Holocene Vegetation Changes and Human Activities Revealed by a Peat Sediment Core in Gaoyao, Zhaoqin

Abstract:

The study site is located in Baizhu Town of Gaoyao County, Zhaoqing, about 800 m away from modern Xinxing Stream that belongs to the river basin area of Xijiang. A peat core of 610cm has been drilled on a low-mountainous depression of 29 m altitude (22°54.072′N，112°20.427′E). The radiocarbon dating shows that the bottom of the core has an age older than 5057 cal B.P.. By linear projection of age-model, this core reveals a history of ~6100 yr local sedimentary evolution, vegetation succession and human impact. An in-situ thick wood layer with peat and abundant Glyptostrobus pensilisoccurs between the depth of 536 cm and 175 cm.

Pollen data reveals that there was a series of obvious changes in local vegetation, successively evergreen broadleaved forest, Glyptostrobus wetland forest, again evergreen broadleaved forest, herbaceous wetland (mainly Cyperaceae), secondary forest and grassland/cultivated land (Poaceae). The evolution pattern of local wetland has been clarified that forest wetland highly developed especially between 4900 cal B.P. and 2900 cal B.P., and a tendency shows that the taxon of wetland Glyptostrobus gradually declined and spatially reduced at around 2900 cal B.P.. The herbaceous wetland and grass replace gradually the forest wetland marked by the increase of Cyperaceae and Poaceae. By ~1700 cal B.P., pollen of Glyptostrobus tends to disappear, indicating local vanishment of the forest wetland. Charcoal analysis demonstrates that fire events initiate at about 3500 cal B.P., which is coinstantaneous with late Neolithic human influence of early agriculture occurred in many regions of the Pearl River Delta during that time. The proportion of arboreal pollen rapidly decreases at around 2660 cal B.P., in association with an increase of Poaceae, Dicranopteris and the secondary conifer plant of pine. This variation process is also marked by greatly increase in micro-charcoal, inferring the development of “slash-and-burn” farming for rice. We conclude that Holocene shift of the coastline; regional water table change and human activity are the multiple causes resulting in local forest wetland migration. The development of deltaic agriculture since ~2600 cal B.P. aggravates the vanishment of local forest of Glyptostrobus.