Exploring Soil Conservation Services in Europe’s Urban and Peri-Urban Forests: A Comparative Analysis ^†

Abstract

With global urbanization on the rise, urban and peri-urban forests (UPFs) have emerged as a critical source of green infrastructure. This study conducts a comprehensive analysis of soil conservation (SC) services provided by UPFs across European Union (EU) member states. Utilizing an erosion modeling approach and open access earth observation (EO) data, the distribution and magnitude of SC services within UPFs are evaluated. Significant disparities in SC service supply among EU countries are revealed, with Mediterranean nations exhibiting higher values compared to central and northern European counterparts. The study underscores the pivotal role of UPFs as nature-based solutions (NbSs) in enhancing ecosystem service (ES) provision for citizen well-being. By integrating SC and ES concepts into forest management strategies, UPFs can effectively contribute to achieving Sustainable Development Goals (SDGs) and improving citizen well-being. This research provides valuable insights for EU policymakers and stakeholders, laying the groundwork for integrated UPF management strategies. Through prioritizing SC measures and adopting integrated approaches, policymakers can ensure the resilience and ecological integrity of UPFs, enhancing their capacity to provide vital ecosystem services in Europe’s urbanized landscapes.

1. Introduction

In recent decades, global population growth has surged, accompanied by a significant migration from rural to urban areas. This trend is particularly evident in Europe, where the level of urbanization is projected to reach approximately 83.7% by 2050 [1]. Concurrently, there has been a noticeable decline in the proportion of the population residing in rural areas, with towns and cities witnessing a steady and consistent increase in population. This demographic shift, coupled with the ensuing urban sprawl, has underscored an increased demand for green infrastructure, like urban and peri-urban forests.

Urban and peri-urban forests (UPFs), defined as tree-dominated ecosystems in and near cities, serve as vital buffers against the adverse effects of urbanization on the human living environment [2]. They not only sustain environmental quality but also enhance well-being by furnishing a diverse array of ecosystem services (ESs) critical for human welfare and biodiversity [3,4]. Their contributions span from local to global scales, as evidenced by their significant impact on achieving 9 out of the 17 Sustainable Development Goals outlined in the UN’s 2030 Agenda [5]. Particularly noteworthy is their role in promoting physical and mental well-being, as evidenced during crises such as the COVID-19 pandemic [6].

The multifunctional role and importance of peri-urban forests as elements of nature-based solutions (NbSs) that could improve the provision of ESs for the well-being of citizens should be a priority of the European Union. To fulfill this objective, forest management strategies must incorporate the concept of ecosystem services (ESs). The criticality of soil conservation (SC) services cannot be overstated, as they play a pivotal role in preserving landscape integrity, enhancing forest health, and mitigating environmental risks, thereby underscoring their paramount importance in peri-urban and urban forests. With the ever-expanding accessibility of earth observation (EO) data and the widespread utilization of geospatial technologies, conducting large-scale assessments of soil erosion and its impact on ESs has become increasingly feasible [7,8].

This study aims to evaluate the supply of SC services from UPFs across the European Union (EU). Employing a RUSLE-based modeling approach, the study leverages open access EO data to facilitate analysis. Specifically, the results enable comparison of soil conservation services among EU member states within a harmonized framework, laying the foundation for integrated management of UPFs regarding their ESs.

2. Material and Methods

The study was conducted in the 27 EU member states shown in Figure 1, which are Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Poland, Portugal, Romania, Slovakia, and Slovenia.

UPFs were determined by employing open access geospatial data from the European Environmental Agency (EEA) data hub (https://www.eea.europa.eu/en/datahub/datahubitem-view/1438a2d6-ec0b-4df4-a8c4-ce83b135bfa3, accessed on 15 January 2024), considering the borders of the functional urban areas (FUAs) and the forested areas in each country. FUAs were defined according to the Organisation for Economic Co-operation and Development (OECD) in cooperation with the EU, consisting of a densely inhabited urban area and a less densely populated commuting zone whose labor market is highly integrated with the city [9]. Similarly, forest areas were defined according to the CORINE dataset (CLC 2018), considering 311, 312, and 313 CLC codes. The overlapping zones between forest areas and FUAs were identified as UPF areas.

To assess SC services, the empirical Revised Universal Soil Loss Equation (RUSLE) [8,10] was employed. The potential (E_p) and actual (E_a) soil erosion rates were estimated from Equations (1) and (2), whereas their difference (Equation (3)) represents the soil conservation service E_c. All rates are estimated in t ha⁻¹ y⁻¹.

Potential soil erosion rate:

$${\mathrm{E}}_{\mathrm{p}}=\mathrm{R}\times \mathrm{K}\times \mathrm{L}\mathrm{S}$$

(1)

Actual soil erosion rate:

$${\mathrm{E}}_{\mathrm{a}}=\mathrm{R}\times \mathrm{K}\times \mathrm{L}\mathrm{S}\times \mathrm{C}\times \mathrm{P}$$

(2)

SC service:

$${\mathrm{E}}_{\mathrm{c}}={\mathrm{E}}_{\mathrm{P}}-{\mathrm{E}}_{\mathrm{a}}$$

(3)

In the above equations, R is the rainfall erosivity factor (MJ mm ha h⁻¹ y⁻¹), compiled from the Rainfall Erosivity Database at European Scale (REDES) and UERRA regional reanalysis rainfall data, spanning from 1990 to 2018 [10]. K is the soil’s erodibility factor (t ha h ha⁻¹ MJ⁻¹ mm⁻¹) determined by data from the 2009 LUCAS soil survey campaign across European Union member states, along with the Wischmeier and Smith nomograph, as outlined by Panagos [11]. LS is the topographic factor (dimensionless), determined by slope length (L) and slope steepness (S), which is computed using high-resolution EU-DEM and Desmet and Govers algorithm [12]. C is the cover management factor (dimensionless), estimated for each CLC forest code per country [13]. P is the support practice factor (dimensionless), estimated by considering the Good Agricultural and Environmental Condition (GAEC) measures in the EU member states, along with ground observations from the LUCAS survey [14]. Detailed descriptions of the factors can be found in Panagos et al. [7] and Stefanidis et al. [15].

