Anthropocene 6 (2014) 10–25
Contents lists available at ScienceDirect
Anthropocene
journal homepage: www.elsevier.com/locate/ancene
Review Article
Terraced landscapes: From an old best practice to a potential hazard
for soil degradation due to land abandonment
Paolo Tarolli a,*, Federico Preti b, Nunzio Romano c
a
Department of Land, Environment, Agriculture and Forestry, University of Padova, Agripolis, viale dell’Università 16, 35020 Legnaro (PD), Italy
GESAAF, Agriculture, Forestry and Biosytems Engineering Division, Florence University, Firenze, Italy
c
Department of Agriculture, Division of Agricultural, Forest and Biosystems Engineering, University of Napoli Federico II, Portici, Napoli, Italy
b
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 12 November 2013
Received in revised form 17 March 2014
Accepted 24 March 2014
Available online 4 April 2014
Among the most evident landscape signatures of the human fingerprint, the terraces related to
agricultural activities are of great importance. This technique is widely used in various parts of the world
under various environmental conditions. In some areas, terraced landscapes can be considered a
historical heritage and a cultural ecosystem service to be adequately preserved. However, terraced
landscapes subject to abandonment can progressively increase gully erosion and cause terrace failure.
Partly because of changes in societal perspective and migration towards metropolitan areas, some
countries have been affected by serious and wide abandonment of agricultural lands in recent decades.
This review aims to discuss the current state of agricultural terraced landscapes, underlining critical
issues and likely solutions. The paper is structured in three main sections. The introduction provides an
overview of the available literature on terraced landscapes and their critical issues. The second section
presents three case studies: the first is located in the so-called Cinque Terre area (Liguria, Northern Italy),
the second is placed in the Chianti Classico area (Tuscany, Central Italy), and the third refers to the
renowned Amalfi Coast (Salerno, Southern Italy). The last section of the review relates to likely solutions
(non-structural and structural management) and future challenges (use of high-resolution topography
derived by lidar) for suitable management of such environments.
ß 2014 Elsevier Ltd. All rights reserved.
Keywords:
Terraces
Land abandonment
Soil erosion risk
Landslide
Lidar
Contents
1.
2.
3.
Terraces: the ancient practice of soil conservation and steep hillslopes cultivation . . . .
Terraces and soil erosion risk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1.
Nepal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1.1.
China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1.2.
1.1.3.
Peru . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Spain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1.4.
1.1.5.
Greece . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1.6.
1.2.
Terrace management: an anthropic geomorphic process? . . . . . . . . . . . . . . . . . . .
Terraces: Italy case study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cinque Terre (Liguria). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.
2.2.
Chianti Classico (Tuscany) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Amalfi Coast (Campania) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.
Integrated view, likely solutions and future challenges . . . . . . . . . . . . . . . . . . . . . . . . . . .
Non-structural management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.
3.2.
Structural management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Future challenges: application of high-resolution topography derived from lidar
3.3.
* Corresponding author. Tel.: +39 049 8272677; fax: +39 049 8272686.
E-mail address: [email protected] (P. Tarolli).
http://dx.doi.org/10.1016/j.ancene.2014.03.002
2213-3054/ß 2014 Elsevier Ltd. All rights reserved.
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P. Tarolli et al. / Anthropocene 6 (2014) 10–25
4.
3.3.1.
Abandoned terraces in vegetated landscapes .
Surface flow path characterization . . . . . . . . .
3.3.2.
Automatic terrace recognition and mapping .
3.3.3.
3D modelling from Terrestrial Laser Scanner .
3.3.4.
Final remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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1. Terraces: the ancient practice of soil conservation and steep
hillslopes cultivation
Terraces are among the most evident human signatures on the
landscape, and they cover large areas of the Earth (Fig. 1). The
purpose of terracing and its effect on hydrological processes
depend on geology and soil properties (Grove and Rackham, 2003),
but they are generally built to retain more water and soil, to reduce
both hydrological connectivity and erosion (Lasanta et al., 2001;
Cammeraat, 2004; Cots-Folch et al., 2006), to allow machinery and
ploughs to work in better conditions, to make human work in the
slopes easy and comfortable, and to promote irrigation.
Terraces reduce the slope gradient and length, facilitating
cultivation on steep slopes. They increase water infiltration in
areas with moderate to low soil permeability (Van Wesemael et al.,
1998; Yuan et al., 2003), controlling the overland flow (quantity)
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20
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23
and velocity (energy), thereby leading to a reduction in soil erosion
(Gachene et al., 1997; Wakindiki and Ben-Hur, 2002; Louwagie
et al., 2011; Li et al., 2012), with positive effects on agricultural
activities. In all Mediterranean basins, terraced landscapes are
considered to be among the most important and characteristic
anthropological imprints on the relief (Douglas et al., 1994, 1996;
Gallart et al., 1994; Dunjó et al., 2003; Trischitta, 2005), and they
symbolize an important European cultural heritage (Varotto, 2008;
Arnaez et al., 2011). During the past centuries, the need for
cultivable and well-exposed areas determined the extensive
anthropogenic terracing of large parts of hillslopes. Several
publications have reported the presence, construction, and soil
relationship of ancient terraces in the Americas (e.g., Spencer and
Hale, 1961; Donkin, 1979; Healy et al., 1983; Beach and Dunning,
1995; Dunning et al., 1998; Beach et al., 2002). In the arid
landscape of south Peru, terrace construction and irrigation
Fig. 1. Modern terraces in Portugal (photo by Feliciano Guimarães) (a) and Germany (source Franzfoto) (b), Inca-era terraces on Pumatallis (photo by McKay Savage) (c) and
Taquile (d) (Perú), and terraces in China (photo by Anna Frodesiak) (e) and Philippines (photo by Adi Simionov) (f). (The photos are licensed under the Creative Commons
Attribution-Share Alike 3.0 Unported, 2.5 Generic, 2.0 Generic and 1.0 Generic license).
P. Tarolli et al. / Anthropocene 6 (2014) 10–25
12
Fig. 2. Dry-stone wall examples within the Chianti Classico Gallo Nero vineyard region (Fattoria Lamole, Tuscany, Italy) (photo courtesy of Fattoria Lamole).
techniques used by the Incas continue to be utilized today
(Londoño, 2008). In these arid landscapes, pre-Columbian and
modern indigenous population developed terraces and irrigation
systems to better manage the adverse environment (Williams,
2002). In the Middle East, thousands of dry-stone terrace walls
were constructed in the dry valleys by past societies to capture
runoff and floodwaters from local rainfall to enable agriculture in
the desert (Ore and Bruins, 2012). In Asia, terracing is a widespread
agricultural practice. Since ancient times, one can find terraces in
different topographic conditions (e.g., hilly, steep slope mountain
landscapes) and used for different crops (e.g., rice, maize, millet,
wheat). Examples of these are the new terraces now under
construction in the high altitude farmland of Nantou County,
Taiwan (Fig. 2).
