Abstract:

In the dry and warm valleys of the middle reaches of the Dadu River, landslides and debris flows occur frequently. Studying vegetation on these slopes is valuable in understanding vegetation succession in regards to ecological restoration of highly disturbed landscapes. In this study, plots were selected along the Dadu River every 5 km to investigate species composition, distribution, topography, soil characteristics, and vegetation change in the middle reaches of the Dadu River valley. Plant communities were classified, compared and sorted using multiple regression tree (MRT), alpha diversity index and canonical correspondence analysis (CCA). The results showed that the landscape were divided into four communities based on three factors: soil carbon, pH and C : N, i.e. Lespedeza floribunda-Arthraxon hispidus-Elsholtzia ciliate, Ficus tikoua-Dodonaea viscosa-Carex schneideri, Pinus yunnanensis-Quercus variabilis and Arthraxon hispidus-Heteropogon contortus. Shrub and grass dominate this area, with occasional areas of bare ground which is liable to debris flow disasters. The species richness, dominance and diversity of shrub-grass (Lespedeza floribunda) community are consistently higher than arbor and grass communities, although species diversity values are not significant. The shrub and grass community is widely distributed, although fragile and unstable as alien species reached 8.33% within these communities. MRT and CCA analysis showed that pH, C : N, slope direction and soil bulk density are the main factors influencing vegetation distribution pattern as soil influences are more important than topography.

Key words: the Dadu River, dry and warm valleys, multiple regression tree, species diversity, canonical correspondence analysis