The effects of drought stress and type of fertiliser on generalist and specialist herbivores and their natural enemies

Abiotic stresses such as drought and nutrient availability can affect invertebrate herbivores feeding on plants, and potentially cascade up to impact their predators and parasitoids. Although these two factors separately been the subject of many studies, there are few tests of their combined effects in the context of pest species and their natural enemies on cultivated plants. Climate change models predict an increase in the frequency and severity of droughts, while the type and amount of fertiliser applied to crops is more under the control of growers. Understanding how these two abiotic factors may interact is key to utilising the potential of natural enemies to control pests under a future climate. To address this, a range of drought and fertiliser type treatments were applied to a model Brassica system in a factorial design, and the performance of two ubiquitous aphid species and their parasitoids was assessed. One aphid species was a specialist on Brassicas (Brevicoryne brassicae, with parasitoid Diaeretiella rapae) and the second a generalist aphid species (Myzus persicae, with parasitoid Aphidius colemani). The performance of both aphid species responded in a similar way to the treatments, and was maximised on plants growing in organic fertilisers under medium levels of drought stress. The strongest effects of drought and fertiliser cascaded up to affect parasitoids. Parasitoid performance responded in a broadly similar way to their aphid host performance in relation to fertiliser type. Some of the smaller effects of fertiliser treatments on aphid performance were not found for parasitoid performance. Aphid performance was greatest on plants under medium drought stress, but the parasitoids only responded consistently to the high drought stress treatment, on which their performance was reduced. Interactions between the drought and fertiliser did not have a large effect on aphid or parasitoid performance, compared with the strong main effects found for each treatment. These results are discussed in the context of previous and future research on the impacts of abiotic stresses on invertebrate herbivores and their natural enemies

Drought and root herbivory interact to alter the response of above-ground parasitoids to aphid infested plants and associated plant volatile signals

Multitrophic interactions are likely to be altered by climate change but there is little empirical evidence relating the responses of herbivores and parasitoids to abiotic factors. Here we investigated the effects of drought on an above/belowground system comprising a generalist and a specialist aphid species (foliar herbivores), their parasitoids, and a dipteran species (root herbivore).We tested the hypotheses that: (1) high levels of drought stress and below-ground herbivory interact to reduce the performance of parasitoids developing in aphids; (2) drought stress and root herbivory change the profile of volatile organic chemicals (VOCs) emitted by the host plant; (3) parasitoids avoid ovipositing in aphids feeding on plants under drought stress and root herbivory. We examined the effect of drought, with and without root herbivory, on the olfactory response of parasitoids (preference), plant volatile emissions, parasitism success (performance), and the effect of drought on root herbivory. Under drought, percentage parasitism of aphids was reduced by about 40–55% compared with well watered plants. There was a significant interaction between drought and root herbivory on the efficacy of the two parasitoid species, drought stress partially reversing the negative effect of root herbivory on percent parasitism. In the absence of drought, root herbivory significantly reduced the performance (e.g. fecundity) of both parasitoid species developing in foliar herbivores. Plant emissions of VOCs were reduced by drought and root herbivores, and in olfactometer experiments parasitoids preferred the odour from well-watered plants compared with other treatments. The present work demonstrates that drought stress can change the outcome of interactions between herbivores feeding above- and belowground and their parasitoids, mediated by changes in the chemical signals from plants to parasitoids. This provides a new insight into how the structure of terrestrial communities may be affected by drought

