Subtropical forest vegetation development and climate change in Baishanzu area of Zhejiang Province, China, since the Holocene

Human activities and climate change pose major challenges for the sustainable development of terrestrial biological forests. The modern vegetation in the Baishanzu area is typical mixed subtropical evergreen broad-leaved, coniferous, and deciduous broad-leaved forest, with a vegetation combination sensitive to climate change. Higher resolution pollen records from the Shangyang Lake Wetland, located in the subtropical monsoon climate of the Baishanzu area in Zhejiang, China, were combined with environmental proxy data, such as data on loss on ignition and charcoal, to reconstruct the vegetation and climate changes since the Holocene. The results show that the climate was cool and dry during the early Holocene (11660-6580 cal. aBP), when the zonal vegetation changed from evergreen deciduous broad-leaved mixed forests dominated by evergreen Quercus (Quercus(E)), Castanopsis, deciduous Quercus (Quercus(D)), and Castanea to coniferous and broad-leaved mixed forests with rich Cryptomeria. Abies pollen spread to lower altitudes during the period 9620-8020 cal. aBP with Abies beshanzuensis covering large areas of land. The increased in the East Asian summer monsoon from 6580 to 2040 cal. aBP led to the Holocene Climate Optimum, when the climate was particularly warm and humid. The zonal vegetation was middle subtropical evergreen broad-leaved forest dominated by Quercus(E), Castanopsis, and Cyclobalanopsis with particularly high forest coverage and few fire events. For the last 2000 years, coniferous and broad-leaved mixed forests, mainly Pinus taiwanensis, have dominated the vegetation in the area. Sharp increase in such flora was observed after the year 980. Decreased temperature, cold climate, and increased anthropogenic disturbances have resulted in a substantial reduction in the arboreal pollen content, including Quercus, Castanopsis, Castanea, and Ilex, and an increase in Pinus and Poaceae. The results of this study will play a positive role in fully understanding the historical background and internal mechanisms of subtropical forest changes

A Preliminary Study on Pollen Distribution in the Surface Soil of the Baishanzu Area in Qingyuan County, Zhejiang Province, China

Baishanzu area in Qingyuan, Zhejiang Province, which is famous for the discovery of Abies beshanzuensis, has the most typical mid-subtropical evergreen broad-leaved forest and complete vertical zones of mountain ecosystems in China, and this provides good natural conditions for paleoclimatic reconstruction using surface soil and airborne pollen data. Based on the pollen spectra of nine surface soil pollen samples collected at 300-1,700 m altitude, the relationship between vegetation and surface soil pollen in this area was preliminarily studied. The results show that surface soil pollen in this area can be divided into three assemblage zones from top to bottom according to altitude and ratios of coniferous pollen/broad-leaved pollen and arboreal pollen/non-arboreal pollen, which correspond to the evergreen deciduous broad-leaved mixed forest and temperate coniferous forest, evergreen broad-leaved forest and warm coniferous forest, secondary forest, and farmland (caused by human interference) zones. The surface pollen assemblages were dominated by the evergreen coniferous tree species Pinus, with an average pollen content of 67.5%. The pollen of Castanopsis (6.2%), Quercus (3.4%), Betula (1.4%), and Corylus (1.4%) is common. In contrast, Cyclobalanopsis, Liquidambar, Symplocos, Tsuga, Oleaceae, and Ericaceae had lower contents. Herbaceous plants are dominated by Poaceae (11.2%), including Artemisia, Chenopodiaceae, Apiaceae, Asteraceae, etc. The spore content of fern vegetation was high, mainly Hicriopteris (38.2%) and Polypodiaceae (7.4%). Pinus pollen appeared in all samples, with the highest average content. With increasing altitude, the mean percentage gradually increased from 54.8% to 77.3%, and it is an overly represented pollen with a low sedimentation rate that is easily preserved and transported to the area. Abies pollen is only observed in the samples under the A. beshanzuensis tree at an altitude of 1,700 m. Its percentage is lower than 1%, which may be related to low pollen yield and the relatively narrow distribution range of A. beshanzuensis in this area. In addition, the pollen diversity analysis results based on Simpson's index show that human interference factors prevent the surface soil pollen at lower altitudes in this area from reflecting the regional zonal vegetation. With decreasing altitude, the deciduous component of arboreal pollen in the pollen assemblage increased from 13.2% in Zone I to 40.9% in Zone III. Zone III shows a coniferous and broad-leaved mixed forest zone caused by human factors. The content of the evergreen component in zone I is high, which is related to the high humidity at higher altitudes. This study selects Baishanzu National Park to study the surface soil pollen and preliminarily discusses the characteristics of the surface soil pollen assemblage and its relationship with vegetation, which provide research materials and the basis for Quaternary paleovegetation and paleoclimate reconstructions in the Baishanzu area, Qingyuan County, China. However, due to a lack of surface soil samples and modern vegetation investigation data, the reliability of the research results is affected. In future research, sampling and density quadrat surveys of surface sampling sites will be increased to cover as many vegetation zones as possible