Sources:
- https://www.britannica.com/plant/Douglas-fir
- https://www.sciencedirect.com/science/article/abs/pii/S1055790318301246
- https://floridalumber.com/blog/douglas-fir-one-of-the-best-wood-species-in-the-world/
- https://www.oregonencyclopedia.org/articles/douglas_fir/#.YkS9MOfMK3A
- https://art-botanical.org/DesertBreeze/122019-douglas-fir-illustrations.html
- https://pubs.cif-ifc.org/doi/pdf/10.5558/tfc68246-2
- https://www.monumentaltrees.com/en/usa/oregon/cooscounty/4471_brummitcreek/9119/
- https://www.aaanativearts.com/legend-douglas-fir-pine-cone