Wind pollination over 70 years reduces the negative genetic effects of severe forest fragmentation in the tropical oak Quercus bambusifolia.

Xueqin Zeng,Gunter A Fischer

doi:10.1038/s41437-019-0258-3

Abstract

Whether wind pollination in trees can offset the negative genetic consequences of anthropogenic forest fragmentation is not clearly established. To answer this question, we examined the demographic genetics of Quercus bambusifolia over a 70-year recovery period in highly fragmented forests in Hong Kong. We sampled 1138 individuals from 37 locations, and genetically analysed the chronosequence through the classification of tree diameters from the same populations using 13 microsatellite markers. Our study reveals that severe fragmentation caused a significant genetic bottleneck with very few remaining but genetically diverse individuals. We observed an enhanced genetic diversity during demographic recovery. We found full-sibs within populations and half-sibs across the study range. This reflects a limited seed dispersal and extensive pollen flow. Despite reduced genetic structure both among and within populations, overall a strong persisting genetic differentiation (F'ST = 0.240, P < 0.01) and significant small-scale spatial genetic structure (F(1) = 0.13, Sp = 0.024, P < 0.01) were observed. Existing bottlenecks and low effective population sizes within the temporal chronosequence suggest that the long-term effect of severe fragmentation cannot be entirely eliminated by wind pollination with demographic recovery in the absence of effective seed dispersal. Our results lead to recommendations for forest management.

Highlights

Tree species have higher levels of genetic diversity and gene flow compared to other life forms in the plant kingdom (Petit and Hampe 2006), which makes them especially resistant to genetic erosion resulting from fragmentation (Hamrick 2004)
Q. bambusifolia has shown a strong regeneration capability in its recovery, with a rapid population expansion after the severe fragmentation that occurred in Hong Kong
Despite the highly localised seed pool within populations of Q. bambusifolia, our study finds an increase in genetic connectivity of fragments

Summary

Introduction

Tree species have higher levels of genetic diversity and gene flow compared to other life forms in the plant kingdom (Petit and Hampe 2006), which makes them especially resistant to genetic erosion resulting from fragmentation (Hamrick 2004). This is mainly attributed to life history traits such as their longevity, that allows trees to persist in remnant populations by coexistence of multiple generations, and their large body size with abundant pollen and seed production, which guarantees efficient reproduction and rejuvenation.

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Conclusion