Increasing plant diversity with border crops reduces insecticide use and increases crop yield in urban agriculture

Trophic cascades regulate arthropods density and plant damage across forest strata

Research Highlight: Sivault, E., Kollross, J., Jorge, L., Finnie, S., Diez Mendez, D., Fernandez Garzon, S., Maraia, H., Lenc, J., Libra, M., Masashi, M., Nakaji, T., Nakamura, M., Sreekar, R., Sam, L., Abe, T., Weiss, M., & Sam, K. (2024). Insectivorous birds and bats outperform ants in the top-down regulation of arthropods across strata of a Japanese temperate forest. Journal of Animal Ecology. https://doi.org/10.1111/1365-2656.14146. Top-down predators exert strong effects on prey populations. Theoretical and empirical studies investigating the cascading effects of predators on biodiversity dynamics and ecosystem functionality have been central to advancing ecology and conservation biology. Yet, how intraguild predation and niche overlap drive the strength and direction of trophic cascades across forest strata is still barely understood. In a study published in this issue, Sivault et al. (2024) investigated the impacts of excluding vertebrate (birds and bats) and invertebrate (ants) predators on arthropod herbivores and plant damage in understory and canopy forest strata. The study finds that birds and bats (but not ants) have negative impacts on herbivore density, which, in turn, benefits plants by reducing leaf damage. Additionally, the effects of vertebrate predators are similar across strata. The authors also show that herbivore density and herbivory are greater in the understory compared to the canopy strata. Sivault et al. (2024) demonstrate that intraguild predation and niche overlap dictate the strength and direction of trophic cascades in forest ecosystems. In addition, these findings shed new light on forest ecology and conservation, especially considering the potential negative effects of climate change on top predators.

Cascading social-ecological benefits of biodiversity for agriculture

Cultivated species diversity can provide numerous benefits to agricultural systems. Many ecological theories have been proposed to understand the relationships between plant species diversity and trophic interactions. However, extending such theories to socioeconomic systems has been rare for agriculture. Here, we establish ten hypotheses (e.g., the natural enemy hypothesis, resource concentration hypothesis, insurance hypothesis, and aggregation hypothesis) about the relationships between cultivated species diversity (i.e., crop diversification, co-cultures of crops and domestic animals, and co-cultures of crops and edible fungi) and trophic cascades of crops, invertebrate herbivores and natural enemies in cropping systems. We then explore the socioeconomic advantages (e.g., yield, economic and environmental performance) of these trophic cascades. Finally, we propose a multi-perspective framework to promote the cascading social-ecological benefits of species diversity for agricultural sustainability. Integrating the benefits of trophic cascades into agricultural socioeconomic systems requires policies and legislation that support multi-species co-culture practices and the willingness of consumers to pay for these practices through higher prices for agricultural products.

Predators control pests and increase yield across crop types and climates: a meta-analysis

Pesticides have well-documented negative consequences to control crop pests, and natural predators are alternatives and can provide an ecosystem service as biological control agents. However, there remains considerable uncertainty regarding whether such biological control can be a widely applicable solution, especially given ongoing climatic variation and climate change. Here, we performed a meta-analysis focused on field studies with natural predators to explore broadly whether and how predators might control pests and in turn increase yield. We also contrasted across studies pest suppression by a single and multiple predators and how climate influence biological control. Predators reduced pest populations by 73% on average, and increased crop yield by 25% on average. Surprisingly, the impact of predators did not depend on whether there were many or a single predator species. Precipitation seasonality was a key climatic influence on biological control: as seasonality increased, the impact of predators on pest populations increased. Taken together, the positive contribution of predators in controlling pests and increasing yield, and the consistency of such responses in the face of precipitation variability, suggest that biocontrol has the potential to be an important part of pest management and increasing food supplies as the planet precipitation patterns become increasingly variable.

Perennial Flowering Plants Sustain Natural Enemy Populations in Gobi Desert Oases of Southern Xinjiang, China

Simple Summary

Natural habitats are essential providers of biological conservation services. The crucial role of the Gobi Desert, a dominant landscape of desert-oasis ecosystems in natural predator conservation is poorly understood, especially in southern Xinjiang, China’s Tarim Basin, where the Gobi Desert is directly adjacent to farmland and characterized by extremely sparse vegetation and more severe climatic conditions. In this context, we investigated the floral composition of the Gobi Desert and gauged the identity, relative abundance, and temporal dynamics of predatory insects associated with the prevailing plant species. We also explored whether certain plant traits and herbivore abundance are related to either natural enemy identity or relative abundance. Our results demonstrate that perennial flowering plants, such as Apocynum pictum (Apocynaceae), Phragmites communis (Poaceae), Karelinia caspia (Asteraceae), and Tamarix ramosissima (Tamaricaceae), are the dominant species of vegetation community in the Gobi Desert, and could sustain diversified arthropod predators, i.e., ladybeetles, spiders, and other natural enemies. This work not only informs sustainable pest management initiatives, but also shows how non-crop habitats at the periphery of agricultural fields underpin ecological resilience under adverse climatic conditions.

