Proportion Of Semi-natural Habitats Research Articles

Organic farming at local and landscape scales fosters biological pest control in vineyards.

While organic farming practices, which are often promoted as models of ecological intensification, generally enhance biodiversity, their effects on the delivery of ecosystem services, such as biological pest control, are still unknown. Here, using a multi-scale hierarchical design in southwestern France, we examined the effects of organic farming and seminatural habitats at the local and landscape scales on biological control services of three pests, including weeds and insects, in 42 vineyards. Organic farming at the local and landscape scales was beneficial to the mean and temporal stability of biological control services, while the proportion of seminatural habitats in the landscape reduced the level of biological pest control potential. The effects of organic farming and seminatural habitats across spatial scales varied with the type of prey considered and with time. Egg moth removal rates were higher in fields under organic management compared to conventional management while weed seed removal rates increased with the proportion of organic farming in the landscape. Larval removal rates as well as seed removal rates were always more stable within time in organic fields than in conventional fields. Moreover, independently of farming system type, local variables describing the agricultural management intensity, such as pesticide use or crop productivity, were also found to be important variables explaining levels of biological control services. Pesticide use tended to reduce biological control potential, while crop productivity was associated with contrasting biological control responses depending on the pest type. Our study demonstrates the need to target multiple spatial scales and to consider farming practices, as well as the proportion of seminatural habitats, to design functional landscapes that optimize biological pest control services.

Organic farming supports spatiotemporal stability in species richness of bumblebees and butterflies

The spatiotemporal stability of wild organisms, such as flower-visiting insects, is critical to guarantee high levels of biodiversity in agroecosystems. Whereas the proportion of semi-natural habitats in the landscapes has been shown to stabilize the species richness of flower visitors, the effect of farming intensity has not yet been studied. In this study, we compared the temporal and spatial stability (continuity of species richness in space and time) of two groups of flower-visiting insects (butterflies and bumblebees) between nine conventional and ten organic farms, distributed along a gradient of semi-natural grassland proportion. We surveyed bumblebees, butterflies and local flower cover during the growing season, covering multiple years and several habitat types per farm (cereal fields, temporary grasslands and semi-natural grasslands). At the field scale we found that within-year stability of bumblebee species richness was higher in organic than in conventional temporary grasslands (leys), because of a higher continuity of in-field flower resources. Further analyses showed that late-season flower resources in organic ley fields were critical to maintain a high within-year stability of bumblebee species richness by reducing resource bottlenecks during that period, when most bumblebee colonies produce new queens. The among-year stability of bumblebee species richness was higher in organic than in conventional cereal fields, whereas the within and among-year stability of butterfly species richness was not influenced by farming system. On the farm scale, we found that the spatial stability of butterfly and bumblebee species richness was higher in organic than in conventional farms, but this was not explained by a greater spatial continuity of flower resources. Our study shows that organic farming reduces the spatiotemporal fluctuations in bumblebee and butterfly species richness. In addition, increasing floral resources as such benefits bumblebees and butterflies irrespective of farming system. Organic farming and increasing availability in floral resources therefore contribute to maintaining the within and between-year stability of bumblebees and butterflies in agricultural landscapes.

Overwintering of pollen beetles and their predators in oilseed rape and semi-natural habitats

