Post-Fire Mortality and Fire Resistance of Old-growth Forests in the Kootenay Lake Timber Supply Area, British Columbia

In an era of climate change, how different tree species in old forests are disturbed by wildfires, and what fire resistance they have are important questions. Old-growth forests are significant because they maintain local biodiversity and ecosystem sustainability, and also contribute to the local economy through timber harvesting. In this research, by analyzing Landsat-8 images of 20 fires from 2016 to 2020, the disturbance data of the forest before and after the fire can be generated. Data from B.C. government and Landsat-8 images are used to analyze fire resistance and recovery of old-growth forests in the Kootenay Lake Timber Supply Area (TSA) by calculating NBR (Normalized burn ratio) and NDVI (Normalized Difference Vegetation Index). Five common tree species (western larch, Douglas fir, western hemlock, Engelmann spruce, subalpine fir) near Kootenay Lake TSA were selected for fire resistance comparison at different burn severities (high, medium, low). The result verified that different tree species have different fire resistance and mortality when facing different burn severities. Western larch and Douglas fir have high fire resistance. Western hemlock has relatively low fire resistance. Engelmann spruce and Subalpine fir have very low fire resistance. This result is highly similar to the report provided by USDA. However, due to the shortage and limitations of data, the NDVI trend after fires cannot well represent the recovery of vegetation. Overall, based on the analysis of Landsat-8 satellite images before and after the fire, this paper verifies the difference in the fire resistance of five tree species in the old-growth forests for different burn severities.在气候变化的时代，老龄林内不同树种如何受野火干扰，以及各自的耐火性如何，是亟待解答的重要问题。老龄林具有重要价值：其既维系着当地生物多样性与生态系统可持续性，亦可通过木材采伐助力地方经济发展。本研究通过分析2016至2020年间20起野火的Landsat-8影像，生成了野火前后的森林干扰数据。本研究借助不列颠哥伦比亚省（British Columbia，B.C.）政府公开数据与Landsat-8影像，通过计算归一化燃烧比（Normalized Burn Ratio，NBR）与归一化植被指数（Normalized Difference Vegetation Index，NDVI），分析了库特尼湖木材供应区（Timber Supply Area，TSA）内老龄林的耐火性与恢复情况。本研究选取库特尼湖木材供应区周边常见的5个树种：西部落叶松、花旗松、西部铁杉、恩格尔曼云杉与亚高山冷杉，针对不同火烧烈度（高、中、低）开展耐火性对比分析。研究结果证实，面对不同火烧烈度时，不同树种的耐火性与死亡率存在显著差异：西部落叶松与花旗松耐火性较强，西部铁杉耐火性相对较弱，恩格尔曼云杉与亚高山冷杉耐火性极差。该结果与美国农业部（United States Department of Agriculture，USDA）发布的相关报告高度吻合。但受数据不足与局限性影响，火灾后的NDVI变化趋势无法准确反映植被恢复情况。综上，本研究通过对野火前后Landsat-8卫星影像的分析，证实了老龄林内5个树种在不同火烧烈度下的耐火性存在差异。