A Quaternary perspective on the conservation prospects of the Tertiary relict tree Prunus lusitanica L.

Aim  To assess the importance of climate and human pressure as factors limiting the past, present and future distribution of Prunus lusitanica L. (the Portuguese laurel), a relict of Europe's ancient subtropical laurel-forest flora.
Location  The Iberian Peninsula.
Methods  A census was taken of the current populations of P. lusitanica in the Iberian Peninsula and the threats they face. The potential distribution of the species was modelled under current climatic conditions and under simulations of the climate for the Last Glacial Maximum (LGM), the mid-Holocene and the year 2080.
Results  The present total population of 31,000 individuals is largely distributed as small, fragmented subpopulations, often threatened by agriculture or forestry. The species' current range is much smaller than its potentially suitable range. During the LGM, P. lusitanica would have been constrained to a limited number of sites along the Atlantic coast. In the mid-Holocene, its potential range was much wider than during the LGM and similar to that of the present day. Under the 2080 climate scenario its potential range is reduced by almost 40% compared to that of the present. This reduction includes the loss of territories currently home to three-quarters of its Iberian population.
Main conclusions  Drastic climatic changes and the existence of refugia are usually invoked to explain the rarity and fragmented distribution – yet persistence – of a subtropical flora in southern Europe. The availability of climatically suitable habitats is, however, not necessarily the main factor limiting its distribution. Human impact would appear to have been – and continues to be – of fundamental importance in the current population sizes and potential range of P. lusitanica in the Iberian Peninsula.