Primary production of pine plantations, 2: net primary production of Pinus kesiya Royle ex Gordon stands planted with three different spacing at Hod, Chiengmai [province in northern of Thailand]

The study was carried out in the 10-year-old Pinus kesiya plantations at Hod, Chiengmai. The stands were initially planted with 2x2, 2x3, and 2x4, m x m spacing. Three random sample plots of 20x20m2 were established in the three stands and measurements of stem diameter at breast height (D) and total height (H) of all trees in each plots were conducted. The results of the study showed that aboveground biomass and stem volume of the 10-year old Pinus kesiya plantations planted with three different spacing could be approximately estimated by using the allometric relation between the square of diameter at breast height multiplied by total height of tree (D2H). Total aboveground biomass or standing crop and stem volume of Pinus kesiya plantation planted with 2x3 m x m spacing was found to be largest and 2x4 and 2x2 m x m spacing plantations were found to be next to the former one in the magnitude of aboveground biomass. Stem and branch biomass were found to be large in the order; 2 x 3 m x m 2 x 4 m x m 2 x 2 m x m spacing stands, respectively while leaf biomass was 2 x 4 m x m 2 x 2 m x m. Leaf area index of the stands were found to be decreased as planting space decreased. The previous year aboveground biomass of the stands were found to be in the same order as for the standing crop. Net primary production was found highest in the 2 x 3 m x m stand with approximately 16.273 ton/ha/yr while 2 x 4 and 2 x 2 m were next with 13.857 and 11.259 ton/ha/yr, respectively. Stem volume increment was also highest in the 2 x 3 m x m stand with 22.250 m3/ha/yr followed by 2 x 4 and 2 x 2 spacing stands with 35.925 and 33.200 m3/ha/yr, respectively. The efficiency of leaf to produce dry matter in forms of net primary production of the total aboveground biomass in 2 x 2, 2 x 3 and 2 x 4 m x m spacing plantations were 2.445 , 2.944, 1.985 and of net primary production of stem were 1.581, 1.499 and 1.224, respectively