Pollen assemblages and anthropogenic influences in the central and western regions of Yunnan Province
Graphical abstract
Introduction
The current plant and forest communities are the result of the long-term interactions between vegetation and site-specific factors, including climate change and human impacts. In an increasingly urbanized landscape, human activities have gradually become one of the major factors that influences the formation of vegetation landscapes. Such activities can damage the original vegetation and increase anthropochory and secondary plants. For example, logging, clearcutting, and road building have resulted in the rapid reduction of the Amazon tropical rainforest (Gascon et al., 2000). Vegetation deterioration in some areas might be related to fires, livestock grazing, and agriculture (Abel-Schaad and López-Sáez, 2013).
Yunnan Province in China has a complex and diverse natural environment with a variety of vegetation, but it also has a long history of human land use. Increasing urbanization has considerably influenced the natural vegetation in this area. Owing to this, the goal of this study was to answer the following questions: 1) What is the degree of naturalness in Yunnan with the current vegetation and forests and 2) How can we determine the degree of anthropogenic influences in Yunnan?
The degree of hemeroby can be used to assess the different degrees of anthropogenic influences on current vegetation and forests. The term hemeroby was introduced by the botanist Jalas (1955) in the 1950s and was developed by Sukopp (1972). It was originally developed to measure human impacts on flora and vegetation and is defined as the degree of human cultural activities (Wang, 1983; Li et al., 2002; Battisti and Fanelli, 2016; Sousa, 1984). This concept is now widely used in plant ecology and is applied, in different research fields, as an indicator of the level of anthropogenic disturbance. Chen et al. (2010) used the concept of hemeroby and systematically assessed the dynamic changes of the landscape patterns and the degree of eco-disturbance in the Shuangtai Estuary Wetland of Liaoning Province, China, using remote sensing technology. Walz and Stein (2014) determined hemeroby during several temporal windows to estimate the cumulative impact of land use changes in Germany on the overall environmental status. Hemeroby has been tested in several disciplines, from plant ecology to zoology (Battisti and Fanelli, 2016; Battisti et al., 2017).
Pollen data is also commonly used as a proxy for detecting the impact of human activities (C.H. Li et al., 2008; Y.Y. Li et al., 2008). Original vegetation is defined as the vegetation that was present prior to the significant interference of human activity, which can be reconstructed using pollen data. Pollen from plants that have been influenced by anthropogenic activity is an ideal indicator of human-influenced vegetation patterns (C.H. Li et al., 2008; Y.Y. Li et al., 2008; Brun, 2011). Thus, pollen data can also be used to reveal the degree of vegetation variation after human disturbances.
Modern pollen data can be used to infer the composition and pattern of modern vegetation (Li et al., 2005; Zhang et al., 2010). In this study, we assessed the degree of human impacts on the natural state of vegetation using modern pollen data from the central and western regions of the Yunnan Province. The impacts of human activities on modern vegetation were assessed by calculating the hemeroby level and by examining the pollen from anthropogenic and secondary plants.
Section snippets
Study area
The study area is located between 21° and 26° N latitude and 97° and 103° E longitude. The central and western regions of Yunnan have high vertical gradients and large horizontal spans. This region has a tropical monsoon climate and the annual precipitation is approximately 1100 mm; it can reach 1600 mm in the southern regions. About 10%–20% of the precipitation occurs during the winter and spring (November to April), whereas 60% occurs during the summer (June, July, and August). The main
Surface pollen assemblages
The pollen assemblages had 286 taxa in the 120 surface samples. There were 39 pollen taxa that were representative of intertropical and semitropical vegetation. Overall, the modern pollen assemblages from the different vegetation types across the central and western regions of Yunnan Province were remarkably distinct from each other. Pinus, Betula, Alnus, and Lithocarpus/Castanea were the dominant woody species, Theaceae and Rhododendron were the dominant shrub species, and Gramineae and
Surface pollen assemblages and vegetation
The pollen assemblages in the central and western regions of Yunnan Province reflect the vegetation composition of the study area. Zone I had endemic plant species, Datiscaceae, and other tropical arboreal pollen, such as Samydaceae, Combretaceae, Rubiaceae, Rutaceae, Sapindaceae, Nerium, Moraceae, Melia, and Palmae, which rarely appeared in the other forest zones. In Zone II, Lithocarpus/Castanea pollen reached a peak occurrence of 25%. The subtropical conifer forest pollen zone (III) mainly
Conclusion
In this study, we analyzed palynology assemblages and hemeroby levels in the central and western regions of Yunnan Province.
A total of 120 surface pollen assemblages reflected the vegetation composition of the study area, which were dominated by arboreal conifer and hardwood. Some tropical tree pollen taxa indicate tropical vegetation characteristics, and they were more represented than Pinaceae.
Surface hemeroby levels were mainly euhemerobic except for Zone I, II, VI, which indicates strong
Acknowledgements
This research was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA19050103) and the National Natural Science Foundation of China (NSFC Grant No. 41230101, 41372183 and 41572331).
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