Climate Change and Dryland Agricultural Ecosystem Management

Spatial heterogeneity of soil resources of Caragana Tibetica
community: “fertile island” and the nebkha effect
Pujin Zhang 1, Jie Yang1,2,*, Liqing Zhao1, Bao Sarula1, Bingyu Song1
1School of Life Sciences, lnner Mongolia University, Hohhot 010021, China.
2Sino-US Center for Conservation, Energy and Sustainability Science in Inner Mongolia, Inner Mongolia University,
Hohhot 010021, China.
Abstract:Nebkhas (or coppice dunes) formed by shrubs are a common phenomenon in arid and
semi-arid areas, which play an important role in preventing soil erosion and improving microclimate
and soil properties. One feature that makes them special is the development of “fertile islands’’
resulting from interactions between shrubs with their soil micro-environment. We investigated
whether such fertile islands are found inside and underneath Caragana tibetica-formed nebkhas in the
northwest of Ordos Plateau of China. We also tested whether the fertile island effect increases with the
age of nebkhas and analyzed how soil nutrients and water inside nebkhas vary with soil depth.
Patterns of soil texture were analyzed to evaluate sand fixation ability of C. tibetica. We analyzed
morphometric characteristics of C. tibetica nebkhas in an area of 450 ha where nebkhas of different
developmental stages were selected. Soil samples were taken inside, underneath and outside of
nebkhas to measure soil organic matter (SOM), total phosphorus (TP) and soil moisture (SM). We
also established a 5 m × 5 m plot divided into a grid of 25, 1 meter cells. Soil texture characteristics
were analyzed from samples taken at the center of each cell and at nebkha tops. Additionally, two
individual nebkhas were used to analyze soil particle-size distributions inside nebkhas.
SOM, TP and SM both inside and underneath nebkhas of stabilizing growth stages were higher than
that at the growing stages, with these properties being smallest outside of nebkhhas. Inside nebkhas of
stabilizing and growing stages SOM and TP first increased and then decreased vertically, but SM
steadily increased. The amount of sand fixed by C. tibetica per unit area was 0.0313 m3m-2. Nebkhas
of C. tibetica mainly accumulated fine sand, which accounted for 76 % of the soil, which is
significantly higher than outside of nebkhas. Spatial variance of fine sands was the highest. Spatial
dependence of soil particles of different size classes was detected to a distance of 0.64 and 1.99 m.
Fine sand particles gradually decreased with depth and other soil particle sizes increased. This work
shows that fertile islands are formed inside and underneath C. tibetica nebkhas. C. tibetica has
significant effects on sand fixation.
Keywords: Ordos plateau, soil characteristics, spatial heterogeneity, Caragana tibetica, nebkhas
* Corresponding author, Jie Yang, Email: jyang@imu.edu.cn
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