Effect of top-pruning in a clonal seed orchard of Pinus koraiensis

Pinus koraiensis is one of the most important economic species in Korea, which covers about 17% of the total reforestation area. Volume growth, timber quality and nut production have been major target characteristics in the breeding program of P. koraiensis. The main purposes of the present study are to survey the effect of top-pruning for strobili and cone production, and to develop a method of cone harvesting for efficient management of seed orchards. The study was conducted at a clonal seed orchard of P. koraiensis that was established at Whasung, Kyonggi province, in 1991. The seed orchard consists of 20 clones. Grafts were selected from superior families based on progeny tests, and planted at 5 m x 5m spacing. Eight clones (a total of 180 ramets) were selected and three treatments were applied in two years. The first treatment was done with top-pruning just above the first whorls from the ground (strong pruning), below the second whorls from the top (weak pruning) and control (no treatment) in 1999, and we surveyed tree growth and cone characteristics in 2000. The second treatment was carried out in 2001, with pruning of branches on the top-pruned stems, and then we measured flowering and cone production in 2006. As a result, branch length and branch diameter of top-pruned trees were longer and thicker than those for control. There was no difference in branch angle between treatments and control, and all trees showed apical dominance. In the first survey (2000), the averages of seedcone production of top-pruning and control were 1.8 and 0.2, respectively. In the second survey (2006), the averages of seed-cone production of the first and second treatments for the strong top-pruning and control were 15.2, 16.8 and 12.1, respectively. In conclusion, toppruning could affect cone production and control tree shape and height. Even though there is some need to study hormone or nutrient analysis, top-pruning could be used for the management of seed orchards in P. koraiensis.