| 英文摘要: | To the Editor de Oliveira Silva and colleagues1 have proposed that, if decoupled from deforestation, increasing beef consumption may reduce greenhouse gas emissions, while at the same time suggesting that reducing consumption may not significantly alter greenhouse gas emissions. However, the analysis contains unrealistic assumptions and disregards a series of other analyses corroborated by historical data, affecting the robustness of the conclusions. Sustainable intensification is presented as a feasible socioecological solution, despite the fact that this concept is still a matter of controversy. At the most general level, it lacks any solid empirically based mechanism. More specifically, it fails to address equity and local governance aspects that ought to be inherent in its definition2. Furthermore, the authors assume a scenario in which deforestation can be decoupled from changes in pasture area, something that has not happened in the historical record of the Brazilian Cerrado. This assumption is based on the idea that increases in yield efficiency will result in spare land returning to its natural state3. Historically, however, agricultural productivity increases have usually been accompanied by farmland expansion4, 5, to meet growing demand: this is often referred to as the Jevons paradox by agricultural economists6. The authors may have reasons to doubt the substantial empirical evidence supporting this issue, but they should acknowledge their rejection of it in their underlying assumptions. Similarly, their assumptions of profit maximization and construction of a production-optimization model are problematic and arbitrary, considering the voluminous existing literature showing the importance of deviations from the maximization motive7 and the need to explicitly grapple with the assumptions made in any optimization analysis. The analysis does not take into consideration the local dynamics of small farming and indigenous resource management. Livestock production by traditional peoples and small farmers is generally regarded as less harmful to biodiversity and more sustainable than intensive livestock on exotic grass monocultures, although the outcomes are very context specific8. The assumption that the Cerrado may behave as a single large profit-maximizing farm does not reflect the socioeconomic diversity of extant landholders or the remarkable gamma diversity of its various ecosystems. Another questionable assumption is the idea that pasture recovery can be accomplished with fertilization in most of the Cerrado, which is implausible even before accounting for its negative effects on soil, water, and greenhouse gas emissions. The model also assumes a fixed value for emissions as a result of deforestation in the Cerrado, neglecting the ecological heterogeneity of the biome. The authors propose recovery of degraded areas using exotic grass, even though such exotic species have potentially profound effects on the functioning and biodiversity of the Cerrado9. Furthermore, the model ignores the regrowth of woody vegetation when pasture is taken out of production. Thus, it effectively assumes that secondary succession back to forest, which results in carbon sequestration in biomass and carbon soil, can never occur10. These assumptions limit the practical utility of this modelling exercise. |