School of Environmental and Forest Sciences, University of Washington, Box 354115, Seattle, Washington 98195-4115, USA.
Ecol Appl. 2012 Jul;22(5):1562-77. doi: 10.1890/10-2089.1.
Repeated perturbations, both biotic and abiotic, can lead to fundamental changes in the nature of ecosystems, including changes in state. Sagebrush steppe communities provide important habitat for wildlife and grazing for livestock. Fire is an integral part of these systems, but there is concern that increased ignition frequencies and invasive species are fundamentally altering them. Despite these issues, the majority of studies of fire effects in systems dominated by Artemisia tridentata wyomingensis have focused on the effects of single burns. The Arid Lands Ecology Reserve (ALE), in south-central Washington (U.S.A.), was one of the largest contiguous areas of sagebrush steppe habitat in the state until large wildfires burned the majority of it in 2000 and 2007. We analyzed data from permanent vegetation transects established in 1996 and resampled in 2002 and 2009. Our objective was to describe how the fires, and subsequent postfire restoration efforts, affected communities' successional pathways. Plant communities differed in response to repeated fire and restoration; these differences could largely be ascribed to the functional traits of the dominant species. Low-elevation communities, previously dominated by obligate seeders, moved furthest from their initial composition and were dominated by weedy, early-successional species in 2009. Higher-elevation sites with resprouting shrubs, native bunchgrasses, and few invasive species were generally more resilient to the effects of repeated disturbances. Shrub cover has been almost entirely removed from ALE, although there was some recovery where communities were dominated by resprouters. Bromus tectorum dominance was reduced by herbicide application in areas where it was previously abundant, but it increased significantly in untreated areas. Several resprouting species, notably Phlox longifolia and Poa secunda, expanded remarkably following competitive release from shrub canopies and/or abundant B. tectorum. Our results suggest that community dynamics can be understood through a state and transition model with two axes (shrub/grass and native/invasive abundance), although such models also need to account for differences in plant functional traits and disturbance regimes. We use our results to develop a conceptual model that will be validated with further research.
重复的生物和非生物干扰会导致生态系统性质发生根本变化，包括状态变化。山艾灌丛草原群落为野生动物提供了重要的栖息地，也为牲畜提供了放牧地。火是这些系统的一个组成部分，但人们担心增加的点火频率和入侵物种正在从根本上改变它们。尽管存在这些问题，但在美国华盛顿州中南部的干旱土地生态保护区（ALE），在 2000 年和 2007 年的大火烧毁了大部分地区之前，大多数以 Artemisia tridentata wyomingensis 为主的火效应研究都集中在单次燃烧的影响上。我们分析了 1996 年建立的永久性植被样带数据，并于 2002 年和 2009 年重新采样。我们的目标是描述火灾以及随后的灾后恢复工作如何影响群落的演替途径。植物群落对反复发生的火灾和恢复有不同的反应；这些差异在很大程度上可以归因于优势物种的功能特征。低海拔社区以前由强制性播种者主导，与初始组成相比，它们移动得更远，并且在 2009 年由杂草、早期演替物种主导。具有再生灌木、本地丛生草和很少入侵物种的高海拔地点通常对反复干扰的影响更具弹性。尽管在以再生植物为主的地方已经恢复了一些灌木覆盖，但 ALE 的灌木覆盖几乎已经全部被移除。先前在广泛分布的地区，通过除草剂应用降低了 B. tectorum 的优势地位，但在未处理的地区，它的数量显著增加。一些再生植物，特别是 Phlox longifolia 和 Poa secunda，在从灌木树冠和/或丰富的 B. tectorum 中获得竞争释放后显著扩张。我们的结果表明，通过具有两个轴（灌木/草和本地/入侵丰度）的状态和转换模型可以理解群落动态，尽管此类模型还需要考虑植物功能特征和干扰模式的差异。我们利用研究结果开发了一个概念模型，该模型将通过进一步的研究进行验证。
