USGS Alaska Science Center, 4230 University Drive, Anchorage, Alaska 99508, USA.
Ecol Appl. 2011 Oct;21(7):2380-96. doi: 10.1890/10-0896.1.
Large fire years in which >1% of the landscape burns are becoming more frequent in the Alaskan (USA) interior, with four large fire years in the past 10 years, and 79 000 km2 (17% of the region) burned since 2000. We modeled fire severity conditions for the entire area burned in large fires during a large fire year (2004) to determine the factors that are most important in estimating severity and to identify areas affected by deep-burning fires. In addition to standard methods of assessing severity using spectral information, we incorporated information regarding topography, spatial pattern of burning, and instantaneous characteristics such as fire weather and fire radiative power. Ensemble techniques using regression trees as a base learner were able to determine fire severity successfully using spectral data in concert with other relevant geospatial data. This method was successful in estimating average conditions, but it underestimated the range of severity. This new approach was used to identify black spruce stands that experienced intermediate- to high-severity fires in 2004 and are therefore susceptible to a shift in regrowth toward deciduous dominance or mixed dominance. Based on the output of the severity model, we estimate that 39% (approximately 4000 km2) of all burned black spruce stands in 2004 had <10 cm of residual organic layer and may be susceptible a postfire shift in plant functional type dominance, as well as permafrost loss. If the fraction of area susceptible to deciduous regeneration is constant for large fire years, the effect of such years in the most recent decade has been to reduce black spruce stands by 4.2% and to increase areas dominated or co-dominated by deciduous forest stands by 20%. Such disturbance-driven modifications have the potential to affect the carbon cycle and climate system at regional to global scales.
在过去的 10 年中，美国阿拉斯加内陆地区发生了 4 次大面积火灾年，超过 1%的景观被烧毁，面积达 79000 平方公里（占该地区的 17%）。我们对过去一个大面积火灾年（2004 年）所有大面积火灾所烧区域的火灾严重程度条件进行建模，以确定在估算严重程度方面最重要的因素，并确定受深燃火灾影响的区域。除了使用光谱信息评估严重程度的标准方法外，我们还结合了地形、燃烧空间格局以及即时特征（如火灾天气和火灾辐射功率）的信息。使用回归树作为基本学习器的集成技术能够成功地使用光谱数据以及其他相关地理空间数据来确定火灾严重程度。这种方法成功地估计了平均条件，但低估了严重程度的范围。这种新方法用于识别在 2004 年经历了中等到高强度火灾的黑云杉林，因此容易受到再生向落叶优势或混合优势转变的影响。基于严重程度模型的输出，我们估计 2004 年所有烧毁的黑云杉林中，有 39%（约 4000 平方公里）的剩余有机层厚度<10 厘米，可能容易受到火灾后植物功能型优势变化以及永冻层损失的影响。如果大面积火灾年份中易受落叶再生影响的区域比例保持不变，那么最近十年中这样的年份已经使黑云杉林减少了 4.2%，并使落叶林或混合林占主导地位的区域增加了 20%。这种由干扰驱动的变化有可能影响区域到全球尺度的碳循环和气候系统。
