Gamasina

Danra, Dieudonné Djackba, Nukenine, Elias Nchiwan & Koehler, Hartmut, 2018, Soil Gamasina from savanna and ReviTec site of Ngaoundéré (Adamawa, Cameroon): abundance and species diversity, Soil Organisms 90 (3), pp. 187-198 : 187-188

1.1 Gamasina as bioindicators for effective soil rehabilitation

Soil degradation is a global problem that is especially severe in the tropics and sub-tropics. It is characterized by the decline in quality or even loss of ecosystem goods and services ( Lal 2015). Global population of 7.3 billion in 2015 is projected to increase to 9.5 billion by 2050, requiring to increase agricultural production by ~70 % between 2005 and 2050. Soil degradation, characterized by decline in quality and decrease in ecosystem goods and services, is a major constraint to achieving the required increase in agricultural production. Soil is a non-renewable resource on human time scales with its vulnerability to degradation depending on complex interactions between processes, factors and causes occurring at a range of spatial and temporal scales. Among the major soil degradation processes are accelerated erosion and depletion of the soil organic carbon (SOC). Unadapted land use practices are the main cause. In savanna ecosystems, deforestation and overgrazing are the predominant anthropogenic drivers ( Osman 2014). Some 38 % of the agricultural area of the earth can be considered as degraded and the share of degraded territories in Africa is 65 % ( Osman 2014). Bai et al. (2008) estimated the degrading area in Cameroon at 151,605 km 2 which represents 32 % of the territory, with a strong bias towards the dry and populated Northern part of the country (North and Far-North regions). More than 26 % of the population is affected. Soil degradation is continuously increasing due to population growth (firewood exploitation) and increasing meat demand (overgrazing).

ReviTec is an ecological rehabilitation approach developed by the Bremen-based partnership KeKo - Kesel, Koehler & partners, biologists, in co-operation with the Centre for Environmental Research and Technology (UFT) of the University of Bremen ( Koehler et al. 2006). ReviTec is based on experience from long-term ecological research ( Koehler & Müller 2003, Koehler & Melecis 2010). The modular design of ReviTec covers three levels of scale with various functions. The basic module is a bag of degradable fabric for initial erosion control, filled with substrate (30 L). The substrate is amended with abiotic and biotic elements (bioactivation) to initiate and accelerate ecological succession ( Koehler 2005, Koehler et al. 2006, Kesel et al. 2006) and to rehabilitate essential ecosystem services of soil. In Cameroon, four demonstration, teaching and research sites have been established since 2012: one on the premises of University of Ngaoundéré (Adamawa region) and three near Maroua (Far North; East Sudanian savanna) ( Kesel 2012, Koehler et al. 2013)). The preparation of the ReviTec site in Ngaoundéré in 2012 included experimental degradation (removal of vegetation and topsoil).

Soils capable to deliver the ecosystem services mentioned above are alive. Apart from above-ground vegetation, soil biota offer important information on the state of the soil. Soil biota are vital for life on earth which is based on the ecosystem services that result from their interactions with the abiotic environment, such as soil fertility, biogenic soil stabilization, water infiltration and storage, carbon sequestration. Pressure on the soil biota undermine the provisioning of ecosystem services ( Gardi et al. 2013, Wagg et al. 2014).

In our study, we focus on predatory mites ( Gamasina ), which are considered to be valuable bioindicators ( Karg & Freier 1995, Koehler 1997, Koehler 1999, Pérez-Velázquez et al. 2011). Gamasina occur in relatively modest abundances, but in high numbers of species ( Petersen & Luxton 1982, Coja & Bruckner 2006). They are sensitive to anthropogenic and natural disturbances ( Koehler 1999, Coja & Bruckner 2006, Bedano & Ruf 2007).

The overarching objective of this study is to contribute to the assessment of the efficiency of the ReviTec approach in a Central African context. The abundance, diversity and ecological roles of microarthropods in Sub Sahara African soil ecosystems are poorly known and understood. Until now there are only a few microarthropod studies of the Sahel and the savannas bordering South of it (e.g. Mosadoluwa & Buny 2000, Iloba & Ekrabene 2008, Gbarakoro et al. 2010, N’Dri & André 2011, Okiwelu et al. 2012, N’Dri et al. 2016). For Cameroonian savanna, the knowledge on soil microarthropods is limited to Oribatida species from the ReviTec site of Ngaoundéré, Adamawa region ( Ermilov & Koehler 2017) and to two unpublished master’s theses from the University of Ngaoundéré ( Danra 2014, Djoussi 2015).

As parameters for this assessment, we use abundance, species diversity and community structure of Gamasina under three selected treatments and two controls. We provide baseline and reference data against which planned future savanna and woodland restoration can be measured.

We hypothesize that: (i) compared to the savanna (sav) Gamasina abundance and species composition would be lower in ReviTec control (ctrl1). The relatively low colonization of ctrl1 is expected to reflect the experimental degradation of the site. (ii) The compost amendments are expected to have a positive effect on Gamasina abundance and diversity, with a positive effect of the biochar amendments.