RESUMEN
This study investigates the reliability of phytolith assemblage analysis for characterizing subtropical vegetation and explores the potential for using these modern phytolith-vegetation relationships for paleoenvironmental interpretation in southeastern China. The samples were collected from five common subtropical vegetation communities in the Daiyun Mountains, southeastern China, with the above-ground vegetation recorded at each plot. Constrained ordination analysis was used to determine the most important factor governing the variations in phytolith assemblages that could be quantitatively reconstructed with weighted averaging partial least squares regression (WAPLS). The relationship between modern phytolith assemblages and the parent vegetation, as well as production, dispersal, and taphonomic processes, was discussed. Results demonstrated that the main subtropical biomes in southeastern China could be well distinguished by soil phytolith assemblages. In particular, the overall amount of tree coverage was well represented by topsoil phytolith assemblages. Grass silica short cell phytoliths (GSSCP) tended to occur in higher proportions in open habitats (shrub-meadow) at higher elevations, whereas non-grass phytolith morphotypes attained higher frequencies under mixed and broadleaf forests at lower elevations. Human-induced deforestation might increase the frequency of GSSCP within the bulk phytolith assemblage. Our results constitute the primary phytolith reference data for the subtropical zone in southeastern Asia where vegetation change during the Holocene period, particularly forest shifts, anthropogenic deforestation, and early agriculture are poorly documented.
RESUMEN
The Urban Heat Island Effect (UHIE) is a widely recognised phenomenon that profoundly affects the quality of life for urban citizens. Urban greenspace can help mitigate the UHIE, but the characteristics that determine the extent to which any given greenspace can cool an urban area are not well understood. A key characteristic is likely to be the properties of trees that are found in a greenspace. Here, we explore the sensitivity of the strength of the cooling effect to tree community structure for greenspaces in Changzhou, China. Land surface temperatures were retrieved from Landsat 7 ETM+ and Landsat 8 TIRS and were used to evaluate the temperature drop amplitude (TDA) and cooling range (CR) of 15 greenspaces across each of the four seasons. Tree community structure of the greenspaces was investigated using 156 sample plots across the 15 greenspaces. We found that a number of plant community structure indicators of greenspaces have a significant impact on the strength of the cooling effect. The Shannon-Wiener diversity index, tree species richness and tree canopy coverage of greenspaces are all positively correlated with the magnitude of the temperature drop amplitude, with the strength of their influence varying seasonally. We also find that mean crown width is positively correlated with cooling range in summer and autumn, while greenspace tree density is negatively correlated with cooling range in winter. Our findings improve understanding of the relationship between plant community structure and the cooling effect of greenspaces. In particular, we highlight the important role that tree species diversity provides for mitigating the UHIE, and suggest that if planners wish to improve the role of urban greenspaces in cooling cities, they should include a higher diversity of trees species.