Surface Pollen Assemblages Of Human-disturbed Vegetation And Their Relationship With Vegetation And Climate In Northeast China

Pollen is an important proxy for past environment change. Modern pollen assemblages,and their relationships to vegetation and climate, are essential to the reconstruction ofpaleoenvironments. Research in recent years has shown that human impacts are not onlydriving current and future environmental changes, but have also played significant roles inenvironmental changes. Palynologists are becoming increasingly interested in the pollenassemblages of human-disturbed or impacted vegetation types, so as to better recognize pasthuman impacts and to predict future environmental changes.Northeast China is one of the cradles of Chinese civilization. Six thousand years ago,humans began to live and multiply in this area. In modern times, large-scale reclamation hasresulted in artificial and human-disturbed vegetation types being the most important, but thereare no reports on modern pollen assemblages. We analyzed87modern surface pollen samplesdifferent terrains and different intensities of human impact. We correlated these pollenassemblages to local vegetation and regional climate to provide basic scientific data withwhich to better recognize human activities in the Holocene and to predict futureenvironmental changes in Northeast China.Northeast China is located in the forest vegetation zone. The pollen assemblages ofhuman-disturbed vegetation usually contained more than30%tree pollen. Moreover, themajor taxa in the pollen assemblages were consistent with the vegetation, suggesting that thepollen assemblages of human-disturbed vegetation reflect the regional vegetation composition.There were differences among pollen assemblages in different geomorphic units. In themountains, there were more types of tree pollens, at higher percentages, than in other areas.The percentage of cereals was distinctly higher in the plains than in the mountains. Theproportions of Pinus and Concentricystes were highest in the low plains. Pollen assemblageswere notably different between farmland and nearby wasteland in the same region. Wastelandhad many more types of pollen and higher pollen concentrations (average15074grains/g,maximum87446grains/g) than did farmland. Cereal pollens in wasteland usually made upless than10%of the total. On the contrary, in farmland, total pollen levels were much lower(average3910grains/g), and fewer pollen types were recorded, but the cereal pollenpercentage was49.9%on average. PCA and RDA analyses indicated that wasteland andfarmland samples could be readily distinguished, as could farmland samples from mountainsversus plains. Human activity was probably a major cause of the lower pollen concentrations in farmland, suggesting that pollen concentration is an important indicator of human activities.More attention should be paid to the pollens of vegetables and other crops, even when theirpercentages are low, in fossil pollen assemblages to recognized historical human activities.Our study and other investigations of pollen assemblages in northern Chinademonstrated that the major pollen types and percentages are closely correlated to latitude andaltitude. The pollen assemblages of human-disturbed vegetation in different areas differed dueto the regional vegetation, the types of crops, human impact intensities, and other factors.Cereals and Cruciferae both increased in frequency with declining altitude. Cereals pollenconcentrations and percentages in farmland varied with geographic area due to differences inplanting habits and climate.Artificial or human-disturbed vegetation reflects regional climate well. RDA showed thatthe pollen assemblages in Northeast China were significantly negatively correlated with Ta(mean annual temperature,0.73) and Tw (July mean temperature,0.81) and were significantlypositively correlated with MAP (mean annual precipitation,0.48).