Comparison of nurse effect zones of shrubs versus trees for dryland rehabilitation in Northeast China

Abstract

Nurse plants can form islands of fertility to rehabilitate degraded land. Areas outside plant canopies may not recover as much as areas under canopies, but the spatial extent of nurse plants' beneficial impacts is not fully understood. This study aimed to quantify the spatial and temporal aggregate nurse effects (zones of influence) of shrubs compared with trees planted for land rehabilitation in a desertified region of Inner Mongolia, China. We conducted vegetation surveys in pairs of replicate 20 × 20 m plots, each subdivided into 100 subplots (each 2 × 2 m), on four types of rehabilitation sites: shrub (Caragana microphylla) plantation sites managed for 6 or 24 years and tree (Populus simonii) plantation sites managed for 5 or 24 years. Surface soil physiochemical properties and litter amount were also measured inside and outside of nine canopies on each site. The aggregate nurse effects of improved understory vegetation and surface soil conditions extended beyond the canopies of individual plants in C. microphylla and P. simonii plantations. However, these effects were more concentrated under the canopies of C. microphylla, whereas the effects under P. simonii were spread evenly over the plantation site. This difference resulted in faster rehabilitation at the site scale in P. simonii plantations. A major factor contributing to the higher rehabilitation performance of P. simonii appeared to be larger plant height, which provides greater windbreak and shading effects compared to shrubs. Xerophytic native trees that require less water than P. simonii may be a better option for rehabilitation.