Vulnerability of a Northeast Mediterranean Island to Soil Loss. Can Grazing Management Mitigate Erosion?

Abstract

Grazing management practices can be erosion abatement actions for lowering soil loss and the subsequent sediment pollution of surface water bodies. Process-based Geographic Information Systems models provide the opportunity to identify critical areas and hence better target such actions across the landscape. This study implemented the SWAT (Soil Water Assessment Tool) hydrologic and catchment management model to estimate the soil loss vulnerability of the nearly pristine but highly erodible Greek island of Samothraki in the North Aegean Sea, with a typical Mediterranean climate and steep topography. Model parameterization and evaluation were carried out by taking advantage of previous modeling experience on areas with data limitations. Inter-annual and intra-annual soil loss variability and the most critical areas (subbasins) of soil loss to waters were adequately identified and grazing management scenarios, including livestock reductions by 50% and 100%, grazing period reduction, and a combination of them, were formulated and applied to investigate the degree to which soil loss could be reduced. The annual reduction results varied between scenarios in the range of 10% to 25% for the entire island, and in wider ranges for its individual subbasins, showing a high potential for reducing the vulnerability of the most pressured ones. However, due to the high importance of the natural factors of rainfall and land slopes, the erosion vulnerability of the island overall could be significantly altered only if grazing management was integrated within a vegetation regeneration plan that included reforestation.

Samothraki in Transition: A Report on a Real-World Lab to Promote the Sustainability of a Greek Island

“…Even more of a challenge derives from a recent plan of an international industrial conglomerate, supported by the Greek national administration to establish an industrial wind park (39 windmills) on the top of Saos mountain, in the centre of the area destined for Natura 2000, to produce electricity for export. Such a wind park would be visible from far and completely disrupt the ecotouristically most attractive virgin mountain area, dry out headwater springs and streams and require, for the transport of infrastructure and hundreds of tons of concrete, a new road in very steep terrain up from the seaside to the mountain tops -thus creating a new source of major erosion [37]. The municipal council has unanimously opposed this plan, the regional authority too, but future is open.…”

“…This derives from tectonically deformed bedrock, steep slopes, and restricted groundwater aquifers creating flash floods. Recent research results [37] showed that soil loss under the present situation of animal grazing was 15.8 t/ha, with most vulnerable being an area extending from the center of the island to the adjacent steep headwater areas of its streams. The simulation of a non-grazing scenario resulted in a soil loss diminishing by 25%, indicating that overgrazing alone cannot explain the high erosion rates of the island.…”

“…It appears mainly around the lower smooth shaped foothills of the pasture farming-based villages. In higher altitudes on the northern and eastern slopes of mount Saos, there are pristine woodlands (Quercus petraea) that drew our special attention for two reasons: First, because they allow us to reconstruct a longer term history of land-use practices, and second, because their survival is essential for the stabilization of soil and the containment of erosion [37]. A detailed investigation of two remaining forest areas [2] came to the conclusion that there has been a long history of intensive silvo-pastoral land use, particularly in the 18th and early 19th century.…”

“…Possibly, the massive deforestation that took place during the last centuries degraded soil cover already before overgrazing became the overwhelming cause for soil erosion. Thus, soil loss prevention actions should not only target grazing management, but should be the subject of an integrated plan for natural vegetation regeneration, including reforestation to the greatest possible extent, as well as constructive practices, e.g., building of terraces, and the extension of Sown Biodiverse Permanent Pastures [37].…”

Residents’ Views on Landscape and Ecosystem Services during a Wind Farm Proposal in an Island Protected Area

“…Two catastrophic flood events in the summer of 2017 [92], less than a year before our survey, were attributed by several respondents to "erosion" caused and/or aggravated by overgrazing. Additionally, the issue of overgrazing has occupied visiting researchers and environmentalists working on Samothraki for over a decade [57,58,93,94] and these efforts have promoted local discourse aiming at conservation and restoration initiatives on this subject in recent years [64]. It has been shown in other protected areas in Greece that the provision of information to local inhabitants significantly influences perceptions on conservation issues [95].…”