Hydro-geomorphological consequences of the abandonment of agricultural terraces in the Mediterranean region: Key controlling factors and landscape stability patterns

Abstract

Traditional cultivation terraces are one of the most ancient and conspicuous agricultural landscapes in mountain and hilly regions of the Mediterranean basin.Spreading out from Asia, the first terraces in the Mediterranean region date from the Bronze Age and the classical Hellenic and Roman periods, reaching their greatest spatial extent during the eighteenth and nineteenth centuries. Under optimum management, these systems contribute to the conservation of soil and water resources by increasing infiltration and decreasing sediment yield. However, traditional management and cultivation ceased on many terraced landscapes of the northern-shore Mediterranean countries during the twentieth century, with variable results. An extensive bibliographic review and meta-analysis was carried out to explore the main effects of land abandonment of Mediterranean agricultural terraces on local hydrological and geomorphological processes. Our results point to the development of vegetation cover and degradation of terraced structures (e.g., walls, terrace risers, channels) as the main critical factors controlling the hydrological behaviour (i.e., runoff production and hydrological connectivity) of abandoned terrace systems. Severe geomorphological problems, in the form of intense surface erosion, aggressive piping and gullying, occurred under special climatic (semi-arid climate), lithologic (dispersive marls) and structural (high vertical hydraulic gradient) conditions. Dense colonization by vegetation proved to be of major importance for controlling surface erosion. Vegetation, however, showed a limited capacity to control the activity of mass movements in most cases. Mass movements in the form of small soil slips primarily affected long-abandoned terraces in hillslope concavities and valley bottom positions that concentrate (surface and subsurface) water fluxes and show recurrent soil saturation. In humid terraced landscapes characterized by high hillslope gradients and terrace risers, the most devastating effects of mass movements took place in the form of 3 debris slips and terrace cascading landslides triggered by extreme rainfall. A variety of management options (non-intervention, stewardship of natural rewilding processes and active rehabilitation) can be applied, depending on vegetation development potential, site hydro-geomorphic vulnerability and local socio-economic interests. Effective conservation approaches will be required to preserve the environmental, socio-cultural and historical values of these ancient anthropogenic landscapes.

Investigation on Farmland Abandonment of Terraced Slopes Using Multitemporal Data Sources Comparison and Its Implication on Hydro-Geomorphological Processes

“…This is in agreement with the evidences reported by other researches performed both in the study area [11,59,[84][85][86][87][88][89][90] and in other terraced environments around the world [58,[91][92][93]. As reported in technical literature, several factors can influence the occurrence of slope instabilities in terraced systems [58]. Some of these factors are related to the geometrical features of terraced slopes (e.g., height of dry-stone walls and slope steepness) [23] while in other cases they are directly associated to the hydrological functions of terraces.…”

“…Accordingly, agricultural terraces become more vulnerable and therefore highly susceptible to collapses and failures [51][52][53][54][55]. Many studies addressed that the degree of abandonment is a crucial factor in regulating the susceptibility of terraced slopes to be affected by rainfall-induced landslides [11,[56][57][58][59].…”

Evaluación de los servicios ecosistémicos proporcionados por las terrazas agrícolas

“…While recognizing the potential difficulties that terraces can produce in terms of access, their maintenance continues to have an incalculable value for the sustainability of agricultural lands and for society. Terraces will only fulfill their ecosystem functions when properly maintained, while their abandonment, especially in semi-arid areas, promotes soil erosion processes and other hydro-geomorphological consequences (Moreno de las Heras et al, 2019). It is necessary to make the multiple benefits that terraces offer to farmers and to society more visible, since they are one of the most effective soil and water conservation measures on hillslopes.…”

Impact of flight altitude and cover orientation on Digital Surface Model (DSM) accuracy for flood damage assessment in Murcia (Spain) using a fixed-wing UAV

“…Both long-term erosion (Ruiz-Sinoga and Diaz 2010) and contemporary erosion processes (García-Ruiz et al 2013;Nadeu et al 2015) have been under study. Erosion features in natural areas (Díaz and Bermúdez 1988;Martínez-Hernández et al 2017;Díaz et al 2007) and in cultivated areas (Romero-Díaz et al 2017;de-las Heras et al 2019) have been studied. In addition, much focus has been put on potential measures to prevent erosion in cultivated areas; both in dryland as well as in irrigated areas (Castillo et al 2007;Calatrava et al 2011;García-Ruiz et al 2013;Hooke and Sandercock 2017).…”