晋西北的气候干旱、寒冷,水土流失严重,土壤贫瘠,据土壤普查结果分析,70～80％土壤有机质含量低于0.5％,养分水平在全国标准5级以下。植被稀少,生物产量低,大面积营造的杨树人工林,多数形成“小老树”。一、形成“小老树”的原因晋西北黄土地区杨树人工林低产的原因 The climate in northwestern Shanxi is arid, cold, with serious soil erosion and poor soil quality. According to the soil census results, the soil organic matter content of 70-80% is less than 0.5% and the nutrient level is below the national standard of Grade 5. Sparse vegetation, low bio-yield, large-scale construction of poplar plantations, most of the formation of “little old tree.” First, the formation of “small old tree” Reasons for the low production of poplar plantations in the loess region of northwestern Shanxi