2.1. Study Area
Campania is a region of southern Italy (
Figure 1), located on the Tyrrhenian shore of the peninsula. It covers about 13.600 sq km, with a population of almost 6 million people, more than half of which live within the metropolitan area of Naples. The morphology and landscapes of the region are considerably heterogeneous in its different parts, so much so that it can be divided into several sub-regions: broad plains, internal hilly areas and mountain ranges, sparse mountains, promontories, volcanoes, and three main islands. The population and most human activities are concentrated on the plains, especially the Volturno and Sele valleys, determining a vast, complex pattern of continuous and discontinuous urban fabric mixed with industrial areas and plots of intensive agricultural land [
25]. The surrounding hilly areas are less populated and mainly shaped by extensive agriculture. Campania holds several important natural or semi-natural areas: broad-leaved forests, Mediterranean coniferous forests, grassland, maquis, wetlands, cliffs, and other bare rock formations. The importance of such natural sites is testified to by the institution of two national parks and several other legally protected areas: 108 Sites of Community Importance (SCIs) and 31 Special Protection Areas (SPAs) (
https://www.mase.gov.it/pagina/schede-e-cartografie (accessed on 24 March 2023)).
Although the primary sector accounts for a minor part of its GDP, Campania is one of the most important Italian regions in terms of agriculture, particularly regarding high quality agri-food products, and much of the territory has been deeply shaped by agriculture (
https://land.copernicus.eu/pan-european/corine-land-cover (accessed on 24 March 2023)). The largest share of GDP is represented by services, among which tourism is the most important resource, thanks to a huge number of historical and archeological sites, such as Naples city center, Pompeii, seaside resorts, and world-famous beautiful landscapes, such as Sorrento, Capri, and the Amalfi Coast. In such a context, environmental recovery and landscape preservation are essential to regional development.
2.3. Land-Use-Change Scenario building
The Campania region, since the sixties, has been subjected to substantial LUCs characterized by the complexity of local dynamics. In compliance with this past trend, it is possible to hypothesize that it is going to undergo an important LUC in the coming years [
19,
29], especially related to the depopulation of inland areas and the abandonment of agricultural uses inside these contexts, with consequent problems related not only to the loss of production and income, but also to landscape maintenance and care.
Future LUCs were simulated in three different scenarios developed under alternative strategies of land management.
The “trend scenario” (TrS): starting from an awareness of past developments, a first scenario, resulting from the projection of the dynamics of the last 12 years, was developed;
The “no-tillage scenario” (NTS): in compliance with CAP’s aim, this scenario investigated the perspectives of cereal crops, as a consequence of European subsidies to farmers for no-tillage farming aimed at reducing soil erosion. Specifically, the scenario refers to the following measures: “ACA3—Reduced soil tillage techniques” Action 3.1—Adoption of no-till/“No tillage” (NT) seeding techniques”; and “Action 3.2—Adoption of minimal tillage/“Mini-mum tillage” (MT) and/or band working techniques/strip tillage”;
The “energy-crop scenario” (ECS): in compliance with RED I, II, and III policies, this scenario proposes the introduction of no-food energy crops as an alternative source of income for farmers and as a means of phytoremediation for polluted areas.
The overall duration of these simulations was 12 years, from 2018 to 2030, subdivided into yearly time steps.
A specific land-use map was developed and was used as the baseline for the comparison of scenarios, starting from the Corine Land Cover (CLC) maps referring to 2006, 2012, and 2018. The CLC maps, created within the European Program for Earth Observation, result from the processing of Landsat images with a nominal scale of 1:100.000, a minimum mapping unit of 25 ha, and a change-detection threshold of 5 ha. In these maps, different land-cover types are classified into 44 main classes on three levels of detail. In order to increase the thematic accuracy, which is currently about 85% [
30], the CLC maps’ precision was improved with information derived from LUCAS surveys [
31] and aerial photographs. In the present paper, the different land-use types were merged into 8 thematic classes with a resolution of 100 m (
Table S1).
The Dyna-CLUE (Dynamic Conversion of Land Use and its Effects) model was used for the simulation of the different scenarios [
32]. This modelling system takes account of both intrinsic and extrinsic driving factors of LUC, so that different land-cover types are allocated at the grid-cell level in compliance with a weighted combination of location characteristics (geomorphology, climate, distance to main facilities and infrastructure, etc.), agents operating in the region, socioeconomic conditions, and spatial policies [
32,
33,
34,
35].
Agents’ competitive strength plays an important role in the Dyna-CLUE modelling framework and it is weighted by setting a parameter known as ‘conversion elasticity’, which can assume values between 0 and 1 for the easy and difficult conversion, respectively, of a land-use type into different ones. The aptitude for conversion is related to the level of capital investment in each single class [
36,
37] so that the lowest value was given to non-irrigated arable land, while the highest value was given to urban fabric (
Table S1).
