Increased salinity and groundwater levels lead to degradation of the Robinia pseudoacacia forest in the Yellow River Delta

Abstract

Forest degradation is a worldwide problem, although its causes vary due to geographical and climatic differences and man-made causes. In recent years, the Robinia pseudoacacia forest in the Yellow River Delta has suffered severe degradation. The causative mechanisms were investigated in the field over two years, and the results show that increased forest degradation was reflected by increased tree mortality, high leaf and soil sodium salt levels and groundwater depth. Average tree diameters decreased, and leaf chlorophyll and soil microbial contents decreased. Redundancy discriminate analysis (RDA) showed that degradation of the forest was correlated positively with soil salt content, but negatively with groundwater depth. Correlation analysis showed that 0.79%–0.95% soil salt content and above 1.20 m groundwater depth caused the death of R. pseudoacacia trees due to localized anthropogenic economic activities, such as rice farming, that disrupted the original water–salt balance. Measures are recommended to prevent further degradation and restore degraded forests.

Keywords

Forest degradation / Groundwater depth / Robinia pseudoacacia forest / Soil salt content / The Yellow River Delta