Definition of favourable conservation status for hedgerows

An output of Natural England’s Defining Favourable Conservation Status (DFCS) project. Hedgerows are a widespread Priority Habitat (i.e. a habitat of principal importance for biodiversity conservation), providing key semi-natural habitat for a broad range of biodiversity, including many threatened species. They occur predominantly in lowland farmland but also in urban areas. The distribution of hedgerows reflects historic and current agricultural and social practices, and underlying biophysical variables. Hedgerows are largely man-made features, which historically were created through the planting of woody species for the specific purpose of dividing up rural land and preventing the movement of stock between land parcels. In urban areas, hedgerows have mainly been planted to create boundaries between properties, for aesthetic or wildlife reasons within gardens and parks. The length of hedgerows in England needs to increase substantially in order to support thriving biodiversity and to achieve Favourable Conservation Status (FCS). There is a moderate amount of evidence supporting the recommended level of increase in hedgerow, but the evidence that is available overwhelmingly supports an increase in length for a range of taxa. Overall confidence in an increase in hedgerow length being required is high. Higher average density of hedgerows (in suitable habitats) due to increased length will result in improvements in the provision of hedgerow habitat for wildlife and in landscape connectivity. The use of hedgerows by mobile species for daily movement (e.g. foraging) is well supported by available evidence, across a range of taxa. There is less evidence for the role of hedgerows for population dispersal or migration, despite their strong potential to support connectivity and the likely importance of this in the context of climate change. Since hedgerows consist primarily of shrubs and trees, their distribution is associated with that of shrubby and/or woodland habitats. There is strong evidence that to achieve Favourable Conservation Status the national distribution of hedgerows is likely to remain broadly unchanged. However, increases in extent will alter the smaller scale distribution of hedgerows in parts of the current range. Evidence about the specific types of landscapes in which additional hedgerows may best be placed to optimise support to biodiversity is limited. The quality of hedgerows, defined through a series of structural and functional attributes, strongly determines how well hedgerows support biodiversity across a broad range of taxa. Hedgerow height and width, the provision of flowers (pollen and nectar resources for pollinators) and berries (for overwintering wildlife), the presence of mature trees, and the density and structural diversity of the hedgerow network are all examples of quality attributes which affect how well hedgerows can support wildlife. Detailed recommendations and thresholds for these quality attributes are given in this document, based both on current hedgerow condition criteria and additional attributes for which good evidence is available. Overall, the evidence for the requirement that hedgerows need to be of good quality (as defined here) to support thriving biodiversity is strong. Currently, the majority of hedgerows in England are not in good condition, which poses a considerable threat to achieving FCS for hedgerows

Improving and expanding hedgerows - recommendations for a semi-natural habitat in agricultural landscapes

•1. Hedgerows provide habitat, shelter and resources for many species including functionally important taxa and threatened species. Hedgerows store carbon both above- and below-ground and provide a range of other ecosystem services. Policies incentivizing increases in the extent and quality of hedgerows require evidence to determine how these increases may best support a wide range of taxa and to improve hedgerow habitat quality. •2. Here, available evidence for increasing hedgerow extent and improving their quality is discussed in the context of current conservation policy. Moderate evidence supports a substantial increase in average hedgerow extent from 4.2 km/km2 to around 10 km/km2 in the United Kingdom, to optimize support for many wildlife taxa, habitat connectivity and carbon storage. •3. Evidence also supports the development of wider and structurally denser hedges with more diverse structures and management approaches, and hedgerow networks that are well connected with each other and with other semi-natural habitats. •4. However, barriers may hinder the implementation of hedgerow policies, and there remain substantive gaps in the evidence base. Knowledge gaps include the current quality or condition of UK hedges, understanding in which landscape contexts new hedges would best be planted to support biodiversity, the role of hedgerows in connectivity as species' ranges change under a future climate, and whether an increase in hedgerow extent might increase the spread of invasive species, tree pests or diseases. •5. These gaps must be filled if conservation policies, including future agri-environment schemes, are to ensure that hedgerows reach their considerable potential in aiding nature's recovery and addressing climate change

Hedgerow rejuvenation management affects invertebrate communities through changes to habitat structure

Hedgerows are an important semi-natural habitat for invertebrates and other wildlife within agricultural landscapes. Hedgerow quality can be greatly affected either by over- or under-management. Neglect of hedgerows is an increasingly important issue as traditional management techniques such as hedgelaying become economically unviable. In the UK, funding for hedge management is available under agri-environment schemes but relatively little is known about how this impacts on wider biodiversity. We used a randomised block experiment to investigate how habitat structural change, arising from a range of techniques to rejuvenate hedgerows (including more economic/mechanised alternatives to traditional hedgelaying), affected invertebrate abundance and diversity. We combined digital image analysis with estimates of foliage biomass and quality to show which aspects of hedge structure were most affected by the rejuvenation treatments. All investigated aspects of habitat structure varied considerably with management type, though the abundance of herbivores and predators was affected primarily by foliage density. Detritivore abundance was most strongly correlated with variation in hedge gap size. The results suggest that habitat structure is an important organising force in invertebrate community interactions and that management technique may affect trophic groups differently. Specifically we find that alternative methods of hedgerow rejuvenation could support abundances of invertebrates comparable or even higher than traditional hedgelaying, with positive implications for the restoration of a larger area of hedgerow habitat on a limited budget

Barriers and enablers to uptake of agroecological and regenerative farming practices, and stakeholder views about ‘living labs’

This report forms the second component of a Defra-sponsored research project entitled “Evaluating the productivity, environmental sustainability and wider impacts of agroecological compared to conventional farming systems”. The first component comprised a rapid evidence review of regenerative/agroecological farming systems. This second component describes and discusses the results of a survey to explore i) farmer and stakeholder definitions of agroecological and regenerative farming, ii) the barriers to the adoption of agroecological and regenerative farming, and iii) farmer and stakeholder views towards the concept of ‘living labs’ as a way to share research and learnings about agroecological/regenerative farming (Figure 1)

