Monitoring long-term biomass dynamics in drylands is of great importance for many environmental applications including land degradation and global carbon cycle modeling. Biomass has extensively been ...estimated based on the normalized difference vegetation index (NDVI) as a measure of the vegetation greenness. The vegetation optical depth (VOD) derived from satellite passive microwave observations is mainly sensitive to the water content in total aboveground vegetation layer. VOD therefore provides a complementary data source to NDVI for monitoring biomass dynamics in drylands, yet further evaluations based on ground measurements are needed for an improved understanding of the potential advantages. In this study, we assess the capability of a long-term VOD dataset (1992–2011) to capture the temporal and spatial variability of in situ measured green biomass (herbaceous mass and woody plant foliage mass) in the semi-arid Senegalese Sahel. Results show that the magnitude and peak time of VOD are sensitive to the woody plant foliage whereas NDVI seasonality is primarily governed by the green herbaceous vegetation stratum in the study area. Moreover, VOD is found to be more robust against typical NDVI drawbacks of saturation effect and dependence on plant structure (herbaceous and woody compositions) across the study area when used as a proxy for vegetation productivity. Finally, both VOD and NDVI well reflect the spatial and inter-annual dynamics of the in situ green biomass data; however, the seasonal metrics showing the highest degree of explained variance differ between the two data sources. While the observations in October (period of in situ data collection) perform best for VOD (r2=0.88), the small growing season integral (sensitive to recurrent vegetation) have the highest correlations for NDVI (r2=0.90). Overall, in spite of the coarse resolution, the study shows that VOD is an efficient proxy for estimating green biomass of the entire vegetation stratum in the semi-arid Sahel and likely also in other dryland areas.
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•A Long-term VOD dataset is evaluated against NDVI and in situ biomass observations.•Both VOD and NDVI reflect the spatio-temporal patterns of biomass in West Sahel.•VOD captures variations of woody plant foliage biomass better than NDVI.•VOD and NDVI seasonal metrics differ for optimal long-term monitoring of biomass.
Human activities in cities, especially those burning fossil fuels, have increased atmospheric carbon dioxide (CO
2
) concentrations. Urban trees play a crucial role in the biogeochemical cycle of ...carbon storage in cities. Many tons of carbon are annually stored by the structural components of trees in urban ecosystems. In the urban forest of San Juan city, Platanus hispanica is one of the most abundant species. The goal of this study is to estimate the amount of carbon stored by this species in its different structural components: trunks, primary, secondary and minor branches. We analysed samples collected from two areas in the city: the urban and suburban areas. We estimated dry matter for each structural component. Significant differences were found between the studied areas. Results indicated that P. hispanica accumulated 5,630 tons of carbon in the urban area and 4,700 tons of carbon in the suburban area. Around 20,662 tons and 17,249 tons of CO
2
, in the urban and suburban areas respectively, are annually sequestered by this species from the atmosphere of San Juan city.
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