Some positive effects of the fragmentation of holm oak forests: Attenuation of water stress and enhancement of acorn production

Received 27 December 2015, Revised 14 March 2016, Accepted 19 March 2016, Available online 31 March 2016The effects of fragmentation on acorn production should be mediated by their impacts on the physiological status of oaks during seed development particularly in water-limited systems, such as Mediterranean forests. The creation of forests edges reduces tree-to-tree competition, which may in turn temper water shortage during summer and, as a result, enhance acorn production. To test these two hypotheses we monitored acorn production and predawn water potential during the 2012–2014 period in two holm oak (Quercus ilex) forest archipelagos of the Iberian Peninsula. Acorn production and fragmentation effects did not differ between localities despite of their contrasting climatic conditions (accumulated water deficit from April to August was a 60% higher in the South). In general, forest interiors showed a high proportion of non-producing trees (∼50%) while trees at small forest fragments showed high acorn crops (acorn score ⩾3, ∼40% of studied trees). Our results confirmed the expectation that intraspecific competition in small forest fragments was reduced, which alleviated summer water shortage of the trees studied. This reduced water stress entailed an increased acorn production. Overall, our results show that local processes such as fragmentation may counteract climatic differences among localities and could even override the impacts of increased aridity on acorn crops.We are also grateful to Laura Barrios for her help in the statistical analysis. Teresa Morán-López was beneficiary of a FPI grant (funded by the Spanish Government (BES-2011-048346). This paper is a contribution to the Spanish-funded projects VULGLO (CGL2010–22180-C03–03), VERONICA (CGL2013-42271-P) and REMEDINAL 2 & 3 (CM S2009 AMB 1783) (S2013/MAE-2719).Peer reviewe