The values of the input parameters for the present study were acquired from different data sources, as described in

Table 1. Summary of spatial datasets used in this study.

Dataset	Data Source	Data Accessibility	Spatial Resolution	Format	References
Soil erodibility (K-factor)	ESDAC	https://esdac.jrc.ec.europa.eu/content/soil-erodibility-k-factor-high-resolution-dataset-europe, accessed on 20 January 2024	500 m	raster	[11]
Slope Length and Steepness (LS-factor)	ESDAC	https://esdac.jrc.ec.europa.eu/content/ls-factor-slope-length-and-steepness-factor-eu, accessed on 20 January 2024	25 m	raster	[12]
Support Practices (P-factor)	ESDAC	https://esdac.jrc.ec.europa.eu/content/support-practices-factor-p-factor-eu, accessed on 20 January 2024	1 km	raster	[14]
Rainfall erosivity (R-factor)	ESDAC	https://esdac.jrc.ec.europa.eu/content/rainfall-erosivity-european-union-and-switzerland, accessed on 20 January 2024	1 km	raster	[10]
Cover Management (C-factor)	CLMS	https://land.copernicus.eu/pan-european/corine-land-cover, accessed on 20 January 2024	-	vector	[16]

. All geospatial datasets used in this study are widely applied in erosion modeling, especially for large-scale assessments [7,15]. The datasets were organized into GIS thematic layers in ArcGIS (v10.2) and the raster calculator tool was employed to estimate the SC values, and statistics for each country were exported. The output pixel size for SC services was set to 100 m, which is considered optimal [7]. Additionally, the standard European Coordinate Reference System was adopted, utilizing the European Terrestrial Reference System 1989 (ETRS89) datum and the Lambert Azimuthal Equal Area (LAEA) projection (EPSG: 3035).

3. Results and Discussion

The results indicate that, on average, forest coverage within the FUAs of EU member states is 27.2%. However, significant differences exist between countries (Figure 2a).

The forestland coverage for most of them (14 countries) is between 20 and 40%, and many (10 countries) have percentages lower than 20%. Its notable, though, that in four countries, the rates exhibit 40%. Specifically, the highest proportions are found in Finland (59.6%) and Sweden (58%), followed by Slovenia (47.2%). Conversely, the lowest proportions are observed in Malta (0.8%), Ireland (6.1%), and the Netherlands (9.2%).

Transitioning the focus to the supply of SC services within these areas, attention is directed towards a comprehensive quantification and examination of their distribution. Specifically, the average values of SC services provided by UPFs in each EU member state are presented in Figure 2b, revealing certain disparities among the countries. Overall, most countries (16 out of the 27) showed SC rates lower than 50 t ha⁻¹ y⁻¹, and in only two, the rates were higher than 150 t ha⁻¹ y⁻¹. Notably, the supply of SC services from UPFs is higher in Mediterranean countries (southern Europe), while it is considerably smaller in central and northern Europe. In particular, the analysis identified the UPFs of Slovenia (226 t ha⁻¹ y⁻¹), Italy (162.2 t ha⁻¹ y⁻¹), Greece (128.4 t ha⁻¹ y⁻¹), and Cyprus (127.7 t ha⁻¹ y⁻¹) as leading suppliers of SC services, while rather lower average SC values were found for Estonia (3.2 t ha⁻¹ y⁻¹), the Netherlands (3.4 t ha⁻¹ y⁻¹), Finland (4.2 t ha⁻¹ y⁻¹), and Latvia (4.4 t ha⁻¹ y⁻¹). These differences are justified due to the higher erosion rates in Mediterranean countries, attributed to the complex terrain and rainfall erosivity [7].

The above results clearly indicate that the soil conservation service provided by European forests is of paramount importance, considering that in all countries, the rates of reduction in soil loss from erosion are much higher compared to the average soil formation rate in Europe, which is estimated at 1.4 t ha⁻¹ y⁻¹ [17].

4. Conclusions

This study presents a comprehensive analysis of the soil conservation (SC) service provided by UPFs across the EU. By leveraging a RUSLE-based modeling approach and utilizing open access earth observation data, the research provides valuable insights into the distribution and magnitude of SC services from UPFs in EU member states. The results reveal significant disparities in the supply of SC services among the countries, with Mediterranean countries (southern Europe) exhibiting higher values and central and northern European countries showing lower average SC values. The findings highlight the importance of incorporating the concept of ecosystem services and soil conservation into forest management strategies in European urban and peri-urban forests, emphasizing their role as elements of nature-based solutions that can improve the provision of ecosystem services for the well-being of citizens. The study lays the foundation for integrated management of European urban and peri-urban forests regarding their ecosystem services, providing valuable insights for policymakers and stakeholders in the EU.

By prioritizing conservation measures and adopting integrated management approaches, policymakers and land managers can effectively safeguard the ecological integrity and resilience of the European urban and peri-urban forests, thereby enhancing their capacity to deliver vital ecosystem services for human well-being and biodiversity conservation in Europe’s urbanized landscapes.