干旱半干旱区草原灌丛化研究进展

Advance in shrub encroachment in arid and semiarid region

干旱半干旱区草原生态系统中原生灌木/木本植物的植株密度、盖度和生物量增加的现象称为草原灌丛化,是全球干旱半干旱区草原面临的重要生态问题,灌丛化研究正成为陆地生态系统全球变化研究的重要领域。引起灌丛化的因素包括过度放牧、草原火、气候变化、大气CO2浓度升高及生物和非生物环境因子的变化等,灌丛化是多种因素共同作用的结果。灌丛化过程表现为地表景观由草本植物占优势转向灌木植物占优势的植被转变过程,此过程改变了原有植物群落的物种组成和结构,增强了地表景观异质性,打破了原生态系统的光照、热量、水分、养分等的分配格局,灌丛斑块成为了灌丛化草地中水分、养分等相对富集的"肥岛"。目前灌丛化研究主要集中在具有强烈地域性和限制性的定点研究和因子控制实验等方面,未来应更多关注气候变化与灌丛化的相互联系和影响、草地生态系统对灌丛化过程的反馈以及与灌丛化的监测、缓解措施等方面的研究,模型模拟将是今后研究灌丛化发生、发展及灌丛化生态系统演替的重要方法和途径。

Shrub encroachment is the increase in density, cover and biomass of indigenous woody or shrubby plants in arid and semiarid grasslands, which become a great ecological problem in arid and semiarid region. It is one of the most important parts of research in the global change of terrestrial ecosystem. Shrub encroach- ment was resulted from the interactions of many factors including over grazing, fire, climate change, elevated atmospheric C（）2, changes about biotic and abiotic environment factors. Shrub encroachment could occurred a suddenly vegetation shift from a stable stage with grasses dominant to a stable stage with shrub dominant, with a great change in the composition and structure of plant community. The whole landscape fragmentation and heterogeneity increased in the processes of shrub encroachment. The light, heat, water and nutrients in ecosys- tem were redistributed with the establishment and development of shrub seedlings. Shrub patches gradually formed ＂fertile islands＂ with water and nutrients enrichment. The current studies about shrub encroachment were mainly concentrated on fixed-point research and factor controlled experiments with distinct locality and re strictions. We should pay more attention on the relationship of climate change and shrub encroachment, feed back of grassland ecosystem for shrub encroachment and research about strategies and countermeasures relative to shrub encroachment, model simulation might be one of important ways to study the occurrence and development of shrub encroachment even to predict the succession of ecosystem.