A global indicator of soil macroinvertebrate communities — Global Soil Biodiversity Initiative

by Dr. Patrick lavelle, Institute for Ecological and Environmental Sciences, Paris Sorbonne University, France

Production of soil based ecosystem services can be assessed using the abundance and diversity of soil macroinvertebrate communities as proxies.

A major challenge for environmental policy is to encourage the production or preservation of soil ecosystem services through appropriate management methods. For example, 133 GT of carbon (C), equivalent to 15 years of anthropogenic emissions at current day rates, were emitted during the industrial era due to inadequate management methods (deep tillage, exclusive use of chemical fertilizers, bare soils during intercropping periods and erosion). Reintegration of this C lost to the soil would be a critical input for climate change mitigation.

Measuring the provision of ecosystem services is, in the current state of knowledge, an arduous task which requires a costly scientific investment, due to the chemical, molecular or physical techniques used.

Our recent work proposes the use of a synthetic indicator of soil macroinvertebrate communities as a simple and cheap proxy to these measurements.

Soil macroinvertebrates, which can be seen by the naked eye, belong to 16 main orders, present around the world (ants, earthworms, centipedes, etc). Their populations are very sensitive to the soil environment, its humidity, temperature, plant cover, texture or its organic matter content and can therefore be precise and reliable indicators of the quality of the soil environment.

This pattern has been confirmed throughout time in diverse environments across the planet. Moreover, when our studies tested for this relationship, we found a very close link between macroinvertebrate communities and the various chemical, physical or biological characteristics of the soils.

About forty years ago a simple method of sampling macrofauna was proposed in the Tropical Soil Biology and Fertility program. This method has become so standard that today data from more than 8000 sampled sites with this method have been collected in a database. The sOilFauna research project led by Nico Eisenhauer and Jerome Mathieu funded by sDiv brings together 25 researchers from 9 countries in an effort to explore and synthesize this data set.

The first analysis published from this data in 2022 showed the extreme sensitivity of these communities to all the major factors of the soil environment (plant cover, climate, latitudinal and altitudinal variations, soil/soil texture, nutrient/organic matter content). On a global planetary scale, communities described by the abundance of the 16 broad taxonomical units responded identically to changes in soil quality. Communities are ranked first according to the abundance of the different groups and the number of different faunal groups present in the sampling. An additional attribute is the relative proportion of social insects (ants and termites) in the community.

This similarity in the response of all communities is remarkable since each of the large groups is locally composed of different families, genera and species whose distributions are much more local.

Hurtado et al. 2024 recently published an indicator that is a simple addition of the densities of each of the groups, of macroinvertebrates estimated using the ISO/TSBF method transformed into logarithmic units and multiplied by a different coefficient depending on the groups. A final arithmetic transformation makes it possible to adjust these indicators in a rank from 0.1 to 1.0 and thus to compare them with all possible sites, locally, regionally and globally.

This macrofauna indicator is significantly correlated with all other proxy indicators of soil services, physically linked to hydraulic services, chemically linked to productive capacity and carbon storage, biologically expressing the biodiversity of smaller organisms. This correlation, verified on local and regional scales, is however not verified on a global scale and future research will be needed to delimit the areas in which this correlation is operative.

Our research has produced an indicator of soil macrofauna that can be used as indicator of overall soil quality. Land managers, farmers, technicians or scientists can use it to evaluate the overall capacity of their land to provide the services sought by the community. This indicator can be used within the framework of public policies intended to link the offer of services from conservation efforts to societal demand. These public policies must be based on detailed knowledge of the links between the different metrics proposed to the indicator, e.g. how much C stored in the soil corresponds to an increase from e.g., 0.5 to 0.7 in the value of the indicator. These relationships remain to be established on a local level, but a significant number of local and regional studies show their feasibility and propose methodologies adapted to calibrate these relationships.

References

Hurtado, E., Lavelle, P., Velasquez, E. 2024. A global indicator of soil macroinvertebrates communities to assess soil-based ecosystem services. Applied Soil Ecology, 193, 105138..

Lavelle, P., Mathieu, J., Spain, A., Brown, G., Fragoso, C., Lapied, E., De Aquino, A., Barois, I., Barrios, E., Barros, M.E., Bedano, J.C, Blanchart, E., Caulfield, M., , Chagueza, Y., Dai, J., Decaëns, T., Dominguez, A., Dominguez, Y., Feijoo, A., Folgarait, P., Fonte, S.J., Gorosito, N., Huerta, E., Jimenez, J.J., Kelly, C., Loranger, G., Marchão, R., Marichal, R., Praxedes, C., Rodriguez, L., Rousseau, G., Rousseau, L., Sanabria, C., Suarez, J.C., Tondoh, J.E., De Valença, A., Vanek, S.J., Vasquez, J., Velasquez, E., Webster, E., Zhang, C. 2022. Soi lmacroinvertebrate communities: a worldwide assessment. Global Ecology and Biogeography 31.1261-1276.

Lavelle, P., Rodríguez, N., Arguello, O., Bernal, J., Botero, C., Chaparro, P., Gómez, Y., Gutiérrez, A., Hurtado, M., Loaiza, S., Xiomara Pullido, S., Rodríguez, E., Sanabria, C., Velásquez, E., Fonte, S.J., 2014. Soil ecosystem services and land use in the rapidly changing Orinoco River Basin of Colombia. Agric. Ecosyst. Environ. 185, 106-117.

Velasquez, E. , Lavelle, P. 2019. Soil macrofauna as an indicator for evaluating soil-based ecosystem services in agricultural landscapes. Acta Oecol. 100, 1034446.