林分密度对云顶山柏木人工林林下植物优势种群生态位的影响

Effects of Stand Density on the Niche of Dominant Populations of Understory Plants in Cupressus funebris Plantation of Yunding Mountain

柏木(Cupressus funebris)人工林是川中盆地森林主要类型,林下植物是森林生态系统重要组成部分。该研究采取典型抽样法,调查分析云顶山柏木人工林现存密度[1100株·hm^(-2)(A)、950株·hm^(-2)(B)、800株·hm^(-2)(C)、650株·hm^(-2)(D)、500株·hm^(-2)(E)]的林下灌、草优势种群Shannon生态位宽度(Bsw)、Levins生态位重叠值(Oik)以及生态位宽度和重叠均值与环境因子的相关性,从生态位特征探究林下植物优势种群对不同林分密度的响应,明确相对适宜的林分密度,分析不同林分密度柏木人工林林下植物种间、群落与环境的关系,筛选出现存相对最优林分密度,为柏木人工林林下植物多样性保育和森林经营措施提供理论支撑。结果表明:(1)研究区共有草本植物38科72属94种,灌木42科65属99种,物种数量随柏木密度的减小呈先增后减的趋势,且在柏木密度为650株·hm^(-2)时达到峰值。(2)随着柏木密度的升高,草本优势种群的Bsw依次分别为28.07、28.45、26.34、25.48和30.77,生态位重叠均值为4.34、5.75、4.12、2.14和5.08,灌木优势种群Bsw分别为26.64、28.05、24.24、23.72和25.65,生态位重叠均值为6.68、6.44、4.28、5.54和6.19,灌、草优势种群生态位宽度和重叠均值都显示在密度为D时较大,群落资源利用能力强,更有利于群落生态适应性。(3)RDA排序结果显示,林分密度、郁闭度、土壤含氮量是柏木人工林林下灌、草优势种群生态位宽度和重叠均值的主要环境影响因子,土壤含水率、pH对其影响较小。研究认为,云顶山柏木人工林现存相对最优密度为650株·hm^(-2),也最有利于柏木林下植物优势种群的资源利用和生态效益。

Cupressus funebris plantation is the main forest type in central Sichuan Basin,and understory plants are important part of forest ecosystems.This study used the typical sampling method,investigated and analyzed the existing density of C.funebris plantation[1100 tree·hm^(-2)(A),950 tree·hm^(-2)(B),800 tree·hm^(-2)(C),650 tree·hm^(-2)(D)and 500 tree·hm^(-2)(E)]on Shannon Niche width(B sw),Levins niche overlap(O ik),the correlation between niche width and mean overlap and environmental factors in understory plants with shrub and herb dominant populations of Yunding Mountain.We explored the response of different densities with dominant population in understory plants from niche characteristics,and determined the relatively appropriate stand densities.We analyzed of the relationship between populations,community and environment in understory plants under different densities of C.funebris plantation,then screened out the optimal stand densities,which were useful for C.funebris plantation understory plants diversity conservation and forest management measures.The results showed:(1)in the study area,there were 94 species of herbs in 38 families,72 genera,and 99 species of shrubs in 42 families,65 genera.The number of species increased first and then decreased with the stand density decrease of C.funebris,then reached a peak at 650 tree·hm^(-2)density of the C.funebris.(2)With the stand density of the C.funebris increased,the B sw values of dominant populations in herb layer were 28.07,28.45,26.34,25.48 and 30.77,the mean niche overlap were 4.34,5.75,4.12,2.14,5.08,the B sw values of dominant populations in shrub layer were 26.64,28.05,24.24,23.72 and 25.65,and the mean values of niche overlap were 6.68,6.44,4.28,5.54 and 6.19,respectively.Both the shrubs and herbs niche widths and the mean overlaps were larger at density D,indicated that at density D,the dominant populations of shrubs and herbs had high resource utilization capacity,this capacity was more conducive to ecological adaptability of community.(3)RDA results showed that stand density,canopy density and soil organic matter were the main environmental factors affected the niche width and niche overlap mean value on dominant populations of shrubs and herbs,soil water content and pH had little effect on them.Therefore,this study shows that the relative optimal density of C.funebris plantation in Yunding Mountain is 650 tree·hm^(-2),which is also the most conducive to the resource utilization and ecological benefits of dominant population of understory plants in C.funebris plantation of Yunding Mountain.