Department of Environment, Climate Change and Water c/- Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
Ecol Lett. 2011 Jul;14(7):709-22. doi: 10.1111/j.1461-0248.2011.01630.x. Epub 2011 May 19.
Encroachment of woody plants into grasslands has generated considerable interest among ecologists. Syntheses of encroachment effects on ecosystem processes have been limited in extent and confined largely to pastoral land uses or particular geographical regions. We used univariate analyses, meta-analysis and structural equation modelling to test the propositions that (1) shrub encroachment does not necessarily lead to declines in ecosystem functions and (2) shrub traits influence the functional outcome of encroachment. Analyses of 43 ecosystem attributes from 244 case studies worldwide showed that some attributes consistently increased with encroachment (e.g. soil C, N), and others declined (e.g. grass cover, pH), but most exhibited variable responses. Traits of shrubs were associated with significant, though weak, structural and functional outcomes of encroachment. Our review revealed that encroachment had mixed effects on ecosystem structure and functioning at global scales, and that shrub traits influence the functional outcome of encroachment. Thus, a simple designation of encroachment as a process leading to functionally, structurally or contextually degraded ecosystems is not supported by a critical analysis of existing literature. Our results highlight that the commonly established link between shrub encroachment and degradation is not universal.
木本植物侵入草原引起了生态学家的极大兴趣。对生态系统过程入侵效应的综合研究在范围上受到限制，主要局限于畜牧业土地利用或特定地理区域。我们使用单变量分析、荟萃分析和结构方程模型来检验以下假设：（1）灌木入侵不一定导致生态系统功能下降；（2）灌木特征影响入侵的功能结果。对来自全球 244 个案例研究的 43 个生态系统属性的分析表明，一些属性随着入侵而持续增加（例如土壤 C、N），而另一些属性则下降（例如草覆盖率、pH 值），但大多数属性表现出可变的响应。灌木的特征与入侵的显著但较弱的结构和功能结果有关。我们的综述表明，在全球范围内，入侵对生态系统结构和功能的影响是复杂的，并且灌木特征影响入侵的功能结果。因此，对现有文献的批判性分析不支持将入侵简单地指定为导致功能、结构或上下文退化的过程。我们的研究结果强调，普遍存在的灌木入侵与退化之间的联系并非普遍存在。
