The correlation between airborne <italic>Betula </italic>pollen content and meteorological factors in the Tianshan Mountains, Xinjiang, China

Abstract

Studies have shown that there is a close relationship between the transport and deposition of airborne pollen and meteorological factors. The aim of this study was to investigate quantitative changes in airborne Betula pollen, its spatial and temporal distribution dynamics, and its response to meteorological factors. In order to do this, we installed three sets of Cour airborne pollen traps at Xinjiang Tianchi Meteorological Station, Fukang Ecological Positioning Station, and Beishawo Experimental Station, which are located in areas of different vegetation types in the central Tianshan Mountains in northern Xinjiang of China, to monitor airborne Betula pollen data for approximately 5 years (July 2001 to July 2006). Our results showed that: (1) The 5-year average airborne pollen dataset showed variation in the dynamics of Betula pollen at different sites. At the Tianchi research site Betula pollen appeared in late April and reached its peak after 2 weeks, in early May, then decreased rapidly. The peak value of Betula pollen at Fukang research site also occurred in early May, and then slowly decreased. At Beishawo research site, it reached its peak value in mid-May, and slowly fell after a week. In autumn, some Betula pollen may remain on trees or on the soil surface, having been blown there by the wind. However, the pollen concentration in winter was extremely low, almost zero. The diversity and abundance of different Betula species present in the pollen dataset corresponded to the flowering periods of different species and varied with season. Over these 5 years, the peak period of Betula pollen has advanced year by year. The flowering phenology of birch plants has also advanced year by year during these 5 years, likely owing to the increasing annual average temperature. Across the three research sites, the concentration of airborne Betula pollen decreased to its lowest level in 2003, which had the lowest annual average temperature. This suggests that airborne Betula pollen production decreased because of lower temperatures. (2) According to the results of a Pearson correlation analysis, the relationship between the airborne Betula pollen content and meteorological factors was significant in Tianchi, but not in Fukang. It was closely related to the distribution and ecological habits of Betula trees. The average annual temperature of Tianchi and Fukang research sites directly affected the pollen concentration of airborne Betula pollen. However, the average annual precipitation showed an opposite correlation with Betula pollen concentration, which indicated that birch plants had different ecological adaptability. Precipitation was a limiting factor for birch plant growth in the Fukang area. Additionally, wind speed and direction also affected Betula pollen transportation to a certain extent. (3) In the Tianchi area, where birch trees are distributed, Betula pollen production can directly reflect the number of birch trees and the ecological environment. The high Betula content in some fossil pollen records from the central Tianshan Mountains in northern Xinjiang of China also reflects the growth and distribution of birch plants, and is closely connected to Holocene climate change and human activities. Therefore, this research on 5-year average airborne pollen dataset from Xinjiang Tianchi Meteorological Station, Fukang Ecological Positioning Station, and Beishawo Experimental Station in the central Tianshan Mountains in northern Xinjiang of China is helpful for the study of fossil and topsoil Betula pollen in the central Tianshan Mountains, and the construction of an ecological civilization in Xinjiang.