Ecological intensification

Agricultural production faces multifaceted challenges of adapting to climate change, addressing socio-economic crises, and providing ecosystem services while tackling pollution and promoting human health and social inclusion. Climate variability emphasizes the need for more resilient agricultural systems. However, conventional agricultural intensification, focused on increasing yield per unit area through low-diversity, high-input practices, has led to unintended repercussions like soil, water, and air degradation, biodiversity loss, adverse health impacts, and social marginalization (Cassman 1999). Critics advocate for a shift towards ecological intensification to fundamentally redesign farming systems for sustainability and improved outcomes (Bommarco et al. 2013). Sustainable intensification, a set of agricultural principles and technologies, aims to boost food production within the existing environmental footprint, reducing negative impacts or enhancing positive environmental benefits (Pretty 2018). While ecological intensification shares similarities with sustainable intensification, it offers a framework grounded in agroecological principles like biodiversity and synergies, emphasizing characteristics such as perenniality and diversity to optimize efficiency and improve soil and crop benefits while mitigating greenhouse gas emissions (Tittonell 2014).

Functional and structural properties of agroecosystems

In agroecosystems, like in all systems, the structure determines the functioning (Gliessman 2006). Productivity, stability, resilience, and provisioning of ecosystem services are essential functional properties of agroecosystems. Food productivity (grain, milk, meat) per unit area is the most studied property. Stability is the consistency of yields over time, while resilience is the capacity to endure and recover from short-term crises or shocks (Hodgson et al. 2015). These dimensions—stability, resilience, and productivity—do not consistently align and may change in opposite directions (Picasso et al. 2019). Ecosystem services encompass the benefits society gains from ecosystems or agroecosystems, including provisioning (e.g., food, water), regulation (e.g., pollination, erosion control), cultural (e.g., recreation, aesthetics), and support (e.g., nutrient cycling, soil formation) functions (Millennium Ecosystem Assessment 2003). Conversely, ecosystem disservices denote the negative impacts of agroecosystems, such as soil erosion, water pollution, greenhouse gas emissions, ecotoxicity, and habitat loss, often leading to trade-offs among different environmental impacts (Modernel et al. 2013; Picasso et al. 2014).

The structure of agroecosystems is defined by the type, number, and arrangement of their biotic and abiotic components, including crops, livestock, associated biodiversity, management practices, soils, etc. Two important structural properties of agroecosystems are perenniality and diversity (Picasso et al. 2022). Perenniality is the property of maintaining continuous year-round soil cover and minimizing disturbances like tillage (Sanford et al. 2021). It is seen in forests, perennial forages, and grasslands, offering numerous environmental benefits like carbon sequestration and long-term soil nutrient retention (Mosier et al. 2021; Shang et al. 2024). Systems dominated by herbaceous perennials are positively associated with improved pollinator habitats, soil conservation, organic carbon accumulation (Schulte et al. 2017), increased soil root biomass, and enhanced soil activity fostering higher soil organic carbon and nitrogen levels (King and Blesh 2018). Reducing tillage in perennial systems enhances soil structure, benefiting water and nutrient supply to crops, reducing runoff, and improving surface water quality (Lal 2020), ultimately reducing yield variability and bolstering yield stability (Sanford et al. 2021). Perennial forages regulate services by diminishing soil erosion and nutrient loss to water (Osterholz et al. 2019).

Diversity in agroecosystems involves many dimensions: planned and associated biodiversity, trophic diversity, genetic, taxonomic, and functional diversity (Altieri 1999; Gliessman 2006). Taxonomic diversity in agroecosystems can be measured through richness (species number), evenness (relative proportions), and indexes that consider richness, evenness, and species abundance (e.g., Shannon and Simpson diversity indices), among others. The relationship between biodiversity and productivity has been extensively studied both in grassland and forest ecosystems (Picasso 2017; Liang et al. 2016). Diverse systems, incorporating multiple species over time (crop rotation), spatial diversity (e.g., intercropping, agroforestry), or both, significantly enhance ecosystem services by driving productivity, resilience (Oliver et al. 2015), disease and pest pressure reduction (Liebman et al. 2008), and stability in long-term crop yields (Sanford et al. 2021).

Silvopastoral systems in Latin America

Silvopastoral systems are agroecosystems that integrate forest production with livestock production on the same farm. There is a great diversity of silvopastoral systems, with multiple uses of both the forest component (wood, fodder, fruit, nuts) and livestock (meat, milk, wool, etc.) and different combinations of them. Pezo et al. (2018), in a review of more than 150 studies on silvopastoral systems in Latin America, found that the highest diversity of silvopastoral systems is in the Tropics, followed by the temperate region and the boreal agroecological zones. These authors also reported that the most prevalent silvopastoral options involving different component arrangements and purposes included (a) scattered trees and shrubs in pastures, (b) grazing under native or secondary forests, (c) grazing under tree plantations, (d) live fences, (e) fodder banks, (f) alley farming with pastures, (g) windbreaks (h) hedgerows and (i) riparian forests.

