ABSTRACT
To manage agroecosystems for multiple ecosystem services, we need to know whether the management of one service has positive, negative, or no effects on other services. We do not yet have ...data on the interactions between pollination and pest‐control services. However, we do have data on the distributions of pollinators and natural enemies in agroecosystems. Therefore, we compared these two groups of ecosystem service providers, to see if the management of farms and agricultural landscapes might have similar effects on the abundance and richness of both. In a meta‐analysis, we compared 46 studies that sampled bees, predatory beetles, parasitic wasps, and spiders in fields, orchards, or vineyards of food crops. These studies used the proximity or proportion of non‐crop or natural habitats in the landscapes surrounding these crops (a measure of landscape complexity), or the proximity or diversity of non‐crop plants in the margins of these crops (a measure of local complexity), to explain the abundance or richness of these beneficial arthropods. Compositional complexity at both landscape and local scales had positive effects on both pollinators and natural enemies, but different effects on different taxa. Effects on bees and spiders were significantly positive, but effects on parasitoids and predatory beetles (mostly Carabidae and Staphylinidae) were inconclusive. Landscape complexity had significantly stronger effects on bees than it did on predatory beetles and significantly stronger effects in non‐woody rather than in woody crops. Effects on richness were significantly stronger than effects on abundance, but possibly only for spiders. This abundance‐richness difference might be caused by differences between generalists and specialists, or between arthropods that depend on non‐crop habitats (ecotone species and dispersers) and those that do not (cultural species). We call this the ‘specialist‐generalist’ or ‘cultural difference’ mechanism. If complexity has stronger effects on richness than abundance, it might have stronger effects on the stability than the magnitude of these arthropod‐mediated ecosystem services. We conclude that some pollinators and natural enemies seem to have compatible responses to complexity, and it might be possible to manage agroecosystems for the benefit of both. However, too few studies have compared the two, and so we cannot yet conclude that there are no negative interactions between pollinators and natural enemies, and no trade‐offs between pollination and pest‐control services. Therefore, we suggest a framework for future research to bridge these gaps in our knowledge.
•Heat and moisture stress interact to affect conservation agriculture performance.•The interaction of heat and moisture stress is modified by soil clay content.•Conservation agriculture yields ...outperform conventional practice in drier seasons.•Heat stress increases relative yield performance on low clay soils.•N fertilizer was not required for a positive relative yield performance.
Conservation agriculture is widely promoted across sub-Saharan Africa as a sustainable farming practice that enhances adaptive capacity to climate change. The interactions between climate stress, management, and soil are critical to understanding the adaptive capacity of conservation agriculture. Yet conservation agriculture syntheses to date have largely neglected climate, especially the effects of extreme heat.
For the sub-tropics and tropics, we use meta-regression, in combination with global soil and climate datasets, to test four hypotheses: (1) that relative yield performance of conservation agriculture improves with increasing drought and temperature stress; (2) that the effects of moisture and temperature stress exposure interact; (3) that the effects of moisture and temperature stress are modified by soil texture; and (4) that crop diversification, fertilizer application rate, or the time since no-till implementation will enhance conservation agriculture performance under climate stress.
Our results support the hypothesis that the relative maize yield performance of conservation agriculture improves with increasing drought severity or exposure to high temperatures. Further, there is an interaction of moisture and heat stress on conservation agriculture performance and their combined effect is both non-additive and modified by soil clay content, supporting our second and third hypotheses. Finally, we found only limited support for our fourth hypothesis as (1) increasing nitrogen application rates did not improve the relative performance of conservation agriculture under high heat stress; (2) crop diversification did not notably improve conservation agriculture performance, but did increase its stability with heat stress; and (3) a statistically robust effect of the time since no-till implementation was not evident.
Our meta-regression supports the narrative that conservation agriculture enhances the adaptive capacity of maize production in sub-Saharan Africa under drought and/or heat stress. However, in very wet seasons and on clay-rich soils, conservation agriculture yields less compared to conventional practices.
