抚育间伐对川西柳杉人工林生长和林下植被多样性的影响

Effects of thinning on tree growth and understory vegetation diversity of Cryptomeria fortunei plantation

【目的】研究不同抚育间伐强度对林木生长和林下植被多样性的影响,为柳杉人工林提质增效探究最适间伐强度和间伐间隔期。【方法】以8年生柳杉人工林为研究对象,按间伐株数强度设置4个处理(CK:对照、T1:20%、T2:30%、T3:40%),连续6年观测不同处理下柳杉林木生长、林下植被多样性等指标。【结果】间伐后第3年和第6年,柳杉胸径、树高、单株材积和单位面积蓄积量均为T3>CK,差异显著(P<0.05);间伐后前3年和后3年,胸径、单位面积蓄积量年生长量均为T3>T2>T1>CK,各处理间差异显著(P<0.05),单株材积年生长量T3>T2>T1>CK,T3、T2与CK存在显著差异(P<0.05),T1与CK差异不显著(P>0.05),树高年生长量各处理间无显著差异(P>0.05);随间伐强度增大柳杉林分较大径阶株数比例增加;间伐能提高柳杉乔木层的平均生产力,但降低了乔木层的平均生物量;间伐能够丰富柳杉林下植被多样性,间伐后前3年和后3年,4种处理样地林下植物Margalef、Simpson、Shannon-wiener和Pielou多样性指数的变化量均为T3>T2>T1>CK;间伐后的后3年与前3年相比,柳杉胸径和单株材积年生长量、乔木层平均生产力、林下植物多样性指数变化量呈现下降趋势,下降程度随间伐强度增大而减缓。【结论】抚育间伐能促进川西柳杉人工林的生长,有利于大径阶林木培养,能够提高乔木层的生产力和林下植被的多样性,这些作用随间伐强度加大而增强,随时间的推移而下降。

【Objective】The effects of different thinning intensities on tree growth and understory vegetation diversity were studied,to explore the optimal thinning intensity and interval,in order to improve wood quality and enhance the ecological benefits of Cryptomeria fortunei plantation.【Method】Four treatments(CK:control,T1:20%,T2:30%,T3:40%)were established according to the number of thinning plants,the forest growth indexes and understory vegetation diversity of C.fortunei plantation were observed for six years.【Result】At three and six years after thinning,the DBH,tree height,volume per plant and volume per unit area of C.fortunei stands in the CK group were significantly smaller than T3(P<0.05).The annual growth of DBH and volume per unit area were in the order of T3>T2>T1>CK,and the difference between the treatments was significant.The annual growth of volume per plant was in the order of T3>T2>T1>CK,and there were significant differences among T3,T2 and CK(P<0.05).Thinning showed no significant effect on tree height(P>0.05).The proportion of large-diameter stands of C.fortunei plantation increased significantly with increasing thinning intensities.Thinning increased the average productivity but decreased the average biomass of the arbor layer.Thinning enriched the understory vegetation diversity of C.fortune plantation.In the six years after thinning,the diversity indices of Margalef,Simpson,Shannon-Wiener and Pielou in the four plots were T3>T2>T1>CK.Compared with the previous three years after thinning,the DBH,annual volume growth per plant,the average productivity of tree layers and understory plant diversity indexes of C.fortunei plantation showed a decreasing trend in the last three years,and the decreasing degree slowed down with the increase of thinning intensity.【Conclusion】Tending thinning may promote the growth of C.fortunei plantation in western Sichuan,facilitate the cultivation of large-diameter trees,and improve the productivity of tree layers and the diversity of understory vegetation.These effects increase with the increase of thinning intensity and decrease with the extention of time.