Characteristic pollen source area and vertical pollen dispersal and deposition in a mixed coniferous and deciduous broad-leaved woodland in the Changbai mountains, northeast China

Pollen influx (number of pollen grains cm(-2) year(-1)) can objectively reflect the dispersal and deposition features of pollen within a certain time and space, and is often used as a basis for the quantitative reconstruction of palaeovegetation; however, little is known about the features and mechanisms of vertical dispersal of pollen. Here we present the results from a 5 year (2006-2010) monitoring program using pollen traps placed at different heights from ground level up to 60 m and surface soil samples in a mixed coniferous and deciduous broad-leaved woodland in the Changbai mountains, northeastern China. The pollen percentages and pollen influx from the traps have very similar characteristics to the highest values for Betula, Fraxinus, Quercus and Pinus, among the tree taxa and Artemisia, Chenopodiaceae and Asteraceae among the herb taxa. Pollen influx values vary significantly with height and show major differences between three distinct layers, above-canopy (>= 32 m), within the trunk layer (8 <= 32 m) and on the ground (0 m). These differences in pollen influx are explained by differences in (i) the air flows in each of these layers and (ii) the fall speed of pollen of the various taxa. We found that the pollen recorded on the ground surface is a good representation of the major part of the pollen transported in the trunk space of the woodland. Comparison of the pollen influx values with the theoretical, calculated "characteristic pollen source area" (CPSA) of 12 selected taxa indicates that the pollen deposited on the ground surface of the woodland is a fair representation with 85-90 % of the total pollen deposited at a wind speed of 2.4 m s(-1) coming from within ca. 1-5 km for Pinus and Quercus, ca. 5-10 km for Ulmus, Tilia, Oleaceae and Betula, ca. 20-40 km for Fraxinus, Poaceae, Chenopodiaceae, Populus and Salix, and ca. 30-60 km for Artemisia; it is also a good representation with 90-98 % of the total pollen deposited coming from within 60 km at a wind speed of 2.4 ms(-1), or 100 km at a wind speed: 6 m s(-1), for the 12 selected taxa used in the CPSA calculation. Furthermore, comparison with the vegetation map of the area around the sampling site shows that the pollen deposited on the ground represents all plant communities which grow in the study area within 70 km radius of the sampling site. In this study, the pollen percentages obtained from the soil surface samples are significantly biased towards pollen taxa with good preservation due to thick and robust pollen walls. Therefore, if mosses are available instead, soil samples should be avoided for pollen studies, in particular for the study of pollen-vegetation relationships, the estimation of pollen productivities and quantitative reconstruction of past vegetation. The results also indicate that the existing model of pollen dispersal and deposition, Prentice's model, provides a fair description of the actual pollen dispersal and deposition in this kind of woodland, which suggests that the application of the landscape reconstruction algorithm would be relevant for reconstruction of this type of woodland in the past.National Science Foundation of China [41371215]; Key Technology R&D Program of Hebei Province [13277611D]; Foundation of Key Discipline of Hebei Province and Hebei Key Laboratory of Environmental Change and Ecological Construction; Recruitment Program of High-end Foreign Experts [GDW20151300002]; Faculty of Health and Life Sciences of Linnaeus University; Swedish Strategic Research Area 'Modelling the Regional and Global Earth system-MERGE'SCI(E)ARTICLExuqinghai@mail.hebtu.edu.cn129-432