Forests and woodlands are the most biodiverse and complex terrestrial habitat in the UK. Home to thousands of iconic and specialist animals, plants and fungi, our ancient forests and woodlands are also deeply entwined with our cultural heritage. But our woodland fauna and flora are under threat due to land-use change, invasive species, climate change and pathogen outbreaks. Understanding and predicting these changes, and mitigating some of them, will require an understanding of how each species responds to challenges at a cellular and molecular level. Reference genomes are fast becoming an essential toolkit in 21st century biology, capable of increasing our understanding in a wide range of fields such as developmental biology, physiology, ecology and behaviour. For example, we can ask which genes are switched on or off in response to an environmental challenge. This requires sequencing the RNA made by each gene and identifying these by comparing them to the genome sequences. Investigations of genetic variation within a species, such as may be used to detect if populations have been fragmented or merged, also require high-quality reference genomes.