Carbon Pools of Berlin, Germany: Organic Carbon in Soils and Aboveground in Trees

The emission of climate-relevant gases, especially carbon dioxide, is often associated with urban areas. However, cities have accumulated organic carbon in their soils and vegetation over centuries and offer important ecosystem services for the city through carbon storage. The aim of this study is to estimate the total carbon storage of the central European city of Berlin by combining the organic carbon (C_org) stored in soils and the carbon found in aboveground biomass. We used 432 soil samples that were taken across 18 different land uses in order to estimate the carbon content for each land use based on the laboratory findings of each sample. This large amount of data, which is excellent for such a study, provides an important basis for the evaluation and analysis of the carbon storage potential. Taking into account the degree of soil sealing, the carbon calculations for each individual land use were then transferred to the total area of Berlin in order to produce a spatially explicit carbon map. Soil carbon stocks are reported as units of carbon either as kg/m² or in t/ha for each block. The carbon storage was estimated for both topsoil and subsoil. In addition, we estimated the carbon stored in 596,975 street trees and park trees according to the biomass equations for each tree species. The results show that more than two-thirds of the carbon present is accounted for by soils, which makes them the largest carbon reservoir of the city. Park trees store the most carbon in urban trees apart from urban forest trees. The total carbon stock of Berlin was estimated to be 24,087,344 tons, which corresponds to an approximate quantity of 270 t/ha. The distribution of carbon storage across the city shows the highest values towards the city boundaries. This holds true for the soil as well as the vegetation. The greatest quantities of total carbon are stored in the subsoils of the city’s suburbs. This study is the first of its kind to combine the carbon stocks of the soil and the vegetation in a city in order to estimate its carbon storage potential. It provides detailed soil carbon maps and biomass estimations, which can contribute to carbon storage investigations in other cities with similar climatic and ecological conditions.