Aim Conservation conflict takes place where food production imposes a cost on wildlife conservation and vice versa. Where does conservation impose the maximum cost on production, by opposing the ...intensification and expansion of farmland? Where does conservation confer the maximum benefit on wildlife, by buffering and connecting protected areas with a habitable and permeable matrix of crop and non-crop habitat? Our aim was to map the costs and benefits of conservation versus production and thus to propose a conceptual framework for systematic conservation planning in agricultural landscapes. Location World-wide. Methods To quantify these costs and benefits, we used a geographic information system to sample the cropland of the world and map the proportion of non-crop habitat surrounding the cropland, the number of threatened vertebrates with potential to live in or move through the matrix and the yield gap of the cropland. We defined the potential for different types of conservation conflict in terms of interactions between habitat and yield (potential for expansion, intensification, both or neither). We used spatial scan statistics to find 'hotspots' of conservation conflict. Results All of the 'hottest' hotspots of conservation conflict were in sub-Saharan Africa, which could have impacts on sustainable intensification in this region. Main conclusions Systematic conservation planning could and should be used to identify hotspots of conservation conflict in agricultural landscapes, at multiple scales. The debate between 'land sharing' (extensive agriculture that is wildlife friendly) and 'land sparing' (intensive agriculture that is less wildlife friendly but also less extensive) could be resolved if sharing and sparing were used as different types of tool for resolving different types of conservation conflict (buffering and connecting protected areas by maintaining matrix quality, in different types of matrix). Therefore, both sharing and sparing should be prioritized in hotspots of conflict, in the context of countryside biogeography.
The conversion of natural, or seminatural, habitats to agricultural land and changes in agricultural land use are significant drivers of biodiversity loss. Within the context of land‐sharing versus ...land‐sparing debates, large‐scale commercial agriculture is known to be detrimental to biodiversity, but the effects of small‐scale subsistence farming on biodiversity are disputed. This poses a problem for sustainable land‐use management in the Global South, where approximately 30% of farmland is small‐scale. Following a rapid land redistribution program in Zimbabwe, we evaluated changes in avian biodiversity by examining richness, abundance, and functional diversity.
Rapid land redistribution has, in the near term, resulted in increased avian abundance in newly farmed areas containing miombo woodland and open habitat. Conversion of seminatural ranched land to small‐scale farms had a negative impact on larger‐bodied birds, but species richness increased, and birds in some feeding guilds maintained or increased abundance. We found evidence that land‐use change caused a shift in the functional traits of the communities present. However, functional analyses may not have adequately reflected the trait filtering effect of land redistribution on large species.
Whether newly farmed landscapes in Zimbabwe can deliver multiple benefits in terms of food production and habitat for biodiversity in the longer term is an open question. When managing agricultural land transitions, relying on taxonomic measures of diversity, or abundance‐weighted measures of function diversity, may obscure important information. If the value of smallholder‐farmed land for birds is to be maintained or improved, it will be essential to ensure that a wide array of habitat types is retained alongside efforts to reduce hunting and persecution of large bird species.
Land‐use change following rapid land redistribution has varied impacts on avian diversity.
Adaptation to climate stress is an unprecedented challenge facing cropping systems. Most adaptation assessments focus on how adaptation options affect yields of a single crop under different weather ...or climate conditions. Yet, cropping systems often comprise more than one crop, and holistic assessments should consider all crops grown in a cropping system. One adaptation option is Conservation Agriculture that is commonly defined around a set of three principles: minimum mechanical soil disturbance, permanent soil organic cover, and crop species diversification.
Here we estimated the statistical effect of Conservation Agriculture on cropping-system yields under historical climate conditions.
