Effects Of Landscape Complexity Research Articles

Effect of landscape complexity, nesting substrate, and nest orientation on cavity-nesting solitary bees in southern Punjab, Pakistan

Effect of landscape complexity, nesting substrate, and nest orientation on cavity-nesting solitary bees in southern Punjab, Pakistan

Grazing and boundaries favour weedy plants with functional traits beneficial for pollinators

Semi-natural grasslands are key habitats for biodiversity, yet are negatively affected by intensified land-use. To mitigate such adverse effects, effective subsidies systems encouraging extensified production need to be developed that focus not only on species richness and functional diversity. We evaluated the effect of two grazing intensities and the effects of landscape complexity on plant functional traits in three grassland types in the Great Hungarian Plain. Regarding plant traits responding to grazing, we found shorter-statured and earlier flowering species in intensively grazed pastures and more disturbance-tolerant species with increasing boundary length. For pollination-related plant traits, there were more later flowering species in extensively grazed sites, while flowering duration and flower colour revealed complex relations between landscape complexity and grazing intensity. Generally, local low-intensity grazing (0.5 cattle/ha) supports specialist plant species, and increasing boundary length promotes generalist disturbance-tolerant species with traits beneficial for pollinators. Especially when designing new agri-environment schemes for low-intensity grazing systems, understanding the complex functional relationships is crucial to maintaining and restoring farmland biodiversity.

Different Distribution Patterns of Hoverflies (Diptera: Syrphidae) and Bees (Hymenoptera: Anthophila) Along Altitudinal Gradients in Dolomiti Bellunesi National Park (Italy).

Simple SummaryHoverflies and bees play a key role in plant pollination. The increasing concern about pollinator reduction forces the planning of a sampling monitoring scheme to evaluate the change in the populations of these important insects. The present research provides baseline data about the distribution of hoverflies and bees in the Dolomiti Bellunesi National Park (Northeastern Italy). The hoverfly community shows a unimodal distribution with peak at middle elevation, while bees display a linear reduction in richness and abundance with increasing altitude. Both hoverfly and bee β-diversity at high altitude is dominated by species turnover more than by nestedness.Hoverflies (Diptera: Syrphidae) and bees (Hymenoptera: Anthophila) are two key taxa for plant pollination. In the present research, the altitudinal distribution of these taxa was studied along two gradients (elevation range: 780–2130 m) in the Dolomiti Bellunesi National Park (Northeastern Italy). Pan traps were used as a sampling device to collect both hoverflies and bees. Other than altitude, the effect of landscape complexity and plant diversity were considered as potential predictors of hoverfly and bee richness and abundance along the two gradients. A total of 68 species of hoverflies and 67 of bees were collected during one sampling year, confirming the efficacy of pan traps as a sampling device to study these taxa. Altitude was the main variable affecting both hoverfly and bee distribution. The two taxa show different distribution patterns: hoverflies have a unimodal distribution (richness and abundance) with peak at middle altitude (1500 m), while bees have a monotonic decline (richness and abundance) with increasing altitude. Both hoverfly and bee populations change with the increasing altitude, but the change in hoverflies is more pronounced than in bees. Species turnover dominates the β-diversity both for hoverflies and bees; therefore, the hoverfly and bee communities at higher altitudes are not subsamples of species at lower altitude but are characterized by different species. This poses important conservation consequences. Some rare species, typical of an alpine habitat were recorded; the present research represents important baseline data to plan a monitoring scheme aimed at evaluating the effect of climate change on pollinators in these fragile habitats.

Effects of landscape complexity on crop productivity: An assessment from space

Agricultural producers have many incentives to clear small natural areas from their fields, as this can expand their cultivated land base. However, natural areas can play a role in delivering ecosystem services that improve crop productivity (e.g., by providing habitat for beneficial arthropods, that deliver pollination or pest control). We assessed the impact of landscape complexity on adjacent canola (Brassica napus) yield at both the field- and subfield-level using remotely sensed products. Fields with higher landscape complexity generally had higher mean yields. However, fields surrounded mostly by either crop or non-crop covers had lower yields, possibly due to a lack of ecosystem services or a strong yield-reducing edge effect. At the subfield-level, we found evidence of a boost in yield between 30 and 100 m from the field edge towards its center, as well as a potential yield-stabilizing effect at the same range.

The effect of landscape complexity on water quality in mountainous urbanized watersheds: a case study in Chongqing, China

The most significant feature of the landscape of mountainous urbanized watersheds is complexity. The geomorphology, composition, and configuration have strong ties with river water quality. In this study, through redundancy analysis, we examined how landscape complexity measured at both landscape and class levels related to water quality within watersheds. The results indicate that water quality is closely associated with both the relief degree of the land surface and patch density at the landscape level. The river water quality of mountainous watersheds is better if the relief degree of the land surface is larger, though river water quality degradation is associated with higher fragmentation of the landscape. At the class level, a greater proportion of non-urban land use may contribute to better river water quality, as do better connectivity and moderate degrees of aggregation. Water quality is more likely to be degraded when the shape of residential land, public service, and commercial land is more complex. We conclude that, in mountainous urbanized watersheds, river water quality can be protected through land use planning and management by regulating a set of landscape metrics for complexity measures.

