【目的】探究徐州市泉山、云龙山50 a侧柏(Platycladus orientalis)人工林林下植物群落物种多样性特征及林下植物多样性对郁闭度的响应,为石灰岩地区山体绿化提升和树种更换提供理论指导。【方法】采用典型样地调查法对侧柏人工林进行郁闭度测定,依据野外林分状况,将其划分为[0.9,1]、[0.8,0.9)、[0.7,0.8)、[0.6,0.7)和[0,0.6) 5个郁闭度等级,研究不同郁闭度林分下植物物种组成和多样性变化。【结果】①侧柏人工林林下乔、灌、草共出现植物65科116属129种,随郁闭度的减小,植物物种数均呈先升高后降低的趋势,林下物种呈由阴生向阳生逐渐过渡的演替格局,同时植物生活型趋于复杂化和稳定。②Shannon-Wiener 多样性指数随郁闭度的减小呈先升高再降低的趋势,郁闭度为[0.6,0.7)和[0.7,0.8)的Shannon-Wiener多样性指数显著高于郁闭度为[0.9,1]、[0.8,0.9)和[0,0.6);Margalef 丰富度指数和Pielou均匀度指数在5个等级郁闭度中无显著差异(P > 0.05);Simpson优势度指数随郁闭度的减小呈先上升后下降的趋势,在郁闭度为[0.6,0.7)时优势度指数达到峰值。③根据侧柏人工林郁闭度与植物物种多样性指数的相关性分析,郁闭度与Shannon-Wiener 多样性指数、Margalef 丰富度指数及Pielou均匀度指数呈负相关;与Simpson优势度指数呈极弱负相关。【结论】侧柏人工林林下植物多样性在中郁闭度为[0.6,0.7)时各指标表现最优,更高或者更低的郁闭度可能会导致林下植物的物种组成及多样性相对减小,不利于侧柏人工林林地的维持。

【Objective】This study explored the species diversity of the understory plant community of a Platycladus orientalis plantation across 50 years in Quanshan Mountain and Yunlong Mountain, Xuzhou City. We then investigated the response of the understory plant diversity to the canopy density.【Method】The canopy density of the plantation was measured using a standard sample plot survey method and divided into five canopy density grades ([0.9,1.0], [0.8,0.9),[0.7,0.8),[0.6,0.7),and [0, 0.6) according to the current field stand conditions. The plant species composition and diversity characteristics were then evaluated for different canopy density forests.【Result】The results identified 129 species of trees, shrubs, and grasses in 65 families and 116 genera in the P. orientalis plantation. As the canopy density decreased, the number of plant species initially increased and subsequently decreased, and the understory species exhibited a gradual transition from shade-tolerant to sun-tolerant succession pattern. Plant life forms were generally complex and stable. Moreover, the Shannon-Wiener diversity index initially increased and subsequently decreased with the decrease in canopy closure. The canopy closure values of canopy density categories [0.6, 0.7) and [0.7, 0.8) were significantly higher than those of categories [0.9,1.0],[0.8,0.9) and [0,0.6). No significant differences were observed in the Margalef richness and Pielou evenness indexes among the five canopy densities (P > 0.05). The Simpson dominance index initially increased and subsequently decreased with the decrease in canopy density, and was the highest at the canopy density [0.6, 0.7). Correlation analysis between the canopy density and the plant species diversity index of the P. orientalis plantation revealed a negative correlation between canopy density and the Shannon-Wiener diversity, Margalef richness, and Pielou evenness indexes. Furthermore, the canopy closure was a very weak negative correlated with the Simpson dominance index.【Conclusion】In summary, the plant diversity in the P. orientalis plantation was optimal under medium canopy density [0.6, 0.7). Higher or lower canopy densities may lead to the relative reduction of the species composition and diversity of the plants in the plantation, which is harmful to the maintenance of the P. orientalis plantation.