Ecological intensification of agriculture through biodiversity management: introduction

A major feature of humans is that they can attain much higher population densities than any non-domestic animal species of similar body size (Damuth 1987). This is most likely due to the invention of agriculture (Herrera and Garcia-Bertrand 2018), which allowed humans to manage ecosystems in such a way that as much biomass as possible is converted into food (Vitousek et al. 1986). Early farmers developed a large diversity of crops in different regions of the world and grew them in various arrangements and rotations (Tariq et al. 2019; Teran and Rasmussen 1995). With the advent of the industrial revolution and ‘chemical’ agriculture in the 19th century in Europe (Liebig 1840), focus shifted on growing fewer high-yielding species over larger areas and time spans. This was made possible by managing soil nutrients (e.g. explored in long-term experiments at Rothamsted in the UK; Jenkinson 1991), controlling pathogens and breeding varieties that in the absence of diseases should convert those nutrients into the highest possible biomass and crop yield (Donald 1968). It was even believed that under optimal environmental conditions there would always be a best monoculture crop that would outyield any more diverse cropping system (Harper 1977). Because of the widespread and intensive use of fertilizer and of chemical plant protection to maintain current industrial agriculture, we are now faced with many negative side-effects on the environment. These negative effects include pollution, loss of soil fertility, global warming and large-scale biodiversity loss (Benton et al. 2021).

The negative impacts of modern industrial agriculture on the environment and the loss of biodiversity led researchers to reconsider over the past three to four decades the relationship between biodiversity and plant biomass production (BEF for biodiversity–ecosystem functioning relationship) and potential uses of biodiversity in a more sustainable, ecological intensification of agriculture (Sanderson et al. 2004; Schmid and Schöb 2022; Vandermeer 1981). BEF experiments have refuted the assumption of a trade-off between productivity and biodiversity in grassland, forest and other ecosystems (Balvanera et al. 2006; Cardinale et al. 2012; Huang et al. 2018) and research shows that the trade-off assumption also does not hold in agroecosystems (Brooker et al. 2023; Schöb et al. 2023). Rather, plant diversity–productivity relationships in agroecoystems are generally positive (Feng et al. 2022; Li et al. 2020; Weigelt et al. 2009). It thus seems appropriate to review and synthesize the new work about biodiversity effects in agroecosystems and its use in ecological intensification of agriculture. This is the goal of this special topic section of five literature reviews. Since many of the new results come from research carried out in China, it is especially appropriate that these reviews are published in this journal.

There are many levels at which biodiversity may enhance the functioning of agroecosystems (Table 1). These range from beneficial effects of genetic diversity and species diversity in plant production systems, to beneficial effects of species diversity at other trophic levels, to beyond within-field diversity and up to landscape-level effects (Rosa-Schleich et al. 2019). In some cases, all involved diversity components are providing harvestable products (e.g. multi-variety and multi-species crops; Brooker et al. 2023; Ji et al. 2023; Kopp et al. 2023; Schöb et al. 2023), while in other cases there are both harvestable and supporting components (e.g. pollinators or biocontrol agents; Buzhdygan and Petermann 2023). Furthermore, biodiversity effects used for ecological intensification of agriculture relate both to harvestable product as well as other ecosystem services, e.g. soil health, carbon storage and cultural services. Thus, ecological intensification by biodiversity management offers the opportunity to maintain high production levels at the same time as agroecosystem sustainability, especially by reducing chemical inputs such as fertilizers and crop protections chemicals.

Table 1:

Examples of applications of beneficial biodiversity effects in agriculture (for references see Schmid and Schöb 2022 and this special topic section)

