Agriculture Reference
In-Depth Information
Soil aggregation
The overall effects of termites on soil aggregate formation and stability depend on the
functional community structure, or the spectrum of ecological strategies represented
among the species of the local termite community. While higher percentages of water-
stable aggregates have been reported by several authors from termite-affected soils
this is not always the case. Garnier-Sillam and Harry (1995) demonstrated differences
in the stabilities of mound materials formed by four sympatric soil-feeding termite
species from Congo rainforests. Judged on the basis of a stability index, materials
from the mounds of two species were more stable, one was similar and one less stable
than those of the adjacent surface soils. These authors noted a much greater structural
stability in materials - in both the mounds and surrounding topsoils - reworked by
the three species that incorporate faecal organic matter into their constructs.
In the same study, mounds of the fungus-cultivating species
Macrotermes mülleri
and their surrounding surface soils, were highly clay-enriched and had the low organic
matter concentrations typical of structures built by these termites. Both the mound wall
materials of
M. mülleri
and associated A1 horizon-soils were markedly less permeable
to water and less stable than the control surface soils (Garnier-Sillam
et al.,
1988b;
Garnier-Sillam, 1989). The surface-sealing effect considered above was also noted in
association with the dispersion of clay-enriched materials from the mounds of
M. mülleri.
Effects on pedogenetic processes
The clay minerals present in termitaria are largely derived from the soil and sometimes
the alteration zone below. In addition to these, 2:1 clay minerals have been found
regularly in the mounds of certain African termites in environments where these are
otherwise uncommon or absent (Boyer, 1982). Boyer reported the widespread presence
of an artificial illite in the mounds of a number of wood-feeding termites although such
neoformation is apparently less common in the soil-feeding termites. The neoformation
of these minerals was considered to result from the direct effects of grinding and
working of mica and other particles with the mandibles in the saliva-rich environment
of the buccal cavity. An indirect effect was also considered to result from placement
within the altered chemical and physical environment of the mounds. Other clay
minerals, calcite, dolomite and certain oxide minerals have also been reported to be
associated with certain African termitaria although Lee and Wood (1971b) could find
no differences between the clay minerals present in the mounds of Australian termites
and in their adjacent soils.
5.3.2
TERMITES AND SOIL ORGANIC MATTER
Termites may profoundly affect SOM dynamics at different scales of time and space.
Short-term effects are associated with digestive processes, whereas storage within
biogenic structures may lead to longer term effects that may extend over scales of years
to decades (Figure IV.65). Such stores may however be partially depleted through
exploitation by the roots of surrounding plants and their associated mycorrhizal fungi.
