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Highlights:
Changes in five functions and two ecosystem services between 2001 and 2018 were evaluated.
Precipitation retention by the cover (40.7 %) and erosion control (35.4 %) decreased.
Flood regulation and climate regulation decreased 6.78 % and 6.80 %, respectively.
Decrease in ecosystem services was associated with replacement of natural grasslands by cropland.
Introduction
Global change comprises dimensions that interact in complex ways and alter the structure and functioning of the Earth's ecosystems (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services [IPBES], 2019). Every ecosystem is vulnerable to climate change; however, the impact and size of the ecosystem response can be highly variable. Therefore, IPBES (2019) highlights that 75 % of the Earth's surface is significantly altered with ecosystem indicators that point to an accelerated decline and that the driving forces of change have increased unprecedentedly over the last 50 years, with land use change having the greatest impact on a global scale (IPBES, 2019). Thus, land management in the current context requires a broad conceptual framework that allows for an understanding of how society interacts with its natural environment.
The growing trend of environmental degradation and the social conflicts involved have led to the development of approaches that explain how changes in ecosystems affect human well-being. Ecosystem services (ES) approach has positioned itself as a conceptual framework of great relevance allowing the development of research in several disciplines (Bennett et al., 2015). Regardless of the diverse definitions, the proposal by Fisher et al. (2009), which refers to ES as those aspects of ecosystems used (actively or passively) to produce human well-being, allows distinguishing three central elements or components: the structure and function of ecosystems relevant to a service (the provision), the service used or enjoyed by the population (the ES itself), and the change resulting in the well-being of the population; i.e., the benefit. Usually, these elements form what is called the cascade model of ES provision (Haines-Young & Postchin, 2010), thus acquiring a more operational approach (Paruelo et al., 2016).
The development of standard procedures for mapping the level of ES provision has become one of the most interesting topics in academia, considering that the availability of spatially reliable information is one of the central issues for making decisions on land use planning (Balvanera et al., 2012). Thus, software or protocols have emerged to provide support for mapping ES and quantifying their level of provision, such as ARIES (Villa et al., 2014), InVEST (Nelson & Daily, 2010) and ECOSER (2022); however, their actual application in socio-environmental conflict resolution is still incipient (Weyland et al., 2019).
Environmental degradation has been accelerated in Argentina by the intensification and expansion of high-input agriculture, as in countries with economies dependent almost exclusively on natural capital and with inequitable distribution of its benefits (Arrieta et al., 2018). Specifically, in the Argentina Pampas, the first major transformations date back to the 16th century, after European colonization, with the introduction of domestic livestock and, later, with the introduction of agriculture at the end of the 19th century. Favorable soil and climate conditions have transformed the Pampean region into the area with the largest agricultural production in Argentina, causing severe changes in the original landscape (Matteucci, 2012).
The process of agriculturization, characterized by the increase of agricultural areas in areas of traditionally livestock or mixed use, which began slowly in the 1960s, has accelerated dramatically and has led to serious ecological and social changes (Mastrangelo et al., 2015). This process has been sustained mainly by deep structural economic changes and the incorporation of the technological package associated with the cultivation of genetically modified soybean (Matteucci, 2012). At the same time, the region has been subject to intense drought and flooding events (Celleri et al., 2018) with considerable impacts on the local and national economy (Bert et al., 2021). In this regard, global climate model projections predict a higher incidence of these extreme weather events accompanied by increases in mean annual temperature and precipitation (Intergovernmental Panel on Climate Change (Intergovernmental Panel on Climate Change [IPCC], 2013) which, in combination with changes in land use, could accentuate impacts on the functioning of ecosystems and the provision of ES (Volante et al., 2012).
This context requires tools and methodologies for the characterization and monitoring of ecosystems and ES provision, which are applicable at various scales and comparable with each other. The objective of this study was to evaluate changes in five functions and two regulating ecosystem services in the Argentina Pampas in the period 2001-2018, and to analyze their relationship with the main land use changes.
