Trade-off between stem growth and acorn production in holm oak

KEY MESSAGE : There were trade-offs between acorn production and stem growth in individuals of Quercus ilex , and these occurred with annual and intra-annual periods. The costs of reproduction differed significantly between two study sites. Reproduction in trees often requires significant resources, and previous studies have documented trade-offs between reproduction and growth in numerous tree species. In the present study, we assessed the relationships of acorn production with annual and intra-annual stem growth of Quercus ilex L. (holm oak) at the level of the individual tree over 6 years (2006–2011) at two study sites in southwestern Spain. There were negative correlations between acorn production and annual and late summer–autumn stem growth during masting years. In other words, the growth rates were lower in trees that had greater acorn production. These results suggest the existence of trade-offs between growth and reproduction in Q. ilex. However, there was no relationship between acorn production and winter–spring growth. Moreover, the costs of reproduction varied between the two study sites. There were negative correlations between acorn production and late summer–autumn growth in both study sites, but there were only negative correlations between acorn production and annual growth in one study site. Trade-offs appear to be greater in smaller trees living under more stressful conditions. These results show the importance of making intra-annual measurements of tree growth for appropriate interpretation of potential trade-offs.