A Study On Human Activities Changes And Its Impact On Envirionment During The Past1600Years In Guangxi And Chongqing, Based On Pollen-spore And Charcoal Data

Recently, the globe changes over the past2000a has become the hottest topic for scientists from various countries. It’s has a correlation with Human and affects the development of human society. Meanwhile, human has also had an important impact on the environment of global during the past2000years, such as, human activity has significantly changed the temperature of the global and fundamentally changed the composition of the Earth’s vegetation system. Therefore, explore the global environmental change under the influence of human activity has become an important issue of global change research.Pollen-spore and charcoal are important ecological indicators for reconstructing the palaeo-environment. Pollen-spore is generally used to reconstruct palaeo-vegetation and charcoal is generally used to reveal the occurrence of fire. Pollen-spore and charcoal is the best way to reconstruct palaeo-vegetation and palaeo-climate change and to identify human activities. Some researchers have done lots of work in reconstructing paleo-vegetation and palaeo-climate(Wang et al,1997; Xu et al,2004; Zhang,2002;Zheng,2004; Luo et al,2012). In recent20years, with the development of environmental archeology, more and more pollen researchers, turned to the environment evolution of human disturbance (Hjelle,1997; Court-Picon,2006; Zhang,2007; Li et al,2008;Li,2009).Southwest karst area is the world’s largest contiguous karst areas, about620,000km2, accounting for1/3of total area of China. Meanwhile, it’s also a densely populated areas, with a population over100million and exceeding20million poor. In such a large population pressure, resulting in a series of problems, for example, environmental pollution, soil erosion, the rocky desertification, floods and drought etc, and rocky desertification has limited the development of the economy and society in southwest karst area. Therefore, resolving this issue relates to economic development and social stability. In recent years, many researchers have done lots of study on rocky desertification, so we have a comprehensive understanding of the issue, but its cause is still not unified. In this context, we use pollen-spore and charcoal, combinning with historical materials, to study human impact on southwest karst envirionment, in order to figure out the cause of rocky desertification.According to the result of surface pollen-spore data in Longzhai,Guangxi province, it is found that:(1) Cave sediments mainly comes from upper and middle reaches of surface river, and its pollen assemblages is related to the vegetation and land use of upper and middle reaches.(2) Human activity is more intense in study area, and its pollen assemblages is mainly composed by herbs and ferns,trees are seldom.(3) Pollen spectrum is different between rice and corn paddies. In rice paddy,the rice pollen accounted for36.39%,while in corn paddy, Zea pollen accounted for an average of13.22%. The sugarcane fields pollen assemblages different from which is in rice and maize filed, and mainly composed by Poaceae herbs and high percentage spore of ferns. Peanut, sweet potato, soybean fields pollen assemblages which are influenced by other pollen are not easy to identify (4) Apart cereal pollen, some weeds and ferns pollen-spore also has significant indicate for different land use, such as, Cyperaceae and Hicriopteris can indicates rice filed,at the same time Poaeae(grass^Composite> Artemisia indicates corn fields.According to the result of pollen-spore data in Longzhai section,Guangxi province,it is found that:(1) Rice cultivating experienced six stages in Longzhai:late Tang, North Song to south Song, Yuan to late Ming, Qing to Republic, new China, and the Tang Dynasty, the Northern Song to the Southern Song Dynasty, Yuan Dynasty to the late Ming periods rice cultivating expanded.(2) The emerge of Brassica campestris L pollen grain indicates the cole was introduced to Guangxi during late south Song and early Yuan Dynasty, following the second population migration in history.(3) Since the Tang dynasty, the land use pattern of the main rice-cultivating was stabilished, undergoing a long and intencely agricultural activities and the nature vegetation was destroyed. According to the result of surface pollen-spore data in Nanping,Chongqing,it is found that:(1)Human impact is very dramatic in rocky desertification area, and the main land use is dry land, the difference of pollen assemblages of various land use is small.(2) In the rocky desertification samples, higher levels of corn pollen may indicate the occurrence of rocky desertification in related to corn planting,but corn planting is not the only factor can induce rocky desertification.(3) It’s easly to distinguish rice paddy and corn fields,but other land uses, such as sweet potatoes, peanuts, soybeans are difficult to distinguish.According to the result of pollen-spore data in Nanping section, Chongqing,it is found that:(1) On the trough slope of Nanping, human activities has gone through five stages:before Song dynasty human activity was weak and vegetation was well preserved. Song Dynasty to the early Ming Dynasty was the first interference stage, after that,the human impact declined again and until Qing Dynasty, human activities re-strengthened, which resulted in forest reduce, replaced by rice paddy and corn fields,and the process of rocky desertification began, and till1830s the rocky desertification occurrence.(2) Rocky desertification is a result of human activities, but its occurrence is not only related to corn planting, other land use and unreasonable agricultural use may also lead to rocky desertification.(3) Large-scale cultivation of food indicated population growth for the demand for food, which is the fundamental driving force of the rocky desertification.Compare the two sections we found:under the same natural conditions, rocky desertification problem does not occur in Longzhai, while Nanping facing serious rocky desertification problems,so we believe that natural factors(geology, topography, climate) provides the basic conditions for rocky desertification, while human activity is the key reason for rocky desertification, and the growth of population is a driving force.In the past1600years, vegetation changes have been affected by human activities.It’s difficult to reconstruct climate changes only by pollen-spore data, but combining climate records with pollen-spore data, we found hat the climate events can affect agricultural activities, such as, in Medieval Warm Period, the climate was warm and humid, agricultural activities was intense, but in Little Ice Age, climate was cold and dry, agricultural activities weakened.