Geoscience Reference
In-Depth Information
sustainable land use in deserts, based on the first and second laws of thermodynamics,
are therefore offered in this final chapter, together with two other key preconditions,
one based on social justice, the other based on the vital role of plants in minimising
or avoiding land degradation.
26.2 Prerequisites for achieving sustainable use of deserts
We have discussed a number of examples of land degradation in the drier regions of the
world that were caused by human activities and climatic variations (
Chapter 24
)and
have also considered how possible future changes in climate may have an impact upon
the desert world (
Chapter 25
). It is now appropriate to consider some fundamental
principles of sustainable land use that should underpin any human interactions with
these ecologically fragile regions.
We begin with the proposition that matter and energy are interchangeable, a pro-
position expressed in 1905 by Einstein in concise mathematical form in his theory
of special relativity. In classical physics, the first law of thermodynamics states that
energy can neither be created nor destroyed, so a system can lose or gain energy only
to the extent to which it passes it to, or takes it from, its immediate surroundings. (The
concept of stream power, discussed in
Chapter 10
, nicely illustrates this point.) The
second law of thermodynamics states that all natural processes lead to an increase in
the entropy of the system concerned. Entropy is a measure of the unavailable energy
in a thermodynamic system and reflects the state of disorder of that system. (Before
beginning work on this volume, my topics and papers were neatly arranged in what I
consider good order; by the end of the writing process, they were scattered in disarray:
entropy within the system had increased.) We are now in a position to reformulate the
first and second laws of thermodynamics in the form of guiding principles for sus-
tainable use of drylands, following the path laid out by the polymath cancer specialist
Dr Karl-Henrik Robert (
1992
) in his topic entitled the
Nodvandiga Steget
(Swedish
for 'natural step'). The fourth prerequisite is based on an appeal to social justice, and
it is explained in number 4.
1. From the outset, we need to recognise that the only source of a
net
increase in primary
productivity on this earth is from solar energy acting through photosynthesis to increase
plant matter. All else is simply applying energy to recycling earth materials (such as coal
and iron) into other forms of matter (such as steel and carbon dioxide). For this process of
photosynthesis to operate effectively, biomass needs to be protected and increased and not,
as is often the case at present, wantonly destroyed.
2. From classical thermodynamics, we can deduce that we should not
systematically
remove
materials from any natural or humanly modified system at a rate faster than that at which
they can be replaced. (For instance, soils need to be maintained or replenished at about
the same rate at which they develop through rock or sediment weathering and biological
activity.)
