Michel Lepage

Termites and Soil Properties

This chapter reviews the advances made in our knowledge of the effects of termites on the physical, chemical and biological properties of soils. Emphasis has been placed on more recent contributions, particularly those that explore new concepts in the ecology of termites and soils. There are sections dealing with the effects of termite activity on soil profile development, soil physical properties, soil chemical properties, soil microbiology and plant growth. The physical effects of termites on soils range from micromorphological to soil profile evolution and structure. Recent evidence points to the substantial positive influence of termites on soil hydraulic conductivity and infiltration rates. Their influence on organic matter decomposition and nutrient recycling rates are well recognized and in some landscapes termite mounds act as foci for nutrient redistribution. New information on the microbiology of termite mounds suggests that most are sites of diverse bacterial and fungal activity. Furthermore, the association between mound-building termites and the microbial population present in the structures has a synergistic effect on organic matter decomposition and hence nutrient cycling and availability. Examination of the effects of termite activity on plant production generally indicates a positive influence.

Population Dynamics of Termites

The population dynamics of termites can be described according to the life history strategies evolved by the species in the different phases of colony life, though few studies have involved the search for patterns in termite life history, linked with the evolution of colony fitness. Dispersal is important for the successful establishment of the new colony, as well as reproductive isolation between species. Possible dispersion by budding is recently recognized The colony founding stage appears a very critical step for the future success, especially the balance of energy income with energy losses and the constraints faced by the first brood of workers. During the different phases of the colony growth, trade-offs are operating within the nest population. With colony sizes and caste dynamics, it is difficult to identify general patterns, due to variable reliability of data. Different methods have been adopted, from direct total sampling of the nest population to indirect estimates, including the mark-release-recapture method. The strategies of resource use within and between colonies are one of the major factors regulating nest density. Functional group assemblages and the territoriality of termite nests could explain their spatial patterns. Intraspecific competition, together with predation are major constraints in the population dynamics of termites.

Influence of large termitaria on soil characteristics, soil water regime, and tree leaf shedding pattern in a West African savanna

Termitaria are major sites of functional heterogeneity in tropical ecosystems, through their strong influence on soil characteristics, in particular soil physico-chemical properties and water status. These factors have important consequences on nutrient availability for plants, plant spatial distribution, and vegetation dynamics. However, comprehensive information about the influence of termite-rehandled soil on soil water regime is lacking. In a humid shrubby savanna, we characterized the spatial variations in soil texture, soil structure and maximum soil water content available for plants (AWC max) induced by a large termite mound, at three deepths (0–0.10, 0.20–0.30 and 0.50–0.60 m). In addition, during a three month period at the end of the rainy season, soil water potential was surveyed by matrix sensors located on the termite mound and in the surrounding soil at the same depths and for the 80–90 cm layer. Concurrently, the leaf shedding patterns of two coexisting deciduous shrub species exhibiting contrasted soil water uptake patterns were compared for individuals located on termite mounds and in undisturbed control areas. For all the soil layers studied, clay and silt contents were higher for the mound soil. Total soil clods porosity was higher on the mound than in control areas, particularly in the 0.20-0.60 m layer, and mound soil exhibited a high shrinking/swelling capacity. AWCmax of the 0-0.60 m soil layer was substantially higher on the termite mound (112 mm) than in the surroundings (84 mm). Furthermore, during the beginning of the dry season, soil water potential measured in situ for the 0.20-0.90 m soil layer was higher on the mound than in the control soil. In contrast, soil water potential of the 0-0.10 m soil layer was similar on the mound and in the control soil. In the middle of the dry season, the leaf shedding pattern of Crossopteryx febrifuga shrubs (which have limited access to soil layers below 0.60 m) located on mounds was less pronounced than that of individuals located on control soil. In contrast, the leaf shedding pattern of the shrub Cussonia barteri (which has a good access to deep soil layers) was not influenced by the termite mound. We conclude that in this savanna ecosystem, termite mounds appear as peculiar sites which exhibit improved soil water availability for plants in upper soil layers, and significantly influence aspects of plant function. Implications of these results for understanding and modelling savanna function and dynamics, and particularly competitive interactions between plant species, are discussed.

The role of subterranean fungus comb chambers (isoptera, macrotermitinae) in soil nitrogen cycling in a preforest savanna (côte divoire)

Abstract Stimulation of total microbial activity (CO 2 production), and soil organic nitrogen mineralization by the subterranean fungus-growing termite Ancistrotermes cavithorax was studied. Soil from the walls of the fungus comb chambers and control soil free from termite and root activities were sampled from the field and held at 28°C for 30 days. CO 2 . NH + 4 -N and NO − 3 -N production were regularly measured. NO 3 − -N production was negligible and only ammonification occurred. The more the soil has been worked by termites, the greater the amounts of CO 2 and ammonia produced. This increased activity of microflora is probably related to the supply of energy-rich substrates by termites.

Impact of subterranean fungus-growing termites (Isoptera, Macrotermitiane) on chosen soil properties in a West African savanna

Fungus-growing termites (Isoptera, Macrotermitinae) play an important role in tropical ecosystems in modifying soil physical properties. Most of the literature regarding the impact of termites on soil properties refers to termite epigeous mounds. In spite of their abundance and activity in African savannas, few studies deal with the properties of underground nest structures (fungus-comb chambers) built by subterranean Macrotermitinae termites. We tested whether these termites significantly modify the soil physico-chemical properties within their nests in a humid tropical savanna and whether these effects are different for two termite species with differing building behaviour. Termite-worked soil material was collected from fungus-comb chamber walls of two widespread species: Ancistrotermes cavithorax, which builds diffuse and ephemeral nests and Odontotermes nr pauperans, which most often builds concentrated and permanent nests for a comparatively much longer period of time. Neither species influenced soil pH but both significantly modified soil texture and C-N content in their nest structures. A strong impact on clay-particle size was also detected but no significant differences in clay mineralogy. Thus Odontotermes has a greater effect on soil properties, that could be explained by its building behaviour and the concentration in space of its nest units. Therefore, spatial pattern and life-span of fungus-comb chambers should be an important parameter to be considered in the functional role of subterranean Macrotermitinae termites in the savanna.

