addition, a long‐standing evolutionary history in the Mediterranean that precedes the origin of the agriculture could also explain the presence of C . siliqua in several types of thermophilous vegetation across the Mediterranean (Baumel et al, ). Therefore, alternative scenarios should be tested when addressing the origin of the carob tree in the Mediterranean.…”

Endozoochory of a dry‐fruited tree aids quarry passive restoration and seed soaking further increases seedling emergence

“…Using an indoor sowing experiment conducted in situ, we examined for the first time whether and how carnivore endozoochorous seeds collected in a quarry potentially influence its passive restoration, through effects on plant emergence and early survival. Most interesting in our analysis were the results for Carob tree, an evergreen species with conservation and socioeconomic value (Zohary ; Ramon‐Laca & Mabberley ; Baumel et al ) being used for the artificial revegetation of the quarry. With likely positive consequences for passive restoration, we found that, irrespective of the carnivore species (Red fox or European badger), endozoochorous carob seeds collected in the quarry performed similarly to untreated local seeds regarding emergence rates.…”