Significant changes in the environment have caused awareness of the strategic importance of forests as a factor in global environmental security, and socio-economic development of territories. Evidence of this are many international acts, including the provisions of the New EU Forest Strategy for 2030. However, in areas where hostilities are taking place, forests are being destroyed en masse, leading to systemic losses, the restoration of which will require large investments, efforts, and a long period of time. Therefore, it is important to improve the mechanisms for recovering compensation from the aggressor country, whose actions have led to losses from loss or damage to forest ecosystems. In this case, justification of the amount of compensation plays a significant role, and therefore there is a need to develop methodological approaches to their definition. Based on the summary of international practices, guidelines of international organizations, regulations of Ukraine, and scientific publications on the assessment and compensation of environmental damage, the author used a systematic approach that combines the assessment of damage from loss or damage to forest ecosystems and the cost of their restoration. The methodology involves taking into account the degree of damage in determining losses, lost profits, and costs of restoration of forest ecosystems in the context of forest ecosystem services – Provisioning Services, Regulating Services, Supporting Services, or other ecosystem maintenance services; Cultural Services, such as educational, aesthetic, and cultural heritage values, recreation, and tourism. The author proposes relevant methods for each component of the assessment and the relevant indicators. In determining the sets of indicators the author used those that can be calculated based on objective data, or that have an international practice of their calculation. The choice of data sources for the calculation of damage and losses from losses or damage to forest ecosystems and objects within them, caused to Ukraine as a result of hostilities, is stipulated.