An investigation on of optimal number of shoots in different Poplar clones at short rotation system

Pruning and eliminating some of the shoots of each poplar tree at short rotation method helps the reminder shoots to use more nutrition, light and water and produce stems with high diameter and height which can be used at high productivity industries such as paper production. The aim of the research was to study the effect of different levels of pruning on wood production per area unit, as well as their effect on wood dimensions. The trial was conducted under the experimental design of split plots at three replicates at four year period (2004-2007) in Alborz Experimental Complex, Karaj city of I.R. Iran. The main treatments consisted of five outstanding poplar clones (Populus x euramericana costanzo, Populus xeuramericana vernirubensis, Populus euramericana triplo, Populus x euramericana 561.41 and Populus x deltoids 63.8) and the secondary treatments consisted of different remaindered shoots at each poplar tree. The shoots height and diameter were measured annually at the end of growth period of the poplars. The wooden biomass wet and dry weight was measured at the end of the trial. The data were analyzed, using the SAS software. The results showed that the average number of the shoots varied between three (minimum) at control treatment for each tree of P.d. 63.8 and 5.8 (maximum) for each tree of P. e. 561.41. These two poplar clones had greater diameter and height than the other clones. The average total height and diameter of the single shoot was more the bishoots and the bishoots were more than the multishoots. The greatest and the lowest average of dbh belonged to P.d. 63.8 at single shoot treatment and P.e. vernirubensis at multishoots treatment, respectively. The greatest and the lowest total height belonged to P.d. 63.8 (9.14 m.) and P. e. 561.41 (4.24 m.), respectively and there were different differences between the clones and different treatments in respect to average of diameter and total height. The highest and the lowest amount of biomass belonged to P.d. 63.8, P. e. 561.41 and P.e. vernirubensis, respectively and there was significant difference between the clones in respect to iomass production. Biomass production in the P. euramericana clones at multishoots treatment (control) was more than the single and bishoot treatments, whereas in P. deltoids it was greater in single shoot treatment than the bio and multishoots treatments. The heighest and the greatest biomass (dry weight) production belonged to P.e. vernirubensis at single  shoot treatment (9.2 tone/ha/yea) and P.d. 63.8 at singe shoot treatment (19.3 tone/ha/year), respectively.