Climate warming is contributing to increases in wildfire activity throughout the western United States, leading to potentially long-lasting shifts in vegetation. The response of forest ecosystems to wildfire is thus a crucial indicator of future vegetation trajectories, and these responses are contingent upon factors such as seed availability, interannual climate variability, average climate, and other components of the physical environment. To better understand variation in resilience to wildfire across vulnerable dry forests, we surveyed conifer seedling densities in 15 recent (1988-2010) wildfires and characterized temporal variation in seed cone production and seedling establishment. We then predicted postfire seedling densities at a 30-m resolution within each fire perimeter using downscaled climate data, monthly water balance models, and maps of surviving forest cover. Widespread ponderosa pine (Pinus ponderosa) seed cone production occurred at least twice following each fire surveyed, and pulses of conifer seedling establishment coincided with years of above-average moisture availability. Ponderosa pine and Douglas-fir (Pseudotsuga menziesii) seedling densities were higher on more mesic sites and adjacent to surviving trees, though there were also important interspecific differences, likely attributable to drought and shade tolerance. We estimated that postfire seedling densities in 42% (for ponderosa pine) and 69% (for Douglas-fir) of the total burned area were below the lowest reported historical tree densities in these forests. Spatial models demonstrated that an absence of mature conifers (particularly in the interior of large, high-severity patches) limited seedling densities in many areas, but 30-yr average actual evapotranspiration and climatic water deficit limited densities on marginal sites. A better understanding of the limitations to postfire forest recovery will refine models of vegetation dynamics and will help to improve strategies of adaptation to a warming climate and shifting fire activity.

中文翻译：

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在美国科罗拉多州南部和新墨西哥州北部的干旱森林中发生野火后恢复的局限性。

气候变暖正在导致整个美国西部野火活动的增加，从而导致植被的潜在持久变化。因此，森林生态系统对野火的反应是未来植被轨迹的关键指标，而这些反应取决于诸如种子的可获得性，年际气候变异性，平均气候以及自然环境的其他组成部分等因素。为了更好地了解脆弱的干旱森林之间对野火的抵御力变化，我们调查了15种近期（1988-2010年）野火的针叶树幼苗密度，并描述了种子球果产量和幼苗建立的时间变化。然后，我们使用降尺度的气候数据，每月水平衡模型，和尚存森林覆盖的地图。每次调查过的大火之后，广泛出现的美国黄松（Pinus tankerosa）种子球果生产至少发生两次，针叶树幼苗建立的脉冲与多年高于平均水平的水分供应相吻合。黄松和花旗松（Pseudotsuga menziesii）的幼苗密度在更多的内陆站点和幸存的树木附近较高，尽管种间也存在重要差异，这可能归因于干旱和耐荫性。我们估计，总燃烧面积的42％（美国黄松）和69％（美国道格拉斯杉）的火后幼苗密度低于这些森林中报告的最低历史树木密度。空间模型表明，没有成熟的针叶树（特别是在大型，高强度斑块）限制了许多地区的幼苗密度，但30年平均实际蒸散量和气候缺水限制了边缘地区的密度。更好地了解火灾后森林恢复的局限性将完善植被动力学模型，并将有助于改善适应气候变暖和火势转移的策略。