Ecological Implications of Acorn Size at the Individual Tree Level in Quercus suber L.

Abstract

Few studies have determined the influence of acorn size on germination and predation percentage at tree level. To evaluate the seed size influence at individual tree level, trees producing two different sizes of acorn were chosen. Our results show that smaller acorns were significantly more infested (49.6-75.3%) than larger ones (11.0-27.33%). About germination, big acorns achieved the best germination percentage compared to the smaller ones (18% in infested and 76% in sound acorns for the small acorn group versus 69.3% in infested and 93.3% in sound acorns belonging to the big acorn group). We also found that there was a difference in behaviour between big and small seeds at tree level. The same size belonging to different functional groups presented a difference at the behavioural level per tree. Infested small acorns from trees 8 and 10 had only 33 and 13% germination, while big acorns from trees 2, 3, and 6 (there was no difference between both sizes) presented 67, 97, and 83%, respectively. These results indicate that the production of acorns with two different sizes could be a strategy for species regeneration, producing each size for a different purpose.

Factors affecting cork oak (Quercus suber) regeneration: acorn sowing success and seedling survival under field conditions

“…Regeneration was evaluated at individual (seedling) and local (site) levels and the following hypotheses were tested: (1) post-dispersal predation of acorns (i.e. cache predation) is higher not only in livestock grazing regimes but also in shrubby areas, considering the positive correlation between shrub cover and acorn removal by rodents (Pons and Pausas 2007;Smit et al 2008); (2) seedling emergence probability is higher for larger acorns, in accordance with recently published laboratory work (Ramos et al 2013); (3) seedling establishment and survival against summer drought is facilitated by shrub and canopy cover, as verified in other Mediterranean evergreen oak systems (Espelta et al 1995;Smit et al 2008Smit et al , 2009); (4) drought tolerance and resprouting are assisted by early emergence and later drying of seedlings, respectively, as well as by larger seedling sizes, because an enhanced physiological performance during establishment is expected to be the outcome of these factors (Schwilk and Ackerly 2005;Verdú and Traveset 2005); and (5) livestock browsing and intensive management practices involving mechanical soil disturbance during early stages of regeneration significantly reduce the number of seedlings. Overall, we expect that the multiple-staged limitations to cork oak regeneration are associated with chronic management differences among sites.…”

“…Seedling emergence and survival probabilities also increased with acorn size. Seedling emergence relies on seed resources (Roach and Wulff 1987), and recent laboratory research showed a positive relationship between acorn size and germination in cork oak (Ramos et al 2013). Nevertheless, our study demonstrated that acorn size has an additional and even more significant influence on seedling survival and resprouting.…”

Grazing hinders seed dispersal during crop failure in a declining oak woodland

“…Interestingly, as the cork oak is the only oak species with annual and biennial acorns of widely varying sizes on the same tree resulting from distinct flowering times (Elena-Roselló et al, 1993;Ramos et al, 2013), our results may imply an even more pronounced adaptation of the species to farther and closer dispersals, both important for the population persistence and expansion. On the other hand, we found no evidence that larger acorns were dispersed more rapidly in the two contrasting crop years, which may indicate that the positive selection, reflected in greater dispersal distances, occurs after the acorns are handled, and less by visual assessment as in the case of the European jay (Pons & Pausas, 2007b).…”

Effect of Tree Shelters and Regeneration Method on Survival and Growth of Cork Oak Plantations in the Maamora Forest, Morocco

“…Another important factor that can significantly limit the success of direct-seeded plantings is seed quality. Indeed, cork oak seedling emergence has been shown to be affected by seed size and therefore available reserves, with studies reporting a generally positive relationship between acorn size and germination and early seedling growth (González-Rodríguez et al 2011; Ramos et al 2013;Arosa et al 2015). Predation on seeds is one of the major factors in decreased viability (Zhang et al 2016).…”