Impacts of Land-use Change on Carbon Stocks and Dynamics in Central-southern South American Biomes: Cerrado, Atlantic Forest and Southern Grasslands - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 244

Introduction

of carbon sequestration by soils in regions
prone to intense land-use change processes
in order to be able to improve climate change
mitigation and adaptation in land use.
In this chapter, we describe the main
processes of past and current agricultural ex-
pansion in the Cerrado, Southern Grasslands
and the Atlantic Forest, representative biomes
of the central and south-eastern portions of
South America. We review data derived from
published research on the impact assess-
ments of land-use and management changes
in the region with a focus on carbon stocks
and dynamics. We end with suggestions of
land-use and management-related policies,
as well as soil and crop management options,
to mitigate some of the reported environmen-
tal impacts of LUC in the region.

The central and south-eastern part of the
South American continent is characterized
by heterogeneous biomes and ecosystems,
with diverse soil, vegetation, climatic, geo-
logic, hydrologic and social configurations
(Plate 13). The varying topography adds
natural complexity to the region, resulting
in a combination of extensive savannah-like
plateaus (Cerrado in Brazil), grasslands (Pam-
pas in Argentina and Uruguay), the largest
tropical wetland area in the world (Pantanal
in Brazil) and both dry and humid forest bi-
omes (Espinal, Chaco and Atlantic Forests,
respectively). Together with this environ-
mental heterogeneity, the diverse human so-
cieties that compose the region have led to
complex patterns of human-induced land-
use change. This has accelerated since the
mid-1970s, as high demands for commodities
such as soybeans, maize, wheat and sun-
flowers have driven major land-use change
processes in the different biomes, mainly in
the Cerrado and the Southern Grasslands.
These changes resulted in substitution of na-
tive ecosystems and traditional extensive cat-
tle ranching. More recently, considerable por-
tions of both grain crops and pastureland
have been converted to sugarcane and for-
estry, to help meet the growing demands of
the biofuel, timber and cellulose industries.
Common effects of agricultural expan-
sion on tropical soil resources described in
the literature include depletion of soil or-
ganic matter, with consequent reduction of
carbon stocks and fertility; soil compaction
and reduction in water-holding capacity;
erosion and desertification; and biological
degradation. These changes in the soil,
coupled with other natural resource impair-
ments such as biodiversity degradation, can
result in severe disruptions in ecosystem
function, affecting services such as hydro-
logic regulation, water quality and erosion
control, as well as increasing CO 2 emissions
to the atmosphere.
Considering the role of agricultural soils
as important modulators of carbon sequestra-
tion and greenhouse gas emissions, we need
to understand how land-use and manage-
ment changes affect the rates and dynamics

Land-use Change

Four agricultural sectors have been respon-
sible for most of the land-use change (LUC) in
the region since the mid-1970s: international
commodities (mainly soybeans, maize, sun-
flowers and wheat), wood (eucalypt and
pine), meat (cattle) and biofuels (sugarcane).
Soybeans and other oilseeds (used for food,
feed and biofuel production), grain crops and
cultivated pastures ( Brachiaria spp., lucerne-
grass mixtures) are widespread and have
replaced portions of all biomes considered in
this review. Biofuel crops, especially sugar-
cane, are expanding to meet the demand of
growing international markets and national
policies (Cerqueira Leite et al ., 2009; Lago,
2012). Sugarcane cultivation is concentrated
in the Brazilian State of São Paulo (approxi-
mately 60% of the Brazilian sugarcane pro-
duction) and has expanded most rapidly in
the states of Mato Grosso do Sul and Goiás
(Goes et al ., 2008; Uriarte et al ., 2009; Mon-
teiro et al ., 2010; Rudorff et al ., 2010). In the
Southern Grasslands, traditional cattle breed-
ing, a more low-impact, environmentally sus-
tainable land-use system, has preserved most
of the biome's integrity (Rótolo et al ., 2007),
but agriculture and forestry expansions have
been decimating the natural ecosystems at
an alarming rate since the late 20th century
(Baldi and Paruelo, 2008).