1.1. Terraces and soil erosion risk
Terracing has supported intensive agriculture in steep hillslopes (Landi, 1989). However, it has introduced relevant
geomorphic processes, such as soil erosion and slope failures
(Borselli et al., 2006; Dotterweich, 2013). Most of the historical
terraces are of the bench type with stone walls (Fig. 3) and require
maintenance because they were built and maintained by hand
(Cots-Folch et al., 2006).
Fig. 3. New terraces construction within a high altitude farmland area in the Central
Mountain Range of Taiwan (Nantou County, Taiwan) (photo by P. Tarolli).
According to Sidle et al. (2006) and Bazzoffi and Gardin (2011),
poorly designed and maintained terraces represent significant
sediment sources. Garcı́a-Ruiz and Lana-Renault (2011) proposed
an interesting review about the hydrological and erosive
consequences of farmland and terrace abandonment in Europe,
with special reference to the Mediterranean region. These authors
highlighted the fact that several bench terraced fields were
abandoned during the 20th century, particularly the narrowest
terraces that were impossible to work with machinery and those
that could only be cultivated with cereals or left as a meadow.
Farmland abandonment occurred in many parts of Europe,
especially in mountainous areas, as widely reported in the
literature (Walther, 1986; Garcı́a-Ruiz and Lasanta-Martinez,
1990; Harden, 1996; Cerdà, 1997a,b; Kamada and Nakagoshi,
1997; Lasanta et al., 2001; Romero-Clacerrada and Perry, 2004).
From 1950 to 1980, the marginal areas of the northern
Mediterranean were affected by an important population migration towards the cities and the coast (Lasanta et al., 2001). The
same process has also been observed in other regions of the world
(Cerdà, 2000; Inbar and Llerena, 2000; Khanal and Watanabe,
2006).
The terrace abandonment resulted in changes to the spatial
distribution of saturated areas and drainage networks. This
coincided with an increase in the occurrence of small landslides
in the steps between terraces Lesschen et al. (2008). The same
changes in hillslope hydrology caused by these anthropogenic
structures that favour agricultural activities often result in
situations that may lead to local instabilities (Fig. 4), both on
the terraces and on the nearby structures that can display evidence
of surface erosion due to surface flow redistribution.
Terraced lands are also connected by agricultural roads, and the
construction of these types of anthropogenic features affects water
flow similar to the manner of forestry road networks or trial paths
(i.e., Reid and Dunne, 1984; Luce and Cundy, 1994; Luce and Black,
1999; Borga et al., 2004; Gucinski et al., 2001; Tarolli et al., 2013).
The same issues could also be induced by the terraced structures
themselves, resulting in local instabilities and/or erosion. Furthermore, several stratigraphic and hydrogeologic factors have been
identified as causes of terrace instability, such as vertical changes
of physical soil properties, the presence of buried hollows where
groundwater convergence occurs, the rising up of perched
groundwater table, the overflow and lateral infiltration of the
superficial drainage network, the runoff concentration by means of
pathways and the insufficient drainage of retaining walls (Crosta
et al., 2003). Some authors have underlined how, in the case of a
P. Tarolli et al. / Anthropocene 6 (2014) 10–25
13
Fig. 4. Terrace dry-stone wall failure within the terraced landscape of Tramonti (Salerno, Italy) (photo by P. Tarolli).
dispersive substrate, terraces can be vulnerable to piping due to
the presence of a steep gradient and horizontal impeding layers
(Faulkner et al., 2003; Romero Diaz et al., 2007). Gallart et al.
(1994) showed that the rising of the water table up to intersection
with the soil surface in the Cal Prisa basin (Eastern Pyrenees)
caused soil saturation within the terraces during the wet season,
increasing runoff production. Studies have also underlined the
strict connection between terraced land management and erosion/
instability, showing how the lack of maintenance can lead to an
increase of erosion, which can cause the terraces to collapse
(Gallart et al., 1994). Terraced slopes, when not properly
maintained, are more prone than woodland areas to triggering
superficial mass movements (i.e., Crosta et al., 2003), and it has
been shown that the instability of the terraces in some areas could
be one of the primary causes behind landslide propagation (Canuti
et al., 2004). The agricultural terraces, built to retain water and soil
and to reduce hydrological connectivity and erosion (Cerdà, 1996,
1997a,b; Lasanta et al., 2001; Cammeraat, 2004), may fail when the
terraces are no longer maintained or when the water level behind
the wall reaches the critical threshold during rain storms (Lesschen
et al., 2008). Crosta et al. (2003) reported the causes of a severe
debris-flow occurring in Valtellina (Central Alps, Italy) to be
intense precipitation and poor maintenance of the dry-stone walls
supporting the terraces. A similar situation was described by Del
Ventisette et al. (2012), where the collapse of a dry-stone wall was
identified as the probable cause of a landslide. Lasanta et al. (2001)
studied 86 terraces in Spain and showed that the primary process
following abandonment was the collapse of the walls by small
landslides. Llorens et al. (1992) underlined how the inner parts of
the terraces tend to be saturated during the wet season and are the
main sources for generation of runoff contributing to the increase
of erosion (Llorens et al., 1992; Lesschen et al., 2008). The presence
of terraces locally increases the hydrological gradient between the
steps of two consecutive terraces (Bellin et al., 2009). Steep
gradients may induce sub-superficial erosion at the terrace edge,
particularly if the soil is dispersive and sensitive to swelling. In the
following section, we present and discuss a few examples of
terraces abandonment in different regions of the Earth and its
connection to soil erosion and land degradation hazard.
1.1.1. Nepal
Gardner and Gerrard (2003) presented an analysis of the runoff
and soil erosion on cultivated rainfed terraces in the Middle Hills of
Nepal. Local farmers indicated that the ditches are needed to
prevent water excess from cascading over several terraces and
causing rills and gullies, reducing net soil losses in terraced
landscapes. Shrestra et al. (2004) found that the collapsing of manmade terraces is one of the causes of land degradation in steep
areas of Nepal. In this case, the main cause seems to be the
technique of construction rather than land abandonment. No
stones or rocks are used to protect the retaining wall of the
observed terraces. Because of cutting and filling during construction, the outer edge of the terrace is made of filling material,
making the terrace riser weak and susceptible to movement
(Shrestra et al., 2004). In steep slope gradients, the fill material can
be high due to the high vertical distance, making the terrace wall
even more susceptible to movements. The authors found that the
slumping process is common in rice fields because of water excess
from irrigated rice. Khanal and Watanabe (2006) examines the
extent, causes, and consequences of the abandonment of
agricultural land near the village of Sikles in the Nepal Himalaya.
They analyzed an area of approximately 150 ha, where abandoned
agricultural land and geomorphic damage were mapped. Steep
hillslopes in the lower and middle parts up to 2000 m have been
terraced. The analysis suggested that nearly 41% of all abandoned
plots were subjected to different forms of geomorphic damage.