Semi-natural habitats (SNH) maintain high levels of biodiversity and ecosystem functioning within agroecosystems. While management recommendations for SNH to promote biodiversity and optimize natural pest control, have mostly focused on improving food resources for predators, overwintering conditions have hitherto received less attention. The success of conservation biological control is often hampered by a lack of knowledge on how different habitats and their associated traits drive the overwintering of both, crop pests and their natural enemies. Moreover, there are concerns that SNH may act as reservoirs for crop pests.We investigated the overwintering of pollen beetles (Meligethes spp.) and their predators (predatory ground beetles) across 40 habitats of all major types of SNH as well as 8 winter oilseed rape (WOSR) fields, to identify the importance of type and key traits of habitats. Overwintering of pollen beetles was higher in WOSR fields (7 individuals per 0.25 m2) and forest edges (4) compared to flower strips (2) or forest interiors (1). Similarly, overwintering of predatory ground beetles was higher in forest edges and WOSR fields (11 and 10 individuals, respectively) than in flower strips, meadows or hedgerows (4, 4 and 2 individuals). The predator-prey ratio (number of predatory ground beetles / number of pollen beetles) was higher in forest edges than in flower strips, meadows or hedgerows, and intermediate in WOSR fields. Pollen beetle numbers were negatively associated with increasing litter cover and positively with increasing bare soil, while predatory ground beetles were positively associated with soil bulk density and bare soil cover. The proportion of SNH at the landscape level (1 km radius) did not affect overwintering pollen beetles, predatory ground beetles or predator-prey ratio.We conclude that WOSR fields, rather than SNH are the major overwintering habitat and source of spring colonisation of WOSR by pollen beetles. Forest edges promote predatory ground beetles rather than pollen beetle populations according to their disproportionally high value of overwintering individuals. Agri-environmental measures to promote predatory ground beetles rather than pollen beetles should promote overwintering habitats with compact soils and high litter cover.

The value of small arable habitats in the agricultural landscape: Importance for vascular plants and the provisioning of floral resources for bees

Small remnants of non-arable habitat within the farmland mosaic are considered important for the conservation of farmland biodiversity, but their contribution to landscape-scale species richness is poorly understood. In the present study, we examined the relative contributions of different habitat types to the landscape-scale species richness of vascular plants within farmland of varying landscape complexity. We also analysed pollen collected by bees to examine the extent to which the different habitat types contributed towards the provisioning of floral resources for three taxa (Bombus terrrestris, Megachile sp. and Osmia bicornis). We found that plant species richness increased with landscape complexity (defined as the proportion of semi-natural habitats). The relative contribution of small fragments of non-arable habitat to total plant species richness was high within all landscape types, especially in relation to the small area they covered. The importance of small non-arable fragments for the provisioning of floral resources to bees varied over time and between taxa. Bombus terrestris used the different habitat types differently during different parts of the growing season: arable fields were important early in the season, leys late in the season, and small non-arable habitat fragments during the mid-season when no mass-flowering crops were in bloom. In contrast, Megachile sp. and O. bicornis mainly foraged on plants occurring within grasslands. We conclude that small fragments of non-arable habitat are important for plant species richness at the landscape-scale and that their importance for plants may cascade to the bees that use them as foraging resources. Consequently, it is important to consider the entire landscape mosaic when taking actions to conserve farmland species.

Positive effects of local and landscape features on predatory flies in European agricultural landscapes

Provisioning of suitable habitats for predatory insects in agricultural landscapes can improve natural pest control and hence the sustainability of agriculture. Apart from Syrphidae, the spatial ecology of predatory flies remains little studied. We investigated the response of Dolichopodidae, Empididae and Syrphidae to local features of seminatural habitats and to the composition of the surrounding landscape. We sampled adult predatory flies with pan traps in 183 field-bordering seminatural habitats along gradients of landscape composition in Italy, Germany and Switzerland. Local habitat type, the composition of the surrounding landscape and proximity to watercourses affected the abundance of predatory flies. Across countries, Empididae and Syrphidae were more abundant in woody (i.e. forests and in particular hedgerows) than in herbaceous habitats, whereas Dolichopodidae had lowest abundance in forests. The abundance of Dolichopodidae in Italy and Empididae in Germany were furthermore enhanced by the proximity of watercourses. Abundance of Dolichopodidae increased with the proportion of seminatural habitats in 1km radius. Empididae were more abundant in landscapes with higher proportion of forests. We identified hedgerows as favorable habitats for predatory flies in agricultural landscapes. Moreover, our study reveals the importance of proximity to watercourses, which has rarely been considered when studying natural enemies of pests in agroecosystems. The varying responses indicate that preserving or restoring habitat-diverse, heterogeneous landscapes guarantees high numbers of predatory flies across families.

Contrasting Pollinators and Pollination in Native and Non-Native Regions of Highbush Blueberry Production.

