Geoscience Reference
In-Depth Information
1999. The ways of living typical for a species can include lasting changes to the
environment. Such changes are effective longer than the lifespan of the generation
undertaking the changes. An ecological inheritance is the result. Dens and burrows
are a good example for the heritable parts of a niche. Such constructed niches can
be quite permanent structures, used (and changed) by several generations of
inhabitants. Progeny inherit a changed lifeworld, which then acts as a selective
force for future generations. Not only the environmental conditions as such, but also
an ecological inheritance (e.g. the burrow) are a means of natural selection.
Humans construct their ecological niche by building their version of dens,
houses, and by permanently and semi-permanently altering natural systems. The
lasting changes they make act as means of natural selection on them. Soils left from
one generation of humans to the next can also bear lasting, discernible marks of
previous cultivation, leaving a particular ecological inheritance.
The
re to alter
vegetation, because vegetation cover is one of the main forces relevant in pedo-
genesis. Soil formation was changed when
rst such change is due to the widespread and extensive use of
res in the post-glacial steppes were set
at times when they might not have occurred naturally, and at human-induced
frequencies.
The second and perhaps most outstanding change is the development of agri-
culture, with smaller distinctions to be made for the shift
rst from hoe to plow, and
then to the moldboard plow. The most important factor changing pedogenesis in
agriculture is again the change of vegetation, in particular the invention of mono-
culture. The uppermost layer of soils was also changed mechanically by plows. In
addition to changing the mechanical properties of soils, in
uencing root growth and
water holding capacity, plowing changed the micro-habitats of soil organisms. The
use of fallowing is somewhat similar to plowing in its effects. Fallowing in addition
changes the water balance of soils, as does the change from fallowing to a rotation
system, which does also impact soil biota.
Manuring is yet another important intervention into soil ecosystems, bringing in
food for soil organisms. The organisms destroy the larger remains of vegetation and
residues of animal metabolism into smaller organic and inorganic compounds,
ideally into a chemical form (as ions) which can be taken up by plant roots as
nutrients. Soil organism turnover is speeded up by the extra food available, and the
ecological niche of the manured soil is made up by organisms in different relative
abundances.
Marling or liming changes the acidity of soils and therefore again intervenes into
soil biota communities, shifting the balance from bacteria to fungi. Finally, irri-
gation techniques need to be mentioned. Besides the fundamental change in water
availability through irrigation, the chemical balance of the soil is changed. Tradi-
tional surface and ground water sources contain dissolved minerals that remain at
the soil surface when the water evaporates or is transpired by plants, salinization
results. The innovation of
elds to cleanse the soil of accumulated
salts marks an early change, as does the 20th century invention of drip irrigation
which reduces the amount of water needed by placing it directly at the plant.
ooding irrigated
