Aboveground biomass and its biotic and abiotic modulators of a main food bamboo of the giant panda in a subalpine spruce-fir forest in southwestern China

中国西南亚高山云冷杉林中大熊猫主食竹的地上生物量及其生物和非生物影响因子

As one of the main food bamboo species of the giant panda(Ailuropoda melanoleuca),Fargesia denudata is widely distributed in the understory of spruce-fir forests in the mountainous area of southwestern China.However,the driving factors of its biomass and distribution in the forests are still unclear.We conducted a systematic investigation of the tree and shrub layers(including bamboos)of 209 subplots(20 m×20 m)in a Forest Global Earth Observatory plot,the Wanglang Plot(25.2 ha),to explore the effects of abiotic(topographic and soil characteristics)and biotic(tree density,total basal area(TBA),shrub coverage,etc.)factors on the aboveground biomass of F.denudata(bamboo biomass hereafter).Bamboo biomass averaged 1.17 ton/ha,with a large variation from 0 to 4.88 ton/ha(95%confidence interval)among the 209 subplots.Bamboo biomass increased significantly with elevation,slope and mean diameter at breast height of trees,and decreased significantly with tree density,shrub coverage and soil pH.However,bamboo biomass was not significantly correlated with tree TBA,aspect,soil organic matter or total nitrogen content.The random forest model indicated that topographic factors and biotic factors had greater influences on the bamboo biomass than soil characteristics in general.Specifically,topographic factors mainly affected the bamboo biomass by changing tree density and soil characteristics.Our results can provide valuable guidance for the protection of giant pandas and the management of subalpine spruce-fir forests.

作为大熊猫(Ailuropoda melanoleuca)的主食竹之一,缺苞箭竹(Fargesia denudate)广泛分布在中国西南山地云冷杉林的林下。然而,缺苞箭竹生物量及其分布的驱动因素仍不清楚。本研究基于对王朗大样地(25.2 ha)209个样方(投影面积为20 m×20 m)中的乔木层和灌木层(包括竹子等木质草本)的系统调查,探讨非生物因素(地形和土壤理化性质)和生物因素(乔木密度、乔木总胸高断面积(TBA)和灌木盖度等)对缺苞箭竹地上生物量的影响。研究结果表明,样方缺苞箭竹地上生物量平均为1.17 ton/ha,在209个调查样方中差异很大(0-4.88 ton/ha,95%置信区间)。缺苞箭竹生物量随海拔、坡度和乔木平均胸径的增加而显著增加,随乔木密度、灌木盖度和土壤pH的增加而显著降低,而与乔木TBA、坡向、土壤有机质或总氮含量无显著线性关系。随机森林模型表明,地形和生物因素对缺苞箭竹生物量的影响比土壤理化性质更大。具体来说,地形主要通过改变乔木密度和土壤理化性质来影响缺苞箭竹的生物量。本研究结果可为大熊猫的保护和亚高山云冷杉林的管理提供科学参考。