Materials and methods
Study area
The Argentina Pampas comprises an extensive plain of 398 966 km2, crossed by the Tandilia and Ventania mountain ranges, and located in central-eastern Argentina, supporting the most important grassland ecosystem in the country and one of the largest in the world (Matteucci, 2012). According to its climate conditions, especially the availability of moisture, the Argentina Pampas has been subdivided into Humid Pampa and Subhumid Pampa, and into 11 ecosystem complexes, according to relief, topography and soil types (Figure 1).
Figure 1 Location of the Argentina Pampas in the South American context (a), the Argentina Pampas and its ecosystem complexes (b) and land covers in 2018 (c).
The climate is characterized as humid temperate with mean annual precipitation of 700 mm to 1 200 mm and mean annual temperature of 14 to 20 °C. Precipitation decreases from northeast to southeast with a distributed regime mainly in the spring and summer months, while mean annual temperature decreases from north to south. The interannual variability found in precipitation patterns determines occasional extreme conditions of floods and droughts over large areas, which are linked, partially, to El Niño and La Niña events, which differentially impact the study area (Aliaga et al., 2016).
Local climate, topographic, edaphic and hydrological conditions determine the distribution of grassland types that differ in their vertical and horizontal structure and in the combination of species that inhabit them (Matteucci, 2012). The intense transformation of the landscape in the sectors of greatest agricultural aptitude, such as the Rolling Pampas, Flat Pampas and Pampas between hills complexes, has led to the almost total replacement of the natural grassland, which has considerably fragmented the natural habitat, affecting the associated local diversity. This process of agriculturization has generated a homogenized landscape with low productive diversity (Lara & Gandini, 2014). In those sectors with limitations for agricultural activity, as occurs in the Flooding Pampas, natural and semi-natural grasslands, used as a source of forage for livestock, represent the main vegetation type forming floristic relicts of the vegetation that dominated this type of landscape (Gandini et al., 2019).
Ecosystem functions and services estimates for the Argentina Pampas
Ecosystem functions and services were estimated with the ECOSER protocol, a collaborative tool intended to provide decision support for land use planning (ECOSER, 2022). There are widespread protocols for mapping ecosystem services (such as ARIES or InVEST), but they differ from the cascade model of ES provision (Haines-Young & Postchin, 2010) and therefore make no clear distinction between functions and ES. In contrast, ECOSER is based on a procedure scheme which, based on edaphic properties, topography, climate variables, spatial distribution of land cover and land use, generates ecosystem functions that are integrated in a weighted linear combination (according to local ecological conditions) to create maps that capture the spatial heterogeneity in the provision of ES (Weyland et al., 2017); that is, there is an explicit separation between functions and ES.
Two regulating ES of great relevance for the Argentina Pampas were evaluated: flood regulation (reduction of frequency, extent and duration) and climate regulation (attenuation of global temperature increase, extreme weather events and changes in precipitation patterns). Considering the topographic and edaphic particularities of the study area, interannual variations in precipitation regimes usually determine flooding conditions in large areas; therefore, the ES of flood regulation is of great importance in the region. Furthermore, mitigating the impacts of climate change is one of the main global challenges and the IPCC (2013) recognizes land use as one of the main drivers of change. Thus, the ES of climate regulation has both global and local relevance due to its close relationship with the process of agriculturization.
For the generation of these ES, five ecosystem functions that support the aforementioned services were mapped: i) soil organic carbon storage, ii) biomass carbon storage, iii) erosion control, iv) soil fertility, and v) retention of excess precipitation by vegetation cover.
Soil organic carbon storage (COSi) is calculated considering the reference conditions (undisturbed native vegetation) and the change factor represented by the current vegetation cover type: COS i = COS ref * F lu * F mg * F a ; where, COS ref = amount of organic C in the soil under the reference condition; F lu , F mg and F a = change factor related to the type of soil cover/use, tillage practices and levels of C input to the soil, respectively. The values used were taken from IPCC (2006).
Biomass carbon storage (tree, shrub, herbaceous and litter carbon on the soil) is estimated according to a value given for each land cover/use by IPCC (2006).
Erosion control was estimated using the Revised Universal Soil Loss Equation (RUSLE), which predicts mean annual sediment losses according to climatic, topographic, edaphic, land use and land cover factors. The function is estimated for bare soil conditions and vegetation cover.
