Off-channel temporary pools on riverbanks have characteristic seasonal wet-dry cycles resulting from direct inflow of river water or hyporheic flow seepage. This study addressed two questions regarding the role of temporary pools in supporting diversity of riparian vegetation in a regulated river in Japan: (1) do temporary pools maintain high native riparian plant species diversity? And, (2) how do physical environmental factors affect the pattern of plant species distribution? The study was conducted on a 1-km section of the Hayade River alluvial fan in Niigata Prefecture, central Japan. Two to five transect belts consisting of 20 contiguous plots (1 m · 1 m) were laid out in two offchannel temporary pools and six other sites classified by physiognomy. Vascular plant presence, relative elevation, and substratum type were recorded in all plots. Species richness, Simpson's reciprocal index (1/D), and Shannon-Wiener function (H¢) were calculated by life form to estimate plant species diversity. Two conclusions could be drawn from the results. First, the temporary pools maintained high native riparian plant species diversity in this regulated river floodplain. Second, several environmental factors (seasonal wet-dry cycle, low elevation, complex micro-topography, and fine substrata) created spatial and seasonal heterogeneity of moisture conditions in the temporary pools, supporting plant species diversity. For sustainable maintenance of riparian plant species diversity, progressive river-management should restore original riverine dynamics to generate a shifting mosaic of diverse geomorphology.

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Abstract. The larval and adult stages of amphibious animals are affected by both aquatic and terrestrial habitat characteristics, and each stage also affects the other. However, this link between life stages has been largely overlooked in previous studies. We examined the effect of aquatic and terrestrial habitat characteristics on the diversity of larval and adult odonates, taking into account the link between the two life stages. Species diversity of adult and larval odonates and aquatic plants, as well as patterns of land use, was investigated in 63 irrigation ponds. We created structural equation models, with paths from land use and aquatic plants characteristics to larval and adult stages of odonates, as well as between the two stages, and chose the best model based on the lowest Akaike information criterion. Adult odonates, but not larvae, were affected by aquatic and terrestrial habitat characteristics, suggesting that the former is the key stage for odonate communities. We observed a positive relationship between the diversity of aquatic plants and larval odonates, but this was in fact due to the effects of aquatic plants on adults, which carried over to the larval stage. Our study showed that a consideration of the link between life stages is crucial for a complete understanding of the relationship between habitat characteristics and amphibious animal populations.

Our objective was to detect environmental and disturbance factors that determine plant species composition in a downstream riverside floodplain of the Shinano River, where both natural flooding and artificial fire disturbances predominate. We classified the natural vegetation into five types by physiognomy, i.e., burnt field, intact (unburnt) field, early-successional forest, later-successional forest, and margin of channel. We deployed 14 transect belts containing 713 plots of 1 m · 1 m at these sites. In the plots, we determined plant occurrences and values of five environmental (soil moisture, soil texture, relative elevation above the river, horizontal distance from the river, and light conditions) and two disturbance factors (scouring of plants by flooding and fire). Plant species compositions and environmental and disturbance factors were different among the sites. Logistic regression analysis showed that burning stimulated the occurrences of herbaceous annuals and conversely constrained those of woody and fern species, suggesting that fire disturbance resets the succession. Scouring of plants by flooding also affected the occurrences of many species, and had a positive influence on that of herbaceous winter annuals in particular. Canonical correspondence analysis indicated that the distributional characteristics of the plant species in the riverside floodplain were influenced primarily by distance from the river, reflecting the magnitude of flood disturbance. We conclude that (1) magnitude of flood disturbance is the primary factor determining plant species composition, and (2) burning maintains early successional vegetation and simultaneously creates a unique plant species composition by stimulating the germination of buried viable seeds transported by flood.