Khanal and Watanabe (2006) found that damage to the terraces
was observed in approximately 35% of all abandoned plots. The
damage consists of cracks, rills, gullies, sheet wash, scars, and
landslides or landslips. According to the authors, every year farm
households spend a great deal of labour on the maintenance of
terraces and the control of gullies, landslides, and floods on
cultivated fields. The phenomenon of abandoned agricultural land
has recently led to pronounced socioeconomic and environmental
problems in Nepal. Such areas require effective management to
reduce environmental risks and improve the livelihoods of farm
households (Khanal and Watanabe, 2006).
1.1.2. China
In mountainous or hilly regions of China, terrace construction is
one of the most important and preferred measures implemented in
land consolidation projects (Fan et al., 2008; Liu et al., 2013), and it
represents one of the greatest demonstrations of land surface
modification (Liu et al., 2013). Xu et al. (2012) discussed a case
study in the Three-Gorges area where several soil conservation
measures, such as terracing hedgerows, are widely implemented in
citrus orchards to control soil erosion. Schönbrodt-Stitt et al.
(2013) described the rapid agricultural changes in the same area.
Due to resettlements, construction of new infrastructure, and new
land reclamation, the degradation of the cultivated terraced
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P. Tarolli et al. / Anthropocene 6 (2014) 10–25
landscape is expected to increase significantly. This region also has
the highest soil erosion rates in China (Zhou, 2008). SchönbrodtStitt et al. (2013) collected data on the state of terrace maintenance
and terrace design to account for terrace stability and thus for the
capability of soil conservation. Mainly the terraces were associated
with oranges (77%), followed by cultivation of dry land crops such
as grape, wheat, and maize (15%), and garden land typically
cropped with vegetables and fruits (7%). They observed several
terraces partially or completely collapsed. The results of their
analysis suggested that the anthropogenic effects, such as the
distance to settlements or to roads, are the major drivers for the
spatial distribution of terrace conditions.
1.1.3. Peru
Inbar and Llerena (2000) addressed the problem of changing
human activities in the fragile environment of the historical
terraces in the Central Andean Mountains of Peru. Peruvian
landscapes are characterized by an old system of agricultural
terraces (Spencer and Hale, 1961). These mountain regions are
now affected by a significant change in land use and human
behaviour. Traditional subsistence agriculture is being replaced by
a market-oriented economy of labour and agricultural production
(Inbar and Llerena, 2000). The young generation living in the
mountain area is now moving to coastal cities for better job
opportunities. The result is soil erosion on traditional terraces that
have been abandoned because of the lack of maintenance of the
drainage systems and of the terracing practices. Inbar and Llerena
(2000) highlighted the fact that the terrace abandonment and
degradation are a function of physical, economic, and social factors,
such as land use and ownership, distance from a village, and
community strength. Londoño (2008) highlighted the effect of
abandonment on the Inca agricultural terraces since 1532 A.D.,
represented by the development of rills and channels on terraces
where the vegetation is absent.
1.1.4. Spain
Lesschen et al. (2008) underlined the fact that that terracing,
although intended as a conservation practice, enhances erosion
(gully erosion through the terrace walls), especially after
abandonment. These authors carried out a study in the Carcavo
basin, a semi-arid area in southeastern Spain. More than half of the
abandoned fields in the catchment area are subject to moderate
and severe erosion. According to these studies, the land abandonment, the steeper terrace slope, the loam texture of the soils, the
valley bottom position, and the presence of shrubs on the terrace
walls are all factors that increase the risk of terrace failure.
Construction of new terraces should therefore be carefully planned
and be built according to sustainable design criteria (Lesschen
et al., 2008). Lesschen et al. (2008) provided guidelines to avoid the
land erosion due to abandonment. They suggested the maintenance of terrace walls in combination with an increase in
vegetation cover on the terrace, and the re-vegetation of
indigenous grass species on zones with concentrated flow to
prevent gully erosion. Lesschen et al. (2009) simulated the runoff
and sediment yield of a landscape scenario without agricultural
terraces. They found values higher by factors of four and nine,
respectively, when compared to areas with terraces. Meerkerk
et al. (2009) examined the effect of terrace removal and failure on
hydrological connectivity and peak discharge in a study area of
475 ha in southeastern Spain. They considered three scenarios:
1956 (with terraces), 2006 (with abandoned terraces), and S2
(without terraces). The analysis was carried out with a storm
return interval of 8.2 years. The results show that the decrease in
intact terraces is related to a significant increase in connectivity
and discharge. Conversely, catchments with terraces have a lower
connectivity, contributing area of concentrated flow, and peak
discharge. Bellin et al. (2009) presented a case study from
southeastern Spain on the abandonment of soil and water
conservation structures in Mediterranean ecosystems. Extensive
and increasing mechanization of rainfed agriculture in marginal
areas has led to a change in cropping systems. They observed that
step terraces have decreased significantly during the last 40 years.
Many terraces have not been maintained, and flow traces indicate
that they no longer retain water. Furthermore, the distance
between the step terraces has increased over time, making them
vulnerable to erosion.
1.1.5. Greece
Petanidou et al. (2008) presented a case study of the
abandonment of cultivation terraces on Nisyros Island (Greece).
The population of this island increased during the late 19th to early
20th century thus marking a significant increase of terrace and drystone wall construction, which facilitated cultivation on 58.4% of
the island. From the mid 20th century, economic and emigration
issues caused the abandonment of cultivated land and traditional
management practices. As a result, the terraces became unstable,
especially in areas that are freely grazed by cattle, sheep, and goats,
leading to an increase in wall structure damage followed by several
collapses. Bevan and Conolly (2011) and Bevan et al. (2013)
proposed a multidisciplinary analysis of terraces across the small
island of Antikythera (Greece). They considered archaeology,
ethnography, archival history, botany, geoarchaeology, and direct
dating of buried terrace soils. Their analysis based on historical
records indicated that the dated soils might come from postabandonment erosion that occurred during the 15th and 16th
centuries. Only with a multidisciplinary approach it is possible to
achieve new insights into the spatial structure of terraces, the
degree of correlation between terrace construction and changing
human population, and the implications of terrace abandonment
for vegetation and soils. According to these authors, the terraces
are more than a simple feature of the rural Mediterranean. They are
part of the evolution of the social and ecological landscape.
Therefore, not only environmental but also historical and social
contexts can affect their cycle of construction, use and abandonment.
1.1.6. Africa
Nyessen et al. (2009) underlined the effectiveness of integrated
catchment management for the mitigation of land degradation in
north Ethiopian highlands. Their analysis indicated the positive
effects of stone bunds in reducing runoff coefficients and soil loss.
