Abstract:

WinEPIC model was used to simulate water productivity and deep soil desiccation of Chinese pine (Pinus tabulaeformis) plantations of Luochuan, a semi-humid region, Yanan, a semi-arid region, and Yulin, a semi-arid prone drought region of the loess plateau in China during 1957－2001. The results showed as the following: in Luochuan,Yanan and Yulin, simulated annual biomass of the 1－45-year-old Chinese pine plantations averaged 4.29, 3.62 and 2.73 t·hm^-2, respectively. Productivity peaked when plantations were 9－17-year-old and then tended to decrease obviously in a pattern that followed the fluctuation of annual rainfall. In 1－22-year-old Chinese pine plantations, average annual water consumptions were higher than annual rainfalls, which resulted in soil drying in 0－10 m depth. The faster soil desiccation occurred in the period of 14－20-year-old plantations of Luochuan, 9－20-year-old plantations of Yanan and 6－19-year-old plantations of Yulin. Soil desiccation rates in Luochuan, Yanan and Yulin were 176, 111 and 69 mm per year, respectively. After that the monthly available water in 0－10 m soil layers fluctuated at a low level in a range of 0－150 mm as annual rainfalls varied in the three sites. The 0－10 m soil humidity profiles sharply varied, with annual declining the humidity and thickening dry soil layers. Dry soil layers exceeded 3 m thick in 15-year-old plantation of Luochuan, 10-year-old plantation of Yanan, and 3-year-old plantation of Yulin. In 19-year-old plantations of the three sites, dry soil layers already exceeded 10 m thick, and in 20－45-year-old plantations the dry soil layers were relatively stable of low humidity in 2－10 m soil layers. There were significant differences in water productivities and soil desiccation effects in the plantations between the three sites, and the soil water could be sustainably used by the Chinese pine plantations on the three sites for about 30 years.

Key words: the loess plateau, Chinese pine(Pinus tabulaeformis) plantations, water productivity, soil desiccation, WinEPIC model