Abstract
The 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.
Highlights
Resource overexploitation and inadequate management are the main drivers of forest degradation in the Mediterranean Basin, and their impacts are expected to be intensified by climate change (Sala et al, 2000; Valladares et al, 2014)
0.26 df Overall, our results show a positive effect of forest fragmentation on acorn production, mediated by the mitigation of summer water stress due to relaxed intraspecific competition
Despite that the southern locality is characterized by more severe summer drought we did not find significant differences in acorn productivity between localities, and the impact of forest fragmentation was consistent among sites
Summary
Resource overexploitation and inadequate management are the main drivers of forest degradation in the Mediterranean Basin, and their impacts are expected to be intensified by climate change (Sala et al, 2000; Valladares et al, 2014). Moister springs involve higher investment on female flowers, which entails enhanced acorn production, but a very severe summer drought can lead to high abortion rates and constrain final acorn production (Ogaya and Peñuelas, 2007; Espelta et al., 2008; Pérez-Ramos et al, 2010; Misson et al, 2011; Rodríguez-Calcerrada et al, 2011; Sánchez-Humanes and Espelta, 2011; Fernández-Martínez et al, 2012; García-Mozo et al, 2012). The increased aridity expected under a climate change scenario may hamper holm oak reproduction. Rainfall exclusion experiments have shown that a 15-30% reduction in summer rainfall, which are similar to that expected by the end of the century for the Mediterranean basin (AEMET 2009), can significantly constrain acorn production
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