Wildfires and climate change push low-elevation forests across a critical climate threshold for tree regeneration
Wildfires and climate change push low-elevation forests across a critical climate threshold for tree regeneration
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DOI：
10.1073/pnas.1815107116
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发表时间：
2019-03-26
影响因子：
11.1
通讯作者：
Maneta, Marco P.
中科院分区：
文献类型：
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作者：
Davis, Kimberley T.;Dobrowski, Solomon Z.;Maneta, Marco P.
气候变化正在增加美国西部的火灾活动，这有可能加速气候引起的植被群落的变化。野火可以通过杀死成年树木来催化植被变化，否则成年树木可能会在不再适合幼苗建立和生存的气候条件下持续存在。最近记录的火灾后针叶树招聘在theswestern美国下降可能是这种现象的一个例子。然而，年度气候变化及其与长期气候趋势的相互作用在推动这些变化方面的作用还没有得到很好的解决。在这里，我们研究了每年的气候和火灾后的树木再生的两个占主导地位的，低海拔的针叶树（黄松和道格拉斯冷杉）使用每年解决的建立日期从2,935破坏性抽样树木在美国西部的四个地区的33个野火之间的关系。我们发现，再生有一个非线性的响应，每年的气候条件下，与不同的阈值招募的基础上蒸汽压赤字，土壤水分，最高表面温度。在我们研究区域的干旱地区，过去20年的季节性到年度气候条件已经超过了这些阈值，使得条件变得越来越不适合再生。高火灾严重性和低种子可用性进一步降低了火后再生的可能性。总之，我们的研究结果表明，气候变化与高严重性火灾相结合，导致野火后幼苗建立的机会越来越少，并可能导致美国西部低海拔黄松和道格拉斯冷杉森林的生态系统转型。
Climate change is increasing fire activity in the western United States, which has the potential to accelerate climate-induced shifts in vegetation communities. Wildfire can catalyze vegetation change by killing adult trees that could otherwise persist in climate conditions no longer suitable for seedling establishment and survival. Recently documented declines in postfire conifer recruitment in thewestern United States may be an example of this phenomenon. However, the role of annual climate variation and its interaction with long-term climate trends in driving these changes is poorly resolved. Here we examine the relationship between annual climate and postfire tree regeneration of two dominant, low-elevation conifers (ponderosa pine and Douglas-fir) using annually resolved establishment dates from 2,935 destructively sampled trees from 33 wildfires across four regions in the western United States. We show that regeneration had a nonlinear response to annual climate conditions, with distinct thresholds for recruitment based on vapor pressure deficit, soil moisture, and maximum surface temperature. At dry sites across our study region, seasonal to annual climate conditions over the past 20 years have crossed these thresholds, such that conditions have become increasingly unsuitable for regeneration. High fire severity and low seed availability further reduced the probability of postfire regeneration. Together, our results demonstrate that climate change combined with high severity fire is leading to increasingly fewer opportunities for seedlings to establish after wildfires and may lead to ecosystem transitions in low-elevation ponderosa pine and Douglas-fir forests across the western United States.