USDA Forest Service, Pacific Southwest Research Station, Davis, California, 95618, USA.
Center for Fire Research and Outreach, University of California, Berkeley, California, 94720, USA.
Ecol Appl. 2017 Oct;27(7):2013-2030. doi: 10.1002/eap.1586. Epub 2017 Aug 17.
Following changes in vegetation structure and pattern, along with a changing climate, large wildfire incidence has increased in forests throughout the western United States. Given this increase, there is great interest in whether fuels treatments and previous wildfire can alter fire severity patterns in large wildfires. We assessed the relative influence of previous fuels treatments (including wildfire), fire weather, vegetation, and water balance on fire-severity in the Rim Fire of 2013. We did this at three different spatial scales to investigate whether the influences on fire severity changed across scales. Both fuels treatments and previous low to moderate-severity wildfire reduced the prevalence of high-severity fire. In general, areas without recent fuels treatments and areas that previously burned at high severity tended to have a greater proportion of high-severity fire in the Rim Fire. Areas treated with prescribed fire, especially when combined with thinning, had the lowest proportions of high severity. The proportion of the landscape burned at high severity was most strongly influenced by fire weather and proportional area previously treated for fuels or burned by low to moderate severity wildfire. The proportion treated needed to effectively reduce the amount of high severity fire varied by spatial scale of analysis, with smaller spatial scales requiring a greater proportion treated to see an effect on fire severity. When moderate and high-severity fire encountered a previously treated area, fire severity was significantly reduced in the treated area relative to the adjacent untreated area. Our results show that fuels treatments and low to moderate-severity wildfire can reduce fire severity in a subsequent wildfire, even when burning under fire growth conditions. These results serve as further evidence that both fuels treatments and lower severity wildfire can increase forest resilience.
随着植被结构和格局的变化以及气候变化的影响，美国西部的森林中大火灾的发生率已经增加。鉴于这种增加，人们非常关注燃料处理和以前的野火是否会改变大型野火的严重程度模式。我们评估了先前的燃料处理（包括野火）、火险天气、植被和水平衡对 2013 年里姆火灾严重程度的相对影响。我们在三个不同的空间尺度上进行了这项研究，以调查对火灾严重程度的影响是否随尺度而变化。燃料处理和以前的低到中等严重程度的野火都减少了高严重程度火灾的发生率。一般来说，没有最近的燃料处理区和以前严重程度较高的区域在里姆火灾中高严重程度的比例较大。经过计划火烧处理的区域，特别是与疏伐相结合的区域，高严重程度的比例最低。高严重程度火烧景观的比例受火险天气和以前为燃料处理或低到中等严重程度野火而处理或燃烧的比例区域的影响最大。为了有效减少高严重程度火灾的数量，需要进行处理的比例因分析的空间尺度而异，较小的空间尺度需要更大比例的处理才能对火灾严重程度产生影响。当中等到高严重程度的火灾遇到以前处理过的区域时，处理区域中的火灾严重程度相对于相邻未处理区域显著降低。我们的结果表明，燃料处理和低到中等严重程度的野火可以降低随后的野火中的火灾严重程度，即使在火增长条件下燃烧也是如此。这些结果进一步证明，燃料处理和较低严重程度的野火都可以提高森林的恢复力。
