Large, severe fires are becoming more frequent in many forest types across the western United States and have resulted in tree mortality across tens of thousands of hectares. Conifer regeneration in these areas is limited because seeds must travel long distances to reach the interior of large burned patches and establishment is jeopardized by increasingly hot and dry conditions. To better inform postfire management in low elevation forests of California, USA, we collected 5‐yr postfire recovery data from 1,234 study plots in 19 wildfires that burned from 2004–2012 and 18 yrs of seed production data from 216 seed fall traps (1999–2017). We used these data in conjunction with spatially extensive climate, topography, forest composition, and burn severity surfaces to construct taxon‐specific, spatially explicit models of conifer regeneration that incorporate climate conditions and seed availability during postfire recovery windows. We found that after accounting for other predictors both postfire and historical precipitation were strong predictors of regeneration, suggesting that both direct effects of postfire moisture conditions and biological inertia from historical climate may play a role in regeneration. Alternatively, postfire regeneration may simply be driven by postfire climate and apparent relationships with historical climate could be spurious. The estimated sensitivity of regeneration to postfire seed availability was strongest in firs and all conifers combined and weaker in pines. Seed production exhibited high temporal variability with seed production varying by over two orders of magnitude among years. Our models indicate that during droughts postfire conifer regeneration declines most substantially in low‐to‐moderate elevation forests. These findings enhance our mechanistic understanding of forecasted and historically documented shifts in the distribution of trees.

中文翻译：

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火灾后气候和种子供应量对火灾后针叶树更新的影响

在美国西部的许多森林类型中，大面积的大火正变得越来越频繁，并导致成千上万公顷的树木死亡。在这些地区，针叶树的再生受到限制，因为种子必须经过很长的距离才能到达大片烧焦的内部，并且由于越来越热和干燥的条件，针叶树的生长受到威胁。为了更好地了解美国加利福尼亚州低海拔森林的火灾后管理情况，我们从2004-2012年燃烧的19场野火的1,234个研究地块收集了5年后的火灾恢复数据，并从216个种子掉落陷阱（1999-1999年）收集了18年的种子生产数据。 2017）。我们将这些数据与空间广泛的气候，地形，森林组成和烧伤严重程度表面结合使用，以构建特定于分类群的，针叶树再生的空间明确模型，其中包含了后火恢复时段内的气候条件和种子供应情况。我们发现，在考虑了其他预测因素后，火灾后和历史降水都是再生的重要预测因素，这表明火灾后湿度条件的直接影响和历史气候的生物惯性都可能在再生中起作用。另外，火灾后的再生可能只是由火灾后的气候所驱动，并且与历史气候的明显关系可能是虚假的。冷杉对杉木后生种子可用性的估计敏感性最高，所有针叶树结合在一起，松树则较弱。种子生产表现出高的时间变异性，其中种子生产在几年中变化超过两个数量级。我们的模型表明，在干旱期间，中低海拔森林火灾后的针叶树再生最大程度地下降。这些发现增强了我们对树木分布的预测和历史记录变化的机械理解。