Abstract: Primary dark coniferous forests,dominated with firs,were cut on a large scale from 1950s to 1980s in subalpine region of western Sichuan,China.At thesame time,native tree species regenerated naturally.As a result,there formed theforests with different restoration period.Roots biomass of forests with different restoration period were investigated in a way of space-for-time substitution.The changes and their distribution patterns of roots biomass were analyzed following forests restoration in western Sichuan.The results showed that roots biomass increased gradually with the restoration of forests whether at lower altitude (2 900~3 250 m) or at higher altitude (3 250~3 600 m).At lower altitude,thefluctuation of roots biomass is between 21.000 and 51.583 t/hm².While at higheraltitude,the fluctuation of roots biomass is between 20.363 and 35.316 t/hm².As for the same forests age,roots biomass located at higher altitude is less than that at lower altitude.In lower altitude,the most value of roots biomass is occurred in the soil layer of 10~20 cm,while at higher altitude,which is occurred inthe soil layer of 0~10 cm.The roots biomass in soil layer of 0~30 cm exceeded 90% of total roots biomass.The biomass of coarse roots (＞5 mm) exceeded 65.0% among the three diameter classes,while the small roots (2~5 mm) accounted for theleast percentage of total roots biomass.As for the same forests age,there isa trend that more roots biomass located at lower altitude than at higher altitude,whether coarse roots,small roots or fine roots (＜2 mm).

Key words: roots biomass, distribution pattern, restoration period, subalpine forests, western Sichuan,China