Vegetation community and factors that affect the woody species composition of riparian forests growing in an urbanizing landscape along the Chao Phraya River, central Thailand

Abstract

Improved knowledge of the environmental factors that affect woody composition is urgently required for species conservation in riparian zones of urbanizing landscapes. We investigated the environmental factors influencing tree abundance and regeneration in diverse forest types growing in the riparian area of an urbanizing landscape along the Chao Phraya River. We established 252 0.1-ha circular plots in remnant forest patches along 372km of the river. Cluster analysis was applied to classify the forest types. The relationships between environmental variables and tree abundance were assessed with ordination analysis, and generalized linear models were used to assess seedling/sapling abundance. The cluster analysis revealed five forest types, including floodplain forest with three sub-forest types, swamp forest, and mangrove forest. The ordination indicated that tree abundance in the floodplain forest was positively affected by distance to the ocean and the proportion of forested area. Swamp forest was positively influenced by the proportion of urbanized area and mean rainfall. Mangrove forest was negatively related to distance to the river. Seedling/sapling abundance of the dominant species in the floodplain forests was positively affected by lowland plain topography and negatively affected by the proportion of urbanized area, whereas swamp and mangrove forest species were positively influenced by the proportion of urbanized area and estuarine topography. Mature tree density influenced seedling/sapling abundance of all forest types. Tree abundance and regeneration of the riparian landscape was prevented by the urbanized area, floodplain, estuarine topography, and mature tree densities in remnant forests. These results suggest that remnant forest patches of conserved riparian forests along the urbanized landscape of the Chao Phraya River must be protected and the factors determining their colonization must be considered to enhance restoration practices.