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2.3 Biological Characteristics
Ants and Termites
Harvester ants, common in arid and semi-
arid grasslands, can influence pH, nitrogen,
phosphorus, potassium, the presence and
proliferation of mycorrhizae, bulk density,
and soil moisture (Snyder et al., 2002).
At the Jornada Basin Long Term Ecological
Research Station, termites have been shown
to increase water infiltration through their nest
building activities (Elkins et al., 1986). Additionally,
as termite numbers and activity increases,
organic matter is consumed and removed from
the soil surface and root zone (Nash & Whitford,
1995). They also affect the soil profile through
physical mixing by bringing material from the
lower soil horizons up to the surface.
Earthworms
Earthworms feed on dead and decomposing
organic material and microbes, and drag
them from the soil surface to deeper layers.
In relocating organic matter, they remove this
top layer from the soil. It has been found that
earthworms actually deplete the O horizon of
organic matter (Brady & Weil, 2010), which can
have substantial effects on the soil ecosystem.
Earthworms burrow through the soil, creating
macropores, and as they eat, they excrete
both digested organic matter and soil mineral
particles, which can increase aggregate stability.
These casts are high in organic matter as well
as bacteria and available plant nutrients.
What should we expect with earthworms in
semi-arid soils? Earthworms prefer cool, moist
well-aerated soils, with ample supplies of
organic matter on the surface. Soils of this type
are not typical in New Mexico or Colorado.
Earthworms are also very sensitive to salinity,
which is a common issue in dryland soils.
Discussion –
What do earthworms do?
What soil physical characteristics might
earthworms affect by their activities? What
chemical characteristics? What biological
characteristics?
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Dung Beetles
In the short grass prairie, which was
once dominated by the American bison,
dung beetles serve an important role in
decomposing and transporting dung to
lower soil layers. This action also serves
to increase soil nitrogen, water infiltration,
and dispersal of the seeds in dung (Barber
et al., 2019). Dung beetles use both cattle
and bison dung, but with the removal
of the bison from their historical range,
which included nearly all of what is now
New Mexico and Colorado, dung beetle
populations have been highly disturbed.
Both native and invasive dung beetle
species can be found in both states.