Tool	Effects
Genetic diversity within crops	• Reduced pathogen levels due to pathogen-niche complementarity between genotypes. • Increased yield due to resource-use complementarity between genotypes. • Increased resilience under environmental variation due to compensatory responses between genotypes.
Mixed cropping	• Increased total yield due to light- and resource-use complementarity. • Facilitation (e.g. by hydraulic lift, N-fixing legumes) between species. • Increased resilience under environmental variation due to compensatory responses between species. • Reduced chemical inputs (fertilizer, plant protection).
In-field cover crops	• Improved soil fertility and reduced soil erosion. • Reduced weed pressure. • Increased trophic diversity and reduced pathogen levels. • Increased soil carbon storage.
Field boarder plant diversity	• Increased pollination and pest control by predators. • ...
Between-field crop diversity	• Insurance against broad-scale economic loss. • Increased farm-scale biodiversity. • Increased landscape services, including aesthetics.
Plant–animal coculture	• Increased rice yield. • Reduced chemical inputs (fertilizer, plant protection).
Mixed grazing systems	• Increased animal yield. • …
Mixed forest plantations	• Increased carbon sequestration. • Increased resilience to extreme events, e.g. drought.

Obviously, there are still many obstacles that slow the application of ecological intensification by biodiversity management in agriculture (Table 2; Schmid and Schöb 2022). Similar obstacles also prevent ecological intensification of forestry. One important category of obstacles is lack of knowledge about beneficial effects of biodiversity (Pearce et al. 2018), which we hope to improve with the present reviews. Another category is the imposition of inappropriate incentives from outside the system, e.g. regulatory or subsidy-providing bodies (Díaz et al. 2021). We hope that the latter ones will also be addressed by better knowledge of beneficial effects of biodiversity. Initial transitions probably need policy support, but once implemented the benefits will pay for themselves.

Table 2:

Examples of obstacles that slow the application of ecological intensification by biodiversity management in agriculture

Tool	Obstacles
Genetic diversity within crops	• Regulatory requirements preventing the use of non-standardized varieties. • Current varieties bred for high monoculture performance. • Lack of genetic resources in highly developed crop species.
Mixed cropping	• Lack of cultivation and harvesting knowledge. • Current varieties not bred for intercropping. • Subsidies for single crops, fertilizers and plant protection chemicals.
In-field cover crops	• Wrongly applied potential competition with crop or attracting pests.
Field boarder plant diversity	• Reduced area for growing crop. • Costs for seed material and management of border.
Between-field crop diversity	• Multiple cultivation and harvesting tools. • Marketing multiple products and smaller amounts per product.
Mixed forest plantations	• Nursery, planting and harvesting costs. • Some species with low economic value.

In the first review, Kopp et al. (2023) investigate mechanisms that explain BEF effects and that may be used to design crop mixtures for ecological intensification. They then develop approaches to identify candidate components for multi-variety crops with increased performance, cautioning against simplistic applications of trait-based methods and suggesting several alternatives. Schöb et al. (2023) review results of a large crop diversity experiment and demonstrate that similar mechanisms of resource complementarity occur between annual crop species as between perennial grassland species in other experiments. The authors conclude that mixed crops can outyield the best monoculture even under favorable environmental conditions and provide benefits in sustainable agricultural production. Brooker et al. (2023) review biodiversity effects in crop systems at multiple levels and spatial scales, including benefits from associated plants that support target crops both in-field and from outside fields. They point out the need for research about the functional traits underpinning biodiversity effects, which will allow development of targeted management for ecological intensification in sustainable productive agriculture. The fourth and fifth articles both provide literature reviews together with systematic analyses of two sets of original papers. Ji et al. (2023) focus on the coculture of rice and aquatic animals, which reciprocally facilitate each other, the plant by providing a beneficial abiotic environment for the animals and the animals eating enemies of the plants. Although some feed must be added for the animals, the combination with the plants allows for a more efficient nitrogen use in the coculture than for plants or animals alone. Buzhdygan and Petermann (2023) provide a very comprehensive assessment of ways by which multitrophic biodiversity can enhance ecosystem functioning and how this could be used in ecological intensification of agriculture and forestry. In their systematic analysis of literature, they find that positive BEF effects are prevalent in agroecosystems across many different contexts.

We hope that the five papers of this section will be used as a source to find orientation in the ever-increasing literature about BEF and ecological intensification. Obviously, we only cover a part of the full spectrum of papers. However, starting from these it should be straightforward to find further information by looking at further references within the cited literature and—as they will become available—more recent citations to these references.

Conflict of interest statement

The authors declare that they have no conflict of interest.