In order to prevent urban areas from being converted into agricultural land, as well as all the other transitions that are actually quite unlikely to happen (
Table S2), a conversion matrix representing the allowed changes between different land-cover types must be set [
37].
The effect of location features on assigning each land-use type at grid-cell level is estimated by a regression analysis correlating every single land cover type, used as a dependent variable, with those factors deemed to be significant on its actual pattern, used as independent variables. Statistics are based on the logit model in compliance with the following formula (1):
where Pi is the probability for the allocation of a specific land cover on the cell I; X1,2…n are the values assumed by the driving factors in the cell I; and β1,2…n coefficients are the weights of each factor in determining that land cover, calculated by running the regression, as well as the β0 constant value [
37].
A stepwise procedure is used in the regression to exclude directly those variables not showing a significant influence on the actual land-use pattern [
36].
Regression analysis was based on dependent variables derived from the 2012 land-cover map. The introduction of a new land-cover type such as energy crops, not yet existing in the current land-use classification, made it necessary to use a proxy variable to represent its hypothetical spatial distribution in compliance with a criterion of suitability [
25,
33]. Then, a suitability map based on Multi-Criteria Evaluation (MCE) was used to simulate a possible land-use pattern of energy crops in the related scenario. The energy-crop scenario map developed in Cervelli’s [
38] study of the Campania region was used. Geophysical and anthropic factors thought to be meaningful driving forces of LUC in the study area were used as independent variables of the regression analysis (
Table 1).
In compliance with Pontius and Schneider [
39], the validation of the regression analysis was performed by the relative operating characteristic (ROC) method, comparing the simulated spatial arrangement of every single land-use type with the actual 2018 one (or the suitability map as regards energy crops). ROC values higher than 0.5 suggest a correlation between predicted and observed land cover, the more significant the closer it is to 1.
The quantity of land undergoing conversion into different classes (demand) was calculated for every year of the simulation in compliance with the different purposes of each scenario [
36,
37].
Land requirements for TrS were computed in compliance with actual LUCs occurring during the period 2012–2018 in terms of absolute surfaces gained or lost by each land-cover class.
As regards NTS and ECS, demands are based on goals thought to be plausible, in compliance with the regional agricultural policies and in the wider context of current European agriculture conditions.
Specifically, regarding the NTS, it is related to the payments for environmental, climate, and other management commitments (ACA payments) that require very specific production and management behaviors of farmers. The ACA payments (which will operate very similarly to those of Measures 10 and 11 of the 2014–2020 programming), will have the objective of offsetting the higher costs and lost income associated with the voluntary adoption of the commitments for the climate and the environment. Among these ACAs, intervention “3” is intended for “ACA3—Reduced soil tillage techniques”, as reported in the Italian National Strategic Plan, sent to the European Commission.
The ACA3 interventions, aimed at improving environmental performance, are divided into two actions (basic commitments):
- -
adoption of no-till/no-tillage (NT) seeding techniques;
- -
adoption of minimum-tillage techniques/minimum-tillage (MT) and/or band-tillage/strip-tillage techniques.
Assuming that not all available soils will be maintained with no-tillage or minimum tillage techniques, an overall +2% was earmarked for non-irrigated arable land (in opposition to the actual negative trend) by the end of the simulation, mostly decreasing the actual positive trend of permanent crops. Regarding the other classes, they follow the trend, though at a lower rate than in the past.
Finally, regarding the ECS, in compliance with the same criteria, a new land-cover class of energy crops was introduced totaling about 40,000 ha, equal to 25% of the eligible areas pointed out by Cervelli [
38], by the end of the simulation.
In Dyna-Clue model, the allocation of different land-use classes at grid cell level is performed by an iterative process, in compliance with location-based conditions, running until the total amount of LUCs meets the demand of each scenario, in a combination of a top-down and a bottom-up approach [
32,
40].
2.4. The Ecosystem-Service Assessment
The ES assessment within each scenario was developed using InVEST software (a system for the Integrated Valuation of Ecosystem Services and Tradeoffs), consisting in a set of models developed solely to quantify the provisioning of ESs as a result of land cover and land management [
41]. The InVEST framework was developed by the Natural Capital Project, a partnership between Stanford University, The Nature Conservancy, and the World Wildlife Fund, with the specific aim of promoting ESs as guiding principles for decision making [
42]. Unlike the common monetary methods, generally assigning flat values to each class of land cover in relation to a specific ES, InVEST models also take into account the effect of landscape configuration (e.g., edge effect, fragmentation, and distance to sources) on the provisioning of the ES [
43]. As a result of modelling, ESs can be expressed both in biophysical and monetary terms, in accordance with the type of ES and the availability of data needed to run each model [
41].