In the Tigray region (northern Ethiopia) the stone bunds were
introduced since 1970s to enhance soil and water conservation
(Munro et al., 2008), reducing the velocity of overland flow and
consequently the soil erosion (Desta et al., 2005). This practice can
reduce annual soil loss due to sheet and rill erosion on average by
68% (Desta et al., 2005). Terracing is a widely used practice for the
improvement of soil management in Ugandan hill landscapes
(Mcdonagh et al., 2014). Bizoza and de Graaff (2012) stressed the
fact that terraces, in addition to reduction of soil erosion, also
provide sufficient financial gains at the farm level. They presented
a financial cost–benefit analysis to examine the social and
economic conditions under which bench terraces are financially
viable in Northern and Southern Rwanda, which indicated that
bench terraces are a financially profitable practice.
1.2. Terrace management: an anthropic geomorphic process?
The study proposed by Cots-Folch et al. (2006) merits
mentioning because it differs from the others proposed previously.
It is an example of how policy on landscape restructuring (in this
case, supporting terrace construction) can significantly affect the
P. Tarolli et al. / Anthropocene 6 (2014) 10–25
surface morphology. The EU Council Regulation policy for vineyard
restructuring supported the construction of new terraces, which
were built utilizing heavy machinery without any environmental
impact considerations (Cots-Folch et al., 2006). In the northeastern
Spanish Mediterranean region, vineyards have been cultivated
since the 12th century on hillslopes with terracing systems
utilizing stone walls. Since the 1980–1990s, viticulture, due to the
increasing of the related economic market, has been based on new
terracing systems constructed using heavy machinery. This
practice reshaped the landscape of the region, producing vast
material displacement, an increase of mass movements due to
topographic irregularities, and a significant visual impact. CotsFolch et al. (2006) underlined that land terracing can be considered
as a clear example of an anthropic geomorphic process that is
rapidly reshaping the terrain morphology.
2. Terraces: Italy case study
Terracing has been practiced in Italy since the Neolithic and is
well documented from the Middle Ages onward. In the 1700s,
Italian agronomists such as Landeschi, Ridolfi and Testaferrata
began to learn the art of hill and mountain terracing, earning their
recognition as ‘‘Tuscan masters of hill management’’ (Sereni,
1961). Several agronomic treatises written in the eighteenth and
nineteenth centuries observe that in those times there was a
critical situation due to a prevalence of a ‘‘rittochino’’ (slopewise)
practice (Greppi, 2007). During the same period, the need to
increase agricultural surfaces induced farmers to till the soil even
on steep slopes and hence to engage in impressive terracing works.
Terraced areas are found all over Italy, from the Alps to the
Apennines and in the interior, both in the hilly and mountainous
areas, representing distinguishing elements of the cultural identity
of the country, particularly in the rural areas. Contour terraces and
regular terraces remained in use until the second post-war period,
as long as sharecropping contracts guaranteed their constant
maintenance. Thus, terraces became a regular feature of many hill
15
and mountain landscapes in central Italy. Beginning in the
1940s, the gradual abandonment of agricultural areas led to the
deterioration of these typical elements of the landscape. With
the industrialization of agriculture and the depopulation of the
countryside since the 1960s, there has been a gradual decline in
terrace building and maintenance, as a consequence of the
introduction of tractors capable of tilling the soil along the
steepest direction of the hillside (‘‘a rittochino’’), which resulted
in a reduction of labour costs. Basically, this means the original
runoff drainage system is lost. The results consist of an increase
in soil erosion due to uncontrolled runoff concentration and
slope failures that can be a serious issue for densely populated
areas. In the last few years during intense rainfall events in
different regions of Italy, especially in Cinque Terre, several
slope failures have been observed, which have caused grievous
damage to the local communities (Agnoletti et al., 2012). Here
we present three typical case studies where the lack of terrace
maintenance characterizing the last few years has increased the
landslide risk. The case studies are located in three different
Italian regions (Fig. 5): Cinque Terre (a), Chianti Classico (b), and
the Amalfi Coast (c).
2.1. Cinque Terre (Liguria)
The Cinque Terre (The Five Lands) is a coastal region of Liguria
(northwestern Italy), which encompasses five small towns
connected by a coastal pathway that represents an important
national tourist attraction. Since 1997, this rocky coast with
terraced vineyards has been included in the ‘‘World Heritage List’’
of UNESCO for its high scenic and cultural value. More recently, in
1999, it has become a National Park for its environmental and
naturalistic relevance. Due to the morphological characteristic of
this area, the landscape is characterized by terraces, supported by
dry-stone walls, for the cultivation of vineyards. These terraces are
not only an important cultural heritage but also a complex system
of landscape engineering (Canuti et al., 2004). However, the recent
Fig. 5. Location map of the three study areas. In the figure are shown also three examples of the typical landscapes: Cinque Terre (photo by William Domenichini, licensed
under Creative Commons Attribution-Share Alike 3.0 Unported) (a), Chianti Classico (b), and Amalfi Coast (c).
16
P. Tarolli et al. / Anthropocene 6 (2014) 10–25
abandonment of farming and the neglect of terraced structures
have led to a rapid increase in land degradation problems, with
serious threats to human settlements located along the coast,
because of the vicinity of mountain territories to the coastline
(Conti and Fagarazzi, 2004). The instability of the dry-stone walls
and the clogging of drainage channels are now the main causes
behind the most frequent landslide mechanisms within the Cinque
Terre (rock falls and topples along the sea cliffs and earth slides and
debris flows in the terraced area) (Canuti et al., 2004). Fig. 6 shows
the typical terraced landscape of the Cinque Terre subjected to
extensive land degradation: the dry-stone walls abandoned or no
longer maintained have collapsed due to earth pressure or shallow
landslides.
The landslide processes and related terrace failures illustrated
in Fig. 6 were triggered by an intense rainfall event that occurred
on 25 October 2011, where more than 500 mm of cumulated
rainfall was observed in 6 h.
2.2. Chianti Classico (Tuscany)
Another example of the acceleration of natural slope processes
caused by anthropogenic activity is represented by the Chianti hills
in Tuscany (Canuti et al., 2004). The terraced area of Tuscany is
particularly vulnerable to the combination of geological and
climatological attributes and economic factors associated with
specialized vineyards and olive groves. The farming changes that
have taken place since the 1960s through the introduction of
agricultural mechanization, the extensive slope levelling for new
vineyards and the abandonment of past drainage systems, have
altered the fragile slope stability, generating accelerated erosion
and landslides, particularly superficial earth flows and complex
landslides (Canuti et al., 2004). Different authors (Canuti et al.,
1979, 1986, 1988) reported the increase of 122% in landslide
activity in this area from 1965 to 1977, following the increase, for
the same period, in the extension of the vineyards by approximately 450%. Another study conducted in the Chianti area showed
that, following the expansion of cultivations in longitudinal rows,
versus continued maintenance of terraces, erosion increased by
900% during the period 1954–1976, and the annual erosion in the
longitudinal vineyards was approximately 230 t/ha (Zanchi and
Zanchi, 2006). As a typical example, we chose the area of Lamole,
situated in the municipality of Greve in Chianti, in the province of
Florence. The area is privately owned. The geological substrate is
characterized by quartzose turbidites (42%), feldspathic (27%)
sandstones, with calcite (7%), phyllosilicates (24%) and silty schists,
Fig. 6. Landsliding and terrace failures (white rounded arrows) within vineyards
triggered by the intense rainfall event of 25 October 2011 (Liguria, Italy) (Agnoletti
et al., 2012).