The cropping-system yields considered all crops grown including maize (Zea mays L.) and legumes in intercropping or rotation, or both. The climate conditions included conditions of heat stress for maize and precipitation balances during the maize growing season. Heat stress for maize was studied using growing degree days over 30 °C. Precipitation balance was the difference between precipitation and reference evapotranspiration. Data included 6296 yield observations from on-farm trials in farmer plots conducted over 14 seasons (2005–2006 to 2018–2019) in ten communities in Malawi. These yield data were coupled with daily weather data. We studied three treatments: (1) a Control Practice treatment where the soil was tilled, crop residues were removed, and there was no crop species diversification, (2) a No-Tillage treatment where the soil was not tilled, crop residues were retained, and there was no crop species diversification, and (3) a Conservation Agriculture treatment where the soil was not tilled, crop residues were retained, and there was crop species diversification through legume intercropping. The use of maize varieties and legume rotation changed over time; however, the treatments studied remained the same over the entire length of the on-farm trials period in all individual communities.
Results of our study showed that heat stress for maize had a negative effect on cropping-system yields for non-stress-tolerant maize varieties and no legume rotation, although the Conservation Agriculture treatment reduced this negative effect compared with the Control Practice treatment. With the use of stress-tolerant maize varieties and legume rotation and Conservation Agriculture, our results suggest that heat stress for maize did not have a negative effect on cropping-system yields.
Our results demonstrate how Conservation Agriculture can improve the adaptive capacity of cropping systems and this provides urgently needed evidence on how farmers can adapt to climate stress.
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•Cropping systems in Southern Africa are vulnerable to climate stress and adaptation assessments should study all crops grown in a cropping system•Examined cropping-system yields based on all crops planted using yield data from 14 seasons across 10 communities coupled with daily weather data•Estimated statistical yield effect of Conservation Agriculture under climate stress•Conservation Agriculture reduced some of the negative yield effect of heat stress•We took an alternative approach to what is typically done in climate adaptation studies as we studied yields for all crops not just the main crop
•Large-scale rainout shelters successfully simulated climate stress in-situ.•CA maize yields outperformed conventional practice in a strong El Niño drought.•CA enhanced maize yield resistance to ...anthesis drought stress.•Inclusion of crop diversification, as rotation, improved CA drought stress resistance.•CA systems can increase adaptive capacity to an increased risk of climate stress.
Smallholder farming in southern African needs climate-smart agricultural approaches to adapt to current climate stress and climate variability, and increasing risk of these under future global climate change. There are a range of climate-smart systems that have been proposed and conservation agriculture (CA) based on minimum soil disturbance, crop residue retention and crop rotation is one of them. A CA trial established in 2007 in Malawi was used during cropping -seasons 2015–2016 (El Niño) and 2016–2017 (La Niña) to assess the performance and resistance of different CA maize systems under climate-related stress at anthesis, a climate sensitive growth stage. Large in-situ rainout shelters were used to simulate increased daytime temperatures and in-season droughts of 18–19 days and 27 days. CA systems better resisted climate stress around anthesis than conventional tillage practices as CA systems showed greater resistance to drought than conventional practice. This was expressed by higher CA maize grain yields, biomass yields or harvest index under conditions of natural (El Niño) or 19 day simulated drought. However, under 27 day drought simulation the resistance benefit of CA was no-longer significant. Crop diversification improved the resistance of CA systems to climate stress, more so when diversification was over time (rotation) than in space (intercropping). In all years CA systems substantially outyielded conventional practice, this highlights the benefits of medium-term (eight years) CA management before the rainout shelter experiment started. Our results from natural and simulated drought conditions confirm that CA systems can increase adaptive capacity to an increased risk of climate stress associated with projected global climate change. We show that large-scale rainout shelters are a useful means of accelerating our understanding of how long-term agricultural management practices can enhance resistance to climate stresses.
