Effect of Site Condition on Cambial Activity and Wood Formation of Yew (Taxus baccata) in Three Regions of Golestan Province

Literature and goals: Yew (Taxus baccata) is one of the most valuable and rare native coniferous in Iran. Surviving remnants of third geological era that unfortunately it has been subjected to extinction due to climate change and excessive grazing. Regarding its valuable wood and lack of data toward the site impact on the tree growth, activities of cambium layer and procedure of increase the number of mature cells were investigated.
Three regions of Golestan province (Afratakhteh, Chahar-bagh and Ponearam) were selected which among them Afratakhteh had the highest temperature. 6 normal trees with upright trunks of each region and almost the same diameter for explanting were studied. Sampling was done from March to early November 2014, with two weeks interval. Micro-cores were examined under a light microscope after sectioning and staining. Then average number of cells in the cambium region and mature tracheids were counted. Climate data (precipitation and monthly temperature) were recorded for the meteorological stations near study area.
The results indicated that cambium activity was began two weeks earlier in Afratakhteh than others in early May and finished in late October at the same time in all sites. Cambium cells enumeration also showed that peak activity occurred in mid-June with 10 cells number. However, cambium activity started sooner in warmer region (Afratakhteh) and cambium cells number was more than other areas in early growth season. But, there were no differences in final mature tracheids among 3 sites in late growth season.
It can be concluded that higher temperature in Afratakhteh has a positive effect on growth, in early growing season, but in the mid-summer, reduces cambium cells number and thus growth rate. This issue can create a negative impression on Afratakhteh Yew trees in near future, as air humidity decreases and become warmer.