Soil fertility index provides a numerical valuation of its productive capacity, assuming it depends on intrinsic properties, under optimal management conditions. Productivity is expressed on the following factors: moisture, drainage, effective depth, texture, structure, base saturation of the absorbent complex, concentration of soluble salts, organic matter content, nature of clay and mineral reserves. Each factor is rated on a productivity scale of 0-100: very good (70-100), good (69-50), fair (49-30) and low (29-0). The values of this index were taken from the soil map (Instituto Nacional de Tecnología Agropecuaria [INTA], 1990).
The retention of precipitation excesses by vegetation cover (REP) is based on a relative SE estimation model proposed by Carreño et al. (2012). It is calculated as REP = B * (1 - CVB) * F cis * F prec * (1 - F slope ); where, B = vegetation biomass, CVB = coefficient of seasonal variation in biomass within a year, F cis = soil infiltration capacity, F prec = precipitation factor, and F slope = slope factor.
These five ecosystem functions were mapped at a spatial resolution of 500 m for the years 2001 and 2018, except for the soil fertility function, which we assumed constant in the region in the study period (ECOSER, 2022). Since the maps derived for the ecosystem functions have different units, they were normalized to the range 0-100. Subsequently, the maps of the regulating ES were obtained using the equation FSE i = ∑b ij * FE j , where the flow of ecosystem service i(FSE i ) derived from the linear combination of j ecosystem functions (FE j ), weighted by their relative contribution (b ij ) to that ES (Figure 2). The factors used for weighting the relative contribution of each of the ecosystem functions to the ES were taken from Weyland et al. (2017).
To assess changes in the provision of regulating ES between 2001 and 2018, relative differences were estimated for each of them at the regional scale. Based on the frequency distribution for the maps, regulating ES were categorized into low, medium and high levels of provision, based on the magnitude of changes between years. Subsequently, the high level of provision was extracted for the year 2018 and those areas of the Argentina Pampas that showed high levels in both flood control and climate control ES, called hotspots, were mapped.
On the other hand, the relationship between changes in the magnitude of ES provision levels, at the regional scale, with the main changes in land cover and land use was determined with a correspondence analysis.
Figure 2 Relationships established between the ecosystem functions (a: soil organic carbon storage, b: biomass carbon storage, c: erosion control, d: soil fertility, e: retention of precipitation excess by vegetation cover), and the ecosystem services (f: climate regulation, g: flood regulation) analyzed for the Argentina Pampas. The numerical values of the arrows indicate the relative contribution of each ecosystem function to each of the ecosystem services.
Land cover and land use in the Argentina Pampas (2001-2018)
Land covers and land uses of the Argentina Pampas for the years 2001 and 2018 were characterized with the MODIS Land Cover product (MCD12Q1, version 6) of a spatial resolution of 500 m which makes it optimal for spatial patterns of covers at a regional scale of a wide extension such as the study area. These were improved and corrected from high spatial resolution images available in Google Earth, auxiliary field data and cover maps elaborated at a scale of greater detail (Gandini et al., 2019; Guevara-Ochoa et al., 2018; Lara & Gandini, 2014). From these maps, the main changes in vegetation cover over the period derived by cross-tabulation in the geographic information systems (GIS) environment.
Results and Discussion
Changes in ecosystem functions and the provision of regulating ecosystem services (2001-2018)
At the regional scale, three of the ecosystem functions analyzed for the Argentina Pampas showed drops in their mean values during the 2001-2018 period (Table 1). The strongest losses were observed in the function of retention of precipitation excesses by vegetation cover (40.75 %) and in the function of erosion control (35.39 %). Soil organic carbon storage only decreased by 0.70 %. In contrast, biomass carbon storage was the only ecosystem function that increased moderately at the regional scale (5.61 %; Table 1).
Concerning the regulating ES analyzed, flood regulation and climate regulation decreased 6.78 % (136.74 to 127.47) and 6.80 % (142.20 to 132.53), respectively.
