Fire-vegetation feedbacks can modulate the global change effects conducive to extreme fire behavior and high fire severity of subsequent wildfires in reburn areas by altering the composition, flammability traits, and spatial arrangement of fuels. Repeated, high-severity wildfires at short return intervals may trigger long-term vegetation state transitions. However, empirical evidence about these feedbacks is absent in fire-prone ecosystems of the western Mediterranean Basin, where the response of fire activity has been enhanced by contemporary socioeconomic and land-use changes. Here, we evaluated whether fire severity differs between initial burns and subsequent wildfires in reburn areas (fire-free periods = 10–15 years) of maritime pine and Aleppo pine forests, holm oak woodlands, and shrublands in the western Mediterranean Basin, and whether there is a relationship between the severity of such interactive wildfire disturbances. We also tested how the type of ecosystem and changes in vegetation structure after the initial wildfires influence these relationships. We leveraged Landsat-based fire severity estimates for initial and last wildfires using the Relativized Burn Ratio (RBR) and Light Detection and Ranging (LiDAR) data acquired before the last wildfire. Fire severity of the last wildfire was significantly higher than that of the initial wildfire for each dominant ecosystem type in reburn areas. These differences were very pronounced in maritime pine forests and shrublands. For consistency, the same patterns were evidenced for the fire severity in reburn and first-entry areas of the last wildfire for each dominant ecosystem type. Fire severity of the last wildfire in forests and woodlands (particularly maritime pine-dominated) raised with increasing severity of the previous wildfire to a greater extent than in shrublands. Pre-fire fuel density in the lower vegetation strata (up to 4 m high in maritime and Aleppo pine forests, as well as in shrublands, and up to 2 m high in holm oak forests) was significantly higher in reburn than in first-entry areas of the last wildfire. Our results suggest that land managers should promote more fire-resistant landscapes to high fire severity by minimizing fuel build-up and thus fire hazard through pre-fire fuel reduction treatments such as prescribed burning.

中文翻译：

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燃料堆积导致西地中海盆地易发生火灾的生态系统中重燃区域的火灾严重程度增加

火灾-植被反馈可以通过改变燃料的成分、可燃性特征和空间排列来调节全球变化效应，从而有利于极端火灾行为和随后再燃地区野火的高火灾严重性。在较短的回归间隔内反复发生、严重程度较高的野火可能会引发长期的植被状态转变。然而，在西地中海盆地易发生火灾的生态系统中，缺乏有关这些反馈的经验证据，当代社会经济和土地利用的变化增强了火灾活动的响应。在这里，我们评估了地中海西部盆地的沿海松林和阿勒颇松林、圣栎林地和灌木丛的再烧区域（无火期 = 10-15 年）的初次燃烧和随后的野火之间的火灾严重程度是否存在差异，以及是否存在差异。这种相互作用的野火干扰的严重程度之间存在一定的关系。我们还测试了最初野火后生态系统的类型和植被结构的变化如何影响这些关系。我们利用上次野火之前获取的相对化燃烧率 (RBR) 和光探测和测距 (LiDAR) 数据，利用基于陆地卫星的火灾严重程度估计来估计最初和最后一次野火。对于重烧地区的每种主要生态系统类型来说，最后一次野火的火灾严重程度明显高于最初野火的严重程度。这些差异在沿海松林和灌木丛中非常明显。为了保持一致性，每种主要生态系统类型的最后一次野火的再燃和首次进入区域的火灾严重程度都证明了相同的模式。森林和林地（特别是以海松为主）的上次野火的火灾严重程度随着上次野火的严重性的增加而增加，其程度比灌木丛更大。再燃烧时较低植被层（海洋和阿勒颇松林以及灌木丛中高达 4 m，圣栎林高达 2 m）的火灾前燃料密度明显高于首次进入时的燃料密度上次野火发生的地区。我们的研究结果表明，土地管理者应通过火前燃料减少处理（例如规定燃烧）最大限度地减少燃料堆积，从而最大限度地减少火灾危险，从而促进更耐火的景观达到高火灾严重程度。