Vertical distribution characteristics of root system of several shrub species on terrace banks

The distribution characteristics of active roots of woody plants are significant for the selection of tree species,spacing decision and management measures for agroforestry system.The authors investigated the vertical distribution characteristics of roots of several shrub species on terrace banks using whole plant excavation.The results show that root length and root biomass of Tamarix ramosissima,Salix integra and Caragana korshinskii decline exponentially with soil depth;a root extinction coefficient could be used as a parameter revealing the vertical distribution characteristics of shrubs planted on terrace banks.The results suggest that T.ramosissima and C.korshinskii should be selected as shrub species for agroforestry system on terrace banks in the arid Loess Plateau;S.integra should be planted on shady slopes with better soil moisture,pruned timely and matched with crops in the autumn;these three shrub species should be planted on transition positions from loose layers to consolidated ones to alleviate competition and ensure their growth.