Abstract In rice fields, the cultivation area itself can play an essential role as a habitat for wetland organisms. Many previous studies showed negative impact of agricultural intensification and abandonment on biodiversity in wet farmland ecosystems. However, verification of the direct impact of aquatic environmental change by the paddy improvement and abandonment still remains. Here, we investigated the effects of the intensification and abandonment on the area of wet fields remaining in paddies during the fallow season, as well as the factors driving the population decline of the Japanese brown frog (Rana japonica), using data of long-term monitoring numbers of egg masses at multiple sites. To quantitatively estimate the spatial and temporal variation in saturated areas with water in the paddies where the frogs spawn in early spring, we used infrared bands of Landsat images. Both paddy improvements and abandonment have affected R. japonica populations through the reduction of wet areas in the fields. Furthermore, the frog's population size was positively associated with the area of surrounding forest. Our findings suggest that conservation in wet farmland requires appropriate water management inside the cultivation area as well as in other landscape elements that serve as secondary habitats.

中文翻译：

---

稻田改良和弃耕对两栖动物种群的水文影响；日本棕蛙 Rana japonica 的长期趋势

摘要 在稻田中，耕作区本身可以作为湿地生物的栖息地发挥重要作用。许多先前的研究表明农业集约化和放弃对湿农田生态系统生物多样性的负面影响。然而，对稻田改良和弃耕对水生环境变化的直接影响的验证仍然存在。在这里，我们利用长期的数据调查了集约化和弃耕对休耕期稻田剩余湿地面积的影响，以及导致日本棕蛙（Rana japonica）种群下降的因素。监测多个地点的卵块数量。为了定量估计早春青蛙产卵的稻田中水饱和区域的时空变化，我们使用了陆地卫星图像的红外波段。稻田改良和弃耕都通过减少田间湿地面积影响了粳稻种群。此外，青蛙的种群规模与周围森林面积呈正相关。我们的研究结果表明，湿农田的保护需要在栽培区域内以及作为次生栖息地的其他景观元素中进行适当的水管理。