Ancient refugia and present‐day habitat suitability of native laurophylls in Italy

Abstract

Questions: European native laurophyllous species are interesting for their biogeography and evolutionary history, as well as for their responses to global changes. We identified Italian native laurophylls on the basis of morphology, biogeographical history and ecological niche to study whether these species are in equilibrium with the present-day climate. Furthermore, we localized Quaternary refugia and areas of potential spread of native laurophylls using distribution patterns of realized and potential aggregations of native laurophylls, respectively. Location: Italy.Methods: We extracted data for 17, 087 forest plots from a phytosociological database. Detrended Correspondence Analysis of these plots with overlay of climatic and environmental variables was performed to identify native laurophylls, i.e., evergreen broad-leaved species of late Tertiary radiation, occupying a warm and humid niche.Potential ranges of laurophylls were calculated using Beals' index of sociological favourability. The realized/potential range-size ratio was calculated for each single laurophyll to understand whether it is in equilibrium with the present-day climate.Distribution patterns of realized and potential aggregations of laurophylls were mapped.Results: Ordination analysis provided a selection of 11 species as Italian native laurophylls. Most of them occupied less than half of their estimated potential range.Realized aggregations richest in native laurophylls were localized in the central Apennines. However, the Italian forests showed high potential for native laurophylls with the richest potential aggregations in the whole Apennines and in the southern Alps. Conclusions:Most of the Italian native laurophylls showed non-equilibrium with the current climate, suggesting that late-Quaternary events could better explain their present-day distribution than on-going climate change. Furthermore, their refugia in central Italy suggest the persistence in sites with temperate climate during Quaternary environmental changes. The high suitability of Italian forests for laurophylls, along with global changes, suggests possible future spreading of these species.

Population structure of Laurus nobilis L. in Central Italian forests: evidence for its ongoing expansion

“…Indeed, fossil traces of the genus Laurus confirms its conspicuous role in the Late Tertiary laurophyllous biome (Ferguson 1974;Palamarev 1989). Moreover, the apparently unchanged preference of L. nobilis for a warm and humid climate since the Late Pliocene (Rodríguez-Sánchez and Arroyo 2008;Alessi et al 2018Alessi et al , 2019 makes the species representative for the laurophyllous species stock. According to macro-climatic species distribution models, a northward shift of the laurels' range has been inferred for the end of this century within the global-warming scenario (Rodríguez-Sánchez and Arroyo 2008).…”

“…Because of the laurophylls' preference for a warm climate, the current global warming has been proposed as the main driver of the laurophylls' spread (Carraro et al 1999;Fujiwara and Box 1999;Walther 2001). However, in more recent studies, the role of the evolutionary history and land-use change have been suggested as key factors of the laurophylls' spread (Alessi et al 2019;Conedera et al 2017). Indeed, the great availability of free niches due to a limited post-glacial dispersal (Alessi et al 2019) combined with an increased propagule pressure due to the widespread use of laurophylls in home gardens and parks (Conedera et al 2017) might favor the expansion of laurophylls more than climate.…”

“…However, in more recent studies, the role of the evolutionary history and land-use change have been suggested as key factors of the laurophylls' spread (Alessi et al 2019;Conedera et al 2017). Indeed, the great availability of free niches due to a limited post-glacial dispersal (Alessi et al 2019) combined with an increased propagule pressure due to the widespread use of laurophylls in home gardens and parks (Conedera et al 2017) might favor the expansion of laurophylls more than climate. Moreover, the ongoing increase of the atmospheric CO 2 concentrations is favoring broad-leaved evergreen species over deciduous ones because of the competitive advantage given by some physiological characteristic of the evergreen habit, e.g., lower mesophyll diffusion conductance of CO 2 (Niinemets et al 2011).…”

“…It is plausible that most of its genetic diversity, inherited by a complex biogeographical history, is harbored within populations located in South European refugia (Hampe and Petit 2005;Rodríguez-Sánchez et al 2009). Since Central Italy has been described as a refuge area for laurophylls (Di Domenico et al 2012;Alessi et al 2019), conservation planners should be aware of the possible spread of L. nobilis and of its drivers, to assess proper management actions targeted to the ongoing dynamics of the involved native vegetation. Especially, if we consider that, L. nobilis in Italy is able to form community types protected by the Annex I of the European Habitat Directive (92/43/CEE).…”

“…Furthermore, following the hypothesis that the increase of forest areas during the last decades promotes the spread of laurophylls, we analyzed various abiotic and biotic factors which might influence the tree regeneration. Indeed, by considering light and moisture availability at the ground level, we aim to test the importance of a closed forest canopy for the regeneration a late-successional species as L. nobilis (Barbero and Quézel 1994;Alessi et al 2019). In addition to the constraints of the local environmental conditions, biotic interactions also affect the species spread.…”