Table 1 Mean values of ecosystem functions (normalized to the range 0-100) in the Argentina Pampas and percentage of change for the period 2001-2018.
| Ecosystem function | 2001 | 2018 | Change (%) |
|---|---|---|---|
| Soil organic carbon storage | 55.86 | 55.47 | -0.7 |
| Biomass carbon storage | 32.26 | 34.07 | 5.61 |
| Erosion control | 70.45 | 45.52 | -35.39 |
| Retention of excess precipitation by vegetation cover | 53.69 | 31.81 | -40.75 |
When analyzing the magnitude of changes in regulating ecosystem services between 2001 and 2018, significant losses were observed in flood and climate regulation (Figures 3 and 4). In that period, for flood regulation service, 16.29 % of the study area went from medium to low levels, 16.23 % changed from high to medium levels and 3.70 % from high to low levels. Only 8.38 % of the area showed an increase in flood regulation, going from medium values in 2001 to high values in 2018, located mainly in the central-eastern sector of the Argentina Pampas (Figure 3c).
Figure 3 Ecosystem service of flood regulation for 2001 (a) and 2018 (b). Changes in provision levels for the Argentina Pampas for the period 2001-2018 (c).
Regarding climate regulating ecosystem service, 24.76 % of the study area experienced changes from high to medium levels for the period 2001-2018, while 2.08 % and 0.51 % went from medium to low values and from high to low values, respectively. Only 7.26 % of the study area presented increases in climate regulation levels which, similarly to the flood control service, was located in the central-eastern sector of the Argentina Pampas (Figure 4c). Thus, 36.22 % and 27.35 % of the entire Argentina Pampas showed significant decreases in flood and climate regulation between 2001 and 2018.
Figure 4 Ecosystem service of climate regulation for 2001 (a) and 2018 (b). Changes in provision levels in the Argentina Pampas during the period 2001-2018 (c).
The spatial patterns of these decreases are similar to those found by Paruelo et al. (2016) in an integrative index of ES, and to the changes observed in the decrease in carbon gains and increase in their seasonality caused by the conversion of natural grasslands to agricultural areas (Lara et al., 2019, 2020).
Although soil fertility has been considered herein as invariant over the period 2001-2018, some authors (Cruzate & Casas, 2016; Schipanski & Bennett, 2012) have found negative net balances in the main soil nutrients caused by agricultural and livestock production in Argentina that would ultimately negatively impact edaphic fertility. However, there is no updated and spatially explicit information that evaluates changes in the soil productivity index at a broad regional scale. Although this function is the least relevant, with lower weighting factors than the others, it is likely that the levels of SE provision of flood and climate regulation have been slightly overestimated by considering soil fertility as constant during the period analyzed.
Using spatial analysis through correspondence analysis of the areas of changes in the levels of provision of regulating ES with the main patterns of land cover change, it was determined that the losses of these services were positively associated with areas of conversion from natural grasslands to annual crops. Areas with no changes in ES provision levels were positively associated with areas with no land cover change between periods. In addition, areas that showed increases in the levels of flood and climate regulation were mainly associated with areas of transition from natural grasslands to the mosaic category of semi-natural grasslands and wetlands and, to a lesser extent, to areas with no land cover change (Figure 5).
Figure 5 Correspondence analysis showing the changes in the levels of provision of the most representative regulating ecosystem services and land cover changes in the Argentina Pampas in the period 2001-2018.
From the final (2018) maps of flood regulation (Figures 3b) and climate regulation (Figure 4b) it was possible to determine the areas with high levels of provisioning, called hotspots (Figure 6). Although most of these areas are closely associated with areas of natural grasslands and the mosaic of semi-natural grasslands and wetlands, they are also associated with crop areas, mainly in the northern sector of the region and, to a lesser extent, in the south of the Argentina Pampas.
