Soil Carbon Transition Curves: Reversal of Land Degradation through Management of Soil Organic Matter for Multiple Benefits - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 28

linked through a conceptual model of land
(soil) degradation and its recovery. Finally,
we integrate these concepts to derive policy
implications for global environmental sus-
tainability, while defining and seeking syn-
ergies between soil functions that develop
through increasing soil carbon stocks.

of local changes in soil carbon stocks through
the environment. This impact chain begins
with the understanding that soil function is
related intimately to soil structure - the for-
mation of water-stable soil aggregates that
can be influenced positively by increasing
soil carbon stocks (Chapter 6, this volume)
( Fig. 3.1 ).
Water-stable aggregates provide phys-
ical protection and regulate habitat for all
sizes of biota and the associated transform-
ation of carbon and nutrients within the
soil, increasing nutrient availability due to
improved soil drainage and aeration, as
well as energy for microbial heterotrophic
processes and belowground biodiversity
(Chapters 1, 8 and 11, this volume). The
synergy of the above physical, chemical and
biological characteristics leads to higher
land productivity, improved water infiltra-
tion and retention, and nutrient transform-
ations, among other processes. Good soil
structure (i.e. high amounts of water-stable
aggregates) improves the capacity of soils to
resist changes, offering a buffering function
(or resilience), resulting in improved regu-
lation of the processes that sustain soil
functions and services (Box 3.1).
Fundamental to the above is the recog-
nition that an impact chain exists for each
of the ecosystem services listed in the rows
of Table 3.1 . These impact chains link
changes in soil organic matter to the deliv-
ery of benefits at different scales. Narratives
of a number of these impact chains have
been outlined in the literature, demonstrat-
ing that gains and losses in soil organic
matter at the local level generally are ex-
pected to lead to an associated gain or loss
of benefits for a range of services at the
local, landscape and global levels (Victoria
et al ., 2012). If this correlation generally
holds, it implies a wide-ranging (water and
nutrient) buffering role for soil organic mat-
ter (Chapter 8, this volume).

Land-use Change Pathways and Soil
Carbon Transition Stages

Local and global benefits and critical
soil services

Land-use decisions are driven by the ex-
pected benefits and costs from the perspec-
tive of the primary land owner, but they can
be shaped by rules and incentives that reflect
external stakes in how land is managed. The
benefits that humans derive from agroecosys-
tems can be analysed under four groups of
ecosystem services: provisioning (allowing
the harvesting of 'goods'), regulating, cultural
and supporting services (MA, 2005). Many of
these are related to soil organic matter con-
tent and are often described collectively as a
state of 'soil health' (Chapter 14, this volume)
or as soil functions (COM(2006) 231, 2006).
Table 3.1 gives examples of ecosystem ser-
vices, distinguishing benefits at three scales:
local (the level at which the primary land
users operate), landscape or watershed, and
global scale (cf. Chapter 15, this volume).
In search of ways to mitigate climate
change, the potential of soil to sequester CO 2
at the global level has put a spotlight on the
multiple and substantial benefits that can be
achieved through increasing soil carbon
stocks worldwide (UNEP, 2012a). Additional
benefits of soil carbon, beyond carbon stor-
age for mitigation of greenhouse gas emis-
sions, arise principally from the central role
of soil organic matter in a range of soil func-
tions that include food production, filtering
water, transforming nutrients and maintain-
ing habitat and biodiversity (Chapters 1 and 14,
this volume). The role of soil carbon in de-
livering benefits at each scale can be assessed
by considering the impact chain; the link-
ages between sets of biological, chemical and
physical processes that propagate the impact

Soil carbon transition stages

Most of the ecosystem services that are
linked to soil carbon are aligned positively
with soil organic matter content, and thus