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

Nicola Alessi, Jakub Tešitel, Stefan Zerbe, Francesco Spada, Emiliano Agrillo & Camilla Wellstein

Old individual of laurel (Laurus nobilis L.) in a forest dominated by the evergreen holm oak (Quercus ilex L.) in Maremma Park, Italy. Photo credit: Emiliano Agrillo.

At the beginning of the Paleocene, ca. 65 Million years ago, Europe was dominated by a warmer and wetter climate. Its vegetation resembled forests of present-day subtropical China and encompassed a high diversity of laurophyllous plants (laurel alike evergreen angiosperms with glossy leaves). A cooler and more arid climate, combined with grassland expansion, triggered a mass decline of laurophyllous forests in the late Neogene and Pleistocene. Climate became more favourable for laurophylls again in the early Holocene but by then, only a few of these species had survived – most of which were confined to refugia in southern Europe. These species are relics of the once widespread laurophyllous forests in Europe.

At the end of the last century, researchers reported a regional expansion of laurophylls in Europe. Given that these plant species are favoured by a warmer climate, the most advocated explanation was that anthropogenic global warming was responsible for this trend. However, land-use change could have also contributed to an expansion of laurophylls. In particular, intense human forest exploitation (e.g. logging, food gathering, grazing) could have slowed down a natural post-Pleistocene expansion of laurophylls. The abandonment of rural life in the last decades could have promoted forest growth, and thus, created new suitable sites for laurophylls.

In this study, we assessed whether climate is driving the expansion of native laurophylls in Italy. Our aim was to localize and map recent Quaternary refugia and to predict future areas of spread in Italy.

We studied the current and potential distribution of laurophylls by analysing vegetation plot data archived in the “Vegetation plots Database – La Sapienza” (Agrillo et al., 2017), one of the largest vegetation databases in Italy.

We found that the richest area in laurophylls is limited to the central Apennines. This area is known to have served as a climatic refuge during the Pleistocene. However, recent climate should have been suitable for laurophylls across a much broader region, even before the current anthropogenic global warming happened. Thus, we could hypothesize that laurophylls had been slowly moving from southern refugia and expanding northward since the end of ice ages. However, intense land exploitation has likely promoted a colonization lag among laurophylls during the Holocene. The recent land abandonment and rural depopulation could have accelerated laurophylls spread. Our results suggest that the current laurophylls distribution is not in equilibrium with climate, but natural biogeography and human land-use shaped it. As anthropogenic global warming and urbanization progress, laurophylls forests will likely expand in the near future.

References

Agrillo, E., Alessi, N., Massimi, M., Spada, F., De Sanctis, M., Francesconi, F., … Attorre, F. (2017). Nationwide vegetation plot database – Sapienza University of Rome: state of the art, basic figures and future perspectives. Phytocoenologia, 47, 221–229.

This is a plain language summary for the paper of Alessi et al. published in the Journal of Vegetation Science.