while in the south there are friable yellow and grey marls of
Oligocene origin (Agnoletti et al., 2011). For this specific area,
where the terracing stone wall practice has been documented since
the nineteenth century (see the detail of Fig. 7, where the year
‘‘1868’’ is carved in the stone), some authors have underlined a loss
of approximately 40% of the terracing over the last 50 years due to
less regular maintenance of the dry-stone walls (Agnoletti et al.,
2011). As of today, 10% of the remaining terraces are affected by
secondary successions following the abandonment of farming
activities. Beginning in 2003, the restoring of the terraces and the
planting of new vineyards follows an avant-garde project that aims
at reaching an optimal level of mechanization as well as leaving the
typical landscape elements undisturbed. However, a few months
after the restoration, the terraces displayed deformations and
slumps that became a critical issue for the Lamole vineyards.
Recently, several field surveys have been carried out using a
differential GPS (DGPS) with the purpose of mapping all the terrace
failure signatures that have occurred since terraces restoration in
2003, and to better analyze the triggering mechanisms and failures
through hydrologic and geotechnical instrumentation analysis.
Fig. 8a shows an example of terrace failure surveyed in the
Lamole area during the spring 2013. In addition to these evident
wall slumps, several minor but significant signatures of likely
instabilities and before failure wall deformations have been
observed (Fig. 8b and c). The Fig. 8b shows a crack failure
signature behind the stone wall, while Fig. 8c shows an evident
terrace wall deformation. The research is ongoing, anyway it seems
that the main problem is related both to a lack of a suitable
drainage system within terraces and to the 2003 incorrect
restoration of the walls that reduced the drainage capability of
the traditional building technique (a more detailed description and
illustrations about this problem are given in Section 3.2).
2.3. Amalfi Coast (Campania)
The third case study comprises two examples of terraced
landscapes in the Amalfi Coast (Southern Italy), a UNESCO World
Heritage Site of a Mediterranean landscape, with extraordinary
cultural and natural scenic values resulting from its dramatic
topography and historical evolution. As reported by Caneva and
Cancellieri (2007), in this area terraces appear to date back to the
period of 950–1025 AC. Since the Middle Ages, these fertile but
steep lands were transformed and shaped, through the terrace
systems, to grow profitable crops such as chestnuts, grapes, and
especially lemons. Since the XI century, the yellow of the ‘‘sfusato’’
Fig. 7. Detail of the terraces located in Lamole (Chianti Classico, Italy): the year
‘‘1868’’ is carved in the stone thus dating the beginning of terracing practice in this
area of Tuscany (photo by F. Preti).
P. Tarolli et al. / Anthropocene 6 (2014) 10–25
17
Fig. 8. Terrace failure (a), piping initiation signature behind the stone wall (white border arrow) (b), and terrace wall deformation before failure (c) (Lamole, Chianti Classico,
Italy) (photo by P. Tarolli).
lemon has been a feature of the landscape of the Amalfi Coast. At
present most of the soils are cultivated with the Amalfi Coast
lemon (scientifically known as the Sfusato Amalfitano) and
produce approximately 100,000 tonnes of annual harvest, with
almost no use of innovative technology. This special type of citrus
has a Protected Geographical Indication (I.G.P.) and is preserved by
the Consortium for the Promotion of the Amalfi Coast Lemon
(Consorzio di Tutela del Limone Costa d’Amalfi I.G.P.).
However, the spatial organization of the Amalfi Coast with
terraces had not only an agronomic objective but also a hydraulic
requirement. Therefore, the use of the word ‘‘system’’ is
appropriate in this case study of terraced landscapes. In fact, an
entire terrace system was made up of not only dry-stone retaining
walls (the murecine and macere, in the local dialect) and a level or
nearly level soil surface (the piazzola, in the local dialect) but also
important hydraulic elements supporting the agronomic practices,
such as irrigation channels, storage tanks, and a rainwater
harvesting facility (the peschiere, in the local dialect). The terrace
system in the Amalfi Coast enabled water collected at the higher
positions of rivers (e.g., the Reginna Major River) or creeks to be
diverted and channelled by gravity flow towards the lower parts of
the landscape. The bench terraces were connected by narrow stone
stairs (the scalette, in the local dialect), which were employed as
both connections among the terraces and stepped conduits for
rainwater flows. As noted by Maurano (2005), ‘‘. . . here the
construction of the irrigation system seems to precede mentally the
one of the terraces, the regimentation of water marks the site, its kinds
of cultivation and the use of the pergola, and gives origin to the
exceptional shape of the hills’’. Therefore, terracing in the Amalfi
Coast represented a complex interweaving between agriculture
and hydraulics. As a result of the major socio-economic
transformations of the post-war period, with the urbanization in
general, but specifically with the explosion of tourism activities in
this area and the related reduced interests towards agricultural
practices, a gradual degradation process of the terraced landscape
has begun (Savo et al., 2013). The excessive fragmentation of the
land ownership and the difficulty of finding manpower resources
at affordable costs – associated with the decrease in the
profitability of certain cultivations and the increase in the
maintenance expenses of dry-stone walls – are making the terrace
system the weak link of the socio-economic chain in the Amalfi
Coast (Mautone and Ronza, 2006). The fertile soils become
extremely vulnerable as soon as rural land abandonment takes
place (see Figs. 8b and 9a). Other factors contributing to the
degradation of the terraces are the lack of effective rules against
land degradation, the reduced competitiveness of terrace cultivation, and the dating of the traditional techniques only seldom
replaced by new technologies (Violante et al., 2009). The
degradation of the terraces is now dramatically under way in
some mountain zones of the Amalfi Coast, historically cultivated
with chestnut and olive trees and also with the presence of small
dairy farms. In the lower zones of the hill sides, the terraces
cultivated with lemons and grapes remain, but with difficulty.
In most mountainous parts of the Amalfi Coast, the landscape is
shaped as continuous bench terraces planted with chestnut or
olive trees and with the risers protected by grass. Whereas terraces
along steep hillsides mainly serve to provide levelled areas for crop
planting, to limit the downward movement of the soil particles
dragged by overland flow, and to enhance land stabilization,
carelessness in their maintenance and land abandonment enhance
the onset of soil erosion by water with different levels of intensity.
