The natural range of variation (NRV) is an important reference for ecosystem management, but has been scarcely quantified for forest landscapes driven by infrequent, severe disturbances. Extreme events such as large, stand-replacing wildfires at multi-century intervals are typical for these regimes; however, data on their characteristics are inherently scarce, and, for land management, these events are commonly considered too large and unpredictable to integrate into planning efforts (the proverbial "Black Swan"). Here, we estimate the NRV of late-seral (mature/old-growth) and early-seral (post-disturbance, pre-canopy-closure) conditions in a forest landscape driven by episodic, large, stand-replacing wildfires: the Western Cascade Range of Washington, USA (2.7 million ha). These two seral stages are focal points for conservation and restoration objectives in many regions. Using a state-and-transition simulation approach incorporating uncertainty, we assess the degree to which NRV estimates differ under a broad range of literature-derived inputs regarding (1) overall fire rotations and (2) how fire area is distributed through time, as relatively frequent smaller events (less episodic), or fewer but larger events (more episodic). All combinations of literature-derived fire rotations and temporal distributions (i.e., "scenarios") indicate that the largest wildfire events (or episodes) burned up to 105 -106 ha. Under most scenarios, wildfire dynamics produced 5th-95th percentile ranges for late-seral forests of ~47-90% of the region (median 70%), with structurally complex early-seral conditions composing ~1-30% (median 6%). Fire rotation was the main determinant of NRV, but temporal distribution was also important, with more episodic (temporally clustered) fire yielding wider NRV. In smaller landscapes (20,000 ha; typical of conservation reserves and management districts), ranges were 0-100% because fires commonly exceeded the landscape size. Current conditions are outside the estimated NRV, with the majority of the region instead covered by dense mid-seral forests (i.e., a regional landscape with no historical analog). Broad consistency in NRV estimates among widely varied fire regime parameters suggests these ranges are likely relevant even under changing climatic conditions, both historical and future. These results indicate management-relevant NRV estimates can be derived for seral stages of interest in extreme-event landscapes, even when incorporating inherent uncertainties in disturbance regimes.

中文翻译：

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笼罩着黑天鹅：由罕见的极端事件驱动的森林景观自然变化范围。

变异的自然范围（NRV）是生态系统管理的重要参考，但是对于由偶发的严重干扰驱动的森林景观而言，其很少被量化。这些政权通常会发生极端事件，例如，在多个世纪的时间间隔内更换林分的野火。但是，有关其特征的数据本来就很匮乏，对于土地管理而言，这些事件通常被认为过大且不可预测，无法整合到规划工作中（众所周知的“黑天鹅”）。在这里，我们估算了由偶发性，大面积，替代林场的野火驱动的森林景观中晚期（成熟/陈旧）和早期（干扰后，林冠层关闭）状况的NRV。美国华盛顿的喀斯喀特山脉（270万公顷）。这两个养蚕阶段是许多地区保护和恢复目标的重点。使用包含不确定性的状态和过渡模拟方法，我们评估了在（1）总体火灾旋转和（2）火灾面积如何随时间分布的广泛文献衍生输入下，NRV估计的差异程度。相对频繁的较小事件（较少发生），或较少但较大的事件（较多发生）。由文献得出的火灾轮换和时间分布（即“情景”）的所有组合均表明，最大的野火事件（或事件）燃烧了105 -106公顷。在大多数情况下，野火动力在该地区约47-90％（中位数为70％）的晚熟森林中产生了5-95％的范围，结构复杂的早期条件组成〜1-30％（中位数6％）。火灾轮换是NRV的主要决定因素，但时间分布也很重要，更多的情节性（临时聚类）火灾会产生更大的NRV。在较小的景观中（20,000公顷；典型的自然保护区和管理区），范围为0-100％，因为火灾通常超过了景观大小。当前状况不在估算的NRV范围内，该地区的大部分地区都被茂密的中性森林覆盖（即，没有历史可比性的区域景观）。各种不同的火灾状况参数之间的NRV估算值具有广泛的一致性，这表明即使在历史和未来气候条件变化的情况下，这些范围也可能是相关的。