云南洱海炭屑记录揭示的近千年来古火演化历史

中国云南地区是森林火灾多发的典型区域, 了解该地区近千年来古火灾的演化历史及其驱动机制对于未来区域森林火灾的防护与治理以及生物多样性的保护具有重要的科学意义。本研究以滇西北地区洱海湖泊的3个沉积岩芯(EHB1岩芯, 58.5 cm; EHN1岩芯, 78.5 cm; EHB2岩芯, 80 cm)为研究对象, 通过对沉积物中高分辨率炭屑记录的分析, 基于 ²¹⁰Pb/¹³⁷Cs和加速器质谱法(AMS)¹⁴C测年技术建立的年代序列, 重建了洱海地区近千年来的古火演化历史。研究结果表明, 基于洱海湖泊沉积岩芯上部大炭屑指标重建的火事件与现代森林火灾记载资料的对比, 确定了大炭屑指标反映湖泊周围约10 km范围即大理市的古火活动情况, 验证了炭屑记录在重建古火灾活动方面的可靠性。古火历史的重建结果显示近千年来洱海地区共发生20次火事件, 其主要集中在1200~1350 A.D.期间和1540~2000 A.D.期间; 近千年来, 洱海地区古火活动的强度整体上呈现先降后升的趋势, 其中火事件的发生频率及其强度在近100年均达到千年来的最高值, 分别对应10次/300年和652.4粒/cm²/peak。炭屑记录和古火活动与区域高分辨率气候记录、植被状况以及人口历史资料的相关分析、冗余分析(RDA)和对比分析结果表明, 大理州人口变化是洱海地区近千年来古火活动最重要的驱动因子, 其次为区域降雨量和植被类型, 温度和植物量则对区域古火活动的影响较小。

Fire history over the past millennium revealed by the charcoal record from Lake Erhai,northwestern Yunnan Province

Yunnan Province is one of the typical fire-prone regions in China. Understanding the evolutionary history and driving mechanisms of palaeofire over the past millennium in this region is of great scientific significance for both forest fire prevention and biodiversity conservation in the future. In this study, we collected three sediment cores(core EHB1 at 25.84°N, 100.18°E, 58.5 cm; core EHN1 at 25.66°N, 100.24°E, 78.5 cm; core EHB2, 80 cm) from Lake Erhai(25.60°~ 25.96°N, 100.08°~ 100.30°E; 1974 m a. s. l) to reconstruct the palaeofire history in northwestern Yunnan Province based on the high-resolution charcoal records, and combined with the 210Pb/137Cs and AMS14C dating techniques for constructing the chronological framework. The results indicate that the fire episodes constructed by the macroscopic charcoal record from Lake Erhai were consistent with the documents of modern forest fires. It was determined that the macroscopic charcoal record reflected the fire activity of Dali City within about 10 kilometers around the lake, and the feasibility of utilizing charcoal records to reconstruct the palaeofire activity was validated. A total of 20 fire episodes were identified from the charcoal record, which was mainly concentrated in 1200~1350 A.D. and 1540~2000 A.D. The intensity of palaeofire activity in Lake Erhai area decreased first and then increased over the past millennium, of which the frequency and intensity of fire episodes within the last century reached the highest values over the past millennium, corresponding to 10 fires 300 a-1 and 652.4 particles/cm2/peak, respectively. The fire returns interval showed a roughly out-phase change compared to the fire frequency, which reached the peak at 1420 A.D., corresponding to 80 years. The Pearson correlation, Redundancy analysis(RDA), and comparative analysis between the charcoal records, palaeofire activity from Lake Erhai, and the regional high-resolution climate records, vegetation conditions, and historical documents show that the population change in Dali prefecture is the most important driving factor of palaeofire activity in the Erhai area over the past millennium, followed by regional rainfall and vegetation type, whereas temperature and plant biomass less influence on the palaeofire activity. The correlation coefficient between the population in Dali Prefecture and the charcoal accumulation rate(and fire event frequency) is 0.55(and 0.71), and the explanation degree of the population in Dali Prefecture to the charcoal accumulation rate and fire frequency can reach 30.5 % and 50.9 %, respectively.