Abstract
AbstractAimImpacts of different global change drivers are altering the performance of plant species worldwide. However, these pressures usually differ across the species' distribution range. To properly assess the combined effect of global change at species level, we need to evaluate its consequences across their complete distribution. We focused on recent decline in Cork oak (Quercus suber L.) populations given its high ecological and economic relevance.LocationWe selected 10 different sites (and two populations per site) separated about one degree in latitude across the core distribution of Q. suber, following a transcontinental aridity gradient.MethodsTo evaluate the current trends in population dynamics across the species' distribution and the factors implied on population decline, we evaluated the effect of latitude, aridity, pathogens (Phytophthora cinnamomi), stand density and tree size on seed and crop size, demographic structure, dominance of recruitment bank, defoliation and mortality.ResultsWe found an increase in seed weight as latitude decreased, with a homogeneous low crop size across the complete distribution. Demographic structure was determined by latitude, precipitation and pathogen abundance. We detected a trend towards reduced sapling densities towards the southern edge of the distribution, with a demographic structure dominated by old trees. The low sapling density at the southern edge translates into a loss of dominance with respect to other woody species, suggesting an alteration of community structure in the mid‐term future. Tree density, precipitation and pathogen abundance determined tree mortality across the species distribution, with a higher abundance of pathogens in central‐latitude populations.Main conclusionsOur results allow the early detection of declining trends and the evaluation of the main risks for species' conservation, suggesting potential for range displacement of the species driven by the recruitment failure at the southern edge of the distribution and a likely range expansion at northern populations.
Highlights
The climate alteration recorded during the last decades has the capacity to modify performance and biotic interactions of plant species worldwide (Parmesan, 2006)
We aim to evaluate the main risks for the conser‐ vation of Q. suber populations across the complete latitudinal dis‐ tribution of the species, analysing the relative importance of aridity and exotic soil pathogens (P. cinnamomi) on population structure
Our results suggest far‐reaching consequences for the distribution of the species on the mid‐ to long term, since the low recruitment, aged demographic structure and lower understorey dominance of Q. suber at its southern range are indicative of ongoing range contraction, while the northern edge of the species evidence the col‐ onization credit to expand its distribution on the coming decades
Summary
The climate alteration recorded during the last decades has the capacity to modify performance and biotic interactions of plant species worldwide (Parmesan, 2006). Changes in climate might impact species across their distributions, the most dramatic effects are expected at species range edges, where environmental conditions are currently at species’ tolerance limit (Hampe & Petit, 2005). At the leading edge of species distributions, populations need enough time to produce and disperse seeds and to effectively establish new individuals beyond current limits once environmental conditions become less limiting, a process known as colonization credit (Jackson & Sax, 2010). It is paramount to explicitly consider the differential trends of the different life stages in population dynamics occurring across the distribution of plant species to properly assess their response to changing climatic conditions. In spite of its relevance, studies comprising the complete range of a species are really scarce due to the difficulties for compiling reliable field data at large geographical scales (Parmesan, 2006)
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