Cropland expansion changes deforestation dynamics in the southern Brazilian Amazon

Abstract

Intensive mechanized agriculture in the Brazilian Amazon grew by >3.6 million hectares (ha) during 2001-2004. Whether this cropland expansion resulted from intensified use of land previously cleared for cattle ranching or new deforestation has not been quantified and has major implications for future deforestation dynamics, carbon fluxes, forest fragmentation, and other ecosystem services. We combine deforestation maps, field surveys, and satellite-based information on vegetation phenology to characterize the fate of large (>25-ha) clearings as cropland, cattle pasture, or regrowing forest in the years after initial clearing in Mato Grosso, the Brazilian state with the highest deforestation rate and soybean production since 2001. Statewide, direct conversion of forest to cropland totaled >540,000 ha during 2001-2004, peaking at 23% of 2003 annual deforestation. Cropland deforestation averaged twice the size of clearings for pasture (mean sizes, 333 and 143 ha, respectively), and conversion occurred rapidly; >90% of clearings for cropland were planted in the first year after deforestation. Area deforested for cropland and mean annual soybean price in the year of forest clearing were directly correlated (R(2) = 0.72), suggesting that deforestation rates could return to higher levels seen in 2003-2004 with a rebound of crop prices in international markets. Pasture remains the dominant land use after forest clearing in Mato Grosso, but the growing importance of larger and faster conversion of forest to cropland defines a new paradigm of forest loss in Amazonia and refutes the claim that agricultural intensification does not lead to new deforestation.

Fig. 1.

Tropical deforestation for cropland agriculture in Mato Grosso state (2001–2004) is concentrated along the existing agricultural frontier. (Inset) Location of the study area subset within Mato Grosso state and the Amazon Basin.

Fig. 2.

Trends in land use after 2001–2004 deforestation events >25 ha in Mato Grosso state, Brazil. (Upper) Summary of conversion dynamics by post-clearing land cover from satellite-based phenology information in the years after forest clearing. A preliminary estimate of 2005 deforestation is shown in gray (INPE PRODES). Inflation-adjusted prices per 60-kg sack of soybeans for the same period as the annual deforestation increment (September–August) are plotted on the right-hand axis in Brazilian Reais (R$). (Lower) Fate of 2003 deforestation events by clearing size.

Fig. 3.

Spatial distribution of 2002–2005 deforestation events larger than 20 MODIS 250-m pixels (≈125 ha) for municipalities in Mato Grosso (32).

Fig. 4.

Relationship between cropland expansion and deforestation in Mato Grosso, Brazil, during 2001–2004. Estimates of forest conversion directly to cropland range from 4,670 (33) to 5,463 km² (this study). Expansion of large-scale mechanized agriculture was estimated from annual land cover maps of Mato Grosso derived from MODIS-based phenology information; only transitions from forest, Cerrado, or pasture/grasslands to double-cropping systems are included in this estimate (33). Estimated cropland expansion from agricultural census data of total planted area is nearly two times the area derived from satellite data, because individual fields are counted separately for each crop rotation in the agricultural census.