12.3Terraced Landscape Management

Fig. 12.6 High-resolution topography of a terrace system in Liguria (Italy). The figure shows: a a shaded relief map obtained by a 1 m LiDAR-derived DTM; b drainage area calculated according to the d-infinite algorithm (Tarboton 1997). Yellow arrows indicate the water surface flow direction deviations due to the presence of terraces. (LiDAR data were provided by the Italian Ministry of the Environment and Protection of Land and Sea, within the framework of the Piano Straordinario di Telerilevamento Ambientale, PST-A)

In the last decade, a range of new remote sensing techniques led to a dramatic increase in terrain information, providing new opportunities for a better understanding of Earth surface geomorphic signatures (Tarolli 2014). Many recent studies proved the reliability of LiDAR (Light Detection and Ranging) technology, both aerial and terrestrial, in many disciplines concerned with Earth surface representation and modelling (Booth et al. 2009; Lin et al. 2013; Sofia et al. 2014a,b; Lo Re et al. 2018). In terraced landscapes, high-resolution LiDAR data can be useful. They allow to readily recognise the topographic signatures of terraces (Fig. 12.6), including those in areas covered by vegetation. The capability of LiDAR technology to derive a high-resolution (*1 m) DTM (Digital Terrain Model) from bare ground data, and by filtering vegetation from raw data, underlines the effectiveness of this methodology in mapping abandoned and vegetated terraces (Tarolli et al. 2014; Sofia et al. 2016).

DTM surface derivatives such as landform curvature, if obtained with small grid cell sizes, can be useful to automatically identify the location and the shape of

terraces through statistics (e.g. Sofia et al. 2014a). Terraces can be considered as ridges on the side of the hill being in a much sharper shape than natural terrain features. Consequently, they represent outliers of surface curvature. It is possible to detect such outliers in a box plot automatically and mapping them as terrace features. This approach can be used for a first and quick assessment of the location of terraces, particularly those abandoned that might require restoration efforts. However, high-resolution topography can be advantageous for other applications. It allows a better recognition of surface water flow paths (Fig. 12.6). Terrace failures are generally related to wall bowing due to subsurface water pressure (Preti et al. 2018). To identify the topographic influence on such pressure or the surface water flow direction, it is necessary to model the presence of the terraces and the surface morphology, considering the importance they have in influencing hydrological (surface flow paths) and geotechnical processes at the slope scale. Using 1 m LiDAR-derived DTM, it is possible to calculate flow direction and drainage upslope area and identify areas where the water flow is deviated or concentrated in specific paths (Fig. 12.6). This process, if not properly managed with a suitable drainage system, can trigger soil erosion that may evolve in gully or, in worst cases, in landslides (Tarolli et al. 2015). However, this approach (purely topographically based), while providing a first useful overview of the problem, needs to be improved with more accurate and physically based analyses because wall failures cannot be related only to surface flow direction changes. In such case, the use of a terrestrial laser scanner, supported by geotechnical instruments, should monitor a portion of a dry-stone wall providing more deep insights into failure mechanisms (Tarolli et al. 2014). A 3D model of a dry-stone wall, obtained with a centimetre grid cell resolution, could allow simulation of the behaviour of the wall in response to back load with high detail and without many artefacts or approximations. Also, the analysis of a direct shear test can offer an estimation of the Mohr-Coulomb failure envelope parameters (friction angle and cohesion) to be considered for modelling. Reference portions of dry-stone walls can be monitored, measuring the lateral earth pressure at the interface between dry-stone wall and its backfill, and the backfill volumetric water content (both in saturated and unsaturated states) and groundwater level. A permanent monitoring system can be implemented in such critical areas, where failures can involve houses or roads, with (a) pressure cells to measure the stress acting on the wall surfaces, (b) piezometers to measure the neutral strains, and (c) rain gauge for rainfall analysis.

