1. American Conifer Society (1983) https://en.wikipedia.org/wiki/Spruce. Accessed 16 Nov 2020
2. Atack D, Tabor D (1958) The friction of wood. Proc R Soc Lond A Math Phys Eng Sci R Soc 246(1247):539–555
3. Brookhaven National Laboratory (2009) https://phys.org/news/2009-04-gene-biofuel-production.html. Accessed 16 Nov 2020
4. Butterfield BG, Meylan BA (1980) Three-dimensional structure of wood: an ultrastructural approach. The structure of palm wood, Chapter 3. Springer, New York, pp 48–55 (ISBN: 978-94-011-8148-8)
5. Chand N, Fahim M (eds) (2008) Tribology of natural fiber polymer composites. Woodhead Publ, Cambridge