Landform type and land improvement intensity affect floristic composition in rice paddy fields from central Japan

Yamada S, Kusumoto Y, Tokuoka Y & Yamamoto S (2011). Landform type and land improvement intensity affect floristic composition in rice paddy fields from central Japan. Weed Research 51, 51–62. Summary Paddy field agroecosystems are floristically highly diverse, but the mechanisms affecting this diversity are not clear, especially at broad spatial scales. To conserve paddy weed species, we aimed to clarify the importance of landscape-scale variables for in-field floristic diversity. Statistical evidence of the shape of the species response along environmental gradients was obtained by Detrended Correspondence Analysis, DCA. Predicted variables were landform type (narrow valley floor, wide valley floor, old river channel, meander plain with dry soil and meander plain with wet soil), intensity of land improvement (six classes) and species attribute. Both landform type and land improvement intensity were important in explaining variations in in-field floristic diversity. Non-paddy weeds and rare threatened species occurred frequently in unimproved plots. Plots in the narrow valley floor and old river channel landform categories had representative species that were categorised as threatened. Unimproved plots also had representative species that were categorised as threatened. The threatened representative species in unimproved plots were confined to old river channels. Unimproved plots in old river channels were the most vulnerable in terms of conservation. Estimation of floristic patterns in paddy fields using landform type and land improvement intensity could be a useful tool for maintaining floristic diversity.