Holocene Wildfire And Ecological Environment Changes In The Weihe River Drainage

Ecological environment in Holoeene is so complicated a phase that it derived from a variety of factors. Only through various climatic proxy for synthetic analysis can we contribute to the recovery of Ecological environment variation in Holoeene .The magnetic susceptibility. Total organic carbon (TOC) indicate a drier and colder , warmer and wetter climate, while charcoal indicates intensity, frequency of Wildfire activity. Under the circumstances of climatic changes, Wildfire is not the only factor interfering the ecological environment, but a direct factor caused great changes of ecological environment in Weihe river drainage. With the enlargement of human scope of activities, Wildfire activity has already become and accelerated the transformation of the ecological environment. So, it is well worth studying the relationship between Wildfire activity, human activity and even the shift of ecological environment .It is significant for us to acknowledge those in ecological environment.It is one of the Chinese cultures which originated from Weihe river drainage, gradually with the development of Dadiwan culture, Yangshao culture, the Longshan culture, Xia and Sang dynasty culture, etc. It is an important area where the human beings first carried on the activity of farming and stockbreeding. With the rapid growth of population, innovation of tools, hunting and gathering, especially the enlargement of many years of farming, human became stronger by interfering and influencing ecological environment with the purpose of improving their own lives. The author attempts to focus on the relationship between Wildfire activity, human activity and the changes of ecological environment during Holoeene. . The main findings are:(1) Change of environment during Holoeene in Weihe river drainage were studied by proxy climate data of magnetic susceptibility, total organic carbon and charcoal: Piled up period in the Malian loess, it is the most typical deposit of Aeolian dust accumulated in the semi-desert environment. An early Holoeene (11, 500~8, 500 a B. P) was much similar to Malian loess, arid but unstable. During the Holoeene "climate optimum"(8,500~3,100 a B.P), it was wetter and warmer, and then was active bio-pedogenic processes during thetime of soil formation, while it was not a continuous warm-humid period. During the late Holocene (3, 100 a B.P~0), it was weak bio-pedogenic processes during the time, which became another relatively arid stage during Holocene. From3, 100a.B.P on, with the increase of human activity, Bio-pedogenic processes during the time of soil formation subsided. In the past 1500 years, mankind has reduced the interference of the region soil -vegetation system for a period of time. This may have already totally cultivated the farmland, with the growth of population, employment of fire and production of trash, and further deterioration of farmland by human.(2) The relationship with charcoal records and total organ carbon by proxy climate data of magnetic susceptibility, total organic carbon and charcoal: As the climatic proxy of total organic carbon and charcoal often exist together in the soil layer, which are linked with the ecological environment, there is a complete difference. Total organic carbon (TOC) includes the organic carbon in bio-pedogenic processes during the time of soil formation and the organic carbon of charcoal in Wildfire .It has irregular form and reflects organic accumulation of soil, while the charcoal is a wooden structure, which can be seen and recognized clearly through microscope, and can reflect objectively that of the Wildfire. It is obvious that total organic carbon (TOC) cannot point out the Wildfire activity in the ecological environment completely and the charcoal point out the Wildfire activity directly.(3) The relationship with Wildfire activity and environmental changes by proxy climate data of magnetic susceptibility, total organic carbon and charcoal: Piled up period in the Ma-Ian loess (15,000a B. P~ 11, 500 a B. P), the climate is arid, on semi-desert grass...