In a new study published in the journal Evolutionary Applications, scientists from the Royal Botanic Gardens, Kew, and Forest Research evaluated the genetic diversity and tree health of new UK woodlands, comparing the advantages and disadvantages of planting versus natural colonisation.

As the Department for Environment, Food and Rural Affairs aims to achieve 16.5% canopy cover in England by 2050, policymakers are interested in knowing whether natural colonisation or tree planting efforts are the best practice in creating resilient woodlands.

Kew and Forest Research scientists examined sites with naturally colonising and planted English oak and silver birch. They compared young trees in these areas and assessed the small differences in the DNA of the saplings.

The scientists concluded that both planting and natural colonisation can create a healthy and diverse forest on the local level. However, it was found that natural colonisation was not a solution by itself to hit canopy targets due to the fragmented nature of the UK’s woodlands.

Dr Guillermo Friis, postdoctoral researcher in plant health and adaptation at Kew and first author of the paper, explains:

“A remarkable finding of our study was that inbreeding – the loss of genetic diversity that occurs when closely related individuals reproduce – was twice as high in naturally colonised young forests compared to planted ones. This is likely due to the lack of connectivity between forest patches, often isolated by large areas of farmland. By choosing seed sources carefully, planting can help grow forests that stay healthy and adaptable over time.”

On the other hand, researchers found that planted woodlands were less genetically diverse than expected. They attribute this uniformity to seeds often being sourced from a limited number of tree stands.

Consequently, the study proposes that government and conservation programs prioritise collecting seeds from a broader range of healthy trees across various regions to balance genetic diversity with local adaptation better.

According to Dr Nadia Barsoum, a senior forest ecologist at Forest Research, the study’s findings suggest that a “hybrid approach to increasing woodland coverage” is necessary to cultivate forests that are more resilient to climate change, pests and diseases.