Sugarcane production is a source of varied opinions and conflicting realities. While on the one hand it is contributing both to the takeover of farmland and to minor clearing of rainforest areas in South America, particularly Brazil, it also has the potential to serve as a renewable source of sustainable energy through its conversion into ethanol. Due to this seemingly dissonant relationship, the use of remote sensing technologies to track the development of the sugarcane industry is a topic of much attention, both to understand in a spatio-temporal sense, as well as to understand the land use changes brought on by the conversion of pasture and cropland. To begin, how much growth are we considering here exactly?
In 2012, Brazil boasted nearly a 40% share of the global sugarcane economy as the number one producer of the crop. The state of São Paulo was historically responsible for the lion’s share of that, with an output exceeding 60% of the country’s total production during the 2012 growing season – an amount equal to more than 80% of India’s total sugarcane production (the second global producer). In São Paulo, sugarcane land usage grew from 2.7 million hectares to more than 5 million hectares from 2002 to 2010, and is expected to increase to as much as 6 million hectares by 2021 (Egeskog et al., 2014). While much of this land use change does not involve the direct deforestation of rainforests in Brazil, it does take place within deforested zones on lands that were originally cleared for use as pasture and crop space.
To study the expansion of the sugarcane industry in São Paulo through remote sensing, it’s important to look at the lifecycle of the plant and the related stages of its cultivation and harvest in order to understand what is being imaged on the ground. Perhaps one of the most iconic images that many people have in association with sugarcane farming is that of smoke rising from burning fields: before a field is harvested manually, fire is often set to it to remove unnecessary leaves and stems, making the sugarcane easier to handle, transport and process. The field burn technique also effectively clears the field of any dangerous critters that may have taken up residence in the stands. This important part of the farming process partitions the two most prominent stages of sugarcane’s lifecycles and development in manually harvested fields: when the crop is growing (8 to 24 months depending on the location), and when the crop has been harvested. While the burned land registers as very dark, mechanically harvested crops leave large amounts of “trash,” or leaves, stems and so on, which are optically reflective and register as very bright areas of images. Regardless, both are readily recognized.
Rudorff et al. (2010) constructed a set of annual thematic maps to track the development of sugarcane in São Paulo spanning the years 2003 to 2008. The data was collected by Landsat 5 and interpreted visually at a scale of 1:50,000, with collections required in both the pre-harvest stage (January to April) and during the protracted harvest season (April to December). Further temporal division became useful in the pre-harvest duration, with images from January – February best able to distinguish renovated fields – which is the practice of cutting the sugarcane to the ground during the harvesting process and allowing it to grow back for reharvesting the following season. ‘Renovation’ slowly degrades the crop after 5 – 7 cycles, significantly influencing the output. Similarly, the March – April time period was shown to be more effective for the identification of newly planted crops.
As stated earlier, Rudorff et al. discovered an increase in sugarcane land use of 1.88 million hectares during the 2003 to 2008 study period, an incredible increase of nearly 70%. Of this increase, 56.5% of the land came from converted pasture land, with 40.2% of the growth represented by repurposed agricultural land. The remaining 3.24% was attributed to “other classes of land use,” which include land used for citrus as well as natural vegetation. Additionally, the study results indicate that the practice of burning fields prior to harvesting is on the decline, with a decrease from 66.5% of sugarcane fields burned in 2006 down to 50.9% by 2008. Due to the burning of the “trash,” the difference in greenhouse emissions from the harvesting process is markedly different between the mechanical and manual techniques, with the mechanical method offering an 80% decrease in the carbon emissions generated by manual harvesting. The workers noted that the number of fields that are harvested mechanically is likely to continue increasing as most of the land being used has <12% slope surface. Slope is the main limiting factor to the use of machinery to harvest sugarcane.
The continued decrease in carbon emissions from sugarcane production, coupled with the emissions benefits of ethanol as an alternative fuel source, may prove crucial to reducing global greenhouse gas accumulation. Regardless, the world’s eyes are likely to stay focused on this crop as a potential source of fossil fuel independence.
Rudorff, B.F.T., de Aguiar, D.A., da Sliva, W.F., Sugawara, L.M., Adami, M., Moreira, M.A., 2010, “Studies on the Expansion of Sugarcane Production in São Paulo State (Brazil) using Landsat Data”, Remote Sensing, vol. 2, pp. 1057-1076, 2010
Egeskog, A., Freitas, F., Berndes, G., Sparovek, G., Wirsenius, S., “Greenhouse gas balances and land use changes associated with the planned expansion (to 2020) of the sugarcane ethanol industry in São Paulo, Brazil”, Biomass and Bioenergy, vol. 63, pp. 280-290, 2010