Seventy-eight pine species, 24 firs, and many other conifers are collected. Some sections collections sample a wide range of genetic diversity, e.g., California conifers such as Pinus lambertiana and Pinus coulterii.
The Arboretum's first plantings were made in 1926. Because genetic diversity is the raw material for breeding, the Arboretum assembled as many pine species and varieties as possible. The origins of individual seeds were recorded, often mapping the location of each parent tree.