Spatial Patterns of Land Cover Dynamics on Samothraki Island, Applying Remote Sensing on complex Mediterranean Pastures
In the Mediterranean Basin land cover and land use are tightly coupled (e.g. Aranzabal et al. 2008; Röder et al. 2008; Plieninger et al. 2011). Grazing is a main contributor to the semi-natural Mediterranean landscape. Land cover change is highly and sensibly linked with alterations of local grazing management (e.g. Verburg et al. 2009). The north-Aegean island Samothraki shows alarming signs of inadequate grazing (Fischer-Kowalski et al. 2011; Biel & Tan 2014; Fuchs 2014). Patterns of overgrazing and accompanying erosion are obvious. Local LC-dynamics seem to put the island's sustainable development at risk. Samothraki may torpedoes its own future possibilities and final intention to become a member of UNESCO’s Man-of-Biosphere Programme. In this sense, a multiple remote sensing approach was employed to assess spatio-temporal land cover information and former dynamics of ecosystem properties on the small island. Present land cover types were combined with time series data of ecosystem properties (NDVI) of the last three decades (1984-2015). LANDSAT-footprints provide high-resolution data (USGS (United States Geological Survey) 2016b). The available open-source dataset was reviewed, adequate data selected and pre-processed. A Maximum-Likelihood-classification delivered discrete vegetation-information of nine LC-types (Congedo 2015). Satellite-calibrated NDVI-values were calculated for 16 data-points. Kmeans-clustering was applied to finally assign NDVI-TS-data to five trend categories that indicate specific increase, decrease or non-dynamics of NDVI. Qualitative on-site assessments of ground-truth LC validate the classification outcomes and document areas that show high dynamics of NDVI. The TS-analysis shows that during the first investigation period vast areas suffered a substantial downturn trend of the vegetation state (hotspots of grazing). Since 2003 most parts of the island experienced a slightly increasing land cover. On the one hand, the course of local land cover dynamics can be explained by highly fluctuant and heterogeneous grazing pressure on Samothraki. Furthermore, Ground-truth assessments highlighted that areas that have once undergone degradation of vegetation cover, are now prone to be affected by irreversible soil erosion. On the other hand, undesired shrub encroachment and weed invasion result in a wide-spread increase of local vegetation during last years. The results were embedded and discussed in the local process framework (e.g. Lasanta & Vicente-Serrano 2012) of the island’s specific grazing regime. Samothraki’s grazing system was strongly influenced by basic land use transitions at greater scales. First the local mode of livestock breeding underwent intensification processes (e.g. Kosmas et al. 2015), accompanied by a general disregard of the local rangeland state (e.g. Kizos et al. 2013) and followed by an effort-minimising style of farming that offers hardly any prospects for local breeders. This assessment reveals that concentrating grazing (e.g. Zervas 1998; Röder et al. 2007) of unregulated livestock as well as abandonment of labour-intensive management practices (e.g. Kizos et al. 2013; Giourga et al. 1998) occurred on the island. Although vegetation cover re-increases, related potentials of general increases in pasture productivity seem to be unused. Rather land abandonment processes influence the landscape development of Samothraki Island. Today accelerating bush encroachment and the loss of top soils are the main limiting factors of re-obtaining a sufficient local grazing capacity. Current land use patterns indicate great missing potentials in terms of a worthwhile grazing- and land-based livelihood in the future. Finally, the applied remote sensing approach can serve as an essential monitoring tool for future LC-dynamics of Samothraki Island.