大兴安岭林区火干扰格局与生态系统回复力关系研究

Ecological resilience is at the heart of how boreal forests absorb natural disturbance and maintain the original forest structure and function. Under the impacts of climatic changes, fire regimes of Great Xing’an boreal forests show severe trends which may cause decline of ecological resilience and further threaten regional ecological security. We propose a combined utilization of remote sensing retrieval approaches and field sampling to characterize dynamics of fire disturbance patterns during the past three decades and to quantify the vegetation restoration status within burned patches. We will systematically evaluate relationships between pre-fire landscape heterogeneity, disturbance patterns and vegetation restoration; indentify the key elements and their thresholding ranges that can influence post-fire vegetation restoration; and highlight those high risk areas and prior restoration areas where forests may face resilience decline within current forest landscapes. We will address the following two essential questions: (1) how do vegetation conditions, topography and fire weather regulate spatial patterns of fire disturbance? (2) How do pre-fire forest composition and structure interact with disturbance patterns and together impact ecological resilience, and what are their relative importance? The results obtained in this project will contribute to a further understanding on relationships between climatic changes and forest landscape dynamics. The results also can be helpful to provide theoretical basis and technical supports for improving the efficiency of forest management and protection in this ecologically important region.

生态系统回复力是保障北方针叶林生态系统吸纳自然干扰并维持系统原有结构和功能的核心所在。受气候变化影响，大兴安岭林火态势呈现出严酷化趋势，极有可能引发生态系统回复力的衰退进而威胁区域生态安全。本研究拟通过野外调查与遥感反演相结合的方法，掌握研究区近30年林火干扰格局的变化动态，量化评估火烧迹地植被恢复状况；在景观尺度上系统评价火前景观异质性、干扰格局与植被恢复状况之间的关系，识别影响火后森林植被恢复的关键因子及其引发生态系统回复力变化的阈值范围；明确当前森林景观中生态系统回复力的高风险区和优先恢复区。核心解决以下两个科学问题：(1) 植被状况如何与地形、火灾天气共同驱动林火干扰的空间格局？(2) 植被组成和结构特征与林火干扰格局如何影响生态系统回复力，其相对重要性如何？研究结果将有助于加深对于气候变化与森林景观动态关系的理解，为改善森林经营和管护措施的实际工作效率提供理论与技术支撑。

大兴安岭森林是我国重要生态屏障，同时也是受林火威胁较为严重的林区。在天然林全面禁伐背景下，研究林火干扰格局与森林生态系统回复力之间关系对于加深气候变化对森林景观动态驱动机制，改善森林经营和管护措施具有重要理论意义和实践意义。本项目基于卫星遥感数据与野外实地采集数据，对大兴安岭地区历史火灾烈度空间格局进行了空间数据挖掘与分析，从像元和火斑尺度明确了林火属性中最重要且最难量化特征-火烧烈度的空间驱动因子，空间明确地预测了研究区潜在林火烈度的空间分布；基于野外调查数据结合高分辨率卫星影像、中等分辨率卫星影像时间序列分析了火后森林生态系统更新苗覆盖度、叶面积指数、密度、组成以及生态系统碳储量的空间格局及演替动态，明确了火烧迹地回复力的控制因子，证明了少量火后存活母树（林火烈度重要指标，存活母树数量与烈度呈反比关系）所提供种源对于火后初期乔木更新苗具有极大促进作用，由未火烧区域产生的边缘效应(外来种源)对于火烧斑块内部更新苗密度增加同样具有促进作用但受限于空间距离（~700 m）；基于Landsat时间序列分析火后植被恢复轨迹结果显示林火烈度的对火后植被更新作用随着演替的进行，逐渐削弱，而环境等因子的作用逐渐增强；野外调查火后碳库演变轨迹显示地上生物量碳库变化轨迹为一条倾斜的U型曲线，生物量碳库于火后27年左右降到最小值，地上碳库大约需要120-150年方能恢复到火前水平的80-90%。该结果系统显示了减低林火烈度与火灾面积是提升森林生态系统抵御火干扰回复力的重要途径，而结合植被分布于地形特征开展的火前可燃物处理能够对林火烈度及其蔓延过程产生重要影响，进而提升该地区森林生态系统的回复力。