Effect of different termite feeding groups on P sorption and P availability in African and South American savannas

Nest structures of six termite species, four with epigeous (above-ground) and two with subterranean nests were analysed to find out how their building and feeding habits could be related to their nests phosphorus status compared with control soils. Termite nest structure was found to affect significantly the P status in savanna soils: mounds of the African Trinervitermes geminatus and the South American Nasutitermes ephratae (both grass-feeders) displayed a greater amount of available P, especially in the inner part of the nest, than the surrounding soil. The abundant quantities of dead grass material stored in the mound can explain the available soil P increase. A similar increase in P availability was also found for the soil-feeder Cubitermes severus. In mounds of Macrotermes bellicosus, on the other hand, there was a drastic increase in P sorption (and a corresponding decrease in available P) compared to adjacent soils, which was attributed to the building strategy of this species. M. bellicosus selected clay from subsoil to build its nest structure. The data obtained for the subterranean species Ancistrotermes cavithorax and Microtermes toumodiensis indicated also that there is an increase in P sorption in mounds when compared with associated topsoils. Consequently, the nest structures of only certain termite species should be considered, and utilised, as a soil amendment in place of fertilisers. This impact on the P cycle in savannas seems to be related to the termite feeding status and to the type of material utilised in nest building. This should be taken into account before using termite nest material in soil fertility status improvement.

Nitrogen transformations associated with termite biogenic structures in a dry savanna ecosystem

Soil structures built by litter-feeding termites are one of the main soil translocation processes in dry tropical savanna. Runways (soil sheeting) made of soil particles cemented with salivary secretions covering the dead plant pieces collected on the ground surface represent the main soil structures. The aim of this study was to determine the impact of this soil engineering activity on the microbially-mediated N transformations (nitrification and denitrification) associated with termite sheeting. We investigated the hypothesis that the physicochemical and microbial properties of termite soil sheeting depend on (i) the termite species and (ii) the type of organic substrate consumed. Soil sheeting built by two of the main savanna species, Macrotermes subhyalinus and Odontotermes nilensis, were sampled on field plots treated with three different types of litter (Acacia leaves, millet straw, both whole and ground (< 500 µm), and cattle manure). The soil’s organic C, total N, inorganic N, microbial biomass, potential CO2 respiration, nitrification and denitrification were measured. For both termite species and all types of litter, the soil sheeting was enriched in organic C and inorganic N, resulting in an increase in soil respiration, whereas the microbial biomass was unchanged with respect to the reference soil. With the exception of the soil nitrification potential, the type of organic substrate did not significantly affect the properties of the soil sheeting measured. However, the nitrogen cycle was affected differently by the two termite species. In O. nilensis sheeting, the denitrification potential was reduced with respect to the reference soil, whereas the nitrification potential was inhibited in M. subhyalinus sheeting. The changes in the nitrogen cycle processes resulted in an increase in NH4+ and NO3− in the termite soil sheeting, increasing the availability of nitrogen to plants. This study reinforces the importance of termites as a keystone savanna group whose building activities have an effect on tropical soil mineralization.

Environmental Constraints on Living Organisms

The high rainfall occurring in Lamto savannas directly reduces the role of water as a limiting factor. It also promotes fire as the key driving factor, especially for tree dynamics. As a result of both of these factors, nutrient losses are potentially high and thus the apparent soil nutrient poverty is reinforced. It is therefore not surprising that nutrients become a major limiting factor, both for grass production and for herbivore diversity. Lamto savannas could thus be qualified as oligotrophic savannas.

Soil Organic Inputs and Water Conservation Practices Are the Keys of the Sustainable Farming Systems in the Sub-Sahelian Zone of Burkina Faso

Rapid population growth and climatic change threaten the sustainability of natural resources in the sub-Sahelian region of West Africa. Environmental changes and degradations can be mitigated by the adaptation of improved farming practices. In Ziga, located in Yatenga region, a research program was implemented between 1980 and 1987. The aim of this research was to describe and to analyze manure practice management and to present their determinants, for deducing their effects on farming system sustainability. In 2005, a survey in the same village was carried out to assess the evolution of farming practices. According to the inquiry made, two practices, called “zai” and “djengo,” were largely used in cereal crop production. The characteristics of “zai” and “djengo” practices were assessed and their effects on grain crop yields measured. The “zai” characteristics depend on the farm manure availability. Zai practice is a complex soil restoration system using manure localization and runoff capture in micro-watersheds on degraded soils to improve their productivity. In addition, another practice called the “djengo” that has not been described in previous works was noticed in Ziga. Like the “zai,” “djengo” is a technique of soil and water conservation characterized by localized supply of organic matter. In the case of “djengo,” the micro-basin is dug after the first rain. The “djengo” is less expensive in time. These two practices revealed a strategy of farming system intensification by localization of organic and mineral fertilization, as well as a better management of rainwater. Tree regeneration occurs where “zai” or “djengo” practice is used. This study highlights the necessity of better controlling soil, water, and organic matter to improve agrosystem viability as a key for the success of the Green Revolution in sub-Saharan Africa.