Highbush blueberry yields are dependent on pollination by bees, and introduction of managed honey bees is the primary strategy used for pollination of this crop. Complementary pollination services are also provided by wild bees, yet highbush blueberry is increasingly grown in regions outside its native range where wild bee communities may be less adapted to the crop and growers may still be testing appropriate honey bee stocking densities. To contrast crop pollination in native and non-native production regions, we sampled commercial ‘Bluecrop’ blueberry fields in British Columbia and Michigan with grower-selected honey bee stocking rates (0–39.5 hives per ha) to compare bee visitors to blueberry flowers, pollination and yield deficits, and how those vary with local- and landscape-scale factors. Observed and Chao-1 estimated species richness, as well as Shannon diversity of wild bees visiting blueberries were significantly higher in Michigan where the crop is within its native range. The regional bee communities were also significantly different, with Michigan farms having greater dissimilarity than British Columbia. Blueberry fields in British Columbia had fewer visits by honey bees than those in Michigan, irrespective of stocking rate, and they also had lower berry weights and a significant pollination deficit. In British Columbia, pollination service increased with abundance of wild bumble bees, whereas in Michigan the abundance of honey bees was the primary predictor of pollination. The proportion of semi-natural habitat at local and landscape scales was positively correlated with wild bee abundance in both regions. Wild bee abundance declined significantly with distance from natural borders in Michigan, but not in British Columbia where large-bodied bumble bees dominated the wild bee community. Our results highlight the varying dependence of crop production on different types of bees and reveal that strategies for pollination improvement in the same crop can vary greatly across production regions.

Organic farming and host density affect parasitism rates of tortricid moths in vineyards

Natural pest control by predators and parasitoids is an important ecosystem service supporting crop production. It is now well known that the proportion of semi-natural habitats as well as organic farming enhance abundance and species richness of natural enemies in agroecosystems. However, few studies have examined how these environmental variables affect natural pest control services. Moreover, most studies have been performed in annual cropping systems and almost nothing is known about the effect of landscape complexity and organic farming in perennial crops, which differ greatly from annual ones in terms of disturbance regimes. In this study, we analyzed how landscape composition and farming systems affect abundance of insect pests of grape and their parasitism rates in 79 vineyards in southwestern France. Our results show that farming systems and host density affect biological control of tortricid moths by their parasitoids. Surprisingly, organic fields had lower parasitism rates compared to conventional ones and this rate was negatively correlated to host density at the field scale. We also found that moth community composition depended on the proportion of grapevine crop in the landscape in a 1km radius but that pest abundance and parasitism rates did not change with landscape complexity. Our results suggest that some farming practices that are frequent in organic farming, such as organic-certified insecticides, copper or sulfur, can reduce parasitoid populations and thus limit biological control in vineyards. Negative density dependence relationship between parasitism rates and host abundance suggest a dilution effect of the biological control potential at the landscape scale and potential mechanisms such as variable parasitoid population sizes, relatively limited female longevity or fecundity, as well as increase in handling time. Further research on the effect of organic and conventional farming practices are now needed to provide a more mechanistic understanding of how these agricultural practices shape ecological processes such as biological control of pests.

Using landscape indicators to predict high pest infestations and successful natural pest control at the regional scale

Designing multifunctional landscapes requires accurate indicators to assess the effect of landscape structure on the provision on ecosystem services. Biological pest control relying on natural enemies is an important ecosystem service considered as a sustainable alternative to chemical control. The aim of this study was to measure and compare the accuracy of landscape indicators computed at various spatial scales to predict pollen beetle infestations and successful biological control in northwestern France. The sensitivity, specificity, and probability of correctly ranking fields were estimated for each indicator based on a survey of 42 fields using the receiver operating characteristic procedure. For pest infestation, the proportion of woodland and the proportion of semi-natural habitats were found to be informative indicators with good discriminatory abilities. For biological control, the proportion of woodland, the proportion of semi-natural habitats and the proportion of the previous year's oilseed rape fields with reduced soil tillage were found to be informative indicators with good discriminatory abilities. By using indicator values and optimal thresholds we were able to compute maps of areas at risk for pest infestation and those displaying successful biological control at the regional scale. This study provides tools that could help extension services, landscape planners, and policy makers in optimizing landscape structure according to the provision of a key ecosystem service. The results of this study also provide new grounds for understanding trophic interactions at the regional scale as well as the ambivalent effect of landscape complexity on pest and natural enemy populations.