It is possible that, in the northern sector, the hotspots are associated with the implantation of double annual crops, a practice that increased considerably at the end of the 1990s with the approval of glyphosate-resistant genetically modified soybean cultivation (Baeza & Paruelo, 2020). Unlike a single annual crop, the winter and summer crop sequences maintain a photosynthetically active plant cover for a longer period. This is reflected in the increase of the evapotranspiration process (Nosetto et al., 2015), which represents more than 80 % of the hydrological balance and is the main control of water outflow in these plain systems (Pinilla et al., 2019), thus increasing the flood control capacity. Evapotranspiration consists of two components: direct evaporation from the surface and transpiration by vegetation. The latter is coupled to carbon fixation by sharing the ecophysiological mechanism of gas exchange regulated by the stomatal opening of plants, so it is expected that this double cropping system will increase carbon sequestration, one of the processes involved in climate control. In this sense, Lara et al. (2018) demonstrated that, in the Argentina Pampas, both in natural and transformed (in this case agricultural) systems, the length of the growing season is closely related to annual carbon gains or sequestration.
On the other hand, in the southern sector of the Pampas, a process similar to that described above, although more recent, would explain the association between high levels in both control ES and the presence of crops. This sector, traditionally an agricultural area of winter crops, has experienced a significant change in the annual double cropping system. This process is based on the replacement of wheat by barley as a winter crop and soybean as a successor crop, since the former has an early harvest resulting in lower yield losses of the following summer crop, particularly soybean (Forján & Manso, 2012). Between 2000-2014, in three emblematic departments of the southern sector, a marked decrease in wheat area (from 560 950 ha to 219 880 ha) and an increase in barley (from 41 500 ha to 147 400 ha) were observed, combined with a significant increase in soybean (from 51 500 ha to 437 300 ha), which was reflected in an increasing trend in carbon gains (Lara et al., 2020).
Land cover and land use changes in the Pampas (2001-2018)
The main process of land use change in the period 2001-2018 is related to the replacement of natural grasslands. From the total area of change, 77 % is crop area, while 20 % is related to areas of semi-natural grasslands and wetlands (Figure 7). The main source of change in this region is directly related to the process of agriculturization, which coincides with other studies (Baeza & Paruelo, 2020; Lara et al., 2018, 2020). It is even a process that predates the study period (Mateucci, 2012), but which continues to further deepen.
On the other hand, the change of cover from natural grasslands to semi-natural grasslands and wetlands is located in the central-eastern sector of the Pampas, a sector that has severe limitations for crop development. In this sense, the change is probably related to the intensification of livestock activity previously analyzed in the region (Gandini et al., 2019; Lara & Gandini, 2014). Despite the loss of natural grasslands to another type of grassland, at the scale analyzed in this study, this change involved no decreases in the provision levels of regulating ES.
Unlike replacement by crops, the change in structure is minor, so it is likely that at the regional scale this type of modification does not have such a widespread negative impact. However, more detailed studies, with a more detailed analysis of a broad set of ecosystem functions, are needed to provide greater certainty about their impacts on local and regional biodiversity.
On a global scale, grasslands are one of the most transformed biomes, either replaced by crops or modified by livestock activity (Sirimarco et al., 2018). Land use change has proven to be the main driving force with the greatest negative impact on terrestrial ecosystems (IPBES, 2019), such that having spatially explicit information on the relationship between land use patterns, functions and ES is fundamental for decision making to delineate strategies on land planning. For the Argentina Pampas, the close relationship found between the decrease in the levels of regulating ES and the replacement of natural grasslands by crops should become a focus of attention to avoid trade-offs between agricultural expansion and the system that supports this type of productive activities within the framework of sustainable development. One of the advantages of the methodology developed in this study is the possibility of incorporating frequent updates of land cover and land use maps for monitoring functions and ES. In this sense, the use of time series images, coming from different sensors in a cloud geospatial analysis platform environment (Gorelick et al., 2017), could allow a more detailed and differentiated description of crops in the region (Guevara-Ochoa et al., 2018).
Conclusions
The combination of land cover and land use maps with biophysical models allowed the spatially explicit analysis of several ecosystem functions and two key regulating ecosystem services in the Argentina Pampas, evaluating their spatio-temporal changes and their relationship with the development of productive activities. At the regional scale, flood and climate regulation services decreased 6.78 % and 6.80 %, respectively, in the period 2001-2018. The spatial patterns of decrease in the levels of provision of these services were associated with the replacement of natural grasslands by crops, a process of agriculturization that has grown significantly in the last 25 years. It is important to note that the areas with increases in the levels of service provision were associated with transitions related to livestock farming, an issue that should be further studied.
