Effects of topography and cultivation model on the growth of balsa trees

To investigate the effects of different topographies and cultivation models on the wind-induced breakage rate, diameter at breast height (DBH), tree height, and timber volume of balsa wood, and to provide a theoretical basis for the domestic production of balsa wood in China, a survey was conducted on 3-4 year-old balsa trees (at harvesting age) from 14 demonstration bases in the Xishuangbanna region. The study found that: (1) In pure balsa plantation, trees on flat land and leeward slopes (semi-shady and shady slopes) were almost unaffected by wind damage, while those on windward slopes (sunny slopes) had a wind-induced breakage rate of 8.85%, and riverside areas had a breakage rate exceeding 20%. The average DBH of 3-4 year-old balsa trees in riverside, flat land, leeward slope, and windward slope areas was 26.72 cm, 24.86 cm, 22.20 cm, and 17.58 cm, respectively, with corresponding tree height was 19.73 m, 21.43 m, 22.52 m, and 14.67 m. (2) In the balsa/rubber intercropping model, the DBH of balsa trees on leeward and windward slopes was 28.30 cm and 21.14 cm, respectively, with corresponding tree height was 23.79 m and 16.13 m. (3) In pure balsa plantation, leeward slopes, flat land, and riverside areas were conducive to balsa growth, with timber volumes of 131.33 m³·hm⁻², 123.90 m³·hm⁻², and 118.21 m³·hm⁻² for 3-4 year-old trees, respectively. Windward slopes were unfavorable for balsa growth, yielding only 40.58 m³·hm⁻². In the balsa/rubber intercropping model, the timber volumes on leeward and windward slopes were 85.77 m³·hm⁻² and 40.58 m³·hm⁻², respectively. Therefore, in Xishuangbanna region, flat land and leeward slopes were suitable for balsa cultivation and the establishment of balsa/rubber agroforestry systems. Windward slopes were unfavorable for balsa growth, as trees were prone to wind damage and should not be used for balsa cultivation or balsa/rubber intercropping. Riverside areas were highly susceptible to wind damage, and unless effective windbreaks were available, balsa cultivation was not recommended in such locations.