Abstract

Natural habitats play crucial roles in biodiversity conservation and shape the delivery of ecosystem services in farming landscapes. By providing diverse resources to foraging natural enemies, they can equally enhance biological pest control. In this study, we described the plant community and foliage-dwelling invertebrate predators within non-crop habitats of the Gobi Desert oases in southern Xinjiang, China. We assessed whether plant-related variables (i.e., species identity, flowering status) and herbivore abundance affect natural enemy identity and abundance. A total of 18 plant species belonging to 18 genera and 10 families were commonly encountered, with Apocynum pictum (Apocynaceae), Phragmites communis (Poaceae), Karelinia caspia (Asteraceae), and Tamarix ramosissima (Tamaricaceae) as the dominant species. Certain plant species (P. communis) primarily provide shelter, while others offer (floral, non-floral) food resources or alternative prey. Predatory ladybeetles and spiders were routinely associated with these plants and foraged extensively within adjacent field crops. Plant traits and herbivore abundance explained up to 44% (3%–44%) variation in natural enemy community and exhibited consistent, year-round effects. Among all plant species, A. pictum consistently had a significantly higher abundance of resident natural enemies, except for August 2019. Our study underlines how perennial flowering plants, such as A. pictum, are essential to sustain natural enemy communities and related ecosystem services in arid settings. This work not only informs sustainable pest management initiatives but also shows how non-crop habitats at the periphery of agricultural fields underpin ecological resilience under adverse climatic conditions.

Comprehensive quantification of global cropland ammonia emissions and potential abatement

Ammonia (NH₃) emissions mostly from agriculture result in air pollution and degrade human health. However, a full picture of soil NH₃ emissions and associated abatement in cropping systems are not well understood. Here we present a thorough analysis of cropland NH₃ emissions, discuss mitigation potential and assess associated abatement costs. Global cropland NH₃ emissions account for 26% of total soil nitrogen losses, and are estimated as 22.8-31.2 Tg N yr^-1 during 1996-2013 with the increase rate of 1.6% yr^-1. Our results also show that, with no increase in nitrogen fertilizer, climate change can contribute to an additional 10% increase in cropland NH₃ emissions in 2100 compared to the 2010 baseline. Instead, our scenario analysis show, cropland NH₃ emissions will decline by 26% from 2010 to 2100 given a 0.5% yr^-1 decrease in N fertilizer (with current technology and agricultural management level), considering the facts stronger control policies are expected to occur worldwide including Western Europe, the United States of America and China. The most ambitious management (with all known mitigation practices) can reduce cropland NH₃ emissions by up (71%, 17.6 Tg N yr^-1) at an abatement cost of US$524 billion. Our findings indicate that cropland NH₃ emissions can be mitigated through adoption of appropriate human management practices with considerable economic costs, providing a critical reference for the future NH₃ abatement strategies.

Questioning the dichotomy: A Latent profile analysis of ecological management practices in Swedish agriculture

Currently, farmers who are not certified according to organic certification schemes are considered to be conventional farmers. Discussions in the farming sector reveal a view that the current organic classification system is too narrow and does not account for the full heterogeneity of the ecological practices that are prevalent in the agricultural sector. The failure to recognise practices within conventional farming, such as low-input farming or conservation agriculture, may therefore undermine efforts to adopt ecological practices. This study investigates heterogeneity in farmer uptake of management practices using factor analysis for dimension reduction and Latent Profile Analysis (LPA) for identification of farmer segments. The findings reveal four farmer profiles with a varying degree of use of chemicals and ecological, alternative, or mixed management approaches. Using seemingly unrelated regression, we find that being certified according to the Swedish organic certification scheme KRAV, or the EU organic label, does not have an impact on a farmer's profile, suggesting that the data do not support the organic/conventional dichotomy. Instead, age, farming income and geographical location are to a greater degree the key factors in determining the larger farmer profile compared with the smaller, more diversified farmer profiles.

Assessing Potential Bioenergy Production on Urban Marginal Land in 20 Major Cities of China by the Use of Multi-View High-Resolution Remote Sensing Data

For the purpose of bioenergy production, biomass cropping on marginal land is an appropriate method. Less consideration has been given to estimating the marginal land in cities at a fine spatial resolution, especially in China. Marginal land within cities has great potential for bioenergy production. Therefore, in this research, the urban marginal land of 20 representative cities of China was estimated by using detailed land-cover and 3D building morphology information derived from Ziyuan-3 high-resolution remote sensing imagery, and ancillary geographical data, including land use, soil type, and digital elevation model data. We then classified the urban marginal land into “vacant land” and “land between buildings”, and further revealed its landscape patterns. Our results showed that: (1) the suitable marginal land area ranged from 17.78 ± 1.66 km2 to 353.48 ± 54.19 km2 among the 20 cities; (2) it was estimated that bioethanol production on marginal land could amount to 0.005–0.13 mT, corresponding to bioenergy of 2.1 × 1013–4.0 × 1014 J for one city; (3) from the landscape viewpoint, the marginal landscape pattern tended to be more fragmented in more developed cities. Our results will help urban planners to reclaim unused urban land and develop distributed bioenergy projects at the city scale.

