云南大理西湖流域工业革命以来的植被、气候与火灾

本研究以云南大理西湖46 cm长的湖泊沉积物岩芯为研究对象, 基于 ²¹⁰Pb-¹³⁷Cs测年和模式定年法建立了岩芯的年代框架, 以0.5~1.0 cm间隔获取了51个样品进行孢粉、炭屑分析, 重建了大理西湖流域工业革命以来(1878~2013年)的植被演替、气候变化及火灾史, 探讨了火灾发生的驱动因素。结果表明, 工业革命以来研究区的植被演替、气候变化及火灾史可以分为6个阶段: 1)1878~1897年, 流域植被以禾本科为主的草本类型占优, 周边林地海拔由低到高主要分布云南松林、常绿阔叶林, 气候凉湿, 火灾发生频率较高; 2)1897~1932年, 云南松林退缩, 气候冷湿, 火灾发生频率偏低; 3)1932~1948年, 云南松林与常绿阔叶林向低海拔地区退缩, 气候冷干, 火灾发生频率稍高; 4)1948~1958年, 云南松林面积扩张, 常绿阔叶林下降, 湿地面积增加, 气候温湿, 火灾发生频率高, 人类活动显著加剧; 5)1958~1995年, 云南松林与旱冬瓜林扩张, 常绿阔叶林进一步退缩, 气候暖湿, 火灾发生频率低; 6)1995~2013年, 云南松林与旱冬瓜林继续扩张, 气候暖干, 火灾发生频率低。大理西湖的火灾在20世纪50年代之前是由自然因素(气候)控制, 可燃物的多少是控制火灾发生频率的关键因素; 之后人类活动成为主控因子, 人类对植被的破坏和用火是触发火灾的主要原因。

Vegetation,climate and fire in the West Lake basin of Dali,Yunnan, China since the Industrial Revolution

The pollen/macroscopic charcoal(> 100 μm) analyses of 51 samples obtained at intervals of 0.5~1.0 cm from a 46-cm core(26°00'54″N, 100°01'54″E) taken from West Lake in Dali(26°00'17″~ 26°01'26″N, 100°01'48″~ 100°03'27″E), Yunnan, were conducted to reconstruct the historical records of vegetation, climate and fires since the Industrial Revolution(1878~2013 A.D.) in the catchment of West Lake in Dali, and the driving factors of fire occurrence were discussed. The age-depth model for this core was established using 210Pb-137Cs dating and model dating method. A total of 27150 pollen grains of woody, herbaceous and aquatic plants, ferns and algae spores were identified from 51 samples, belonging to 95 families and genus(types). 7760 macroscopic charcoals were identified. Our results reveal six stages of vegetation, climate change and the fires since the Industrial Revolution in the West Lake basin: (1) 1878~1897 A.D. saw vegetation dominated by grasslands consisting of Poaceae, the occurrence of Pinus yunnanensis forests and evergreen broadleaved forests from low to high elevation, cool and wet climatic conditions, and frequent fires. (2) 1897~1932 A.D. witnessed the shrink of forests dominated by Pinus yunnanensis and Alnus nepalenisis, cold and wet climatic conditions, and low risk of fires.(3) 1932~1948 A.D. saw a drop of lake water level, the movement of pine forests and evergreen broadleaved forests from high to low elevations, cold and dry climatic conditions, and high frequent fires.(4) 1948~1958 A.D. witnessed the rise of lake water level and thus the expansion of wetlands, the shrink of broadleaf forests, warm and wet climatic conditions, the highest frequency of fires, and intensified human activities intensified.(5) 1958~1995 A.D. saw the expansions of Pinus yunnanensis and Alnus nepalenisis forests, continued shrink of broadleaved forests, warm and wet climatic conditions, and low frequent fires.(6) 1995~2013 A.D. witnessed further expansions of Pinus yunnanensis and Alnus nepalenisis forests, a drop of lake water level, warm and dry climatic conditions, and low frequent fires. The fires of the West Lake basin in Dali were largely controlled by natural factors before the 1950s, and the amount of combustible material was a key factor controlling the frequency of fire. After the 1950s, human activities became the main controlling factor, and human destruction of vegetation and human activities as ignition sources were the main causes of triggering fires.