per hectare per year. According to the Australian geologist T. Ron
Paton, the record in this activity is ten tons of earth per hectare
per year, established by species living in sub-tropical regions,
whether humid or temperate. Thus ants, albeit quite unwittingly,
bring about considerable changes in the physical properties of the
soil, by increasing its porosity and improving drainage and aer-
ation. As diggers and delvers, they may be not quite as good at
these jobs as earthworms; but by being more widely distributed
on the face of the planet, the total effect of their earth-moving and
soil-renewing activity is probably equivalent to that of the worms.
Ants do not only turn over the earth. They also drag scraps of
vegetable material into their nests and accumulate refuse and
excreta, the effect of which is to alter the chemical properties of
the soil. The surroundings of ants’ nests are rich in mineral
compounds, especially nitrogen, phosphorous, and potassium,
as well as in organic matter. In a single chamber created by
Brazilian Atta capiguara (a space, mind you, that measured 1.5
metres across and five metres high), the amount of organic
material found amounted to 500 kilograms. It should be added
that, for the purpose of cultivating their fungus, Atta bring back to
the nest huge quantities of leaves; and in the closed space of the
underground chambers this vegetable matter decomposes much
more rapidly than it would if left to its own devices. In humid
forests, where it is generally difficult for nutrients to penetrate
the soil, the leaf-cutting species are in fact largely responsible
for the deep fertilization of the ground. Generally speak ing,
though, the effect of ants’ nests on their surroundings is to enrich
them with humus. So, indirectly, the ‘ecosystem engineers’ often
have a beneficial effect on agricultural production, especially in
grasslands where the soil is naturally poor, as Folgarait has estab-
lished. As for harvester ants, they contribute to the spread of
seeds, since they lose some of their booty along the way to the
nest. In the many parts of the world where harvesters occur, from
Europe and America to Africa and Australia, they considerably
A HUGE IMPACT ON THE ENVIRONMENT
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