The effect of Robinia pseudoacacia afforestation on soil and vegetation properties in the Loess Plateau (China): A chronosequence approach

Revegetation is one of the primary management approaches for solving the problems caused by severe soil erosion worldwide. Robinia pseudoacacia was considered a promising tree for afforestation in the highly eroded region of the Loess Plateau due to its fast growth and ability to fix atmospheric nitrogen. However, its beneficial role protecting soils from erosion has been now questioned and several negative effects on soil and vegetation have been described. In this study we aimed to analyze the effects of R. pseudoacacia plantation on plant community composition and dynamics through the effects that R. pseudoacacia has on light, soil fertility and soil water availability. We used a chronosequence from 10-40-year-old plantations and compared the environmental and vegetation characteristics of that areas with that of natural control areas with similar age. The results showed that R. pseudoacacia plantations reached maturity around 30 years and then declined in density and canopy cover. We also found that soil nutrients and moisture at the superficial soil layer improved with age until maturity of plantations, but photosynthetically active radiation at the ground level and soil moisture at deeper soil layers decreased with maturity in relation to control conditions. Plots with R. pseudoacacia of all ages had higher cover values, lower number of species but higher β-diversity values than control conditions and they also differed in species composition. These differences in structure and species composition were related to the fertilizer effect of R. pseudoacacia that favored colonization by weeds and ruderal species, and to the light interception by the canopy of trees that exclude light-demanding species, most of them perennial herbaceous species which were the dominant species in control conditions.