青海东部上喇家村黄土剖面全新世野火历史及人类活动

由于不同燃烧指标存在明显的差异，致使人们对于火燃烧方式的理解尚不确定。本研究选取黄河上游青海上喇家典型剖面(深度464 cm，年代范围14.5~0 ka B.P.)为对象，结合炭屑和黑碳以及古生态指标，揭示该区域全新世以来的野火历史演变过程。研究结果表明末次冰期和全新世早期，气候较为干旱，以明烧为特征的草原区域野火时常发生，与东亚季风气候所控制燃料特征和湿度密切相关。全新世中期，气候较现在温暖而湿润，生物成壤作用强烈，该地区整体上自然野火发生处于较低水平。其中，4200~3850 a B.P. 和3400~3000 a B.P. 这两个阶段的粗颗粒炭屑通量峰值分别是齐家文化中晚期(4200~3800 a B.P.)和辛店文化时期(3400~2700 a B.P.)人类频繁放火烧荒和开垦农田以及生活等活动的结果；而3850~3600 a B.P. 阶段以焖烧为特征的低强度野火发生，与气候持续干旱和人类森林砍伐活动加剧有关。与此同时，该区域遭遇2次大规模的地震和山洪泥流地质灾害，生态环境恶化，使得农耕为主的齐家文化被半农半畜牧的辛店文化所替代，从而导致该期间炭屑通量整体下降。全新世晚期，气候进一步干旱，1500年以来本地大幅度生物质燃烧增加与农业扩张和耕地面积增大密切相关。总之，全新世中期先前人类长期频繁森林砍伐活动所诱发的低强度焖烧火模式是导致该区域植被减少和土地退化的不容忽视的重要因素，而东亚季风所控制的季节性降水变化仍是野火发生必要条件。

Holocene fire history and human activities at Shanglajia archaeological site in eastern Qinghai Province of China

As various fire proxies indicate different burning patterns, there are still great gaps in understanding the evolution of fire. In this paper, a typical loess-soil profile was selected at the Shanglajia site in the upper reaches of the Yellow River, which is located at Lajiacun(35°51′49″N, 102°48′27″E), Guanting Basin, Minhe County, Qinghai Province. A total of 110 samples were collected at intervals of 4 cm or 5 cm from the loess-soil profile. The age of the section at the lowest depth of 464 cm is 14500 a B.P. at the study site. We introduce charcoal and black carbon(BC, including char and soot)records from a loess-soil profile, combined with robust Optically Stimulated Luminescence(OSL)dating, archaeological documents, and paleo-environmental proxies (i.e., magnetic susceptibility, total organic carbon, XRF-derived elemental data, etc.), to reveal the evolution of wildfire in this area since the Holocene. The results show that the frequent occurrence of the flaming fire in open forest steppe was closely related to the fuel characteristics and the humidity controlled by the East Asian monsoon climate during the Early Holocene. In the Middle Holocene, the climate was warmer and wetter than the present, so the natural wildfire in this region was at a low level. Higher macro-charcoal flux in the study site has been attributed to the intensified anthropogenic biomass burning from dry crop cultivation during the periods of 4200~3850 a B.P., and 3400~3000 a B.P., corresponding to the Chinese settlements during the middle and the late Qijia Culture(4200~3600 a B.P.)and the development of the Xindian Culture(3400~2700 a B.P.). However, the smoldering fire with low intensity was related to the continuous drought and the intensification of human deforestation between 3850 a B.P. and 3600 a B.P. At the same time, two mudslides and earthquakes occurred during those periods, which caused the deterioration of the ecological environment in the region, population migration, and the decline of settlements. Subsequently, Qijia Culture of both agriculture and animal husbandry was replaced by the Xindian Culture of half agriculture and half animal husbandry, as well as the decline in biomass burning. In the Late Holocene, anthropogenic biomass burning for cereal cultivation has increased with more arid climate over the past 1500 years. According to the principal analysis, since the Holocene, the wildfire burning pattern was primarily due to the change of seasonal precipitation controlled by the monsoon climate, and the intensified anthropogenic biomass burning from dry crop cultivation. In the past 1500 years, human activities have played a more important role in the biomass burning across this region. It is worth emphasizing that the smoldering fires with low-intensity caused by long-term and frequent deforestation activities could be an important factor to the enhancement of biomass combustion and land degradation across this region, and the seasonal precipitation change controlled by the East Asian monsoon is still a necessary condition. The results of this study have important implications for understanding wildfire history and human activities as both respond to regional climate change in the northeastern part of the Qinghai-Xizang Plateau during the Holocene.