Forest carbon stock and sequestration is an important ecosystem service for long recognized of major importance to mitigate the increase of greenhouse gases and climate change, supporting the EU Biodiversity Strategy to 2020 (Maes et al., 2016). Numbers of CO2 sequestration deficits for Portugal were estimated in 2,739 × 103 Mg regarding the target of the government program for creating new forestry areas (Palma et al., 2014). To the best of our knowledge, there are no previous national studies on Carbon sequestration considering riparian forests, and few studies worldwide address the importance of riparian species as an additional strategy for mitigation of climate change (Garrastazu et al., 2015), besides the traditional agro-forestry and forestry systems (but see Rieger et al., 2015).

Widespread modeling approaches are used to estimate carbon stock and sequestration but frequently lacking of proper validation with real ground base measurements (Clerici et al., 2016).
To quantify the riparian forest carbon stock we will collect biomass in a set of plots along the rivers of different case studies. The number of samples will rely on the heterogeneity of the riparian forests. Main steps for field data collection are summarized below:
1) Selection of representative floristic homogeneous areas based on visual analysis of airborne images (50 cm of spatial resolution, real color composition) along the studied area
2) Tree inventory with measurements of diameter at breast height and tree height with estimation of aboveground biomass carbon stock using species-specific allometric models available in the literature. The conversion of biomass to carbon will be done using carbon conversion factors.
3) Understory biomass collection by the harvesting method using quadrats of a fixed area, measurements are made in field and a sample is taken to laboratory for dry weight calculations. The ratio dry/wet weight will be used for extrapolation to all the floristic homogeneous areas.
Then, the estimations of carbon stocks using the field data will be compared with the data obtained using remote sensing data, namely green vegetation indices, total vegetation cover and density of the riparian zone. The correlations obtained combined with vegetation changes will be used to estimate the carbon sequestration over time. Vegetation changes will be derived from multispectral imagery (airborne images, RGB-NIR, 50 cm of spatial resolution). The current overall carbon stocks will be calculated using the UAV imagery.