Evaluating genetic bottlenecks in planted and naturally colonised young woodlands

The establishment of 30,000 hectares of new woodlands annually by 2050 is a key commitment of the UK government. Genetic diversity is crucial for the resilience and adaptive potential of woodlands. However, there is a major knowledge gap around the resulting genetic diversity in planted versus naturally colonised tree populations and its potential impact on resilience to environmental change, pests and diseases. This study aims to fill this gap, focusing on common oak and silver birch. The objectives are threefold: (i) to compare tree health and genetic diversity in these woodlands, (ii) to identify potential genetic bottlenecks and selection pressures in afforestation pipelines, and (iii) to provide recommendations to industry collaborators. To achieve these objectives, we conduct a comprehensive geographic sampling at various life stages, including recently established, naturally colonised populations and individuals from neighbouring ancient forests as putative parents. We also collect samples from seed orchards, nursery germinated accessions, and recently afforested woodlands. Along with sample collection, we score plant health, growth, and the incidence of pests and diseases. Using whole genome sequencing, we assess diversity indices and track changes in allele frequencies over time to identify potential selection pressures and genetic bottlenecks during production stages, comparing them with naturally colonised forests. Additionally, we implement genotype-phenotype and genotype-environment association studies to explore the genetic basis of local adaptation and potential genomic offset in afforested populations. This study seeks to inform forestry sector policy, with the knowledge necessary to guide ambitious afforestation goals. By addressing the challenges posed by genetic bottlenecks in afforestation protocols, we contribute to the preservation of locally adapted genetic resources, reduce vulnerability to pests and diseases, and facilitate the establishment of resilient woodlands.