不同密度路域巨桉人工林群落结构和物种多样性

Community structure and species diversity of Eucalyptus grandis plantations with different stand densities in road area

以成都绕城高速路域5种林分密度巨桉人工林为研究对象,采用典型样地法,根据调查数据综合分析比较其群落结构(胸径级、高度级、物种组成和重要值)及林下物种多样性(Shannon-Wiener指数H、Simpson优势度指数H’、Patrick丰富度指数S、Pielou均匀度指数J_(sw))。结果显示,共记录林下植物54科101属148种,在草本层林分密度C的物种数最大,在灌木层林分密度D的最大。随着林分密度的降低,灌木层H、S均先增后减,在林分密度D最大,而J_(sw)则一直增加,草本层H、H’、S均呈先增后减的趋势,H、H’同在林分密度D达到峰值,且H在林分密度D显著大于林分密度A和E(P<0.05),J_(sw)呈先增后减再增再减的变化趋势,分别在林分密度B和D达到峰值。高林分密度会限制小胸径级、小高度级个体生长,高度级个体分布差异较大,高度级结构接近偏峰形,以中高度级、高高度级为主;胸径级结构接近正态分布,群落逐渐向衰退的方向发展。冗余分析表明,显著影响灌木层物种多样性的林分因子为林分密度、郁闭度、平均枝下高;显著影响草本层的为郁闭度、平均胸径、平均枝下高。结果显示,林分密度D为路域巨桉人工林相对最适密度,及时对其进行密度调控有利于提高林下物种多样性和维持群落稳定性。

A typical plot method was used to investigate the vegetation on Eucalyptus grandis plantations with five stand densities in the Chengdu ring expressway area to assess and compare community structures(diameter class,height class,species composition,and importance value)and to assess understory species diversity(Shannon-Wiener index H,Simpson index H’,Patrick richness index S,Pielou index J_(sw)),based on survey data.In total,148 understory plant species belonging to 54 families and 101 genera were recorded.The largest number of species was found in the herb layer of density C and in the shrub layer of density D.With decreasing stand density,the shrub layer H and S showed a trend of first increasing and then decreasing and reached the maximum at density D,where J_(sw) had been increasing,and herb layer H,H’,S values all showed a trend of first increasing and then decreasing;H and H’reached peak values at density D,and H at density D was significantly larger than density A and E(P<0.05),whereas J_(sw) of the herb layer showed a bimodal effect of first increasing and then decreasing,as well as increasing and subsequently decreasing,with peak values at densities B and D.High stand density may limit the growth of trees with small diameter at breast height(DBH)and short trees;the distributions of individuals by height class showed marked differences.The structure of height class individuals was close to the peak shape;the middle-height class and large-height class were predominant.DBH class structure approached a normal distribution,and the community tended to a gradual decline.Redundancy analysis showed that stand density,canopy closure,and average branch height were the main stand factors significantly affecting the diversity of the shrub layer;canopy closure,average DBH,and average branch height were the main stand factors affecting the herb layer.Density D was the optimal density of Eucalyptus grandis plantations in road areas,and timely regulation of density can improve understory species diversity and thus maintain community stability.