Abstract The influence of landscape features on the occurrence and size of forest fires in Northern Europe has not been well-studied. In this paper, we analyzed the impact of human-related landscape properties (road and human population density), biotic features (amount of firebreak area and vegetation zone) and fire weather indices (Buildup Index, BUI and Initial Spread Index, ISI) on the occurrence and size of forest fires in Sweden from 1998 to 2017. To analyze the environmental controls of fire occurrence and fire size under different levels of climatological fire hazard, we divided the data into two subsets: (1) large fire years (LFY), defined as the years with the total amount of burned area being higher than the dataset-wide average (2002, 2003, 2006, 2008 and 2014), and (2) the remaining years (nLFY). Our analytical approach was based on spatial models using Integrated Nested Laplace Approximations (INLA). Models built on both LFY and nLFY subsets suggested a strong human influence on fire occurrence: road density, the number of firebreaks, and population density, all were positively associated with fire occurrence, suggesting an important role of human-related ignitions. The southernmost vegetation zones in Sweden (boreo-nemoral and nemoral) exhibited the highest fire occurrence (LFY), a pattern potentially related to a higher population density in combination with weather more conducive for fires in this part of the country. The patterns that emerged from the fire size models pointed to the climate as the main factor controlling fire size, irrespective of the type of years analyzed. Road density, number of firebreaks and population density showed a negative association with fire size, possibly indicating higher efficiency of fire suppression in the areas with higher human presence. Vegetation zones were selected as an informative predictor, indicating that the fire activity varies across the zones, with those in mid-Sweden being the most prone to large events. The ISI correlated strongly and positively with fire size in both subsets (LFY and nLFY), pointing to the role of weather conditions favorable for fire spread, primarily that of surface fires. The BUI showed a weak negative correlation to fire size, indicating that dryness of organic horizon, specifically its deeper layers, is less relevant for predicting fire size. Contemporary fire activity in Sweden is driven by a combination of human-related ignitions, and weather conditions controlling fire spread with a moderate effect of vegetation composition and generally efficient fire suppression. Human-related landscape features (roads and population density) play a major role in shaping ignition patterns, whereas climate (ISI) and vegetation properties appear informative as predictors of fire size, even under a modern fire suppression effort.

中文翻译：

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人类相关和生物景观特征对瑞典现代森林火灾发生和规模的影响

摘要 景观特征对北欧森林火灾发生和规模的影响尚未得到充分研究。在本文中，我们分析了与人类相关的景观特性（道路和人口密度）、生物特征（防火区和植被区的数量）和火灾天气指数（建立指数、BUI 和初始蔓延指数、ISI）对火灾的影响。 1998-2017年瑞典森林火灾发生和规模。为了分析不同气候火灾危害等级下火灾发生和火灾规模的环境控制，我们将数据分为两个子集：（1）大火灾年（LFY） ，定义为燃烧面积总量高于数据集范围平均值的年份（2002、2003、2006、2008 和 2014），以及（2）剩余年份（nLFY）。我们的分析方法基于使用集成嵌套拉普拉斯近似 (INLA) 的空间模型。建立在 LFY 和 nLFY 子集上的模型表明人类对火灾发生的影响很大：道路密度、防火带的数量和人口密度都与火灾发生呈正相关，表明与人类有关的点火起着重要作用。瑞典最南端的植被区（boreo-nemoral 和 nemoral）表现出最高的火灾发生率 (LFY)，这种模式可能与较高的人口密度以及该地区更利于火灾的天气有关。从火灾规模模型中出现的模式表明，气候是控制火灾规模的主要因素，而与分析的年份类型无关。道路密度，防火带的数量和人口密度与火灾规模呈负相关，这可能表明在人员密集的地区灭火效率更高。植被区被选为信息性预测因子，表明不同区域的火灾活动各不相同，瑞典中部的火灾活动最容易发生大型事件。ISI 与两个子集（LFY 和 nLFY）中的火灾规模呈强正相关，表明天气条件有利于火势蔓延，主要是地表火灾。BUI 与火灾规模呈弱负相关，表明有机层的干燥度，特别是其更深层，与预测火灾规模的相关性较小。瑞典的当代火灾活动是由与人类有关的点火组合驱动的，和天气条件控制火势蔓延，具有适度的植被成分影响和普遍有效的灭火。与人类相关的景观特征（道路和人口密度）在塑造点火模式方面发挥着重要作用，而气候 (ISI) 和植被特性似乎可以作为火灾规模的预测指标，即使在现代灭火努力下也是如此。