This situation is clearly illustrated in Fig. 9, taken in a chestnut
grove located at a summit of a hillside near the village of Scala. The
circular lunette surrounding the chestnut tree disappeared
completely because of an increase in runoff as a result of more
soil crusting and the loss of control on water moving as overland
flow between the trees. The erosion process here is exacerbated by
the fact that the soil profile is made up of an uppermost layer of
volcanic materials (Andisols) deposited on a layer of pumices, both
lying over fractured limestone rocks. This type of fertile volcanic
soil developed on steep slopes is extremely vulnerable and prone
to erosion. Fig. 9 shows that soil erosion was so intense that the
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P. Tarolli et al. / Anthropocene 6 (2014) 10–25
collapse observed in Fig. 10b is indicative of the loss of local lore
(oral communication) in building retaining stone walls and of the
importance to properly regulate overland flow.
3. Integrated view, likely solutions and future challenges
The literature review proposed in Section 1 and the practical
examples described in Section 2 underline how human actions
connected to the presence and maintenance of terraced structures
are capable of accelerating or diverting natural events such as
landslides and land degradation. Connected to these issues, the
following section is divided in three parts: first are the nonstructural management suggestions for the correct management of
terraces; second are the structural measures to be implemented for
the management of the dry-stone walls; third are the new remote
sensing technologies, such as Airborne Laser Scanner (ALS) and
Terrestrial Laser Scanner (TLS), for managing the critical issues
related to the terrace landscapes, especially to better understand
the surface drainage paths, which is a future challenge for terrace
landscape management and planning.
3.1. Non-structural management
Fig. 9. Land degradation in the upper mountainous part of the Amalfi Coast (Italy)
devoted more to chestnut cultivation (photo by N. Romano).
pumices are now exposed and transported by unchannelled
overland flow. A form of economic degradation is added to this
physical degradation because it is not cost-effective to restore
terraces that were exploited with nearly unprofitable crops, such
as chestnut or olive plantations.
Fig. 10 shows two examples of terrace failure documented
during surveys carried out recently in some lowlands of the Amalfi
Coast. The picture in Fig. 10a was taken near the head of Positano
and depicts a slump in a dry-stone wall. The observed partial
collapse can be mainly attributed to fracturing and splintering of
some individual cobble stones together with an increase in earth
and water pressures behind the inner face of the retaining wall
caused by slow upstream mass movements and lack of water
drainage along the terraces. Instead, the terrace failure shown in
Fig. 10b is an example of restoring and rebuilding of the walls,
steps, and cisterns of an old terraced landscape originally planted
with lemon trees that will be used as a vineyard. However, the
During the last century, the agriculture system has changed
deeply with an increase in productivity. The maintenance of
terraced structures became problematic due to the hard mechanization of these areas and the reduction of people in agriculture
(Mauro, 2011). The rapid disappearance and undermanagement of
the traditional terraced agricultural landscapes became a worldwide concern, and how to balance the needs between conservation
and development has become a major policy issue. Non-structural
management approaches have begun worldwide. In 2002, the Food
and Agriculture Organization of the United Nations (FAO) launched
the Globally Important Agricultural Heritage Systems (GIAHS)
project, with the aim of mobilizing global awareness and support
for dynamic conservation and adaptive management of agricultural systems and their resulting landscapes (Dela Cruz and
Koohafkan, 2009). The cultural importance of the terraces was also
underlined by UNESCO, which over the years has started projects
for the management of world heritage sites of terraced areas (i.e.,
the Honghe Hani Rice Terraces in China, the Wachau Cultural
Landscape in Austria, the Konso Cultural Landscape in Ethiopia, the
Upper Middle Rhine Valley in Germany, the Tokaj Wine Region in
Hungary, the Cinque Terre and Costiera Amalfitana in Italy, the Rice
Terraces of the Philippine Cordilleras in the Philippines, the Alto
Douro Wine Region in Portugal and the vineyard terraces of Lavaux
in Switzerland). With the same protection purposes, in 2003, the
Fig. 10. Terrace dry-stone wall failure near Positano (a), and terrace failure of a new terraced construction system for Citrus cultivation near Maiori (b) (Amalfi Coast, Italy)
(photo by N. Romano).
P. Tarolli et al. / Anthropocene 6 (2014) 10–25
European Dry-Stone forum brought together not-for-profit
organizations with the objective of raising awareness and
training people to protect and develop the cultural heritage of
the terraces at the European level, by organizing practical
initiatives (restoration work sites, training sessions, etc.) and by
carrying out research and other activities (Carrefour, 2003).
Connected to this forum, the European Dry Stone Walls Project
was changed to create a European network, which built on interregional co-operation for local development based on dry-stone
walls inheritance. In Italy in 2005, the ALPTER project was built
to counteract the abandonment of terraced agricultural areas in
the alpine region of Europe, a problem that only recently has
raised the attention of both institutions and citizens, due to the
loss of cultural heritage and the natural hazards it can produce.
The project, co-financed in the framework of the EU program
Interreg Alpine Space, began in 2005 with the collection of data
on eight terraced areas, aimed at defining procedures for
mapping, assessing geological hazards, enhancing agricultural
production and promoting tourism in terraced zones (ALPTER).
In 2010, the First Terraced Landscapes World Conference took
place in Yunnan (China), gathering not only scholars but also
indigenous peoples from all over the world to bring together
knowledge and operative perspectives about the terraced
landscapes worldwide (Du Guerny and Hsu, 2010). After the
conference, the participants established the International Alliance for Terraced Landscapes (ITLA), working to connect existing
projects worldwide with regard to the conservation and
revitalization of terraced areas.
These forums and projects are examples of non-structural
measures for terraces management. They share the recognition
and preservation of traditional terracing procedures thanks to the
gathering of professionals and scholars around agreements in the
context of National or International associations. They also propose
the development and improvement of basic and advanced training
for young people, based on reference knowledge that can be
19
transferred to other regions of Europe or to other countries
worldwide. Other non-structural measures should comprise local
action programmes that integrate terrace heritage into local
development strategies, by raising the awareness of young people
and adult volunteers in the countries involved in the programmes,
with practical field-based activities. Pilot activities for the
restoration of terraces should be pursued as well, such as model
work sites that can both preserve threatened heritage items (walls)
and be used to train professionals in traditional building methods.
Terrace maintenance can also benefit directly from the return of
this peculiar landscape (tourism, or cultural and leisure activities),
or indirectly (commerce of the products) from the improvement of
agricultural production from the maintenance of active rural
people and from the involvement of youth in terrace management
and maintenance.
3.2. Structural management
Proper planning, layout, and maintenance of terrace structures
should always be considered if they are to function as conservation
measures. All these actions start from monitoring of the terraces and
from identification of the failure mechanisms, including their causes
and consequences. The analysis of the direct shear test on
undisturbed and remoulded soil samples, for example, 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 backfill-retaining wall interfaces, and the
backfill volumetric water content (both in saturated and unsaturated
states) and ground-water level. Fig. 11 shows an example of a
monitoring system implemented on a terrace in Lamole (Section 2.2),
with (a) pressure cells to measure the stress acting on the wall
surfaces and (b) piezometers to measure the neutral stresses.
