Using multiple seedlots in restoration planting enhances genetic diversity compared to natural regeneration in fragmented tropical forests

Abstract

Abstract Catastrophic degradation of forests is ongoing worldwide and leads to severe forest fragmentation. Restoration plantings are often necessary to restore fragmented forests, complementing the limited natural regeneration. High genetic diversity is critical for the long-term viability of restored forests. However, there is limited knowledge of whether planted populations capture a genetic variation comparable to natural populations. We measured the efficiency of two forest restoration strategies using the common tropical oak Quercus bambusifolia. The multi-seedlot planting was established over ten years by collecting seeds from several locations in fragmented secondary forests of Hong Kong, while the single seedlot planting was established in just one year with seeds from a single natural location. We analysed the genetic diversity and genetic structure from both plantings and compared them with natural populations. The multi-seedlot planting exhibited a higher rate of genetic recovery, greater genetic diversity (He\xa0=\xa00.69), and higher effective population size (Ne_p\xa0=\xa086.5) compared to natural populations (He\xa0=\xa00.66, Ne_p\xa0=\xa064.3, on average) and the single seedlot planting (He\xa0=\xa00.50, Ne_p\xa0=\xa030.8). The multi-seedlot planting erased the effect of seed shadows which was detected in natural populations while the single seedlot planting strengthened the effect. We conclude that capturing high levels of genetic diversity in the collection of propagules is a standard requirement to ensure the long-term viability of forest restoration. Propagule collection over multiple years is required when only a few parental trees are available to avoid founder effects.