11. Effect of Afforestation on Soil and Water Conservation

Reforestation of bare land has a good effect upon our environment. It has usually been assumed that reforestation can control erosion. However, in the early years of reforestation, things were complicated. Experiments showed that after the tending of young trees, runoff clearly increased until 2–3 storm events had occurred. Soil loss increased within 1 month after staddle tending and it was especially large during storm events. It was estimated that if there are 250–1500 fish scale pits per hectare for tree planting on sloping land, then 362.5–725 m³ hm^–2 year^–1 sediments could be conserved in place. The amounts of nutrient elements in the surface runoff were highest in the bare land; the amounts were second highest in Chinese fir (Cunninghamia lanceolata) forest, and those in the level terrace areas were the lowest, indicating that changes in the topography and improvements in vegetation coverage had an important effect on nutrient loss. Second, reforestation can improve biodiversity. The understory plant, physical, chemical, and microbial properties were investigated for several types of forests over 10 years of reforestation at Yiyang County and Taihe County. Before reforestation, there were only shade-intolerant herb species. After reforestation, some shade-loving plants that like a wet, shady environment were found growing well. Third, reforestation has a good effect on micrometeorology. After reforestation the maximum temperature inside the forest in summer was 2.3°C lower than that outside the forest, and the relative humidity increased by 9%. The daily variation amplitude of temperature inside the forest was 2.8°C lower than that outside the forest; the amplitude of variation of humidity increased by 5.5%.