Numerous works have analyzed the causes and mechanisms of
failures by using numerical (Harkness et al., 2000; Powrie et al., 2002;
Fig. 11. Example of a monitoring system implemented on a terraces in Lamole (Chianti Classico, Italy), with (a) pressure cells to measure the stress acting on the wall surfaces,
and (b) piezometers to measure the neutral stresses (photo by F. Preti).
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P. Tarolli et al. / Anthropocene 6 (2014) 10–25
Zhang et al., 2004; Walker et al., 2007) or analytical models at
different scales (Villemus et al., 2007), or by combining the two
approaches (Lourenço et al., 2005). Other studies (including Brady
and Kavanagh, 2002; Alejano et al., 2012a,b) focused their attention
on the stability of the single wall artefact, from which it is possible to
trace the complex phenomenology of terrace instability to aspects
related to construction issues or independent from them, which can
originate as a result of natural and anthropic causes.
Once the failure mechanism is identified, it is possible to
correctly approach the maintenance of the walls, which should be
done considering an integrated view involving the dry-stone walls
themselves and the system connected to them. The components of
the traditional drainage system are often no longer recognizable,
and the incorrect restoration of the walls can be a further cause of
failures. Fig. 12a shows an example where the construction of
brickwork behind the dry-stone wall, built incorrectly to increase
the wall stability, resulted in the reduction of the drainage
capability of the traditional building technique, resulting in greater
wall instability. As well, Fig. 12b shows how drainage pipes in
plastic material located on the terrace can be partly blocked by dirt,
mortar and vegetation.
Proper wall management should therefore include the maintenance of more traditional techniques: broken sections of the walls
should be cleared and their foundations re-established. Likewise,
where other damage to the structure of the wall has occurred,
repairs should be carried out as soon as possible to prevent the
spreading of such deterioration. Copestones, which have been
dislodged or removed, should be replaced because the lack of one
or more stones can constitute a starting point for erosion. The
reconstruction of the stone wall should also be accompanied by the
simultaneous reconstruction of irrigation channels and complementary structures. The work should also include the cleaning of
the drainage ditches that might be present at the base of the drystone wall, or the creation of new ones when needed to guarantee
the drainage of excess water. Other structural measures include
the removal of potentially damaging vegetation that has begun to
establish itself on the wall and the pruning of plant roots. Shrubs or
bigger roots should not be completely removed from the wall, but
only trimmed to avoid creating more instability on the wall.
Furthermore, to mitigate erosion on the abandoned terraced fields,
soil and water conservation practices should be implemented, such
as subsurface drainage as necessary for stability, maintenance of
terrace walls in combination with increasing vegetation cover on
the terrace, and the re-vegetation with indigenous grass species on
zones with concentrated flow to prevent gully erosion (Lesschen
et al., 2008). All structural measures should be based on the idea
that under optimum conditions, these engineering structures form
a ‘hydraulic equilibrium’ state between the geomorphic settings
and anthropogenic use (Brancucci and Paliaga, 2006; Chemin and
Varotto, 2008).
3.3. Future challenges: application of high-resolution topography
derived from lidar
This section presents some examples that aim to support the
modelling of terraced slopes, and the analysis of the stability of
retaining dry-stone walls. In particular, we tested the effectiveness
of high-resolution topography derived from laser scanner technology (lidar). Many recent studies have proven the reliability of lidar,
both aerial and terrestrial, in many disciplines concerned with
Earth-surface representation and modelling (Heritage and Hetherington, 2007; Jones et al., 2007; Hilldale and Raff, 2008; Booth et al.,
2009; Kasai et al., 2009; Notebaert et al., 2009; Cavalli and Tarolli,
2011; Pirotti et al., 2012; Legleiter, 2012; Carturan et al., 2013; Lin
et al., 2013; Tarolli, 2014).
3.3.1. Abandoned terraces in vegetated landscapes
The first example is an application of high-resolution
topography derived from lidar in a vegetated area in Liguria
(North-West of Italy). Fig. 13 shows how it is possible to easily
recognize the topographic signatures of terraces (yellow arrows in
Fig. 13b), including those in areas obscured by vegetation
(Fig. 13a), from a high-resolution lidar shaded relief map
(Fig. 13b).
The capability of lidar technology to derive a high-resolution
(1 m) DTM from the bare ground data, by filtering vegetation
from raw lidar data, underlines the effectiveness of this
methodology in mapping abandoned and vegetated terraces.
3.3.2. Surface flow path characterization
In the Lamole case study (Section 2), several terrace failures were
mapped in the field, and they were generally related to wall bowing
due to subsurface water pressure. To identify the topographic
influence on such pressure or on 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. Fig. 14 provides a useful example. Fig. 14b shows the
morphology captured by a 5 m DTM, and in Fig. 14c, the derived
drainage upslope area is displayed. Fig. 14d and e depict the airborne
lidar 1 m DTM and the derived drainage upslope area, respectively.
We used the D1 flow direction algorithm (Tarboton, 1997) for the
calculation of the drainage area because of its advantages over the
methods that restrict flow to eight possible directions (D8,
introducing grid bias) or proportion flow according to slope
(introducing unrealistic dispersion).
Fig. 12. Construction of brickwork behind the dry-stone wall (a), and drainage pipes in plastic material located in the terrace can be partly blocked by dirt, mortar and
vegetation (b), within the terraces (Lamole, Chianti Classico, Italy) (photo by F. Preti).
P. Tarolli et al. / Anthropocene 6 (2014) 10–25
21
Fig. 13. Aerial photograph (a), and shaded relief map derived by 1 m LIDAR DTM (b) and related to abandoned terraces (yellow arrows) covered by vegetation and located in
Punta Mesco (Liguria, Italy).
It is clear from the figure that it is possible to correctly detect
the terraces only with high-resolution topography (1 m DTM,
Fig. 14d), thus providing a tool to identify the terrace-induced flow
direction changes with more detail. Another interesting result can
be extracted from this picture. Significant parts of the surveyed
terrace failures mapped in the field through DGPS (red points) are
located exactly (yellow arrows) where there is an evident flow
direction change due to terrace feature (Fig. 14e). However, this
approach (purely topographically based), while providing a first
useful overview of the problem needs to be improved with other
specific and physically based analyses because some of the
surveyed wall failures are not located on flow direction changes
(Fig. 14e).
3.3.3. Automatic terrace recognition and mapping
To automatically identify the location of terraces, we applied a
feature extraction technique based on a statistical threshold.
