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a b s t r a c tEnergy balances of farm systems have overlooked the role of energy flows that remain within agroecosystems. Yet, such internal flows fulfil important socio-ecological functions, including maintenance of farmers themselves and agro-ecosystem structures. Farming can either give rise to complex landscapes that favour associated biodiversity, or the opposite. This variability can be understood by assessing several types of Energy Returns on Investment (EROI). Applying these measures to a farm system in Catalonia, Spain in 1860 and in 1999, reveals the expected decrease in the ratio of final energy output to total and external inputs. The transition from solar-based to a fossil fuel based agro-ecosystem was further accompanied by an increase in the ratio of final energy output to biomass reused, as well as an absolute increase of Unharvested Phytomass grown in derelict forestland. The study reveals an apparent link between reuse of biomass and the decrease of landscape heterogeneity along with its associated biodiversity.

Abstract'Formiguers' are structures similar to charcoal-kilns that were used to burn piles of biomass with a soil cover in order to produce fertilizers for agricultural plots. Their use was widespread in Spain up to the 1960s and similar structures are still in use in India and Bhutan. Our objective was to study the effects of the 'formiguer' on its soil cover in terms of changes in nutrient availability. We built an experimental 0.5 m 3 -'formiguer' with 68 kg of plant material with a 12% moisture content and 550 kg of soil with a 16% moisture content. The content of organic carbon and mineral nitrogen decreased in the soil cover as a result of burning. After aerobic incubation all samples had a similar content of mineral nitrogen. Exchangeable potassium and total and labile phosphorus increased after burning as a result of the soil cover mixing with the ashes of the biomass as the 'formiguer' collapsed during burning in the first two cases, while mineralization of organic compounds produced the increase in labile phosphorus. This input of nutrients for the agricultural plots occurs at a net loss of 0.4-2.5 Mg organic C.ha -1 . Very small amounts of charcoal were produced and this may be the reason for their low occurrence in soils today. Burning of 'formiguers' required the harvest of vegetation from a considerable forest area (10-25 ha per hectare of agricultural land) and represented a significant disturbance of these systems.

Energy efficiency in biomass production is a major challenge for a future transition to sustainable food and energy provision. This study uses methodologically consistent data on agroecosystem energy flows and different metrics of energetic efficiency from seven regional case studies in North America (USA and Canada) and Europe (Spain and Austria) to investigate energy transitions in Western agroecosystems from the late nineteenth to the late twentieth centuries. We quantify indicators such as external final energy return on investment (EFEROI, i.e., final produce per unit of external energy input), internal final EROI (IFEROI, final produce per unit of biomass reused locally), and final EROI (FEROI, final produce per unit of total inputs consumed). The transition is characterized by increasing final produce accompanied by increasing external energy inputs and stable local biomass reused. External inputs did not replace internal biomass reinvestments, but added to them. The results were declining EFEROI, stable or increasing IFEROI, and diverging trends in FEROI. The factors shaping agroecosystem energy profiles changed in the course of the transition: Under advanced organic and frontier agriculture of the late nineteenth and early twentieth centuries, population density and biogeographic conditions explained both agroecosystem productivity and energy inputs. In industrialized agroecosystems, biogeographic conditions and specific socio-economic factors influenced trends towards increased agroecosystem specialization. The share of livestock products in a region's final produce was the most important factor determining energy returns on investment.Keywords Agroecosystem energy transition . Long-term socio-ecological research . Energy return on investment . Energy efficiency Electronic supplementary material The online version of this article (https://doi

More than energy transformations: A historical transition from organic to industrialised farm systems in a Mediterranean village (Les Oluges, Catalonia, 1860-1959-1999)The analysis of energy efficiency of agroecosystems from a sociometabolic perspective is a useful way to assess the sustainability of farm systems. In this article we examine the transition of a Mediterranean agroecosystem from an organic farm system in the mid nineteenth century to an industrialised one at the end of the twentieth century by means of the technologies and ideology of the Green Revolution. Given that many of the world's agricultural systems have experienced, or are currently experiencing this transformation, our results are relevant for building more sustainable agricultural systems in future. Our results highlight the relevance of livestock density, and the flows of biomass reused and unharvested biomass as key elements affecting the sustainability of the agroecosystem not only from a socioeconomic perspective, but also from an agroecological point of view. Additionally, from a biocultural perspective our investigation sustains the relevance of the study of traditional farm systems for the development of a sustainable agriculture.