Field Evidence of Colonisation by Holm Oak, at the Northern Margin of Its Distribution Range, during the Anthropocene Period

Abstract

A major unknown in the context of current climate change is the extent to which populations of slowly migrating species, such as trees, will track shifting climates. Niche modelling generally predicts substantial northward shifts of suitable habitats. There is therefore an urgent need for field-based forest observations to corroborate these extensive model simulations. We used forest inventory data providing presence/absence information from just over a century (1880–2010) for a Mediterranean species (Quercus ilex) in forests located at the northern edge of its distribution. The main goals of the study were (i) to investigate whether this species has actually spread into new areas during the Anthropocene period and (ii) to provide a direct estimation of tree migration rate. We show that Q. ilex has colonised substantial new areas over the last century. However, the maximum rate of colonisation by this species (22 to 57 m/year) was much slower than predicted by the models and necessary to follow changes in habitat suitability since 1880. Our results suggest that the rates of tree dispersion and establishment may also be too low to track shifts in bioclimatic envelopes in the future. The inclusion of contemporary, rather than historical, migration rates into models should improve our understanding of the response of species to climate change.

The high vulnerability of Quercus robur to drought at its southern margin paves the way for Quercus ilex

“…Indeed, Q. robur is mostly present at the bottom of the dunes where water is more readily available (lower depth of the water table), and several diebacks of mature trees of Q. robur located in the slopes or the top of the dune were observed (ONF 2010 and personal observations). Since the end of the 19th century, Q. ilex colonized this area (Delzon et al 2013) and nowadays constitutes the most abundant tree species in this forest with higher relative abundance (close to 100 %) at the top of the dune.…”

“…Under these scenarios we hypothesize: (i) a high risk of mortality for Q. robur as a response to drought events and (ii) its progressive replacement by a more prone drought-tolerant species such as holm oak (Quercus ilex L.). Delzon et al (2013) indeed evidenced the colonization of Q. ilex along the French Atlantic coast during the last century in response to climate change. To test these hypotheses, we studied the abundance of Q. robur and Q. ilex along a gradient of water availability and their ecophysiological responses to drought.…”

“…range, respectively. An increasing body of empirical studies has shown that tree species populations located at their colder limits moved poleward or upward due to global changes (e.g., Walther et al 2005;Penuelas et al 2007; Batllori and Gutierrez 2008;Beckage et al 2008;Devi et al 2008;Parolo and Rossi 2008;Zhu et al 2012;Delzon et al 2013). On the contrary, evidences of extirpation events at their warmer edges remain rare (Allen and Breshears 1998;Penuelas and Boada 2003;Beckage et al 2008;Zhu et al 2012;Urli et al 2014).…”

“…P. pinaster was massively planted from the 19th century to date (Buffault 1942), but Q. robur and Q. ilex are still naturally present on the dunes where Q. robur is considered as a high patrimonial value species. Q. ilex, long considered as an undesirable species by the forest managers (Delzon et al 2013), is now appreciated for its potential ecological (biodiversity) and forestry services. These populations of Q. robur and Q. ilex are located at the warmer edge and colder edge of their distribution range, respectively.…”

Combined LM and SEM study of the middle Miocene (Sarmatian) palynoflora from the Lavanttal Basin, Austria: part IV. Magnoliophyta 2 – Fagales to Rosales

“…The most widespread species, Q. ilex, extends its range into fully humid, mostly subtropical habitats (e.g. Petroselli et al 2013), profiting from global warming trends (Delzon et al 2013) and is a common element in various habitats of the Mediterranean region including dry and mesic forests.…”