Granivorous Rodent Loss Poses Greater Threats To Oak Trees With Large Acorns Than Those With Small Ones In Urban Forests

The local extinction or reduction of a species or even a small functional group as a result of forest fragmentation may have different consequences on the sympatric plants. Here, we investigated acorn dispersal and seedling recruitment, along with the mortality of two oak species, Quercus variabilis with large acorn and Quercus chenii with small acorn, in an isolated forest patch in Wuhan city, central China, where rodents are rare, but birds (e.g., Eurasian jay) are present. We hypothesized that a reduction of rodents would induce greater threats to the regeneration of oaks with large acorn than that with small acorns because bird dispersers may prefer to disperse small acorns. The results showed that, for both of the oak species, very few acorns were dispersed on the ground surface, leading to a clustered distribution of newborn seedlings underneath adults, which was followed by a high mortality in the next year. However, due to the existing Eurasian jay preferring to harvest small acorns, more small Q. chenii acorns were dispersed than large Q. variabilis acorns, resulting in a less clustering and a lower mortality of Q. chenii seedlings than Q. variabilis in the experimental patch. These results suggest that the loss of granivorous rodents in urban forests may result in low regeneration of rodent-dispersed species, but this degradation of ecological function can be partially buffered by bird dispersers (e.g., Eurasian jay) for smallseeded trees. Ecological-based management of rodents and birds are needed in urban forests to ensure their sustainability.