Evaluation of cambial activity in seedlings of Populus deltoides by pinning method

Wood formation in seedlings of Populus deltoides was studied at Dahka village in Astaneh ashrafieh city in Gilan province, Iran in the growth year 2008. Three seedlings at three heights, 0.5, 1.5, 2.5 m, were selected for pinning technique. It is necessary to know cambium reactions through pin insertion. Samplings were carried out at monthly intervals from 23^rd March until 23^rd October. According to examination of cross sections under light microscope, the onset of cambial activity was seen in April about breaking of apical bud. Cambial activity ceased in 22^nd October coinciding with apical bud dormancy. Leave fell completely after cambial dormancy. The Gopmpertz charts showed the maximum percent of daily growth at three height of seedlings befell in July, whereas measurements showed the maximum percent of monthly growth at 2.5 m height was in July and at 0.5 and 1.5 m were in August. Cambial activity positively correlated with average rainfall in July and August. According to Gompertz function, the timing of wood production during the growing season was similar for 2.5 and 1.5 m heights. The cambial activity at upper and middle height of the seedlings is Sooner begun and later ended than the lower height.