Floristic characteristics and underlying environmental factors of paddy field dikes at a restoration site in Ichinoseki, Iwate Prefecture, Japan.
We investigated the vascular plant species composition and underlying factors for paddy dike vegetation in a small river basin in the southernmost part of Iwate Prefecture, Japan, where traditional terraced paddy fields remain. In total, 455 vascular plant species, including 41 naturalized and 14 endangered species, were recorded from 92 dikes (13,784.2 m2). Indigenous herbaceous species found in these dikes could be classified into wetland (36.0%), grassland (40.3%), and forest (23.7%) species with different habitat requirements. Generalized linear mixed models revealed that the most important factor affecting floristic composition in a paddy dike was the land-use type of adjacent areas. Considering the distributions of wetland and endangered species, we concluded that paddy dikes satisfying the following conditions had the highest conservation priority: (i) directly bordering traditional irrigation ponds or ditches; and (ii) larger and steeper, and located in terraced paddy fields.