Effect of fluvial and geomorphic disturbances on habitat segregation of tree species in a sedimentation-dominated riparian forest in warm-temperate mountainous region in southern Japan
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We investigated habitat segregation and patterns of species diversity of trees in relation to variations in fluvial and geomorphic disturbances (erosion or sedimentation) along a longitudinal stream gradient from V-shaped valley to alluvial fan and between valley and adjacent hill slopes in a warm-temperate mountainous riparian forest in Kyushu, southwestern Japan. We divided the riparian area longitudinally into four geomorphic zones: V-shaped valley (VV-zone), upper fan (UF-zone), middle fan (MF-zone) and lower fan (LF-zone). We surveyed the distribution of tree species (DBH>=3cm) in the four riparian zones and in additional plots on hill slopes (SL-zone) representing the broader, non-riparian forest matrix. Detrended correspondence analysis (DCA) ordination demonstrated variations in species composition along the longitudinal stream gradient. Species guild analysis based on the detection of species' preferred zone by a bootstrap method revealed a guild structure corresponding to each geomorphic zone. The four riparian zones were differentiated from the SL-zone by having a low proportion of SL-guild species and high proportion of infrequent species that were characterized by deciduous leaf habit. The LF-zone was the most differentiated and was characterized by low tree density and specialist species established on the flat and unstable soil surface created by frequent deposition of sediment. The UF- and MF-zones were characterized by a high tree density and species richness (particularly of infrequent species) established on the stable ground surface of a high alluvial terrace. Micro-site heterogeneity produced by channel formation may also maintain a high species diversity in the riparian zones.
- Journal of forest research
Journal of forest research 11(6), 405-417, 2006-12-01