Several reviews of silvopastoral systems have been published (e.g., Calle et al. 2012; Cubbage et al. 2012; Broom et al. 2013; Soler et al. 2018; Pezo et al. 2018; Jose & Dollinger 2019; Chará et al. 2020) and it is not the scope of this brief perspective paper to repeat or synthesize them. To provide context for discussing the different trajectories, we describe some contrasting examples of silvopastoral systems in Latin America. For instance, in the Amazon rainforest environments of Brazil and Colombia (northern South America), in areas that have suffered deforestation from 10 to 80 years ago, Lavelle et al. (2016) characterized seven production systems clusters from grazing livestock in degraded pastures to agroforestry systems, and forests, using farm size, human capital, incomes, farm products, and production intensity data. In the tropical dry forests of Jalisco, in western Mexico, Sanchez-Romero et al. (2021) identified four silvopastoral system clusters based on different proportions of forest, use of forages, and livestock stocking rate. In the Campos grasslands of Uruguay (southeastern South America), Bussoni et al. (2017) identified seven strategies for integrating forestry and livestock, using numerical clustering techniques based on land tenure, land use, livestock management, and socioeconomic data.

Trajectories towards silvopastoral systems

Agroecosystems can be characterized by their degree of perenniality and diversity (Franco et al. 2021). The different agroecosystems can be represented in a space defined by two axes (Fig. 1): perenniality (i.e., continuous soil cover by vegetation) and diversity (i.e., richness and evenness of species managed in the system). Native ecosystems like grasslands or tropical forests are examples of maximum levels of diversity and perenniality. When those native ecosystems are destroyed via tillage or herbicides (in the case of grasslands for agriculture or forest plantations) or logging and burned (in the case of tropical forests), both diversity and perenniality are lost, with the consequence of loss of ecosystem services, stability, and resilience (Fig. 1, red arrows). For instance, Kusuma et al. (2018) reported a reduction of 48% in phylogenetic diversity of understory plant communities in monoculture plantations compared to the rainforest. Monocultures of annual crops like soybeans are examples of minimum diversity and perenniality. Sown pastures may provide relatively more soil cover (perenniality) and increase diversity in the case of forage mixtures. Forest plantations have increased perenniality but minimal diversity. Silvopastoral systems with trees, forages, and livestock are usually higher in perenniality and diversity. Increasing diversity, perenniality, or both can move systems forward on a trajectory of ecological intensification (Picasso et al. 2022).

Fig. 1
figure 1

Possible trajectories of agroecosystems in the space of perenniality and diversity, from native ecosystems to degraded simplified systems (red arrows), from simple systems to silvopastoral systems (green arrows), and from native ecosystems to silvopastoral systems (yellow arrows)

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From the point of view of the structural properties of agroecosystems presented above, silvopastoral systems, depending on their arrangement, may have high perenniality and diversity. Therefore, transitions to silvopastoral systems could generally be associated with ecological intensification trajectories. However, the starting point of the trajectory is relevant. For example, if an agricultural system based on annual crops (e.g., a soybean monoculture or soybean-wheat rotation) is transformed into a silvopastoral system through the planting of forage (e.g., perennial grasses and legumes) and forest species (e.g., Eucalyptus) and the integration of livestock (e.g., beef cattle), the changes in the system’s characteristics will cause an increase in species diversity and perenniality (Fig. 1, green arrows). This could translate into greater provision of ecosystem services, greater stability, and resilience of production in the long term (Altieri 1999). A second case starting from a Eucalyptus plantation has low species diversity but high perenniality and integrates pastures (e.g., grass-legume mixtures) and livestock. This new system increases diversity and may have beneficial environmental and socioeconomic effects (Bussoni et al. 2017). A third case is starting from a conventional pasture-based system with annual warm season grasses; re-integrating the forest component increases diversity and adds many ecological benefits (Jose 2012; Chará-Serna et al. 2023).

However, if the trajectory towards silvopastoral systems starts from native ecosystems, the outcomes may not be so positive (Fig. 1, yellow arrows). Let us consider, for instance, a livestock grazing system based on native grasslands (e.g., Campos in Uruguay) where part of the area is replaced with exotic forest plantations (e.g., Eucalyptus or Pinus). This case reduces diversity because it increases the proportion of a single species (i.e., exotic forest species) and reduces the proportion of areas with high diversity (i.e., the biodiverse native grassland). If the starting point is a highly biodiverse rainforest, a tropical dry forest, or a secondary forest, transitioning towards silvopastoral systems would reduce diversity. For instance, Lima et al. (2017) have found that the implementation of silvopastoral systems in a savanna resulted in a reduction of 43% in tree species richness.

Conclusion

A wide diversity of silvopastoral systems have been promoted in Latin America for their production and environmental outcomes. However, the native ecosystems and the starting agricultural systems provide a relevant context to assess the alternative transitions toward silvopastoral systems. In the Amazon rainforest and dry forest contexts, re-introducing native trees into degraded pastures can increase biodiversity, perenniality, and ecosystem services. In the Campos grasslands context, plantations of exotic trees may have the opposite outcomes, but reintroducing pastures and livestock into exotic forest plantations can be beneficial. Contrary to the commonly accepted narrative, transitioning to silvopastoral systems is not always a trajectory of ecological intensification but depends on the contexts and native ecosystems.