CAN THE SPAWN OF JAPANESE BROWN FROGS (Rana japonica, Ranidae) BE A LOCAL ENVIRONMENTAL INDEX TO EVALUATE ENVIRONMENTALLY FRIENDLY RICE PADDIES?

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Year:
2016
Type of Publication:
Proceedings
Keywords:
Environmentally Friendly Agriculture, Geographically Weighted Regression, Habitat evaluation, Transdisciplinary Science
Authors:
Asano, Satoshi; Wakita, Kenichi; Saizen, Izuru; Okuda, Noboru
Abstract:
Since the 1950s, rice cultivation in Japan has remarkably changed owing to paddy field consolidation for improved irrigation and drainage practices. However, consolidated paddies negatively affected the biodiversity in the agricultural landscapes because of the disjunction between forests and paddies and differences in the land grading level between paddies and concrete waterways. However, recently, the biodiversity at the study site, i.e., Kosaji village, Shiga Prefecture, has started to recover, owing to the efforts of farmers who have been using environmentally friendly products to boost rural development. The farmers of this village have established waterways at the marginal edge of paddy fields that has helped maintain the water levels during winter, thereby providing a stable habitat for aquatic organisms. The primary habitat of the target species―the Japanese brown frog (hereafter, JBF; Rana japonica Boulenger, 1879; Ranidae) ―is paddy fields and the surrounding forests. This study aimed to evaluate whether the presence of frog spawns can be used as an indicator of environmentally friendly rice cultivation. The habitat characteristics of JBF oviposition were analyzed in relation to the changes the in paddy fields cultivated using ecofriendly farming practices by spatial analyses. The number of JBF spawns was determined weekly in every paddy field in Kosaji village from February to March 2016. Moreover, the following indicators were monitored in each paddy field: the ratio of still water pool to the parcel of land, order in the line from the valley mouth, paddy size, and existence of marginal canal. Results of geographically weighted regression analyses showed that the environmentally friendly cultivation methods effectively maintained the habitat of JBFs via the first 3 above-mentioned variables. Furthermore, the marginal canals played an important role in raising wet ratio and providing water space in winter.
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