林分密度对四川云顶山柏木人工林林下物种多样性和土壤抗冲性的影响

Effects of stand density on understory species diversity and soil antiscourability of Cupressus funebris plantation in Yunding Mountain,Sichuan, China

为构建荒山生态保护屏障,川中丘陵区于20世纪80年代末大量营造柏木(Cupressus funebris)人工林,近年来柏木人工林面临生物多样性降低和土壤侵蚀等问题.为研究不同林分密度对云顶山柏木人工林林下物种多样性和土壤抗冲性的影响,采用典型样地法,调查该地5种不同林分密度(1 100、950、800、650、500株/hm2),分析物种多样性指数和土壤抗冲性及根系指标的相关性.研究区共记录植物176种,隶属69科128属,草本层物种数大于灌木层.灌木层的物种多样性指数随林分密度降低,呈先增后减的趋势,物种丰富度指数D、Shannon-Wiener多样性指数H在密度650株/hm2出现峰值;草本层物种丰富度指数D、Shannon-Wiener多样性指数H、Simpson优势度指数H′随林分密度降低均呈先增后减再增再减的双峰型变化趋势,在密度650株/hm2和950株/hm2出现峰值.土壤抗冲性随林分密度减小,呈先增后减单峰型变化趋势,在密度650株/hm2达峰值.物种丰富度指数D与土壤抗冲性正相关关系明显.本研究表明650株/hm2相对更利于该地柏木人工林物种多样性稳定和土壤的抗冲性能.(图4表3参28)

To protect the ecosystem of barren mountains, massive Cupressus funebris plantations were allowed in hilly areas of the central Sichuan Basin in the late 1980s. In recent years, Cupressus funebris plantations have faced problems such as biodiversity decline and soil erosion. To study the effects of different forest densities on understory species diversity and soil anti-scourability of Cupressus funebris plantations in Yunding Mountain, a typical sampling method was used to investigate the five different forest densities(1 100, 950,800, 650, and 500 trees/hm~2) and to analyze the correlation between the species diversity index, soil antiscourability, and root index. In total, 176 species from 128 genera and 69 families were recorded in this area.The number of species in the herb layer was higher than that in the shrub layer. The species diversity index of the shrub layer first increased and then decreased with the decrease in stand density;and the species richness index D and Shannon–Wiener diversity index H showed peak values at a density of 650 trees/hm~2.The species richness index D, Shannon–Wiener diversity index H, and Simpson dominance index H’ in the herb layer showed a bimodal trend of increasing, then decreasing, increasing again, and finally decreasing with the decrease in stand density;and the peak values were found at the densities of 650 and 950 trees/hm~2. When soil anti-scourability decreased with stand density, it showed a trend of increasing and then decreasing, reaching a peak at a density of 650 trees/hm~2. The positive correlation between the species richness index and soil antiscourability was evident. Thus, 650 trees/hm~2 is relatively more conducive to the stability of species diversity and soil anti-scourability in cypress plantations.