Discussion: Confronting ELIA results with Margalef’s hypothesis
We have checked Margalef’s hypothesis on the capacity to host high biodiversity in cultural landscape mosaics resulting from a complex distribution of external energy flows of farming, by testing the links of the spatial energy-information structure with the species richness of butterflies and bird populations observed in the Barcelona Metropolitan Region (31 ,37 ,40 ). The results confirm that agroecosystems are key to halt the serious decline of butterfly populations in Europe (41 ), which can also be taken as proxy of many other current biodiversity threats (42 ). The importance of the energy landscape redistribution (I ) carried out by farmers is coincident with recent research highlighting that the worrying decline of common birds’ populations in European cultural landscapes is related to the abandonment of long land use patterns of human-made agroecosystems (43 ).
The Energy-Landscape Integrated Analysis has demonstrated to be an efficient predictor of butterfly and bird locations in the human-transformed landscapes studied. Indeed, ELIA can better predict these biodiversity locations than landscape composition or configuration metrics taken alone. Farmers’ uneven spatial distribution of the biomass energy flows (I ) of agroecosystems appears to be the key factor to explain butterfly observations and species richness, but also breeding and wintering species richness. This is an important outcome that points out to the role of farmers’ knowledge in designing the ecological functionality of biocultural landscapes through a subtle human-nature relationship (40 ). It confirms that the interplay between the energy reinvested (E ) and redistributed (I ) by farmers affects the landscape functional structure (L ) and its associated biodiversity through the harnessing of biomass flows that loop within these human-transformed landscapes.
The analytical advances and positive results obtained mean that the usual methodology of energy flow analysis of social metabolism and the classical landscape ecology metrics need to be adapted, enlarged and integrated to account for the complex cyclical character of human-driven land use changes in cultural landscapes. Traditional farm systems with a solar-based metabolism tended to organise their land usages according to different gradients of spatiotemporal intensity, keeping an integrated management of different land patches because their whole subsistence depended on the endurance of that landscape functional structure (40 ). In order to offset the energy lost in the inefficient human exploitation of animal bioconversion, on which they had to rely to obtain traction and manure, past organic farmers kept livestock breeding carefully integrated with cropland, pastureland and forestland (44 ).
While the traditional organic farm management scheme of closing energy cycles within complex agroecosystems led to landscape mosaics which allow a land sharing strategy for biological conservation (45 ), the agroindustrial farm systems that rely on external flows of inputs coming from underground fossil fuels have enabled society to overcome the age-old energy dependency on bioconverters (46 ). As a result, integrated land-use management was no longer necessary, and overcoming that former necessity led to the loss of its agroecological virtues. Nowadays biodiversity conservation in land matrices mostly occupied by cultural landscapes cannot be guaranteed only through the protection of natural areas (land sparing ) in exchange for promoting an ever more intensive industrial agriculture. It requires, instead, an improvement of the ecological connectivity and functionality of the whole land matrix by recovering and enhancing agroecology landscape mosaics (land sharing ). This also means to start scaling up the agroecosystems’ functioning at the landscape level to cope with and offset the land cost of sustainability (47 ). Therefore, the integration between social metabolism and landscape ecology approaches is crucial for further developments of sustainable land-use planning.