SOIL MACROFAUNA ABUNDANCE AND DIVERSITY UNDER TREES WOODLOTS IN EASTERN DEMOCRATIC REPUBLIC OF CONGO

Abstract

Background. Soil macrofauna are key components of agricultural processes due to their ability to enhance major soil functions such as nutrient cycling and organic matter decomposition. Yet, in the Democratic Republic of Congo, their compositions and dynamics are threatened by the intensification of agricultural activities on small pieces of land characterised by integration of trees into crops farms. Objective. To assess the effect of diverse tree species on soil macrofauna abundance and diversity and selected soil chemical properties. Methodology. Eucalyptus saligna and Grevillea robusta woodlots were considered for this study, together with a natural forest, an indigenous tree (Ficus benghalensis) and an agricultural farm (with beans grown on it), and were set up as treatments. A complete randomised design was used whereby each treatment was replicated five times in four different locations. Soil macrofauna were collected using soil monoliths as well as Pitfall and Winkler traps, while composite soil samples were taken from monoliths after macrofauna catching. Soil macrofauna were identified at the order level and soil nutrients analysed in the laboratory following standard procedures. The analysis of variance and correlations were carried out using R programming software. Results. Soils under natural forest showed significantly low pH as compared to grevillea, eucalyptus, ficus and beans. Soil C levels were significantly low in beans (33.6 g kg-1), than grevillea (45.0 g kg-1), ficus and eucalyptus (46.2 g kg-1 and 47.7 g kg-1), and natural forest (60.7 g kg-1), whereas N was significantly low in beans (3.7 g kg-1) as compared to ficus and eucalyptus (4.3 g kg-1 and 4.7 g kg-1), and grevillea and natural forest (5.3 g kg-1 and 5.3 g kg-1). Soil Ca was significantly higher under ficus, than beans, grevillea, natural forest and eucalyptus. Same trends were observed for P, K and Mg. Highly significant (p <0.05) macrofauna abundance was observed for Araneae (spiders) under beans with an average of 7.3 individuals, compared to grevillea and eucalyptus (6.0 and 5.1 individuals respectively), and natural forest and ficus (3.3 and 2.8 individuals respectively). Inversely, Coleoptera (beetles) were significantly lower under beans than natural forest, ficus, eucalyptus and grevillea, whereas Haplotaxida (earthworms) and Hymenoptera were both higher under ficus. Soils in natural forest and ficus revealed highly significant richness index (9.8 and 9.5) than grevillea and eucalyptus (9.0 and 8.8) and beans (7.5). The Shannon diversity index together with the evenness index were both significantly (p <0.05) higher under beans and lower under ficus. Implication. The diversification of soil macrofauna under specific tree species for this study indicates their importance towards the preservation of soil macrofauna communities whose activities impact on soil chemical and physical properties and contribute to maintaining soil ecological functions. Conclusion. Thus, in order to maximize positive interactions between tree species, soil macrofauna and soil properties, hence to sustain soil health and maintain a better soil biodiversity, it is important to take into consideration the integration of appropriate tree species into farming systems.