北京市自然保护区植物群落对干扰胁迫的抵抗力分析

A functional analysis of resistance of plant communities to disturbance:a case study of Beijing nature reserves

在城市规模不断扩张的过程中,北京市自然保护区植物群落正面临着前所未有的干扰胁迫。研究植物群落对干扰的抵抗力具有理论和实践意义。在北京市松山和喇叭沟门两个自然保护区植物群落中调查了22个样地,记录到213种植物,测度了33个植物功能性状。在集成前人成果的基础上,量化了每个性状在基建工程、放牧或旅游践踏、火烧以及外来种入侵干扰下的功能属性;计算了物种、功能群和群落尺度上的功能指数;利用回归分析方法描绘了物种丰富度与功能指数间的关系。结果表明:(1)植被恢复力指数(plant restoration index)在4.36-10.15之间,草本植物大于木本植物;物种对不同干扰的抵抗力功能指数(resistance index to disturbance)变化范围分别为:放牧10.27-23.15,乔木和灌木大于其他生长型植物;火烧9.01-22.15,乔木大于灌木,后者又大于草本;外来种入侵4.41-10.54,乔木大于其他生长型。(2)以山杨(Populus davidiana)为优势种的群丛,其植被恢复力以及对干扰的抵抗力较其他群丛强。(3)在乔木层和草本层,物种丰富度与功能指数不相关;在灌木层,物种丰富度与放牧、火烧和外来种入侵的功能指数正相关,与植被恢复指数不相关。作者建立了研究区域物种、功能群和群落尺度上的植被功能指数数据库,为自然保护区植被结构调整和恢复提供了技术支撑。群落尺度的功能值取决于优势种的功能值,物种多样性是生态系统功能维持的重要基础。物种的功能冗余可能与植物群落结构层次以及干扰类型有关。本文结果为生态系统物种功能冗余假说提供了一个例证。

Plant communities in Beijing nature reserves are undergoing unprecedented disturbance due to city expansion. To examine the resistance of plant communities to disturbance is thus of both theoretical and practical significance. We surveyed 22 plant community plots in Labagoumen and Songshan nature reserves. A total of 213 plant species were recorded, and 33 plant functional traits were measured for each species. The functional implications of each trait to disturbance, such as potential for restoration, resistance to fire, grazing and exotic invasion, were quantified according to published information. We calculated a functional index for each species, growth form and plant association, respectively, Regression analysis was used to detect the relationship between species richness and functional index at the community level. We found that the plant restoration index ranged between 4.36 and 10.15, and was significantly higher for herbs than for woody plants, while index of resistance to disturbance by grazing ranged between 10.27 and 23.15, and was significantly higher for woody plants than for herbs. Resistance to fire ranged between 9.01 and 22.15, with trees showing greatest resistance followed, in turn, by shrubs and herbs, while resistance to exotic invasion ranged from 4.41 to10.54, and was again highest for trees. At the community level, plant associations with Populus davidiana as the dominant species were at the top position of a decreasing sequence as determined by functional index of each association. Species richness was not correlated with any functional index at the layer of trees and herbs, but was significantly and positively correlated with resistance index to fire, grazing and exotic invasion within the shrub layer. The information obtained from our research will be important to the future vegetation restoration and management of Beijing nature reserves. Although the functional index of a community is determined to a large extent by the dynamics of dominant species, species richness is fundamental to ecosystem stability. Species redundancy may be detectable in a specific community layer or under a given type of disturbance, but might not be so in all situations.