Data_Sheet_1_Interactions Between Fire Refugia and Climate-Environment Conditions Determine Mesic Subalpine Forest Recovery After Large and Severe Wildfires.docx

Infrequent stand-replacing wildfires are characteristic of mesic and/or cool conifer forests in western North America, where forest recovery within high-severity burn patch interiors can be slow, yet successful over long temporal periods (decades to centuries). Increasing fire frequency and high-severity burn patch size, under a warming climate, however, may challenge post-fire forest recovery, promoting landscape-level shifts in forest structure, composition, and distribution of non-forest patches. Crucial to a delay and/or impediment to this shift, fire refugia (i.e., remnant seed sources) may determine forest recovery trajectories and potential forest state-transitions. To examine how fire refugia attributes (i.e. extent, composition, and structure) interact with local climate and environmental conditions to determine post-fire forest recovery responses, we developed fine-grain maps of fire refugia via remote sensing and conducted field-based assessment of post-fire conifer tree establishment largely originating (i.e., dispersed) from fire refugium in the Central Cascade Range of the Pacific Northwest United States. We found that limitations on seed availability, represented by the distance2-weighted density (D2WD) of fine-grain refugia extent, largely explained post-fire tree establishment responses within our relatively mesic and cool subalpine study sites. Interactions between seed availability, climate, and environmental conditions indicated that the structural attributes of refugia (e.g., tree height) and site abiotic/biotic environmental controls (e.g., climate water deficit, canopy cover, and coarse woody debris cover) interplayed to constrain or enhance species-specific tree establishment responses. Importantly, these interactions illustrate that when seed availability is critically low for a given area, climate-environment conditions may strongly determine whether forests recover following fire(s). Toward modelling and predicting tree establishment responses and potential forest state-transitions after large stand-replacing fires(s), our study demonstrates the importance of accurately quantifying seed availability via the fine-grain extent, configuration, and attributes of remnant seed source legacies.

北美西部湿润及/或冷针叶林中，不频繁发生的替代主树冠火灾是其典型特征。在高强度燃烧区域内部，森林的恢复过程可能缓慢，但经过长时间的推移（数十年至数百年）仍能成功实现。然而，在气候变暖的背景下，火灾频率的增加以及高强度燃烧区域规模的扩大，可能会对火灾后森林的恢复构成挑战，从而促进森林结构、组成以及非森林区域分布的景观级转变。延迟或阻碍这种转变的关键因素，即火灾避难所（即残留种子来源），可能决定了森林恢复的轨迹和潜在的森林状态转变。为了探究火灾避难所属性（即范围、组成和结构）如何与当地气候和环境条件相互作用，以确定火灾后的森林恢复响应，我们通过遥感技术制作了火灾避难所的高分辨率地图，并在太平洋西北部美国中卡斯凯德山脉的现场对火灾后针叶树的建立进行了评估，这些针叶树主要来自火灾避难所。我们发现，在相对湿润和凉爽的亚高山研究地点，种子可获取性的限制，以细粒度避难所范围的距离加权密度（D2WD）表示，在很大程度上解释了火灾后树木建立响应。种子可获取性、气候和环境条件之间的相互作用表明，避难所的结构属性（例如，树木高度）和地点的物理/生物环境控制（例如，气候水短缺、冠层覆盖和粗木质残体覆盖）相互作用，以限制或增强特定物种的树木建立响应。重要的是，这些相互作用说明，当特定区域的种子可获取性处于临界低水平时，气候-环境条件可能强烈决定森林是否能够在火灾后恢复。为了模拟和预测大型替代主树冠火灾后的树木建立响应和潜在的森林状态转变，我们的研究证明了通过残留种子来源的细粒度范围、配置和属性来准确量化种子可获取性的重要性。（i.e., '即即'为英文原文缩写，意为'即'，在此处保留以保持原文格式和术语准确性。"