The study of the formation of xylem and the variability of wood formation dynamics in five different spruces on Pokljuka in 2005, 2006 and 2007 was conducted by using the "pinning" method. All the trees were pinned once a week with a needle. The pinning started in 2005 (from 11. 5. to 5. 10.), continued in 2006 (from 12. 5. to 11. 10.), and finished in 2007 (from 26. 4. to 12. 9.), after which the trees were cut down. 197 anatomical specimens were extracted and prepared for microscopy. Pinning caused necrosis of cambial cells, the formation of callus and typical wound wood. The method enabled us to determine the start of cambium division activity, which differed significantly in all three years and for individual trees. The cambium activity started first in 2007, in spruces 1 and 2 as early as 3. 5. - 11. 5., and in spruces 3, 5 and 6 between 11. 5. - 18. 5. In 2005, the cambium activity took place in the period from 25. 5. - 1. 6. 2005 in spruces 1, 2, and 6, while in spruces 3 and 5, it happened a week later, from 1. 6. - 8. 6. 2005. Finally, in 2006, it started in spruces 1, 2 and 6 in the period from 23. 5. - 1. 6. 2006, and only between 14. 6. - 21. 6. 2006 in spruces 3 and 5. The end of growing season differed for individual trees as well. Cambium division activity finished first in 2007 in spruces 3, 5 and 6 in the week between 2. 8. - 8. 8. 2007, in spruce 1 between 8. 8. - 16. 8. 2007 and in spruce 2 between 16. 8. - 22. 8. 2007. In 2006, it finished between 2. 8. - 8. 8. 2006 in spruce 3, followed by spruces 1, 5 and 6 between 16. 8. - 24. 8. 2006, and between 30. 8. - 6. 9. 2006 in spruce 2. The longest cambium activity took place in 2005, with the first finish during the week of 17. 8. - 24. 8. 2005 in spruce 3, followed by spruces 1, 2 and 5 between 24. 8. - 31. 8. 2005 and finally by spruce 6 between 31. 8. - 7. 9. 2005. The beginning and the end of the division activities in the cambial zone are affected by the health status of individual trees, as well as by external factors, e.g. temperature and precipitation.
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