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

Nicola Alessi,Francesco Spada,Stefan Zerbe,Camilla Wellstein

doi:10.1007/s12210-021-00981-7

Abstract

During the last decades, an ongoing spread of broad-leaved evergreen laurophyllous species has been reported for forests of Southern Europe. Several factors were suggested as the main drivers of the phenomenon, namely global warming, land-use change, evolutionary history, and increase in atmospheric CO2. Among laurophylls, Laurus nobilis L. is considered one of the most prominent from the morphological, evolutionary, and ecological point of view. We studied the population structure of L. nobilis in Central Italy in its natural habitat to investigate its regeneration and potential expansion along with the influence biotic and abiotic factors. To define types of population structures, we collected proportions of six growth classes of L. nobilis in 16 sites. We obtained three types of population structure, i.e., (1) stable, (2) dynamic, and (3) regressive. The first two types are the most frequent, suggesting a potential increase of L. nobilis abundance within forests of Central Italy. The regressive population type occurs mainly in sites with heavy ungulate impact. High propagule pressure along with shaded and moist environmental conditions favor L. nobilis regeneration. Accordingly, we found evidence of a recent L. nobilis spread in Central Italian forests. We suggest the increase of forest cover and age, due to the abandonment of traditional rural practices, as key factors for the regeneration of this apparently late-successional laurophyll. In conclusion, the recent expansion of L. nobilis that we observed in the Italian forest stands can therefore be ascribed to a process of natural recover of a potential niche following land-use change.

Highlights

Relic European laurophyllous species, such as Laurus nobilis L., Rhododendron ponticum L., Prunus lusitanica L., were traditionally studied for their biogeography and evolutionary history, because they are considered remnants of the subtropical forest covering the southern part of Paleo–Europe during the late Tertiary (Axelrod 1975; Mai 1989; Palamarev 1989)
The three types of population structure obtained from the clustering of the proportion of L. nobilis juveniles, resembled those quoted in the literature (Fig. 2)
In the near future, L. nobilis might become an important element of particular forest stands in Central Italy where it showed a stable or dynamic regeneration process in the near future

Summary

Introduction

Relic European laurophyllous species, such as Laurus nobilis L. (laurel), Rhododendron ponticum L., Prunus lusitanica L., were traditionally studied for their biogeography and evolutionary history, because they are considered remnants of the subtropical forest covering the southern part of Paleo–Europe during the late Tertiary (Axelrod 1975; Mai 1989; Palamarev 1989). It is noteworthy that during the last 2 decades, in several studies describing the species composition of forest communities in Central Italy, a high level of rejuvenation of L. nobilis has been observed (Viciani and Moggi 1997; Bertacchi et al 2004; Foggi et al 2006). This evidence suggest expansion dynamics of L. nobilis among the Italian populations. Quantitative studies on L. nobilis populations’ status based on empirical data are yet missing for the Mediterranean region

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