Cognition and suggestions on some issues related to clonal forestry:taking poplar as an example

With progress of tree breeding, vegetative propagation technique and forest industry, clonal forestry has already played a significant role in the world plantation cultivation, and gradually step into the orientational clonal selection, silviculture, and utilization era. In this paper, author's own cognition and suggestions on some issues related to clonal forestry were provided. Based on the characteristic clonal forestry, reasons for dwarf-old trees, serious forest diseases and insect pest damage, recession of plantation were also analyzed in the Three-North Region of China. Not only clonal breeding and clonal afforestation but also clonal utilization should be included in clonal forestry. When developing main cultivated varieties for different planting sites, genotype by environment interaction and matching planting sites with genotype should be fully considered. Moreover, ramet production of main cultivated varieties with high quality was formulated via scientific vegetative propagation techniques by reinforcing the formulation of vegetative propagation technique standard for important tree species. Therefore, there were some advantages in decreasing age and position effects in clonal forestry development. It was necessary to select suitable varieties for developing clonal forestry according to planting environment and aims of utilization. Combining good planting methods and varieties and economic maturity was also required to obtain maximum benefit from forestry industry. The concept of population recession of clonal plantation was brought about. Among the plantations, with age increasing, the ramets with the same genetic constitution need more water and nutrition. Negative competition would be observed among these ramets if forestland could not provide enough nutrition, resulting in uniformly weak growth potential, forest diseases and insect pest damage, unless pruning was conducted to decrease the spacing. Gradually, all the ramets in plantation will be dead. We suggested that related forestry policy and law should be revised according to the characteristics of clonal plantations. Tree species with timber or ecological function, such as poplar, could be considered as ligneous crop. Spacing control by pruning or reafforestation could be used to prevent population recession of clonal plantation owing to the shortage of fertilization and water after economic maturity of clonal plantation. In this condition, not only better ecological benefits could be obtained from clonal forestry, but also national valuable forestland resources were also effectively used.