Oak, Quercus chenii, dispersal in fragmented urban forests: acorn horizontal and vertical dispersal, seedling establishment and growth

Abstract

Habitat fragmentation results in the loss of seed dispersers and subsequently leads to low regeneration and functional decline of forests. However, very few studies on disperser decline and seedling regeneration have been conducted in urban forest systems. In three isolated forest patches in Wuhan, central China, acorn dispersers, acorn dispersal, acorn deposition patterns in soil seed banks and seedling recruitment of the dominant animal-dispersed tree species (Quercus chenii) were investigated over four consecutive years (2014 to 2017). The hypothesis tested was that the loss of acorn dispersers caused by forest fragmentation leads to low regeneration and functional degradation of the urban forest system. As predicted by the hypothesis, very few acorn dispersers (only a few Chinese white-bellied rats, Niviventer confucianus, and Eurasian jays, Garrulus glandarius, were observed) existed in the forest patches; thus, almost all of the acorns were left on the soil surface under the mother trees, where conditions are not favorable for germination and establishment. Large acorns had higher probabilities of germination and seedling establishment than did small acorns when they were buried in the soil. These results suggest that regeneration of fragmented urban forests is increasingly hampered by sharp reduction in seed disperser abundance. Planting large seeds in the soil may compensate for the low regeneration caused by disperser loss in fragmented urban forests.