The climate crisis highlights the importance of forests in both mitigating and adapting to climate change, as well as in supporting the UN's Sustainable Development Goals (SDGs). To promote the better understanding and valuing of the critical role forests play, and to develop holistic approaches to protecting and maintaining them, the Center for International Forestry Research (CIFOR) has adopted the mission "to bring scientific knowledge to bear on major decisions affecting the world's tropical forests and the people who depend on them". This paper highlights an important topic in CIFOR's research portfolio -forests' diverse roles in climate change mitigation and adaptation and how forest governance ensures the equitable and sustainable wellbeing of people, both locally and globally. As one of the founding donor countries of CIFOR, the Government of Japan has consistently supported CIFOR's research through Japanese scientists collaborating in research projects and/or serving as members of CIFOR's Board. This paper, therefore, specifically highlights research projects funded directly by the Government of Japan, in particular.

Tree cover has recently expanded in floodplains and riparian areas, and river administrators cut the trees and excavated the areas for flood management in Japan. Trees, such as willows, recolonize and expand quickly on bare land after the work but little information is available on the speed at which trees expand. We examined the expansion rates of the tree cover on the bare land after the excavation and the differences in the rates depending on the slopes of the riverbed. We estimated temporal trends in the area covered by the willows using aerial and satellite photographs at 26 reaches located in alluvial plain. The expansion rates of the tree cover increased rapidly 5 years after the excavation. Thereafter, about 50％ of the excavated area was again covered by trees in 10 years. After about 5 years, some individuals are considered to have grown to a size that could cover the parts of the bare lands with their canopy, likely leading to a rapid increase in the area covered by trees. The expansion rate was faster in reach with a gentle slope than a steep slope. Trees are less likely to be destroyed owing to the low flow velocity on the gentle slope. We demonstrated the tree expansion rates on the excavated bare land, and our findings contribute to decisions on when the river administrator should cut trees and excavate the tree-covered area again.

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