Recent studies underlined how physical processes and anthropic
features leave topographic signatures that can be derived from the
lidar DTMs (Tarolli, 2014). Statistics can be used to automatically
detect or extract particular features (e.g., Cazorzi et al., 2013; Sofia
et al., 2014). To automatically detect terraces, we represented
Fig. 14. Surveyed terrace failures (red point) in Lamole (Chianti Classico, Italy) (a). ALS DTM at 5 m resolution (b) and derived upslope area (c), and ALS DTM at 1 m resolution
(d) and derived upslope area (e). The terrace failures were mapped in the field with a DGPS.
22
P. Tarolli et al. / Anthropocene 6 (2014) 10–25
surface morphology with a quadratic approximation of the original
surface (Eq. (1)) as proposed by Evans (1979).
Z ¼ ax2 þ by2 þ cxy þ dx þ ey þ f
(1)
where x, y, and Z are local coordinates, and a through f are quadratic
coefficients.
The same quadratic approach has been successfully applied by
Sofia et al. (2013), and Sofia et al. (2014). Giving that terraces can
be considered as ridges on the side of the hill, we then computed
the maximum curvature (Cmax, Eq. (2)) by solving and differentiating Eq. (1) considering a local moving window, as proposed by
Wood (1996).
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
(2)
C max ¼ k g ða b þ ða bÞ þ C 2 Þ
where Cmax is the value of maximum curvature, the coefficients a,
b, and c are computed by solving Eq. (1) within the moving
window, k is the size of the moving window and g is the DTM
resolution. The moving window used in this study is 5 m because it
was demonstrated in recent studies (e.g., Tarolli et al., 2012) that
the moving window size has to be related to the feature width
under investigation. Terraces show a much sharper shape than
natural terrain features, and, consequently, they represent outliers
within the derived geomorphometric parameters (maximum
curvature). Sofia et al. (2014) used the boxplot approach (Tukey,
1977), and identified outliers as those points verifying Eq. (3).
C max > Q 3 Cmax þ 1:5:IQRC max
(3)
where Cmax is given by Eq. (2), Q 3 Cmax and IQRC max are the third
quartile and the interquartile range of Cmax, respectively. Fig. 15
shows for the Lamole case study an example of a curvature map (b),
the derived boxplot and the identified threshold (d), and the
topographic features (terraces) derived after thresholding the
map (c).
This approach can be used for a first and rapid assessment of the
location of terraces, particularly in land previously abandoned that
might require management and renovation planning. This method
could also offer a rapid tool to identify the areas of interest where
management should be focused.
3.3.4. 3D modelling from Terrestrial Laser Scanner
The fourth example is an application of high-resolution
topography derived from a Terrestrial Laser Scanner (TLS) for an
experimental site in Lamole specifically designed to monitor a
portion of a dry-stone wall. A centimetric survey of approximately
10 m of a terrace wall (Fig. 16a) was performed with a ‘‘time-of-fly’’
Terrestrial Laser Scanner System Riegl1 LMS-Z620.
This laser scanner operates in the wavelength of the near
infrared and provides a maximum measurement range of 2 km,
with an accuracy of 10 mm and a speed of acquisition up to
11,000 pts/s. For each measured point, the system records the
range, the horizontal and vertical alignment angles, and the
backscattered signal amplitude. The laser scanner was integrated
with a Nikon1 D90 digital camera (12.9 Mpixel of resolution)
equipped with a 20 mm lens that provided an RGB value to the
acquired point cloud (Fig. 16b). After a hand-made filtering of the
vegetation, the topographic information was exported, flipping the
order of the x, y, z values such that every point’s coordinates were
exported as y, z, x. A front viewed 3D digital model of the retaining
wall was generated by interpolating the x value with the natural
neighbours method (Sibson, 1981) (Fig. 16c). In the created wall
model, with a resolution of 0.01 m, every single stone that compose
the wall can be recognized (Fig. 16c). This level of precision could
allow simulation of the behaviour of the wall in response to back
load with high detail and without many artefacts or approximations. These results underline the effectiveness of a centimetric
resolution topography obtained from the TLS survey in the analysis
of terrace failure, thus providing a useful tool for management of
such a problem.
4. Final remarks
Terraces are one of most evident landscape signatures of man.
Land terracing is a clear example of an anthropic geomorphic
process that has significantly reshaped the surface morphology.
Since ancient times, humans have used terracing practices for
agricultural activities in different environments (both hilly and
mountainous areas) and regions of the world, and also for
mitigating soil erosion and stabilizing hillslopes. The study of
Fig. 15. Aerial photograph of terraces located in Lamole (Chianti Classico, Italy) (a), maximum curvature map (b), the features derived after thresholding the map (c), and the
derived boxplot and the identified threshold (d).
P. Tarolli et al. / Anthropocene 6 (2014) 10–25
23
Fig. 16. Surveyed wall failure in Lamole (Chianti Classico, Italy) (a), 3D-view of the TLS point cloud of the same wall with coupled RGB colours (b) and 3D-view of the TLS DTM
at 0.01 m resolution (c).
terraces represents a challenge for our modern society and
deserves particular attention. The reasons are several: their
economic, environmental and historical–cultural implications
and their hydrological functions, such as erosion control, slope
stabilization, lengthening of the rainfall concentration time, and
the eventual reduction of the surface runoff. However, land
abandonment and the different expectations of the young
generation (people are moving from farmland to cities where
job opportunities are plentiful) are seriously affecting terracedominated landscapes. The result is a progressive increase in soil
erosion and landslide risk that can be a problem for society when
these processes are triggered in densely populated areas. Another
result, less evident but in our opinion still important, is the fact that
we are progressively losing and forgetting one of the historical and
cultural roots that has characterized entire regions and cultures for
centuries. Terraced landscapes need to be maintained, well
managed (including the use of new remote sensing technologies
such lidar), and protected. While these actions can help overcome
the critical issues related to erosion risk and landslides, they can
also offer another benefit, possibly more relevant because it is
related to the economy. Terrace maintenance can improve tourism,
leisure activities, and the commerce of products related to
agricultural production, and can offer new job opportunities for
the younger generations.
Acknowledgements
Analysis resources and terrestrial laser scanner data were
provided by the Interdepartmental Research Centre of Geomatics—
CIRGEO, at the University of Padova. Aerial lidar data were
provided by the Italian Ministry of the Environment and Protection
of Land and Sea (Ministero dell’Ambiente e della Tutela del Territorio e
del Mare, MATTM), within the framework of the ‘Extraordinary
Plan of Environmental Remote Sensing’ (Piano Straordinario di
Telerilevamento Ambientale, PST-A).
We thank the Fattoria di Lamole di Paolo Socci for granting us
access to the Lamole study area for the field surveys. This study has
been partly supported by the following projects: PRIN
20104ALME4_002 Rete nazionale per il monitoraggio, la modellazione e la gestione sostenibile dei processi erosivi nei territori
agricoli, collinari e montani, funded by the Italian Ministry of
Education, Universities and Research, and MONACO, funded by the
Italian Ministry of Agricultural, Food and Forestry Policies
(Ministero delle Politiche Agricole, Alimentari e Forestali, MiPAAF).
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