SOIL FORMATION - Soil Ecology - page 152

Table II.2 illustrates the approximate minimum times required for fully-developed
profiles to differentiate from their parent materials in selected orders of Soil Taxonomy
(Birkeland, 1984). However, full development within these orders may take
considerably longer. Further, a number of soils may develop sufficiently over
time to require classification into other orders. As pointed out by Birkeland (1984),
categorisation of the landscape distributions of soils at the level of order provides
information on the relative and approximate actual ages of the different parts.

2.4 Biota

As developed further in later chapters, the biota is the major factor in soil formation in
that its effects define the difference between soils and 'not soils'. The biota has continuing
inputs into soil genesis from its earliest stages and in soil maintenance and long-term
development. In the past, the effects of this factor have been wholly or largely attributed
to the effects of higher plants (see, for example, Jenny, 1941; Birkeland, 1984).
However, it is clear that the important roles of other sections of the biota must not be
neglected if further progress is to be made in understanding soil formation (see, for
example, Johnson and Hole, 1994). The biotic factor is now considered to include the
trophic and non-trophic effects (Jones et al., 1997) of all living organisms that impinge
on the soil, both directly and through the products of their metabolism and decay.
The initial colonisation of a new parent material by organisms marks the start of its
stabilisation and of soil formation. Links between initial ecosystem establishment and
development processes and those of soil formation are so complete that it is inappropriate