12.3.2 Landscape Agronomic Approach

Once the geomorphological features of the terraced systems have been correctly mapped, it is necessary to revitalise their management, which was mainly ensured by farmers and farming activities. Terraced landscapes have been long neglected by agronomists due to their hard optimisable production. We claim here that the landscape perspective could help agronomy to address new management strategies of

terraced systems, primarily to pursue soil conservation goals. This requires shifting the focus from the terrace field level to embrace the whole landscape for the management of surface water and soil in cultivated areas. Although the agronomist can be defined as the “overseer of the land”, accordingly to the Greek etymology of the word (Buisson 2013), in recent history agronomists have frequently replaced the “land” by the cultivated field. This led agronomy to narrow the focus on the improvement of field performances finally addressing only issues related to crop yield, crop growth, and soil–crop relations (Cañas-Guerrero et al. 2013). However, agronomy intrinsically embraces multiple levels of the land, spanning from the cultivated field to its wider context. To this end, the cultivated field can play a critical role for interdisciplinary approaches to land management issues because it is a piece of land that is managed according to its socio-ecological context (Deffontaines 1991; Duru et al. 2015). In general terms, an agricultural field is bounded by natural or anthropic features (e.g. edges, channels and rivers, roads), by changes in cover or management (e.g. different crops, cultivation, and abandonment) as well as by land tenure (e.g. Deffontaines 1991; Inan et al. 2010; Levin and Nainggolan 2016). For terraced fields, we can add clearly visible attributes of risers, taluses and the intensive network of ditches required for the surface water and soil management on the hillside. Beyond the field level, multiple perspectives coexist because different stakeholders’ land property may overlap (Rizzo et al. 2013). Accordingly, the description, understanding, and management of terraces require inherently to be addressed from a system perspective to relate the spatial configuration of agricultural practices and the natural resource management. Significantly, Cavazza (1996) pointed out two complementary perspectives within the single discipline: farm agronomy and land agronomy. On the one hand, agronomy should tackle the farmers’ decision-making process in a clear organised spatial context defined by the farmers. On the other hand, agronomy should also deal with the context of farming activities and the interaction with the various stakeholders operating in a given area. The landscape agronomy approach (Benoît et al. 2012) recently proposed a transdisciplinary conceptual framework pursuing the integration of knowledge and perspectives from different scientific disciplines and societal stakeholders (Lardon et al. 2012; Moonen et al. 2016). An important pillar in this framework comes from the Italian Constitution (1948 art. 9) that reads: “The Republic promotes the development of culture and of scientific and technical research. It safeguards natural landscape and the historical and artistic heritage of the Nation”. So it joins culture, research, and protection of the landscape. “Landscape” can be further defined, according to the European Convention, as “[…] an area, as perceived by people, whose character is the result of the action and interaction of natural and/or human factors” (COE 2000 art. 1a). This convention also inspired the Terraced Landscape Manifesto that calls for the protection and long-term maintenance of terraces (cf. http://www.terracedlandscapes2016.it/ en/outcomes/). The landscape agronomy approach provides a timely answer to the call for actions discussed at the Third World Meeting on Terraced Landscapes, by framing the methods for mapping and inventorying terraced landscape features while supporting the understanding of their history, geography, social, and physical structures (Fig. 12.7).

Fig. 12.7 Conceptual framework for designing management strategies of terraced systems, based on the landscape agronomy approach (Benoît et al. 2012). To ensure a suitable management, the three poles must be addressed. Each pole illustrates a couple of examples further discussed in the text

Early applications of the landscape agronomy framework concerned the characterisation of the farming system component of European agricultural landscapes (Andersen 2017; van Zanten et al. 2013) also through remote sensing techniques (Bégué et al. 2015) and the design of a simple tool for extending agronomic management on a landscape basis (Orchard and Hackney 2016). Based on the landscape agronomy framework, we stress the need to tackle the terraced system management taking into explicit account the relationships between the spatial configuration of agricultural practices and the expected and the observed impacts on soil, water, and other natural resources (Fig. 12.7). This implies to develop geographic information systems to map all the three agricultural landscape components: farming practices, land patterns, and natural resources. The underpinning rationale is to relate the single terrace field management to the landscape it belongs to. In this perspective, farming practices include both the different forms of soil and water management (at the microand meso-scale) and of the zoning of actual