Genetic structure and the influence of neighbor genetic similarity in shaping seedling growth after disturbance

Global climate change increases the frequency and intensity of natural disturbances such as landslides, leading to forest loss and further biodiversity degradation. Although natural colonization by early successional species is a key component of forest restoration, the outcomes of post-disturbance colonization are highly variable and remain poorly understood. Because the genetic structure of populations can strongly influence individual performance, a population genetic perspective may provide critical but still underexplored insights into early population establishment following disturbance. This study focused on newly colonized seedlings of Abies sachalinensis during the first growing season at three geographically proximate artificial landslide sites. We recorded the spatial positions and performance of seedlings, mapped rill erosion as a source of post-landslide environmental heterogeneity, and genotyped seedlings using MIG-seq–based SNP markers. We examined how increased environmental heterogeneity following landslides shapes the genetic structure of populations, and how the resulting genetic context among neighboring individuals mediates intraspecific interactions. Significant genetic differentiation was detected among populations across the three landslide sites. A weak but significant fine-scale isolation by distance was observed at one site. Rill erosion reduced within-population genetic diversity. The influence of genetic similarity on seedling growth depended on spatial distance, with positive effects evident only at short distances between neighboring seedlings. Our findings indicate that in newly recruited populations following disturbance, post-landslide environmental heterogeneity together with species-intrinsic characteristics, such as dispersal limitation, shape population genetic structure. This genetic structure, in turn, interacts with spatial proximity among neighboring seedlings to shape interaction outcomes and individual performance, with implications for natural forest restoration processes.