Impacts of the Three-North shelter forest program on the main soil nutrients in Northern Shaanxi China: A meta-analysis

摘要

Vegetation restoration in arid and semi-arid areas plays an extremely important role in improving the ecological environment and preventing soil erosion. The construction of the Three-North Shelter Forest (SF) in Northwestern China commenced several decades ago to increase forest productivity, improve soil fertility, and achieve better ecological benefits in arid and semi-arid zone. To date, many studies have researched the effect of SF on the soil nutrients in Northern Shaanxi, China, but their results have often been contradictory. Therefore, we could comprehensively review these studies to evaluate the impacts of SF on soil nutrients from the following three aspects: soil layer, planting year and tree species. This study compiles the results of 2308 observations from studies ranging from 1978 to 2018 to assess the effects of SF on the distribution of the soil organic carbon, total nitrogen, available phosphorus, and available potassium contents in Northern Shaanxi, China. Compared with farmland or abandoned land, the results showed that the greatest increases in the soil organic carbon (118.57%) and total nitrogen (86.19%) contents were observed in the 0-20 and 20-40 cm soil layers, respectively. However, compared with farmland or abandoned land, the greatest increases in both the soil available phosphorus (14.17%) and available potassium (71.13%) contents were observed in the 0-20 cm soil layer. Planting Pinus Sylvestris var. mongolica (PS) is more conducive for increasing the soil organic carbon (120.86%) and available phosphorus (74.33%) contents. Additionally, Pinus tabuliformis (PT) is more beneficial for increasing the soil total nitrogen content (73.82%). Meanwhile, Robinia pseudoacacia (RP) and Caragana korshinskii (CK) are more effective for increasing the available potassium (72.93%) content. This study demonstrated that soil organic carbon (104.07%), total nitrogen (130.28%), and available potassium (125.60%) contents were most affected in planting years > 30 years, and the available phosphorus content was most affected in planting years 0-10 years (27.33%). In conclusion, SF can significantly increase soil nutrient contents in areas of Northern Shaanxi, China. Planting shelter forest is recommended to improve the soil environment and achieve the greatest soil fertility benefits.