Trends in Integrated Valuation of Forest and Wetland Ecosystem Services (2005 2025): Implications for Rwanda's Integrated Valuation Framework (RIVF)

Since the Millennium Ecosystem Assessment, ecosystem service (ES) valuation has expanded rapidly, with forests and wetlands at the centre because of their dense bundles of regulating services and importance for livelihoods and climate policy. Yet a persistent divide remains between biophysical modelling, economic valuation and socio-cultural assessment. This paper presents a systematic literature review and meta-analysis of 1,240 peer-reviewed articles (2005 2025) on forest and wetland ES. Following PRISMA 2020, we examine temporal and regional trends, valuation methods and the degree of methodological integration. Studies are classified as biophysical-dominant, economic-dominant or integrated (tri-dimensional). We then draw out implications for the design of the Rwanda Integrated Valuation Framework (RIVF), which aims to operationalise spatially explicit, three-dimensional valuation for Rwanda’s forests and wetlands. Three main findings emerge. First, although ES valuation studies increased by more than 400% since 2010, most remain compartmentalised: 46% are biophysical-dominant and 40% economic-dominant, while only 14% achieve tri-dimensional integration of biophysical, monetary and socio-cultural data for overlapping ES bundles. Second, a random-effects meta-analysis of 17 high-quality valuation studies yields a pooled mean ES value of 7,922 USD/ha/year (median 2,584 USD/ha/year) for forests and wetlands, with extreme heterogeneity (I² = 100%), confirming that global benefit-transfer coefficients are poor predictors of local values. Third, the most recent period (2021 2025) is characterised by a shift from ad hoc valuation toward natural capital accounting and macro-indicators such as the System of Environmental Economic Accounting Ecosystem Accounting (SEEA EA) and Gross Ecosystem Product (GEP), while Sub-Saharan Africa contributes less than 8% of the global ES valuation literature and only a small fraction of integrated studies. We conclude that tools for valuing regulating services and for spatially explicit ES modelling are mature, but truly integrated, tri-dimensional frameworks remain rare, especially in the Global South. These gaps create a protection gap, where robust valuations fail to inform fiscal policy or conservation. The review provides empirical and methodological guidance for RIVF, highlighting where global practice can be adapted and where Rwanda requires new primary data and participatory methods.