History, not age, determines the genomic importance of ancient trees

Ancient trees are not merely defined by their age, but also their genetic history, according to a groundbreaking genomic study of the critically endangered Chinese swamp cypress. The research, published in Nature Plants, found that the genetic significance of ancient trees depends less on their age than on their evolutionary past.

While it may appear that older trees preserve unique genetic variation, the study revealed that this is not always the case. Some ancient trees carry rare genetic diversity that is poorly represented in younger populations, while others largely share genetic variation already found in surviving wild or cultivated populations. The study defined ancient trees as those over 100 years old and surveyed 147 individuals across southern China and Vietnam.

The findings suggest that genetic diversity, inbreeding levels, and the burden of deleterious mutations vary more by genetic lineage than by whether a tree is ancient, wild, or cultivated. Natural relics, which are ancient trees representing former natural populations, retained substantially more rare genetic variation than historically introduced ancient trees.

Losing these natural relics or certain ancient tree lineages could reduce the species' overall nucleotide diversity by up to 15.1%. Conservation efforts should prioritize individuals that embody distinctive evolutionary lineages or preserve genetic variation not found elsewhere, the researchers argue.