1. Introduction
The adoption of an ecosystem service (ES) approach to land and resource management has gained considerable traction globally in the last decade, due to the increased awareness of the importance of ES for human well-being [
1,
2]. However, the attention given to the importance of soils in this context is still limited. The failure to fully appreciate the contributions of soils to human well-being beyond food production has led to soil degradation issues at a global scale [
3,
4]. Despite the increasing importance of these issues, there is still a lack of information about the economic value of soil ES, as highlighted in a recent review [
5]. Furthermore, most of the existing studies adopt cost-based market valuation methods, thus disregarding the non-use component of soil ES values and failing in fully capturing the benefits that soil ES provide to society. This also affects the number of ES evaluated, which is still quite limited. Studies have pre-eminently focused on ES, the value of which can be estimated relatively straightforwardly [
5] from market values, such as carbon sequestration and water quality. Some studies have considered the loss or degradation of topsoil, the replacement of this soil or the loss of productivity as a surrogate to measure the value provided by soil [
6,
7]. Proxies such as gross margins have been used to demonstrate the value that soil has supported [
8], and more comprehensive studies have focused on replacement costs to overcome soil nutrient loss and repair physical degradation [
9]. Focusing only on a few ES limits the capability of valuation studies to explore trade-offs among different services. Accounting for such trade-offs is crucial as soils are multifunctional and it is not possible to simultaneously maximize the provision of all ecosystem services at one location. For example, increasing the food provisioning service may result in a low provision of habitats for farmland species [
10].
Only a few studies have used non-market valuation methods to elicit the benefits provided by soil ES. Among these, refs. [
6,
11] investigated preferences towards soil erosion prevention programs in Spain. In both cases, the authors found citizens to be willing to financially support such programs. Reference [
12] elicited preferences for a soil carbon program in Scotland. Reference [
13] also analyzed the benefits associated with carbon sequestration in Australia, jointly with soil erosion prevention. They found citizens to be willing to pay to support carbon sequestration programs, but not preventative soil erosion ones.
The above non-market valuation literature has the main limitation of not accounting for the spatial distribution of the benefits that soil ES provide to the population. This is important because welfare estimates might vary across space due to the influence of several factors (socio-demographic, geographic, psychological traits, etc.). Measuring taste heterogeneity (i.e., how preferences for soil ES vary across the population) can have direct relevance to the design and application of public policies and provide insight into public preferences.
In the analysis of the spatial component in the study of environmental resources using discrete choice experiment (DCE) applications, two main approaches have been recognized in the literature to investigate consumer preferences: (i) spatial econometrics and (ii) spatial statistics. Spatial econometrics is a common approach that directly includes spatial variables in regression models, referring to characteristics of the goods to be valued, the geographical context or respondents’ features [
14,
15]. Meanwhile, spatial statistics allows a comprehensive and exploratory analysis of taste patterns. This exploratory spatial data analysis can be helpful in detecting spatial heterogeneity in resident preferences for non-market valuation.
For instance, ref. [
16] included geographical variables (altitude) and socio-demographic characteristics (population size and income) in the choice model to control for preference heterogeneity towards key features of heating systems in an Italian study. The findings suggest how the benefits from reducing carbon emissions can vary spatially across the study area, evidencing a wider range of preferences from respondents living in mountain areas than those from the plains. Similarly, ref. [
17] included a variable representing the distance from respondents’ location data to a recreational site with the presence of forest attributes in France (dominant tree species, recreational facilities, absence or presence of water bodies). Results provided evidence of spatial taste heterogeneity and suggested unsurprisingly how respondents prefer forests close to their residence.
Through the use of spatial statistics, ref. [
18] mapped the distribution of welfare measures towards peatland restoration in Scotland and found the presence of specific patterns related to environmental attitudes, place identity beliefs and socio-demographic features. The authors found that people with more aspirational environmental attitudes and more informed place identity show higher WTP values. Furthermore, spatial statistics also allow for applying multiple analysis types for individual-specific WTP estimates, as [
19] demonstrated in their seminal study. The authors provided evidence of spatial dependence of welfare estimates obtained from DCE. Using Moran’s I statistic, they observed positive spatial autocorrelation among WTP values for rural landscape improvements in Ireland.
In this study we contributed, at least partially, to filling the above gaps by investigating the spatial heterogeneity of attitudes and preferences towards improving soil condition and soil ES. We used data generated via a specifically designed survey addressed to a sample of householders of the Veneto Region (Northeast Italy). The survey included several sets of attitudinal questions on soil-ES-related aspects and elicited willingness-to-pay values of several soil ES via a choice experiment approach. More specifically, the attitudinal questions aimed at measuring the degree to which citizens are aware of the need to maintain soil condition, feel a moral obligation to contribute to its conservation and—more generally—are concerned about environmental issues. We note that such traits can be seen as indicators for the “connectivity” dimension of the soil security framework proposed by [
4], which refers to the degree to which people feel connected to soil.
We investigated the spatial heterogeneity of both attitudes and welfare measures via GIS techniques. This approach allowed us to explore whether there is a link between the geographical distribution of WTP values and the distribution of attitudinal scores across municipalities. We note that the attitudinal traits do not directly refer to any specific action that citizens could perform in order to contribute to soil conservation but only measure the degree to which they feel they should act (regardless of how) in favor of preserving soil ES. On the other hand, WTP values directly measure citizens’ willingness to dedicate part of their income to support policies aimed at increasing the provisioning of soil ES. Our hypothesis is that people with positive attitudes towards soil security (and are hence highly connected to it and inclined to act to maintain or improve soil condition) show positive WTP values for soil ES, i.e., that connection is one of the drivers of individuals’ willingness to pay for soil conservation. High connection to soil and positive WTP values, in turn, would suggest how high attention should be afforded to preserve soil capability to generate well-being for societies.
