The effect of different watering regimes and fertilizer addition on the growth of tree species used to afforest the semi-arid steppe of Mongolia

The environmental restoration of the semi-arid steppe of Mongolia is currently being addressed by creating new plantations able to protect the soil from the advancement of desertification and to improve the economy of the population living there. The success of these interventions relies on a high survival rate and good long-term growth performance of the transplanted trees. In the present work we analyzed stem height and root collar diameter (RCD) over 10 years for two native tree species (Populus sibirica and Ulmus pumila) grown with different water regimes and fertilizers. The investigated duration is sufficiently long to provide a reliable indication of the adaptation of these tree species to the steppe’s harsh environmental conditions. Results suggest that both species could be used for environmental restoration projects, although P. sibirica requires the support of additional irrigation to achieve the best growth performance. U. pumila, on the other hand, shows good growth performance even with rainfall as the only water source. However, the higher water use by P. sibirica trees seems to be compensated by a more rapid ground cover compared to U. pumila. The addition of fertilizers to the soil before transplantation does not improve the growth performance of either species.