Evaluating agroecological farming practices

There are a range of definitions for agroecologically-related farming systems and practices. In brief, organic farming places strong restrictions on inputs, agroecological analyses often focus on principles, and regenerative farming typically emphasises the enhancement of soil health and the diversity of agricultural and wild species at a farm-scale. Perhaps surprisingly the role of agroecological systems in reducing net greenhouse gas emissions from food and farming is implicit rather than explicit. Despite some literature contrasting agroecological and technical approaches, many authors indicate that the desirability of farming practices should be determined by their impact at the appropriate scale. Sustainable intensification has been defined as maintaining or enhancing agricultural production while enhancing or maintaining the delivery of other ecosystem services. Approaches such as the Global Farm Metric and LEAF Marque Certification can support the integrated assessment of 12 groupings of attributes at a farm-scale covering inputs and outputs, and environmental and social impacts. In this report we reviewed the following 16 practices: crop rotations, conservation agriculture, cover crops, organic crop production, integrated pest management, the integration of livestock to crop systems, the integration of crops to livestock systems, field margin practices, pasture-fed livestock systems, multi-paddock grazing, organic livestock systems, tree crops, tree-intercropping, multistrata agroforestry and permaculture, silvopasture, and rewilding

Characterising current agroecological and regenerative farming research capability and infrastructure, and examining the case for a Living Lab network

Agriculture is a major cause of greenhouse gas (GHG) emissions, biodiversity loss, and pollution. Agroecological and regenerative farming have been advocated as alternative approaches that may have fewer negative (or even net positive) environmental impacts than conventional agriculture at farm- and landscape-scales, leading to considerable interest in these approaches (Newton et al. 2020; Bohan et al. 2022; Prost et al. 2023). This report forms the third part of a Defra-funded project Evaluating the productivity, environmental sustainability and wider impacts of agroecological and regenerative farming systems compared to conventional systems. The first part of this project was a rapid evidence review of agroecological and regenerative farming systems and their impacts (Burgess et al. 2023), and the second reported interview findings to examine farmer and stakeholder perspectives on barriers and enablers in agroecological and regenerative farming (Hurley et al. 2023). This third part of the project characterised the current research capability in agroecology and regenerative farming, and explored the potential role of a new ‘living lab’ trial network

Little and late: how reduced hedgerow cutting can benefit Lepidoptera

Hedgerows are a key semi-natural habitat for biodiversity in intensive agricultural landscapes across northern Europe and support a large invertebrate fauna. Management can have large effects on the value of hedgerows as a wildlife habitat, thus sensitive management is incentivised through agri-environment schemes (AES). We tested how current and potential future AES hedge management regimes affected the diversity and abundance of Lepidoptera species that utilise the hedge as a breeding resource, using a long term, multi-site, manipulative field experiment. Hedgerow management in some current AES options (reduced trimming frequency and cutting in winter) increased Lepidoptera abundance and the diversity of components of the Lepidoptera community linked with specific lifecycle traits. However, the most frequently applied hedgerow AES option currently applied in the UK (cutting once every 2 years in autumn) did not benefit Lepidoptera compared to standard hedgerow management outside AES (annual trimming in autumn). Decreasing the intensity of hedgerow trimming improves the diversity of the whole Lepidoptera assemblage, and should be considered as part of biodiversity conservation in farmed landscapes

Re-structuring hedges: rejuvenation management can improve the long term quality of hedgerow habitats for wildlife in the UK

Hedgerows provide key wildlife habitat in intensive agricultural landscapes, but are declining in length and structural condition due to a lack of rejuvenation management, neglect and over-frequent trimming with mechanised flails. Here, we test cheaper, alternative methods to traditional hedge laying methods using a multi-site manipulative field experiment. In the first quantitative test of new approaches to hedge rejuvenation management, hedge regrowth, structure, berry provision for over-wintering wildlife and cost of rejuvenation were assessed in response to five methods, for three years following rejuvenation. Three ‘laying’ methods and coppicing were effective at improving hedgerow condition by stimulating basal regrowth, thus increasing the density of woody material at the base and reducing gap size. The pros and cons of coppicing are discussed in relation to its impact on different wildlife groups, and it is recommended in limited circumstances. Differences between the three ‘laying’ methods reduced over time, so a cheaper conservation hedging method is recommended as an alternative to traditional hedge laying. This new approach to hedge management offers the potential to restore twice the length of hedgerow currently rejuvenated under agri-environment schemes