桉树人工林更新方式对林下植物功能群的影响

Effects of different regeneration modes on understory plant functional group in Eucalyptus plantations

该研究综合运用野外调查和室内分析的方法,评估桉树人工林林下植物功能群的组成、分布及更新方式和相关环境因子之间的关系。结果表明:林分更新5 a后,除了非禾本科杂草功能群外,其他林下植物功能群的物种丰富度均呈现不同程度的增加,但与对照组(砍伐迹地)相比,其差异程度均不显著(P>0.05);与对照组相比,藤本和蕨类功能群的相对多度也出现增加趋势,但禾本科草本功能群显著减少(P<0.05);木本、藤本和蕨类功能群的相对盖度也呈现增加趋势,但禾本科草本功能群与对照组相比显著减少(P<0.05);主成分分析(PCA)发现萌芽更新或植苗更新林的林下植物功能群组成和分布与对照组相比均发生了显著的变异,但不同更新方式(萌芽和植苗)下其林下植物功能群组成和分布差异不明显;通过冗余分析(RDA)确定了冠层透光系数、土壤孔隙度、坡向和土壤氮磷比是影响该林地林下植物功能群的主要因子,它们的叠加效应能解释大于75%的林下植物功能群的变异,最终模型通过排序得到冠层透光系数是影响该林地林下植物功能群的最主要因子。短期的研究发现萌芽和植苗这两种不同的更新方式对桉树林下植物功能群的影响有限,这可能与这两种更新方式形成的林冠结构和土壤理化性质差异性较小有关。

We evaluated the relationships between composition, distribution and regeneration modes of understory plantfunctional groups and environmental factors, through the combination methods of field investigation and analyzed experi-mental to elucidate the changing rules of understory plant functional group in two different regenerated Eucalyptus planta-tions and the related influencing factors. Our results. indicated that the species richness of understory plant functionalgroups in forest generated after five years increased but not significantly ( P >0.05) compared to control plots ( cut-overland) except for forbs. The 5-year forest regeneration caused increasing of relative abundance of vines and ferns,. but thatof grass was significantly decreased ( P<0.05). The relative coverage had a great resemblance to relative abundance,which exhibited increasing in woody plants, vines and ferns in 5-year regeneration forest, but decreasing in grass (P<0.05). Principal component analysis ( PCA) showed that the composition and distribution of understory plant functionalgroups significantly changed in sprouting regeneration forest and planting regeneration forest compared to controlplots. Redundancy analysis ( RDA ) revealed that canopy light transmittance, slope aspect, soil porosity and N/P ratioswere key factors in regulating plant functional groups in Eucalyptus plantations, and the accumulative effects explainedmore than 75.0% of total variations in understory plant functional groups. The sequencing mode analysis suggested thatcanopy light transmittance was the most significant factor in affecting understory plant functional groups in Eucalyptusplantations. We found in short-term studies that sprouting and planting regeneration had limited efects on the understoryplant functional groups in Eucalyptus plantations, and which may be caused by similar caпopy structure and soil physico-chemical properties.