The ESs investigated in the present paper were the sediment-delivery ratio (SDR) and carbon storage and sequestration (CSS). The choice of these ESs arises from the need to verify the main impacts potentially linked to the hypothesized changes in land use. The three scenarios are closely related with the soil-erosion issue which, in many Mediterranean areas, represents the first step towards progressive desertification [
44]. Soil erosion is mainly due to climate conditions, soil composition, and land management [
45,
46,
47,
48,
49,
50]. Since the first two factors are not directly manageable in compliance with human policies, land-management policies play a fundamental role in the mitigation of the phenomenon, encouraging or sustaining the incentivization of new crops in place of the current crops [
51], as well as conservative agricultural practices like cover cropping and reduced tillage [
21]. Particular attention was given also to soil carbon, considering the positive relation that it has with the erosion issue and in general with soil bio-physicochemical properties [
52]. Moreover, the analysis of the landscape carbon stock was intended to relate a typically regional issue, erosion, with one of the greatest international issues, that is, global warming. In the present paper, the carbon storage and sequestration (CSS) service (InVEST software) was assessed as a measure contributing to Earth’s climate-change mitigation. Landscape management, as well as affecting an ecosystem’s survival, plays an important role also in removing greenhouse gases (GHGs) such as CO
2 from the atmosphere; a landscape composed of forests, grasslands, peat swamps, and other terrestrial ecosystems collectively stores carbon [
52,
53], keeping CO
2 out of the atmosphere, where it would contribute to climate change.
2.4.1. The Erosion-Risk-Mitigation Ecosystem Service via the Sediment- delivery-ratio Model (InVEST Software)
The InVEST model dedicated to erosion is based on the universal soil-loss equation (USLE) [
54], which is a widely acknowledged approach for estimating soil loss at watershed level. In compliance with this equation, the amount of soil loss (ton ha
−1 yr
−1) is given by the following formula (2):
where R is the rainfall erosivity, K is soil erodibility, LS is the slope-length gradient factor, C is the cover-management factor and P is the support-practice factor. For a better understanding of these parameters, please refer to Wishmeier and Smith [
54].
Not all the soil eroded generally reaches the catchment outlet, with the proportion that does depending on land morphology, which affects the shape and extent of the sediment stream. So, part of the sediment removed from an upslope location is held in a lower one, showing a certain retention effect. Hence, the InVEST model estimates the sediment export (ton pixel
−1 yr
−1) as follows (3):
where SDR
i is the sediment-delivery ratio, intended to be the proportion of soil loss in location i actually reaching the catchment outlet.
Since we worked at a resolution of 100 m, the final unit of measurement is ton ha
−1 yr
−1. The SDR calculation is based on the concept of a connectivity index illustrated by Borselli [
55] and it relies on a high-resolution DEM as a function of the slopes.
Table 2 shows the data needed to run the model for every scenario. While R, K, and LS factors were considered to be constant over time, human-activity-dependent factors, such as land cover and management, were weighted in compliance with the different contexts investigated. As not enough data about anti-erosion support practices were available, the P-factor was assumed to be equal to 1.
2.4.2. The C-Factor Deepening
In order to evaluate the impact on soil erosion of future LUCs driven by alternative strategies of land management, an estimation of the cover-management factor (C-factor) within the universal soil-loss equation (USLE) was carried out. The C-factor is a parameter ranging between 0 and 1 that takes into account the influence of land cover and management on soil loss, with bare soil having a C-factor value of 1 [
54]. Despite the wide portion of the literature assigning uniform C-factor values in compliance with land cover [
21,
58,
59], or remote sensing techniques [
60,
61,
62], the present study attempted to consider the effect of different agricultural practices on arable lands, with special regard to conservative and no-tillage practices, as they are incentivized by CAP. The C-factor land-use and management model (LANDUM) [
21] was therefore used to estimate a C-factor for each scenario. In compliance with LANDUM, the C-factor for arable lands is calculated as follows (4):
where C
crop is a constant depending on the crop type, while C
management is a value depending on land-management practices.
The crop factor is calculated as a weighted average value based on the actual crop composition of arable lands in the region as follows (5):
where n is the crop type while S is its share at regional level.
Data about the crop composition of arable land in the Campania region are available on the Italian Institute of Statistics web portal [
63] (ISTAT, 2016). Although crop rotation alters the pattern of arable lands quite quickly, crop composition can be considered stable in purely quantitative terms [
21]; thus, it was approximated through an analysis over a period of six years, from 2006 up to 2011, years for which the most up-to-date information was available. In this way, it was possible to calculate the current C
crop, thought to stay the same up to 2030 in the TrS, while for the NTS and ECS, different coefficients were found in accordance with the supposed alterations in crop composition because of alternative policies.
