不同干扰等级下常绿阔叶次生林林分结构及树种多样性

研究人为干扰对福建将乐林场常绿阔叶次生林林分结构及树种多样性的影响，为常绿阔叶次生林的植被恢复和生物多样性保护提供科学依据。以将乐林场常绿阔叶次生林为研究对象，通过踏查选择试验区立地条件相似且具有代表性的地段，设置25块（0.04~0.12 hm2）固定样地，采用相对影响法将常绿阔叶次生林分为5个干扰等级，采用方差分析和LSD多重比较法分析不同干扰等级林分结构及树种多样性变化。结果表明:不同干扰等级下常绿阔叶次生林直径结构均呈倒"J"型分布，干扰等级Ⅴ各径阶个体数显著小于其他干扰等级（P=0.022），林分潜在更新能力和生产力较低；干扰等级Ⅰ~Ⅳ树高呈单峰山状曲线，干扰等级Ⅴ为多峰山状曲线，林分垂直结构不稳定。随着干扰强度的增加，角尺度（P=0.045）逐渐增大，大小比数（P=0.039）和混交度（P=0.017）逐渐减小。α多样性指数随着干扰等级的升高呈递减的趋势（P < 0.05），Simpson优势度指数随着干扰等级的升高而呈上升趋势（P=0.000）。不同干扰等级林分之间物种相似度较低（Jaccard's相似指数 < 47%）。不同干扰等级常绿阔叶次生林林分结构差异显著，随着干扰等级的增加，乔木多样性及林分结构稳定性降低，不利于植被恢复及多样性保护。

Forest structure and tree species diversity across a disturbance gradient in evergreen broadleaved secondary forests

To provide scientific evidence for vegetative recovery and biodiversity protection of evergreen broadleaved secondary forests, changes in stand structure and tree species diversity across a disturbance gradient of evergreen broadleaved secondary forests in Jiangle Forest Farm, Fujian Province were studied. The representative locations with similar site condition were selected through the field surveys, then a total of 25(0.04-0.12 hm2) permanent sample plots were set using typical sampling methods for evergreen broadleaf secondary forests. Five disturbance gradients (Ⅰ-Ⅴ with Ⅴ having the most disturbance) were assigned based on the relative value of major disturbance indicators. Then using ANOVA and LSD multiple comparision to analyze changes in stand structure and species diversity along a disturbance gradient. Results showed that for the five disturbance gradients, individual tree diameter conformed to an inverse J-shape curve. The individual number of Ⅴ disturbance gradient was significantly lower than other disturbance gradients (P=0.022) indicating the lowest capacity of natural regeneration and productivity. The individual tree heights of Ⅰ-Ⅳ disturbance gradients conformed to a normal curve; whereas, the Ⅴ disturbance gradient conformed to a bimodal curve indicating the lower stability in the forests vertical structure. With an increasing disturbance gradient, uniform angle indexes(P=0.045) increased, but neighborhood comparison indexes(P=0.039) and mingling indexes(P=0.017) decreased. The alpha diversity measures declined(P < 0.05) along the disturbance gradient as dominance increased(P=0.000). In addition, the similarity in species composition between each pair of disturbed forests was generally low (Jaccard's similarity index < 47%). With an increase in disturbance gradient, average DBH, average tree height, and alpha diversity measures decreased(P < 0.05), but the dominance index increased(P=0.000). Overall, as the disturbance gradient increased in the evergreen broadleaf secondary forests, the diversity index and stability of the forest structure decreased, which was not conducive to vegetative recovery and species diversity.