Effects of spacing on the growth performance and site modifications of six years old Simao pine [Pinus kesiya Royle ex Gordon var. langbianensis (Ca. Chev.) Gaussen ex N.S. Biu] plantations in Yunnan Province, P.R. China

The study sought to determine the suitable spacing regimes of simao pine plantation to achieve sustainable management of simao pine woodlands in Yunnan Province, China. Six stands with uneven row spacings of 1 x 1 x 3, 1 x 1 x 5, 1 x 2 x 4, 2 x 2 x 5, 1 x 2 x 10, and 1 x 1 x 11 m for six years old simao pine plantations were established along Qingshiu River, Simao City, Yunnan, P.R. China. Analysis of variance (ANOVA) and linear stepwise programs were employed to analyze growth, morphological and ecological parameters. Mean DBH [diameter at breast height], height and timber volume ranged from 7.88-9.36 cm, 5.64-6.16 m, and 0.0181-0.0249 cu m, respectively in uneven row spacing stands, and 7.80 cm, 5.16 cm, and 0.0164 cu m in even 2 x 2 m spacing stands. There were significant differences in mean DBH but had no significant differences in mean height and timber volume were observed between different uneven row spacings. Total timber income ranged from 462.01-1,368.01 and 747.50-1881.47 US $/ha in SWSG [southwestern slope group] and NW-NSG [northwestern and northern slope group], respectively. Uneven row spacing regimes improved merchantable height (MH) growth, but induced imbalance development of crowns and the first living branches (FLB) between narrow and wide space directions. Soil bulk density, total N and P, available N, P and K did not significantly differ in stands with different uneven row spacings and space directions. Potassium (K) was relatively abundant in simao pine woodlands (4.61-6.03 g/kg). The N, P and K contents of simao pine trunks, roots, branches and needles ranged from 0.118-1.540, 0.182-1.139, and 0.643-4.729 g/kg, respectively. Uneven row spacing stands facilitated understorey species regeneration, and increased understorey biomass and litter yield in simao pine plantations. Litter decomposition was relatively slow (with 33.06 percent of decomposition rate) during the whole duration (6 months) of the study. The simao pine plantations moderated light intensity (2469.00-5056.73, 14839.71-31049.94, and 6684.82-18686.03 lux under different uneven row spacing stands at 9:00-13:00 and 17:00 o'clock), air relative humidity (19.90-76.80 in the daytime), soil moisture content (11.61-16.78 percent from January to June), air and soil temperature (differences less than or equal to 1.14 and 1.19 deg C and soil temperature, respectively, under different uneven row spacing stands at the same observed time). Integrating growth parameters, morphological characteristics, ecological maintenance and economic analysis, the ideal uneven row spacings for establishing simao pine plantations are 1 x 2 x 4, 1 x 1 x 3, 1 x 1 x 5, and 2 x 2 x 5 m.