The C-factor values taken as a reference in the present study were those suggested by Panagos [
21].
The management factor is calculated as the result of different agricultural practices which affect soil loss as follows (6):
where C
tillage is related to tillage practices, C
residues to the maintenance of crop residues on the field, and C
cover to eventual cover cropping.
Tillage practices, which represent one of the main issues of the present study, can be classified into three different types: conventional, conservative, and no-tillage (also known as zero tillage or sod seeding). Conventional tillage is meant as traditional preparation of soil for sowing by ploughing and harrowing; residues of previous crops are often harvested as byproducts. Conservative tillage is a type of land management which keeps a part of plant residues on the ground and, generally, adopts a lower level of soil processing, for instance not inverting the soil layers (vertical tillage), or at least choosing once-off ploughing. No-tillage farming involves sowing directly into the ground without any mechanical soil processing, in which case weed control is obtained through herbicides or mulching. As they can improve soil structure and stability, conservative and no-tillage practices represent an important strategy to reduce soil loss [
16,
64,
65]. Among these different kinds of land management, untilled soils are those showing the lowest rate of erosion, ceteris paribus. In compliance with this assumption, the tillage factor is estimated by the following Equation (7):
where S is the surface treated, respectively, by conventional, conservative, and no-tillage practices.
Data about the share of tillage at the European, national, and regional level are available on the European Statistics Office web portal [
66].
For TrS and ECS scenarios, the Ctillage coefficients were considered to stay equal to the current value, since no reliable forecast can be made regarding the future share of arable land treated by different tillage practices.
For the NTS scenario, the achievement of 25% tilled surfaces has been hypothesized. Specifically, the conservative and the no-tillage scenarios were treated equally (12.5% + 12.5%).
Maintaining crop residues on fields and cover cropping, which consists in growing any kind of intermediate plantation with the specific aim of reducing soil loss during periods when land would be normally bare, can have a significant impact on soil protection [
67,
68]. As no data related to crop residues and cover crops are available at any scale, the C
residues and C
cover parameters were considered equal to 1.
The C-factor values for non-arable land were obtained from Diodato [
58] and Fagnano [
69] studies (
Table 3).
2.4.3. The Carbon-Sequestration Ecosystem Service via Carbon Storage and Sequestration Model (InVEST Software)
Global warming seems to be deeply connected with the increasing atmospheric concentration of greenhouse gases, among which carbon dioxide (CO
2) represents a serious concern, since a significant part of its emission is caused by human activities, in particular the combustion of fossil fuels and deforestation [
70,
71,
72]. In the light of this, carbon sequestration is probably the most acknowledged ES [
53]. The photosynthetic activity of organisms removes CO
2 from the atmosphere and stores it in biomass such as wood, which is one of the most important carbon stocks in terrestrial ecosystems. This is why LUCs, especially as regards the conversion of natural areas into agricultural or built-up land, play a key role in the carbon cycle [
3]. Living beings are not the only carbon stock, but a considerable amount of organic matter is stored in the form of undecomposed dead material, humus, peat, and fossils, so much so that soil is actually the largest carbon stock of terrestrial ecosystems [
73].
Land management, especially as regards crop rotation, fertilization, and tillage, has a deep impact on soil carbon stocks. Parenthetically, it should be noted that increasing soil organic content improves the stability of aggregates, helping mitigate erosion as well [
16,
20,
52,
74].
The InVEST model for mapping carbon sequestration calculates the total amount of elementary carbon stored in each grid cell, in terms of Mg ha
−1, as the sum of the four main carbon pools, that is, the aboveground biomass, belowground biomass, dead organic matter, and soil organic carbon. Thes carbon pools show different values, depending primarily on land cover but also on land management. In principle, forests show greater stocks in every pool. Grasslands also generally show high levels of carbon storage, while for agricultural land greater stocks of soil carbon can be found under a system of reduced tillage compared to conventional practices [
74], all other things being equal. Each land-use class was therefore assigned a value for every single carbon pool estimated in accordance with the protocol proposed by the Intergovernmental Panel on Climate Change [
75], which takes into consideration many different variables influencing carbon storage including the main species, latitude, land management and, as regards agricultural surfaces, even input level and tillage practices.
Table 4 shows the carbon stocks of each land-cover type derived from IPCC reference values.
As a result of modelling, a map of carbon storage was prepared out for each scenario. The amount of carbon sequestration can be calculated as the difference between the carbon storage at baseline and those estimated for future scenarios.