The remainder of the paper is structured as follows:
Section 2 describes the methods used in the study, and
Section 3 reports our results. Finally,
Section 4 discusses the results of the study, and in
Section 5 we present the conclusions.
4. Discussion
The maps presented in this study provided evidence of generally positive attitudes towards conserving and improving soil condition and associated ecosystem services across the sampled municipalities (
Figure A2). The individuals’ attitudes towards environmental issues, soil conservation and moral obligation to protect soil generally appeared to be positive, indicating a high level of concern, awareness and involvement, respectively. This suggests high connectivity between citizens and soil; however, this may have been influenced by the detailed information provided in the survey about the role of soil in providing ES, as connectivity is strictly linked to knowledge and information about soil [
4]. The positive attitudes seem to be corroborated by the positive average WTP values retrieved in most municipalities, which suggest how householders would generally benefit from an improvement of the current level of the ecosystem services provided by soil (
Figure A3). The results showed a majority of areas among those included in the survey with positive values and only a few locations with negative WTP, evidencing a considerable degree of heterogeneity in the spatial taste distribution.
The results regarding spatial autocorrelation show weak global clustering of the averaged WTP estimates. The low level of spatial autocorrelation might be influenced by the sampling procedure, as the survey targeted a representative and not homogenously distributed sample in space, with a concentration of observations in densely populated areas and a lower number of respondents in the northern part of the region (i.e., mountainous areas). In this light, it would be advisable for further studies to explore the influence of spatial features on preferences towards soil ES to acquire spatially balanced data for clearer insights into the spatial patterns.
Concerning the link between connectivity (i.e., innate propensity to feel it is right to preserve soil ES) and WTP values (i.e., concretely act to protect soil by dedicating financial resources to this purpose), we found that more than 50% of the sampled municipalities display a positive relationship between all CE attributes and the attitudinal scores (
Figure 2). This finding suggests that spatial and psychological determinants such as motivations, beliefs, attitudes and perceptions might contribute to explaining the taste heterogeneity evidenced in our results. This also seems to imply a link between connectivity to soil and willingness to financially contribute to its conservation in most of the sampled area. This suggests how it would be beneficial to increase the awareness of the importance of soil conservation among the population to increase public acceptance of soil conservation policies and citizens’ willingness to dedicate financial resources to support them.
As [
5] pointed out in their review of economic valuation of soil ES, information about people’s preferences based on stated preference methods is scarce. Our results provide an overview of the preferences of the residents of the Veneto region with respect to soil management—an essential aspect to guide political decisions—and of their spatial distribution. Nevertheless, our results are mainly descriptive and have, due to the nature of collected data, limited predictive power restricting generalization to other regions. Given the promising results of our study, however, future investigations into predicting soil preferences for other regions around the world should account for spatial characteristics when drawing the sample. This way, they might increase the predictive power of their results.
5. Conclusions
Despite the global threat to soil and its capability to provide ecosystem services, there is still a paucity of information about the value that people attach to soil conservation. The few existing valuation studies focused in most cases on a limited number of soil ES and did not account for the public component of ES values. Furthermore, there is a lack of knowledge about the spatial heterogeneity of attitudes and preferences towards soil conservation. In this study, we tackled such issues by collecting survey data on attitudes and preferences towards soil ES and by estimating their economic value. Attitudes were investigated via specific questions retrieved from well-established psychological theories, while the valuation was performed via a choice experiment focusing on several soil ES. Spatial heterogeneity of both attitudes and values was explored via GIS techniques.
Our results highlight how individuals generally have positive attitudes towards soil conservation. More specifically, we found that citizens of most municipalities of the study area (the Veneto Region in Italy) are aware of the importance of preserving soil and feel a moral obligation towards contributing to it. This indirectly suggests how citizens are highly connected to soil. This generally positive view towards soil conservation and high connection is corroborated by the positive willingness-to-pay values for soil ES estimated in most of the study area. Both attitudes and welfare measures are highly heterogeneous across space, although no specific patterns were detected, and heterogeneity seems driven by random spatial processes, as suggested by non-significant Moran’s I values. We also found some evidence for the spatial correspondence between the distribution of attitudes and welfare measure, validating individual responses to WTP questions and providing evidence that respondents with pro-environmental attitudes display a higher WTP. However, this will need to be corroborated in future research via statistical tests.
From a policy perspective, our results suggest how it is important to preserve soil capability to generate well-being for societies and how being able to account for spatial distribution of the perception of soil ES benefits can be useful to design soil conservation programs that are coherent with public preferences. Given the link between connectivity to soil and willingness to pay for its conservation highlighted by the correspondence maps, it also seems that increasing the awareness of soil importance among the population would be beneficial to increasing the public acceptance of soil conservation policies, which requires financial support from citizens.
Overall, our study highlights the importance of accounting for spatial heterogeneity in valuation studies focusing on soil ES. Future research on this topic may concern the estimation of more formal spatial econometric models to further explore how spatial factors affect the perception of benefits provided by soil. It would be also of interest to measure more specifically the connectivity with soil, its effect on WTP values (for example by eliciting such value before and after provisioning of information about soil) and how it is distributed spatially.