Land Use Transitions in the Cerrado : Impacts on Ecosystems and Future Paths from the Perspective of the Water, Energy, and Food Nexus

Abstract

The Brazilian Cerrado is the most biodiverse savanna in the world, yet 50% of its original cover has been cleared to make way for crops and pastures by 2022. These rapid land-use transitions are expected to influence regional climate and water balance, with implications for energy generation, food production, livelihoods, and biodiversity conservation. The demand for key commodities is likely to rise in the coming years, intensifying the pressure for the conversion of native vegetation areas to commercial export-oriented farms. Expanding agriculture over already cleared areas for pastures has been indicated as an opportunity to reconcile production and conservation. Still, deforestation in the Cerrado is advancing at a fast pace, with increasing rates in the last three years. Our goal is to understand the interaction between agriculture, climate, and water cycling in the Cerrado, focusing on accumulated impacts, future scenarios, and opportunities to increase commodity-driven production without further deforestation. Chapter 1 presents the theoretical framework that justifies and contextualizes this research. We investigated the water, energy, and food nexus (WEF Nexus) concept, its origins, applicability to understand human caused impacts on ecosystems, and current developments. Then, we discussed why the Cerrado is an emblematic case study of complex land use and land cover change dynamics, requiring an integrated nexus approach. In Chapter 2, we investigated how the accumulated land-use transitions (LUT) affect regional climate and water cycling in the Cerrado through changes in mean annual evapotranspiration (ET) and average land surface temperature (LST), as well as implications on future land use options. We performed regression analyses to quantify the effects of six common LUTs on ET and LST across the entire gradient of Cerrado landscapes from 2006-2019. Results indicate that clearing forests for cropland or pasture increased average LST by ~3.5°C and reduced mean annual ET by 44% and 39%, respectively. Transitions from woody savannas to cropland or pasture increased average LST by 1.9°C and reduced mean annual ET by 27% and 21%, respectively. Converting native grasslands to cropland or pasture increased average LST by 0.9 and 0.6°C, respectively. Conversely, grassland to pasture transitions increased mean annual ET by 15%. To date, land changes have caused a 10% reduction in water recycled to the atmosphere annually and a 0.9°C increase in average LST across the biome, compared to the historic baseline under native vegetation (prior to large-scale human occupation). Global climate changes from increased atmospheric greenhouse gas concentrations will only exacerbate these effects. Considering potential future scenarios, we found that the absence of deforestation control enforcement or allowing legal deforestation to continue (at least 28.4 Mha) would further reduce yearly ET (by -9% and -3%, respectively) and increase average LST (by +0.7 and +0.3°C, respectively) by 2050. In contrast, policies encouraging zero deforestation and restoration of the 5.2 Mha of illegally deforested areas would partially offset the warming and drying impacts of land-use change. In Chapter 3, we investigated the potential for cropland expansion without new deforestation in the Cerrado, by assessing the spatial and temporal dynamics of land use transition over the past 35 years (1985-2021). We performed correlation analyses between four key types of land transitions in the Cerrado: (a) pasture expansion over native vegetation, (b) direct conversion of native vegetation to cropland, (c) cropland expansion over pasture, and (d) pasture abandonment. We also calculated the remaining area with high crop suitability over pastures and over native vegetation and spatio-temporal patterns of cropland expansion over pastures. Between 1985-2021, the expansion of pasture over native vegetation was the prevailing land use transition (18.8 Mha), followed by pasture abandonment (8.9 Mha). Even though deforestation for pasture has decreased, it is still the main land use transition, driving the loss of 414,000 ha yr-1of native vegetation between 2011-2020. Pasture expansion over native vegetation and pasture abandonment are negatively correlated (ρ = - 0.38), while cropland expansion over pasture is positively correlated to cropland expansion over native vegetation (ρ = 0.48). Direct conversion from native vegetation to cropland has increased in the last three decades, amounting to 113,000 ha yr-1in 2011-2020, mainly in the Matopiba region.Promoting pasture intensification could free land for cropland expansion without deforestation. There are 18 Mha of pasture with moderate to high crop suitability, mostly in the states of Goiás, Mato Grosso do Sul and Minas Gerais. Of the current 27 Mha of cropland in the Cerrado, 27% were established in the last 10 years and 28% (7.5 Mha) over pastures. A considerable area of croplands (2Mha) replaced newly created pastures (<7 yr), suggesting pastures may be an intermediate land use, before selling or renting for cropland production. There are 20 Mha of native vegetation areas with moderate to high crop suitability, signaling that stopping deforestation in the Cerrado will require a combination of conservation policies and incentives for cropland expansion over pastures. By looking into the impacts associated to cropland and pasture expansion over native cerrado vegetation and opportunities to reverse this process while increasing agricultural productivity, our results may help to foster a new development pathway to the Cerrado, with food, energy, and water security.