Distribution pattern of soil moisture space-time of forestland in semi-arid valley of Lhasa, southwestern China.

Soil moisture is one of the main limiting factors of vegetation restoration. As the research objects of seven typical site types which belong to the layers of 0-20 cm, 20-40 cm, 40-60 cm depth soil, the paper studies the change and pattern of space-time distribution of soil moisture in semi-arid valley of Lhasa, southwestern China. The results showed that the soil moisture changing trends of different site types were roughly same and the shape was unimodal distribution. The minimum and maximum water content occurred in January and August respectively, and its range was between 2.43%-30.03%. The order of soil water content from high to low was as follows: high water level of flood land upper part of shady slopelower part of shady slope low water level of flood land upper part of sunny slope terrace lower part of sunny slope. The time spatial pattern of soil moisture could be divided into three periods, ie soil water accumulation period (from June to September), soil water consumption period (from October to the January of next year) and soil water stationary period(from February to May). The space distribution of soil moisture could be divided into three layers, ie soil water comported layer (0-20 cm), soil water active layer (20-40 cm) and soil water relatively stable layer (40-60 cm). This conclusion has a certain guiding significance for the vegetation construction in this area.