Native forests in agricultural landscapes : An option for sustainability

Abstract

Abstract. Society has traditionally assumed that the supply of ecosystem services (ES) provided by forests is unlimited. This has caused the degradation of a large part of the world´s forests and an accelerated rate of conversion to other land uses. Agriculture is recognized as the land use that has spread with greater speed and extension. Since native forests are the ecosystems with the most biomass, and around 50% of it is carbon, the conversion of forests has a great impact on the global atmosphere. Furthermore, the importance of the forest biomass goes much further, since it constitutes the fundamental support of the ecological functions that will enable the provision of ES. Given that the land use conversion is threatening the existence of native forests, is commanding to progress in the generation of knowledge about them and their ES supply, but also in translating this knowledge into practical tools and instruments based on easy to register and comprehend variables. This work seeks to make a contribution in this direction, providing data, tools and thoughts for discussion. It is presented an approach that recognizes the importance of biomass as a key element of the ecosystem and have been applied in the contrast native forest (Pizarro Reserve) vs crops (soybean), as a typical case of land cover change. Starting from the field data collection on 10 vegetation and soil variables (absolute values) a methodology was constructed to estimate the relative total ecosystem value (TEV) and the yield of the five ES for each land use. Pizarro´s TEV was 44% ("critical" situation) and crop was TEV = 11.2% ("collapse"). The last value implies a loss of 74.5% of ecosystem benefits with respect to the forest, given that the ES are linked to the biomass stocks. Therefore, the soy crops despite having a high market value and short-term economic benefits, shows a comparative low ecological value. Moreover their ecological value is transitory and in an annual cycle the aboveground biomass (AGB) becomes zero. Although the analysed ecosystem has undergone processes of degradation, it is estimated that the AGB could be between 21% and 36% higher than the current (156.7 t/ha). Now it is providing at least five fundamental ES: water, climate and biogeochemical regulation, soil protection and bioenergy supply. On the other hand, the current forest AGB and ES supply could potentially be improved through the implementation of a technical management plan and effective control measures within the Reserve. This proposal seeks to encourage analysis and dialogue on the need for an adequate comprehensive evaluation of different land uses, bringing to light technical elements for a more sustainable territorial planning.