In the Inland Pacific Northwest of the United States, fire is a dominant driver of ecological change. Within wildfire perimeters, fire effects often vary considerably and typically include remnant patches of unburned islands. As fires reburn the landscape, some unburned islands remain persistently unburned. These persistent unburned islands can serve an important ecological function as fire refugia; however, their characteristics have not been quantified. The objective of this study was to assess the characteristics of persistent unburned islands and compare them to the burned areas that surround them. Using an existing database of unburned islands from 1984 to 2014, overlapping unburned islands were delineated. We sampled points in both persistent unburned islands and in areas burned by wildfire. At these sample points, we derived several topographical and other geospatial metrics, and we compared the characteristics of these groups. Because the study area covers many ecosystems, we stratified the analysis by different fire regime groups. Our analysis revealed that persistent unburned islands are not randomly distributed across the landscape. While the topography and vegetation fuel type that underlie persistent unburned islands differ from burned areas, these differences are dependent upon fire regime group and are less pronounced than what other studies have found. The topographic features that differed the most between persistent unburned islands and burned areas were terrain ruggedness, slope, and transformed aspect. We also found that, as unburned islands increased in persistence (i.e., remained unburned for an increasing number of overlapping fires), they decreased in size and shape complexity. Our research shows that the biophysical setting underlying persistent unburned islands differs between forests and rangelands, and also differs from burned areas, which has potential applications for fire refugia prediction and management. Characterizing fire refugia and understanding the processes that contribute to their creation and maintenance will be important for land management as climate changes and increasingly large areas are affected by wildfire.

中文翻译：

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表征美国西北内陆地区未燃烧的持续性岛屿

在美国西北太平洋内陆地区，火灾是生态变化的主要驱动力。在野火范围内，火灾影响通常会相差很大，并且通常包括未燃烧岛屿的残余部分。随着大火重燃景观，一些未燃烧的岛屿仍然持续燃烧。这些持续不断的未燃烧岛屿可以起到重要的生态功能，例如防火。但是，它们的特征尚未被量化。这项研究的目的是评估未燃烧的持续岛屿的特征，并将其与周围的已燃烧区域进行比较。利用现有的1984年至2014年未烧毁岛屿数据库，划定了重叠的未烧毁岛屿。我们在未燃烧的持续岛屿和野火燃烧的地区取样。在这些样本点，我们得出了几个地形和其他地理空间指标，并比较了这些组的特征。由于研究区域涵盖了许多生态系统，因此我们按不同的火灾状况分组对分析进行了分层。我们的分析表明，未燃烧的持久性岛屿并非随机分布在整个景观中。尽管持续的未燃烧岛屿所依据的地形和植被燃料类型与燃烧区域不同，但这些差异取决于火灾状况组，并且没有其他研究发现的那么明显。持久性未烧毁岛屿和烧毁区域之间最大的地形特征是地形的崎，度，坡度和坡度。我们还发现，随着未燃烧的岛屿的持续生存能力增加（即，由于重叠的火灾数量不断增加，未燃烧的岛屿），它们减小了尺寸和形状复杂度。我们的研究表明，森林和牧场之间未燃烧的持续岛屿所具有的生物物理环境有所不同，而燃烧的地区也有所不同，这对于火灾避难所的预测和管理具有潜在的应用价值。随着气候变化和越来越大的地区受到野火的影响，表征避难所的特征并了解有助于其创建和维护的过程对于土地管理至关重要。