Food insecurity is a major world problem, with ca. 870 million people in the world being chronically undernourished. Most of these people live in tropical, developing regions and rely on smallholder ...farming for food security. Solving the problem of food insecurity is thought to depend, in part, on managing ecosystem services, such as the pollination of crops and the biological control of crop pests, to enhance or maintain food production. Our knowledge regarding regulating ecosystem services in smallholder-farmed (or dualistic) landscapes is limited and whilst pollination has been the focus of considerable research, the provision of natural enemy services, important for every crop worldwide, has been relatively neglected. In order to assess whether ecosystem-service research adequately represents smallholder-farmed landscapes, whilst also considering climatic region and national economic status, we examined the constituent studies of recent quantitative reviews relevant to biological control and pollination. No regulating ecosystem service meta-analysis, to our knowledge, has focussed on smallholder agriculture despite its importance to billions of peoples’ local food security. We found that whilst smallholdings contributed 16% of global farmland area and 83% of the global agricultural population (estimated using Food and Agriculture Organisation’s (FAO’s) World Census of Agriculture 2000) only 22 of 190 studies (12%) overall, came from smallholder-farmed landscapes. These smallholder studies mostly concerned coffee production (16 studies). Individual reviews of biological control were significantly and strongly biased towards data from large-scale farming in temperate regions. In contrast, pollination reviews included more smallholder studies and were more balanced for climate regions. The high diversity of smallholder-farmed landscapes implies that more research will be needed to understand them compared to large-scale landscapes, but we found far more research from the latter. We highlight that these skews in research effort have implications for sustainable intensification and the food security of billions in the developing world. In particular, we urge for balance in future ecosystem-services research and synthesis by greater consideration of a diverse range of smallholder-farmed landscapes in Africa and continental Asia.
Acute/early HIV infection is a period of high risk for HIV transmission. Better understanding of behavioral aspects during this period could improve interventions to limit further transmission. ...Thirty-four participants with acute/early HIV infection from six US cities were assessed with the Mini International Diagnostic Interview, Beck Depression Inventory II, State-Trait Anxiety Inventory, Brief COPE, and an in-depth interview. Most had a pre-HIV history of alcohol or substance use disorder (85%); a majority (53%) had a history of major depressive or bipolar disorder. However, post-diagnosis coping was predominantly adaptive, with only mild to moderate elevations of anxious or depressive mood. Respondents described challenges managing HIV in tandem with pre-existing substance abuse problems, depression, and anxiety. Integration into medical and community services was associated with adaptive coping. The psychiatric context of acute/early HIV infection may be a precursor to infection, but not necessarily a barrier to intervention to reduce forward transmission of HIV among persons newly infected.
Acute/early HIV infection is a period of high HIV transmission. Consequently, early detection of HIV infection and targeted HIV prevention could prevent a significant proportion of new transmissions. ...As part of an NIMH-funded multisite study, we used in-depth interviews to explore understandings of acute HIV infection (AHI) among 34 individuals diagnosed with acute/early HIV infection in six US cities. We found a marked lack of awareness of AHI-related acute retroviral symptoms and a lack of clarity about AHI testing methods. Most participants knew little about the meaning and/or consequences of AHI, particularly that it is a period of elevated infectiousness. Over time and after the acute stage of infection, many participants acquired understanding of AHI from varied sources, including the Internet, HIV-infected friends, and health clinic employees. There is a need to promote targeted education about AHI to reduce the rapid spread of HIV associated with acute/early infection within communities at risk for HIV.
Acute/early HIV infection plays a critical role in onward HIV transmission. Detection of HIV infections during this period provides an important early opportunity to offer interventions which may ...prevent further transmission. In six US cities, persons with acute/early HIV infection were identified using either HIV RNA testing of pooled sera from persons screened HIV antibody negative or through clinical referral of persons with acute or early infections. Fifty-one cases were identified and 34 (68%) were enrolled into the study; 28 (82%) were acute infections and 6 (18%) were early infections. Of those enrolled, 13 (38%) were identified through HIV pooled testing of 7,633 HIV antibody negative sera and 21 (62%) through referral. Both strategies identified cases that would have been missed under current HIV testing and counseling protocols. Efforts to identify newly infected persons should target specific populations and geographic areas based on knowledge of the local epidemiology of incident infections.
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