Agriculture Reference
In-Depth Information
IV.5
THE TERMITOSPHERE
5.1
Introduction
The termitosphere is defined as the zone of influence of termites within the biosphere.
It comprises that part of the soil and above-ground ecosystem components influenced
by the termite communities present and a rather specific microbial community that,
in combination with the termites' own enzymes, allows them to use almost all the plant
resources available in the ecosystem (see Chapter III.4.3.2.1). The social organisation of
termite populations also allows them to carry out considerable engineering activities. They
produce four categories of organo-mineral biogenic structures that profoundly affect soil
function: epigeic and subterranean nests, surface sheathings and runways, subterranean
galleries and chambers, and aggregates. Some termites also produce holorganic structures
in the form of near-surface and arboreal carton nests, and fungal combs.
Where termite communities are diverse, their functional domain may extend throughout
and below the soil horizons to the tree tops. It may include the external and internal parts
of standing trees and shrubs (both living and dead), standing dead grasses and other
herbaceous plants, the layer of litter on the soil surface (including such materials as dead
leaves and other small plant parts), fallen timber and higher animal faeces. Below ground,
it particularly encompasses the upper soil horizons and, diminishing in influence with
increasing depth, the weathering zone beneath and intermittently down to the phreatic zone.
Termites strongly modify soil physical and chemical properties within their zones
of influence. Over long periods, they substantially influence soil profile development
and some termite groups effect changes to soil organic matter concentration and quality.
The parts of the weathering zone affected will depend on the depth distributions of roots,
whether the termites gather fine particles for their mounds from the weathering zone
and the depth of the water table. The termitosphere also includes plant roots, both living
and in all stages of decomposition.
Termites influence vegetation distribution and productivity directly through their
effects on individual plants and indirectly through the creation of mounds and other
constructs and through their influences on soil properties. Epigeal mounds, subterranean
nests and their associated systems of galleries modify drainage patterns in the immediate
environs of their mounds while certain groups influence soil fertility and thereby affect
plant distributions. While a few species are spectacularly destructive of mans' constructs,
food and other stored materials, few termite species are able to effectively attack healthy,
undamaged plants in natural ecosystems. Nonetheless, a range of termite species causes
severe economic losses to crop and other cultivated plants.
Relationships with micro-organisms are important for termites in several ways.
As considered in Chapter III, their nutrition is partly dependent on interactions with
internal prokaryotes and protists and, in the Macrotermitinae, with an external
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