Towards a harmonised dataset of forest soil properties to support mapping and modelling in Europe

Forest soils provide important ecosystem services, including biodiversity support, nutrient cycling, carbon sequestration, water regulation and erosion control, which underpin economic sustainability. The health and sustainability of forest ecosystems depend on the health and functioning of forest soils themselves, making their conservation and management essential for the well-being of both natural ecosystems and human societies. Hence it is fundamental to have good information to inform European forest management and policies, such as up-to-date spatial information on forest soils in Europe.

ISRIC – World Soil Information is a partner in the HoliSoils project, working to improve forest soil data for Europe. During the 2nd General Meeting of the HoliSoils project in Barcelona in April 2023, the ISRIC team discussed two major topics to tackle which will yield improved forest soil data for Europe:

  1. How shared forest soil datasets from different sources were cleaned, integrated and harmonised;
  2. How the data will be used to map soil properties of forest soils.

How shared forest soil datasets from different sources were cleaned, integrated and harmonised

Forest soil data shared in the framework of HoliSoils (~ 7.2k points) were processed following updated Extract Transform Load (ETL) procedures implemented for the World Soil Information Service (WoSIS) which is a service provided by ISRIC – World Soil Information. The ETL procedure is visualised below:

Around 3.500 out of 7.200 points are under forest, as identified using the EU Corine Land Cover dataset (for 2018):

Key soil properties such as pH, organic carbon content, bulk density and soil texture of the shared soil profile data can be viewed and queried using a dashboard. The data can be filtered according to various criteria. Importantly, the dashboard also shows the licenses (i.e., open (33%) or restricted (67%)):

Descriptive statistics are presented also for key soil properties:

Luis Calisto, Database development expert at ISRIC, is happy with the achieved results, the soil data provided will increase forest soil knowledge and allow world community to better understand European forest soils.  

How the data will be used to map soil properties of forest soils

For the soil property mapping itself (ongoing), the set of soil profile data provided by HoliSoils will be complemented with forest soil holdings for Europe held in WoSIS, representing ~ 28k profiles to obtain a better spatial coverage:

As indicated by Laura Poggio, senior digital soil mapping and remote sensing expert at ISRIC, for the mapping itself we will use a digital soil mapping approach featuring model tuning, covariates selection and regression random forest to map key soil properties at a resolution of 100 m and assess the spatial uncertainty for each pixel.

Results of the ETL work and soil property mapping will be presented later this year during the Wageningen Soil Conference. Niels Batjes, senior soil science expert and scientific/technical lead of the HoliSoils project at ISRIC, indicated “it is important for stakeholders to have access to quality-assessed, harmonised data when mapping and modelling across countries at continental scale to support decision making towards climate and sustainability goals.” Hence, ISRIC always welcomes new profile data for consideration in WoSIS.

Ultimately, the geo-referenced, harmonised soil profile data and maps will be made freely available through the HoliSoils website. Long-term preservation, and maintenance, of the data after completion of the project will be ensured by ISRIC in its capacity of ICS World Data Centre for Soils.