West Africa, already highly influenced by the negative effects of climate change, is additionally characterized by rapid population growth, endemic poverty, and insecurity. This is affecting the natural capital of its ecosystems and the services they provide. Natural capital accounting (NCA) provides the fundamental evidence base required for informing economics and environmental decisions, thus strengthening the conservation and management of natural resources. The objective of this study is to showcase the development and evaluation of a semi-automated NCA platform (Sys4ENCA) designed to support decision making in the context of protected areas management in a multi-level example in western Africa. The accounting results highlight that simulations at the broader scale using national public data show that the natural capital of ecosystems in western Africa depends strongly on the mean climate and its variability. Evaluating regional datasets, the simulation with the platform shows that pressure on land in combination with weak governance reduces the capability of the ecosystem to deliver the required services in a sustainable manner, i.e., in the eastern part of the Bafing-Falémé landscape, where mining and intensive agriculture are fueling loss of natural capital. The results of Tier-3 accounting using local datasets enhanced the spatial variability and highlighted additional hotspots of degradation compared to the regional results, i.e., the prospective construction of a hydro-electricity dam (Koukoutamba) in the southern part of the Moyen-Bafing National Park located in the Bafing-Falémé landscape. The Sys4ENCA platform, combined with a multi-level approach, showed itself to be a valuable tool to facilitate protected area management as it provides not only consolidated information at a local scale but also the broader context and external pressures, i.e., climate change and demand for land. Given its automatized nature, the platform reduces human errors and increases the efficiency, speed, and harmonisation of computation over long timeframes and spatial scales.

Over the past thirty years (Rio Conference, 1992), the climate has become an important issue in world politics. With the Kyoto Protocol (1997), atmospheric carbon accounting has gradually been introduced with the aim of raising awareness of national and international decision-making systems for the implementation of an energy transition. However, this carbon approach does not take into account ecosystems despite their fundamental role in climate regulation. A global assessment of all natural resources and ecosystem services, known as natural capital, is necessary from a sustainable development perspective. This assessment must then be taken into account in national accounting systems. The aim of this article is to test, on the national territory of the Republic of Guinea, the ecosystem-based natural capital accounting method developed by Jean-Louis Weber (Weber, 2014). Based on three accounts (ecosystem infrastructure, ecosystem carbon and water resources), this method aims to measure the sustainable capacity or 'sustainability' of ecosystems to provide services. Based on land use & land cover layers produced in the framework of the agroecological zoning project (Jaffrain et al., 2021), we have operationalised this ecosystem accounting methodology in the Republic of Guinea to calculate the total sustainability of the ecosystem. The land cover layers are the basic structural data for monitoring and describing the evolution of the territory at different temporal intervals. Thus, several environmental indicators were defined from these combined geospatial data and eventually allowed to define the evolution of the total sustainability of the territory's ecosystem between 2005 and 2015. A clear degradation of this sustainability value was identified, which reflects the numerous land use changes affecting the country in the recent period (2005-2015).