Climate change is increasing the frequency of droughts and the risk of severe wildfires, which can interact with shrub encroachment and browsing by wild ungulates. Wild ungulate populations are expanding due, among other factors, to favorable habitat changes resulting from land abandonment or land‐use changes. Understanding how ungulate browsing interacts with drought to affect woody plant mortality, plant flammability, and fire hazard is especially relevant in the context of climate change and increasing frequency of wildfires. The aim of this study is to explore the combined effects of cumulative drought, shrub encroachment, and ungulate browsing on the fire hazard of Mediterranean oak woodlands in Portugal. In a long‐term (18 years) ungulate fencing exclusion experiment that simulated land abandonment and management neglect, we investigated the population dynamics of the native shrub Cistus ladanifer, which naturally dominates the understory of woodlands and is browsed by ungulates, comparing areas with (no fencing) and without (fencing) wild ungulate browsing. We also modeled fire behavior in browsed and unbrowsed plots considering drought and nondrought scenarios. Specifically, we estimated C. ladanifer population density, biomass, and fuel load characteristics, which were used to model fire behavior in drought and nondrought scenarios. Overall, drought increased the proportion of dead C. ladanifer shrub individuals, which was higher in the browsed plots. Drought decreased the ratio of live to dead shrub plant material, increased total fuel loading, shrub stand flammability, and the modeled fire parameters, that is, rate of surface fire spread, fireline intensity, and flame length. However, total fuel load and fire hazard were lower in browsed than unbrowsed plots, both in drought and nondrought scenarios. Browsing also decreased the population density of living shrubs, halting shrub encroachment. Our study provides long‐term experimental evidence showing the role of wild ungulates in mitigating drought effects on fire hazard in shrub‐encroached Mediterranean oak woodlands. Our results also emphasize that the long‐term effects of land abandonment can interact with climate change drivers, affecting wildfire hazard. This is particularly relevant given the increasing incidence of land abandonment.

中文翻译：

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有蹄类动物减轻干旱和灌木侵占对地中海橡树林地火灾危险的影响

气候变化正在增加干旱的频率和严重野火的风险，这可能与灌木侵占和野生有蹄类动物的啃食相互作用。除其他因素外，由于土地废弃或土地利用变化导致有利的栖息地变化，野生有蹄类动物的数量正在扩大。了解有蹄类动物的觅食如何与干旱相互作用，从而影响木本植物的死亡率、植物的可燃性和火灾危险，在气候变化和野火频率增加的背景下尤其重要。本研究的目的是探讨累积干旱、灌木侵占和有蹄类动物啃食对葡萄牙地中海橡树林地火灾危险的综合影响。在模拟土地废弃和管理疏忽的长期（18 年）有蹄类动物围栏排除实验中，我们调查了原生灌木的种群动态岩蔷薇，它自然主导了林地的林下层，并被有蹄类动物啃食，比较了有（没有围栏）和没有（围栏）野生有蹄类动物啃食的区域。我们还考虑了干旱和非干旱情景，对浏览过和未浏览过的地块中的火灾行为进行了建模。具体来说，我们估计C. 拉丹尼弗人口密度、生物量和燃料负荷特征，用于模拟干旱和非干旱情景下的火灾行为。总体而言，干旱增加了死亡人数C. 拉丹尼弗灌木个体，在浏览过的地块中较高。干旱降低了灌木植物的活死比，增加了总燃料负荷、灌木林可燃性以及模拟火灾参数，即表面火势蔓延速度、火线强度和火焰长度。然而，无论是在干旱还是非干旱情况下，浏览过的地块的总燃料负荷和火灾危险均低于未浏览的地块。浏览还降低了活灌木的种群密度，阻止了灌木的侵占。我们的研究提供了长期的实验证据，表明野生有蹄类动物在减轻干旱对地中海橡树林的火灾危险影响方面的作用。我们的研究结果还强调，土地撂荒的长期影响可以与气候变化驱动因素相互作用，从而影响野火危险。鉴于土地废弃率不断增加，这一点尤其重要。