Impact of poplar shelterbelt plantations on surface soil properties in northeastern China

The Three-North Shelterbelt Program in China is one of the largest ecological rehabilitation programs in the world, but its impact on soil properties has not been thoroughly investigated. We collected 144 soil samples from soil depths of 0-20 cm in farmlands and neighbouring shelterbelts in Songnen Plain, northeastern China. The sample plots covered six locations in the study area. The analysis of variance (ANOVA) showed that there were significant location-related differences (P < 0.05) among 9 of 10 parameters, while the land use effects were much weaker and smaller. The pooled data statistics showed that shelterbelt establishment caused a 3.5% decrease in soil bulk density, a 10.6% decrease in soil total phosphorus (P), and a 63.1% increase in available potassium (K). To exclude the location effects, forest-farmland ratios were used to find possible associations to climatic conditions and forest characteristics. The poplar-induced changes in soil bulk density, soil moisture, total K, and total P were closely related to mean annual temperature, while the larger variations in available nutrients could be explained by height, diameter at breast height, and tree density. Our findings can help explain soil changes in poplar shelterbelt plantations in degraded farmland in China, especially in the black-soil region in northeastern China.