FUNCTIONING OF THE SOIL SYSTEM - Soil Ecology - page 506

5.2.2.3 Aggregates, voids and other structures

In addition to the biofabrics discussed in Chapter II, a wide range of micromorphological
structures have been described from the mounds and galleries of a range of termites
(see Sleeman and Brewer (1972) for those of a number of Australian species and
Mermut et al. (1984) for four species of Macrotermitinae). The structures of the fungus-
cultivating species (Macrotermitinae) were shown to be distinct from those of most
other termites in that they do not incorporate faeces into their mound structures.
Wielemaker (1984) and Kooyman and Onck (1987) used similar methods to categorise
termite-derived structures in gallery systems distant from mounds. Garnier-Sillam et al.
(1985) described organo-mineral micro-aggregate structures from the faeces of four
species of termites of different ecological strategies and Eschenbrenner (1986) noted
the similarity of aggregates found in certain termite-inhabited soils and those from
termite mounds.
In addition to the gallery systems described above, termites create a range of voids
both in epigeal mounds and within the soil. In both locations, these voids differ widely
in size and in shape (Table I.10) and may serve as nests, food storage areas, burial
chambers and, in some species of the subfamily Macrotermitinae, as chambers within
which the colony's fungus combs are located. Such voids are not static: they are created
by the termites to serve their designated purposes and, following this may be actively
backfilled with organic or inorganic materials or subject to infilling by soil particles
moving under the influence of gravity or in flows of water. Such voids may also be occu-
pied by termites distinct from the original creators or other animals, and re-modelled
according to their specific designs.
In stable environments, the continued cycles of void creation and infilling to which
termites contribute have a considerable influence on landscape dynamics and soil
formation. Humphreys (1994) described the systems of voids and related biologically-
formed aggregates of termites, ants and other animals from sandy ultisols and entisols
in southeastern Australia. He concluded that approximately 8 % of the surface A and
E horizons consisted of recognisable faunally-derived structures and that the topsoil
at the site formed a biomantle (Chapter II.3.3.2).
Other important structures built by termites include surface covers and runways.
The former are temporary structures built over food materials to provide shelter for
the termites from predators and from desiccation; most of these structures are constructed
predominantly of inorganic soil materials. Runways are hollow linear structures formed
by termites to cover their movements over exposed areas and may be constructed
predominantly of either organic or inorganic materials.
Two examples of predominantly organic runways are those built by the higher
Australian wood-feeding termites Nasutitermes graveolus and Nasutitermes walkeri. Their
nests are built on the exteriors of trees, often many metres above the ground, although
workers forage for woody materials around the bases of their host trees.
The nests are joined to the ground by runways which are normally built over the bark
of most tree species, but also within grooves cut through the soft flaky bark of Melaleuca
and Lophostemon (Myrtaceae). Runways constructed by these species may be 1-2 cm
across and are constructed of carton; they appear to contain little inorganic material.