Agricultural landscape simplification and insecticide use in the Midwestern United States

Agronomic intensification has transformed many agricultural landscapes into expansive monocultures with little natural habitat. A pervasive concern is that such landscape simplification results in an increase in insect pest pressure, and thus an increased need for insecticides. We tested this hypothesis across a range of cropping systems in the Midwestern United States, using remotely sensed land cover data, data from a national census of farm management practices, and data from a regional crop pest monitoring network. We found that, independent of several other factors, the proportion of harvested cropland treated with insecticides increased with the proportion and patch size of cropland and decreased with the proportion of seminatural habitat in a county. We also found a positive relationship between the proportion of harvested cropland treated with insecticides and crop pest abundance, and a positive relationship between crop pest abundance and the proportion cropland in a county. These results provide broad correlative support for the hypothesized link between landscape simplification, pest pressure, and insecticide use. Using regression coefficients from our analysis, we estimate that, across the seven-state region in 2007, landscape simplification was associated with insecticide application to 1.4 million hectares and an increase in direct costs totaling between $34 and $103 million. Both the direct and indirect environmental costs of landscape simplification should be considered in design of land use policy that balances multiple ecosystem goods and services.

Intensification of agriculture, landscape composition and wild bee communities: A large scale study in four European countries

The impacts of agricultural practices and landscape composition on bee communities were investigated in 14 sites located in four Western European countries (Belgium, France, the Netherlands and Switzerland). Standardized interviews with farmers assessed agricultural practices in terms of agricultural inputs (nitrogen fertilization and pesticides), livestock density and crop types. The proportion of semi-natural habitats was calculated for each site. We showed negative effects of agricultural intensification on species richness, abundance and diversity of wild bees. By contrast, bee species richness increased with the amount of semi-natural habitats in the landscape. Using a co-inertia analysis, we found an opposition between two types of agricultural specialization: towards crop production or towards animal husbandry. Species richness, abundance and diversity of wild bees were greater in sites turned towards crop production. In these sites, flowering crops provided abundant food resources for bees whereas, in the other group of sites, intensive animal husbandry led to landscapes dominated by forage crops rather than flower-rich permanent grasslands. We also showed that bumblebees seemed to be less sensitive to agricultural intensification than solitary bees.

Genetic diversity and mass resources promote colony size and forager densities of a social bee (Bombus pascuorum) in agricultural landscapes

Although habitat fragmentation and agricultural intensification are known as threads to pollinator diversity, little is known about consequences for population size and genetic diversity. Here, we combined detailed field observations, molecular approaches and GIS-based quantification of landscape structure (measured by proportions of seminatural habitats and proportions of mass flowering crops) to get new insights into driving forces of population dynamics of the bumblebee species Bombus pascuorum. Comparing 13 agriculturally dominated landscape sectors, we found the proportion of mass flowering crops to positively influence bumblebee abundance whereas the proportion of seminatural habitats was of minor importance. We used microsatellites to quantify landscape-related colony densities, inbreeding and population substructure. Detected colony densities did not correlate with landscape parameters or with local worker abundance, measured by field observations. These results indicate that increased worker abundances within landscapes are rather due to greater colony sizes than due to an increased number of nests. We found significant population substructure, measured by F(ST) and seven landscape sectors to bear significantly increased inbreeding values (F(IS)). F(IS) was strongly varying between sectors but did not correlate with landscape structure. Moreover, F(IS) had a significantly negative effect on colony size, demonstrating the importance of genetic diversity on population fitness at a landscape scale. We suggest that inbreeding levels might be related to the temporal variation of food resources and population sizes in agricultural landscapes.