Abstract:To evaluate the water conservation function of Betula luminifera plantations with different ages in Northwestern Guangxi, the representative 11 and 16-year-old B. luminifera plantations and 16-year-old Cunninghamia lanceolata were selected as main research object, and the water conservation capacities in three layers including the forest canopy, litter layer and the soil layer, as well as the comprehensive water conservation capacity were analyzed quantitatively. The results showed that:(1) The water holding capacity of the canopy, shrub layer and herb layer of the 11 and 16 year-old B. Luminifera plantations ranged from 12.54 to 21.06 t/hm2, 2.15 to 3.05 t/hm2 and 1.27 to 1.52 t/hm2. The total litter reserve was 4.54~7.42 t/hm2, and the maximum water holding capacity was 12.55~16.00 t/hm2, which of 16-year-old plantation was significantly higher than that of 11-year-old plantation (P<0.05). There was a good linear relationship between the water absorption rate and water soaking time (R2>0.86, P<0.05). (2) The pore condition of soil followed the order of 16-year-old B. Luminifera forest > 11-year-old B. Luminifera forest > 16-years-old C. lanceolata forest, and the pore condition of soil was significantly higher in 0-20 cm soil layer than that in 20-40 cm and 40-80 cm soil layer. (3) The variation range of maximum water holding capacity, capillary water holding capacity and non-capillary water holding capacity of the 11-year-old B. Luminifera soil was 28.97%~60.55%, 25.35%~47.21% and 3.71%~13.34%, and the range was 26.06%~63.45%, 25.63%~48.70% and 3.34%~14.75% in 16-years-old B. Luminifera plantation, respectively, and all the values decreased with the increasing of the soil layer. The natural water content ranges of 0-80 cm soil layer in 11 and 16 year-old forest were 27.46~30.16 g/cm3 and 28.12~30.22 g/cm3, respectively, and total water storage capacities were 3 813.4 t/hm2 and 3 732.2 t/hm2, respectively, and all the values were greater than those in 16-year-old C. lanceolata forest (3 659.2 t/hm2). On the whole, the older B. luminifera plantation had stronger water conservation function, and it was superior to the same age C. lanceolata plantation. The results could provide scientific basis for the management of B. luminifera plantation in this area.