Rice-crayfish systems are not a panacea for sustaining cleaner food production

Integrated rice-crayfish systems are expanding rapidly and are the most widely applied planting-breeding modes in Jianghan Plain in China. We conducted nutrient use efficiency, economic, and emergy analysis of three rice production modes, namely, rice monoculture (RM), rice-crayfish rotation (RCR), and rice-crayfish coculture (RCC), in Jingzhou City, which is located in the Jianghan Plain. Compared with RM mode, rice-crayfish systems using the RCR and RCC modes increased rice yield by 5-7%, showed more than 8% higher chemical nutrient use efficiency, and increased the value-to-cost ratio from 1.5-fold to 2.7-fold and the benefit-cost ratio from 2.5-fold to 3.8-fold, while decreasing irrigation water consumption and land occupation by 31% and 82-86%, respectively. RCC resulted in 10% higher crayfish yield, 12% higher phosphorus use efficiency, and 38% higher feed use efficiency than RCR. However, compared with RM, rice-crayfish systems decreased renewable fraction by 10-14%, emergy yield ratio by 9%, and emergy sustainability index by 23-26%, and they increased environmental loading ratio to 18-23%. Labor and service, fertilizer utilization, and machine and tools play important roles in these negative environmental effects. Scenario analysis showed that the rice-crayfish systems increased sustainability index by 38-45%. The technical training of new planting-breeding technology should be adopted by farmers for the efficient use of fertilizers and improvement of food yield. This study suggests that rice‑crayfish systems are not a panacea to sustain cleaner food production.

What Constraints the Expansion of Urban Agriculture in Benin?

Propelled by rapid urbanization, city administrations in low- and middle-income countries face a raft of challenges to secure food and nutrition for its poor urban dwellers. Urban agriculture (UA) seems a viable intervention to address urban food insecurity, however, experience has shown that urban gardens do not expand at the expected rate. Tackling this issue requires a deeper understanding of the main constraints that block UA expansion. Benin is not an exception; the country witnesses a breathtaking growth of its main cities that is in synchronization with a mounting food insecurity. Our research aims, therefore, to identify the main constraints for the expansion of UA in Benin, and adopt a three-pronged approach combined with a systematic literature review, a survey held among experienced urban gardeners, and in-depth interviews with stakeholders. Altogether, the synthesis shows a predominance of five main constraints: lack of land and tenure insecurity, insufficient government support, restricted market access, limited access to productive factors, and inequality issues. Specifically, while the review showed that most barriers are linked and could be tackled together, the survey indicated a political unwillingness which in our in-depth interviews is explained by the unperceived benefits of investing in UA and the lack of enforcement of urban development plans. We suggest that Beninese authorities and academics move in synchronization where the former coordinates the planning of urban gardens and the latter provides evidence to trigger public and private investments in UA. The findings could be the basis for further research on UA in West Africa and the wider continent.

Global synthesis of effects of plant species diversity on trophic groups and interactions

Numerous studies have demonstrated that plant species diversity enhances ecosystem functioning in terrestrial ecosystems, including diversity effects on insects (herbivores, predators and parasitoids) and plants. However, the effects of increased plant diversity across trophic levels in different ecosystems and biomes have not yet been explored on a global scale. Through a global meta-analysis of 2,914 observations from 351 studies, we found that increased plant species richness reduced herbivore abundance and damage but increased predator and parasitoid abundance, predation, parasitism and overall plant performance. Moreover, increased predator/parasitoid performance was correlated with reduced herbivore abundance and enhanced plant performance. We conclude that increasing plant species diversity promotes beneficial trophic interactions between insects and plants, ultimately contributing to increased ecosystem services.

Plant domestication disrupts biodiversity effects across major crop types

Plant diversity fosters productivity in natural ecosystems. Biodiversity effects might increase agricultural yields at no cost in additional inputs. However, the effects of diversity on crop assemblages are inconsistent, probably because crops and wild plants differ in a range of traits relevant to plant-plant interactions. We tested whether domestication has changed the potential of crop mixtures to over-yield by comparing the performance and traits of major crop species and those of their wild progenitors under varying levels of diversity. We found stronger biodiversity effects in mixtures of wild progenitors, due to larger selection effects. Variation in selection effects was partly explained by within-mixture differences in leaf size. Our results indicate that domestication might disrupt the ability of crops to benefit from diverse neighbourhoods via reduced trait variance. These results highlight potential limitations of current crop mixtures to over-yield and the potential of breeding to re-establish variance and increase mixture performance.