日本甘藍、結球白菜與萵苣長期產量變化趨勢及其區域分布模式

Long-term Temporal Trends of Cabbage, Napa Cabbage, and Lettuce Yields and Their Spatial Patterns in Japanese Prefectures

瞭解農作物產量的長期變化趨勢，有助於制定相關政策來解決大量的糧食需求。然而，在蔬菜上的相關研究報告卻相當有限。本研究根據農業生產數據資料，利用簡單的統計模型，辨別甘藍、結球白菜與萵苣年單位面積產量在日本47個城市從1973到2016年共44年間長期變化趨勢。模型將各城市的產量變化歸類為成長、停滯、衰退與不曾改變共四種長期變化趨勢，藉由地圖來描繪各城市的變化類別，並討論這三種蔬菜單位面積產量長期變化趨勢的地區分布。結果顯示，甘藍和萵苣在日本超過一半的城市中，單位面積產量依然在成長或停滯中，且產量衰退的城市大多分布在日本海沿岸。另一方面，結球白菜的單位產量卻在日本超過一半的城市中呈現衰退的趨勢，且分布在全國各地。本文結果建議最適合甘藍發展的區域為北部東部和南部城市，最適合萵苣發展的區域為除了日本海沿岸以外的城市，最適合結球白菜發展的區域只有東部城市。藉由了解農作物產量的長期變化，將有助於長期農業政策的制訂與評估。

Long-term trends in agricultural crop yields are essential to establish the strategies to face the growing demand in staple foods. However, studies reporting long-term temporal trends of vegetable yields are rare. In this study, statistical models were used to find spatial patterns in long-term temporal trends of vegetable yields in Japan. Furthermore, changes in annual yields of cabbage, napa cabbage, and lettuce over the period of 1973-2016 in the 47 Japanese prefectures were analyzed according to the agricultural dataset of government. The yield trends for each prefecture were classified into four categories by using regression models: increasing, stagnating, collapsed, and never improved yields. Afterward, these different temporal trends in the prefectures were mapped and the spatial patterns detected in the three vegetables were discussed. The annual yields of cabbage and lettuce were increasing or stagnating in more than half of the Japanese prefectures. Prefectures with collapsed yields for these two crops were found mostly along the coast of the Sea of Japan. On the other hand, the annual yields of napa cabbage were collapsed in more than half of the prefectures all around the country. For cabbage, the best regions were suggested in northern, eastern, and southern prefectures. For Lettuce, the best regions were suggested in most of the prefectures, except of the prefectures along the coast of the Sea of Japan. For napa cabbage, the best region was suggested in the eastern prefectures. The analyzed spatial patterns of long-term temporal trends of vegetable yields may aid in the establishment of strategies and investments that increase or maintain agricultural production in to meet food demands.