Impacts of human activities on ecosystems during the past 1300 years in Pingnan area of Fujian Province, China
Introduction
Approximately one quarter of China is characterized by subtropical vegetation. This area harbors high plant diversity (about 14,600 seed plants) with many endemic species. Emblematic Neogene relic plants such as Ginkgo biloba (L.), Cathaya argirophyla (Chun & Guang), Metasequoia glyptostroboides (Hu & Cheng), Davidia involucrate (Baill.) and Liriodendron chinensis (Hemsl.) Sarg etc. are found in this area (Wu, 1980). Nowadays, the subtropical zone is dominated by secondary vegetation and cultivated crops, which occupy the plains and the low-altitude mountain regions. The natural vegetation (evergreen broad-leaved forest) is very fragmented, and can only be found at higher elevations and remote areas. The modern vegetation is the result of both a long-term climatic change and artificial disturbances that have taken place during the Holocene. A range of proxy data from archaeological, palynological and sedimentological studies shows that the beginning of human disturbances was asynchronous in different parts of China, particularly in the subtropical zone (Zheng et al., 2004). In some sites in the Yangtze river basin, human disturbances of the natural vegetation may have begun as early as ca. 5000 cal BP (Xu et al., 1996; Zhang, 1996; Li et al., 2010), whereas in southern China such disturbances may have only occurred later, after about 3000 cal BP (Weng, 1994; Huang, 1996; Zhang and Yu, 1999; Zheng, 2000; Li et al., 2001; Zheng et al., 2001; Zhu et al., 2001).
Fujian province is suited at the southern boundary of the subtropical zone of China. Until now, most of the available Holocene pollen studies in Fujian were undertaken mainly to analyze the vegetation and environmental changes in the coastal areas, flood plains and river deltas, but rarely in the mountain areas (Chen, 1982; Lan et al., 1986; Zheng, 1986, 1991; Jin and Zheng, 1993; Wu, 1993; Lu, 1994; Yang, 1994; Wang et al., 1995; Chen et al., 1997a, 1997b, 1998a, 1998b; Zheng et al., 2002; Zhi et al., 2003; Qiu, 2006; Zhu et al., 2006). Only one study has attempted to identify the impact of human activities on natural ecosystems (Liu and Qiu, 1994).
The present study investigated a site in Pingnan, a mountainous area in northeastern Fujian province. Apart from rich cultural history of the study area, the presence of Glyptostrobus pensilis (Staunt.) Koch (Cupressaceae), one of the most threatened species in China that is naturally present and protected today, marks this as a region of significant sensitivity and conservation importance. The approach integrates fossil pollen, stable isotope and historic evidence to reconstruct the past vegetation dynamics and environmental changes in the area and to analyze the influence of human activities on the natural ecosystem during the past 1300 years.
Section snippets
Geography, modern climate and vegetation
The Chinese subtropical area extends between 22 and 34°N. In the north it is bordered by the Qinling Mountain and Huaihe River, to the south it is limited by the Leizhou Peninsula, and in the west it extends to the Hengduan Mountain (Wu, 1980). Fujian Province, located at the southern boundary of the subtropical area of China, is mostly mountainous and faces the South China Sea to the southeast (Fig. 1). Fujian has a long coastline where the fisheries are historically famous. The northwestern
Materials and methods
A 3-m sediment core was collected from a wetland located within the evergreen-broad-leaf forest zone in the Pingnan county (26°55′12″N, 119°01′12″E, 855 m a.s.l.) during Spring 2009 (Fig. 1). The pollen content of 61 samples (5 cm resolution) and the carbon isotopic composition (δ13C) of 151 samples (2 cm resolution) were analyzed.
The core's chronology was based on three radiocarbon AMS dates. All samples have been analysed in Institute of Earth Environment, Xi'an, China (Table 1). The 14C
Results
Pollen assemblages of Pingnan record exhibit high taxonomic diversity (Fig. 4). A total of 90 pollen/spore types were identified, most of which are angiosperms (70 types). Gymnosperms consist of three genera of Pinaceae (Pinus, Abies, Tsuga), Cupressaceae, Taxodiaceae and Podocarpaceae (Podocarpus). Ferns were assigned to 14 types: dominated by trilete-types (Osmundaceae, Lycopodium, Pteris and other trilete-types) and monolete-types (Polypodiaceae and other monolete-types).
The dominant
Discussion
Southern China has a high plant diversity that is related to the various climatic features such the Asian monsoons (Shen et al., 2005; Wei et al., 2010; Lopez-Pujol et al., 2011). This biodiversity has been impacted by the increasing human disturbance that has taken place over the last few millennia. Pollen records indicate that the early human disturbances (4000-1000 cal BP) mainly affected the coastal flood plains and river delta plains (Wang et al., 1990; Zheng, 1991, 1998; Li and Yao, 1993
Conclusions
Pollen data from Pingnan County, Fujian province, China indicate that prior to ∼800 cal BP the study area was covered by a natural evergreen forest, dominated by Quercus (evergreen) and Castanopsis, mixed with Symplocaceae and Ilex. The disruption of the natural vegetation type occurred at ∼800 cal BP. Since ∼450 cal BP, the secondary vegetation, dominated by Pinus is progressively mixed with the natural forests including deciduous oaks, Taxodiaceae, Liquidambar etc.
Increasing human disturbance
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant Nos. 41001118 and 41072128) and the research Fund for the Doctoral Program of Higher Education of China (Grant No. 20100171120002). JX thanks J. Ferrier for helping in identifying pollen and spores and S. Muller, S. Fauquette and C. Martin for their kind help during his visit at ISEM. This is an ISEM contribution number ISEM 2012-051.
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