Pollen assemblages and anthropogenic influences in the central and western regions of Yunnan Province

Highlights

• The hemeroby and pollen data are two good bio-indicators of human disturbance and impact.

• Largely euhemerobic surface hemeroby levels indicate continuous human impact.

• Strong human impacts influence modern vegetation in the midwestern Yunnan Province.

Abstract

The goal of this study was to provide information on the representation of pollen taxa and the human impact on vegetation by exploring the relationship between modern pollen and vegetation in the central and western regions of Yunnan Province of China. A total of 120 modern pollen samples were collected throughout the study area. The surface pollen assemblage was divided into eight pollen zones (Zones I–VIII) based on vegetation types. We analyzed the palynology and determined the hemeroby levels of each zone in the area. Our results showed that human activity is one of the most important factors that can result in the damage of natural vegetation and increase anthropochory and secondary plants. The hemeroby levels of the surface pollen samples were mainly euhemerobic except for Zones I, II, and VI, which indicates a strong and continuous anthropogenic influence in the central and western regions of Yunnan Province in recent decades. The lowest hemeroby values were observed in Zone I samples, which were collected from Mengla and Jinghong. These areas are in the Xishuangbanna region, which is the most biodiverse region in China and has been well preserved since 1959. Therefore, the extent of human influence of a region can be estimated from the degree of hemeroby established from pollen data, which can be used in the future for nature conservation.

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.