SOIL FORMATION - Soil Ecology - page 175

Termites
In the tropical areas of the world where they are dominant, termites can be potent agents
of pedogenetic change and their activities may extend throughout the whole soil profile
and well into the underlying regolith. The mass of soil brought to the surface annually
to be built into mounds and temporary foraging shelters has been estimated at up to 1.8
Mg , in African savannas (Nye, 1955c; Lepage, 1974; Roose and Lelong, 1976).
Roose (1980), however, calculated that, in the savannas of Burkina Faso, 4 to 33 % of
this clay-enriched soil was washed away by sheet erosion, resulting in the formation of
a poor, sandy top soil (Josens, 1983).
To a limited degree, termites select the sizes of the particles that they ingest or transport.
Most select the finer particles, although this varies with the soil and species involved
(Lee and Wood, 1971a). For example, Kemp (1955) found that the mounds of Cubitermes
sankurensis have a small proportion of particles between 100 and in diameter but
greater proportions less than and greater than This results from the trans-
port of fine particles in their crops while larger particles are carried in their mandibles.
Wielemaker (1984) reported the upwards and downwards transport of soil materials
by termites in Kenyan soils and the illuviation of clays through galleries created by
these animals.
The effects of termites on soils are further considered in Chapter IV.
Ants
Although perhaps of less pedogenetic importance than termites, ants are ubiquitous,
especially in the tropics and may effect substantial changes to the soil (see also Chapter III).
At a local scale, ant bioturbation (Lévieux, 1976; Cowan et al ., 1985; Lockaby and
Adams 1985) involves continuing profile modification with differences between species
largely related to their nesting habits. Such effects also depend on whether they are mound-
building species or nest underground and whether the ground is sloping or not so that
bioturbated materials deposited on the surface may eventually be transported downslope.
Within the soil, their effects form part of continuing cycles of void formation and
infilling and they contribute to processes influencing infiltration, gas exchange, organic
matter incorporation and nutrient flows in the ecosystems of which they form a part.
Information available on their roles in soil processes is limited to effects recorded from
a small range of sites and species and, beyond acknowledging their undoubted impor-
tance, only limited generalisation appears possible at our current state of knowledge.
Many ants build sub-surface nests and their contributions to soil mixing and transport
have been considered as largely restricted to the surface deposition of soil excavated
from their subterranean nests on the surface. The amounts may be considerable. Lévieux
(1976) estimated that 0.3 Mg of B horizon material was deposited on the soil
surface by the ant Paltothyreus tarsatus in the humid savannas of the Côte d'Ivoire.
Lyford (1963) reported the surface deposition of some 0.6 Mg over the course of one
year in a North American oak forest. In a Nearctic desert environment, Whitford et al.
(1986) estimated that 0.8 Mg was moved to the surface during the same time period,
a similar amount to that reported by Humphreys (1981) from an open forest environment
in southeastern Australia.