Genetic Diversity of Kauri ( Agathis australis ) in Northern Aotearoa New Zealand Is Consistent With Last Glacial Maximum Refugia Followed by Post‐Glacial Range Expansion

Agathis australis (D.Don) Lindl. (kauri) is an endemic conifer species of Aotearoa New Zealand and is among the largest of the forest trees. We used genotyping‐by‐sequencing to genotype 231 samples collected from across its natural range. Population structure analysis using 1337 high‐confidence SNPs recovered two regional provenances of kauri from Northland/Auckland and Bay of Plenty. Low levels of admixture were observed between individuals from all locations. Ancestral admixture was apparent between individuals of all sampled populations, suggesting high levels of gene flow and integration between individuals and populations. Pairwise F st values were low, with the highest value measured being 0.0564. A weak positive, but significant, relationship was identified between genetic and geographic distance, via isolation by distance analysis. This reflects a north–south pattern of variation in the genetic data. We suggest these SNP data and the current distribution reflect in situ refugia populations persisting throughout its range during the Last Glacial Maximum and subsequent local expansion from these in the later Holocene. There is no support for southward post‐glacial migration from a northernmost refugia. Investigating the genetic diversity and structure of kauri informs its conservation and can be used to assist with managing the threats presented by kauri dieback.