Xiao Zhang

Reconstructing Holocene vegetation history and human impact on vegetation is critical for understanding past interactions between humans and nature. This study concentrates on the lower West River area in Southern China, offering high-resolution reconstructions of vegetation changes over the last 9000 years. Our findings reveal that during the Holocene Climatic Optimum (9–5 ka BP), the area was predominantly covered by dense evergreen broad-leaved forests. Around 5.1 ka BP, the emergence of marsh forests, as evidenced by abundant pollen of Glyptostrobus and in situ buried woods and roots, indicated a transition towards a wetland ecosystem. Notably, a thriving wetland environment and high production of peat deposits dating from 4.3 ka to 2.5 ka BP reflect the continuous drop of lake levels and the formation of swamps driven by a climatic pattern marked by decreased precipitation, potentially linked to a reduction in summer monsoon intensity during the latter part of the Holocene. This period of wetland expansion also coincides with the earliest evidence of rice cultivation in Southern China, suggesting a relationship between agricultural development and regional landscape changes. Additionally, millennial-scale paleo-megafloods are not only identified by lithological features but also by pollen taxa and principal component analysis. Despite the temporary disruptions of the marsh forest, it demonstrated resilience, quickly recovering within decades. By approximately 2.5 ka BP, a significant increase in rice-type Poaceae pollen and Pteridophyte spores, alongside the sharp decline of Glyptostrobus and a decrease in arboreal taxa, were observed. This shift in pollen spectra, coupled with a PC1 curve of principal component analysis, points to intensified human activity as a primary driver behind the collapse of the local wetland ecosystem. These findings align with regional evidence from the Pearl River Delta and coastal Southern China, highlighting extensive human intervention in natural forests and the onset of large-scale agriculture post-2.5 ka BP.

Relative pollen productivity (RPP) is a key parameter for quantitative reconstruction of past vegetation cover. However, RPP estimates are rarely obtained in the subtropical and tropical regions. In this study, the extended R-value (ERV) model was used to estimate RPP for major plant taxa in the evergreen broadleaved and mixed forests in middle subtropical China based on soil samples and vegetation data from 23 sites. The best result was obtained with the combinations of ERV sub-model 3 and Prentice’s or 1/d vegetation distance-weighting method. The relevant source area of pollen (RSAP) of the soil samples was estimated to be ca. 500 m. RPP on the basis of ERV sub-model 3 and Prentice’s model was obtained for seven taxa and the ranking is as follows: Castanopsis (1 ± 0), Ilex (0.352 ± 0.031), Mallotus (0.221 ± 0.028), Liquidambar (0.115 ± 0.007), Cyclobalanopsis (0.107 ± 0.006), Camelia (0.033 ± 0.001), Symplocos (0.010 ± 0.002). RPPs for Cyclobalanopsis, Camelia, Ilex, and Symplocos which are dominant elements in the subtropical evergreen broadleaved forests were first obtained. Our result demonstrates a significant effect of pollen dispersal models on the estimates of RPPs. The RPPs obtained in this study provide an important basis for quantitative vegetation reconstruction in the subtropical region of China.