Centre for Ecosystem Science, University of New South Wales, Sydney, New South Wales, Australia.
New South Wales Office of Environment and Heritage, Hurstville, New South Wales, Australia.
Ecol Appl. 2017 Mar;27(2):458-468. doi: 10.1002/eap.1449. Epub 2017 Feb 16.
Effective conservation requires an understanding not only of contemporary vegetation distributions in the landscape, but also cognizance of vegetation transitions over time with the goal of maintaining persistence of all states within the landscape. Using a state and transition model framework, we investigated temporal transitions over 31 years in species composition among five upland swamp vegetation communities in southeastern Australia. We applied fuzzy clustering to document transitions across communities; evaluated the resilience and resistance of communities to change; and explored the relationship between ecosystem states and major environmental factors posited to structure the system. We also evaluated the predictive ability of an established vegetation dynamics model. We found that community composition remained stable or underwent reversible or directional transitions depending on the vegetation type. Wetter communities (Ti-tree thicket and Cyperoid heath) were more stable (i.e., resistant) while drier communities showed a greater propensity to transition (i.e., had lower resistance) under the observed disturbance regime (low variance fire intervals). The resilience of drier communities differed under this regime, with Banksia thicket showing reversible compositional change, while Restioid heath and Sedgeland showed directional change. In accord with an established conceptual model, we found that communities were distributed along a hydrological gradient. In addition, vegetation structure, along with light penetration to ground level, differentiated communities. However, internal dynamics of drier communities were complex: differences in fire regime (penultimate fire interval in 2014 and number of fires since 1965) were unable to predict differences in community membership among sites. Aspects of the fire regime are expected to be more important predictors if fire intervals vary more strongly among sites in the future. Fuzzy clustering of compositional data allows managers to track community transitions over time and facilitates planned interventions for conservation purposes.
有效的保护不仅需要了解当前景观中的植被分布，还需要认识到植被随时间的变化，以维持景观中所有状态的持续性。本研究使用状态和转换模型框架，调查了澳大利亚东南部五个高地沼泽植被群落中物种组成在 31 年内的时间转换。我们应用模糊聚类来记录群落间的转换；评估群落对变化的恢复力和抵抗力；并探讨生态系统状态与主要环境因素之间的关系，这些因素被认为是构建系统的结构。我们还评估了一个已建立的植被动态模型的预测能力。我们发现，群落组成保持稳定或经历可逆或定向转换，具体取决于植被类型。较湿润的群落（Ti-树灌丛和 Cyperoid 石南灌丛）更稳定（即具有抵抗力），而较干燥的群落在观测到的干扰模式（低方差火灾间隔）下更倾向于发生变化（即具有较低的抵抗力）。在这种模式下，干燥群落的恢复力不同， Banksia 灌丛表现出可逆的组成变化，而 Restioid 石南灌丛和 Sedgeland 则表现出定向变化。与一个既定的概念模型一致，我们发现群落沿着一个水文梯度分布。此外，植被结构以及光线到达地面的穿透度区分了群落。然而，干燥群落的内部动态是复杂的：火灾模式的差异（倒数第二次火灾间隔在 2014 年和自 1965 年以来的火灾次数）无法预测不同地点之间群落成员的差异。如果未来不同地点的火灾间隔变化更剧烈，火灾模式的各个方面有望成为更重要的预测因素。对组成数据进行模糊聚类可以使管理者跟踪群落随时间的变化，并促进有计划的干预措施，以达到保护目的。