High land-use intensity in grasslands constrains wild bee species richness in Europe

There is widespread concern regarding declines in bee populations given their importance for the functioning of both natural and managed ecosystems. An increasing number of studies find negative relations between bee species richness and simplification of agricultural landscapes, but the role of land-use intensity and its relative importance compared to landscape simplification remain less clear. We compared the relative effects of nitrogen inputs, as a proxy for land-use intensity, and proportion of natural and semi-natural habitat, as a measure of landscape complexity on total bee species richness, rare species richness and dominant crop-visiting species richness. We used data from 282 grasslands across five countries, covering the entire range of low intensity, no-input systems, to high-input sites (>400 kg N/ha/year). We found consistent negative impacts of increasing land-use intensity at a regional scale on total bee species richness and dominant crop-visiting species across Europe, but no such effects of landscape complexity. In contrast, the richness of rare bee species was not significantly related to increasing land-use intensity. Nevertheless, based on species accumulation curves, grasslands with no nitrogen inputs had higher total bee richness and higher shares of rare species compared with sites with high nitrogen inputs (>125 kg N/ha/year). Our results highlight the importance of retaining grasslands characterised by low land-use intensity across agricultural landscapes to promote bee diversity.

Effects of landscape complexity and stand factors on arthropod communities in poplar forests.

The arthropod communities are influenced by both local conditions and features of the surrounding landscape. Landscape complexity and stand factors may both influence arthropod communities in poplar forests, but the multiscale effects of these factors on poplar defoliators and natural enemies are still poorly understood. We collected poplar arthropods at 30 sampling sites within five forest landscapes in Xinjiang, China, and assessed whether landscape complexity and stand factors influence species abundance and diversity of poplar arthropods. Landscape complexity was quantified by several independent metrics of landscape composition, configuration, and connectivity at three spatial scales. We also determined the most powerful explanatory variables and the scale effect of each arthropod. Results found that landscape complexity and stand factors had different effects on different poplar arthropod communities. Landscape complexity promoted natural enemies at different spatial scales, but it inhibited the population of poplar defoliators at the scale of 200 m. Specifically, the abundance and diversity of all defoliators decreased with increasing proportion of nonhost plants. Landscape diversity only had a negative effect on defoliator abundance. The shape complexity of habitat patches increased the abundance of carabid beetles but reduced the abundance of green leafhoppers and migratory locusts. The abundance and diversity of predators increased with increasing structural connectivity of forest landscape. Additionally, both the abundance and diversity of all defoliators were positively correlated with the average height of herbaceous plants. Diversity of all defoliators increased with increasing size of host trees. The distance from sampling site to the nearest village positively influenced the abundance and diversity of all predators. Arthropod abundance and diversity in poplar forests were driven by stand factors and landscape complexity. Therefore, maintaining complex shape and structural connectivity of habitat patches and keeping poplar stands away from the village are crucial for management of forest landscape to enhance natural enemies. And in order to reduce the abundance of defoliators in poplar forest, the diversity of surrounding habitat types should be promoted within 200 m radii.

Effects of landscape complexity on pollinators are moderated by pollinators' association with mass-flowering crops.

Conserving and restoring semi-natural habitat, i.e. enhancing landscape complexity, is one of the main strategies to mitigate pollinator decline in agricultural landscapes. However, we still have limited understanding of how landscape complexity shapes pollinator communities in both crop and non-crop habitat, and whether pollinator responses to landscape complexity vary with their association with mass-flowering crops. Here, we surveyed pollinator communities on mass-flowering leek crops and in nearby semi-natural habitat in landscapes of varying complexity. Surveys were done before and during crop bloom and distinguished between pollinators that visit the crop frequently (dominant), occasionally (opportunistic), or not at all (non-crop). Forty-seven per cent of the species in the wider landscape were also observed on leek flowers. Crop pollinator richness increased with local pollinator community size and increasing landscape complexity, but relationships were stronger for opportunistic than for dominant crop pollinators. Relationships between pollinator richness in semi-natural habitats and landscape complexity differed between groups with the most pronounced positive effects on non-crop pollinators. Our results indicate that while dominant crop pollinators are core components of crop pollinator communities in all agricultural landscapes, opportunistic crop pollinators largely determine species-richness responses and complex landscapes are local hotspots for both biodiversity conservation and potential ecosystem service provision.

The effect of landscape complexity and microclimate on the thermal tolerance of a pest insect

Landscape changes are known to exacerbate the impacts of climate change. As such, understanding the combined effect of climate and landscape on agroecosystems is vital if we are to maintain the function of agroecosystems. This study aimed to elucidate the effects of agricultural landscape complexity on the microclimate and thermal tolerance of an aphid pest to better understand how landscape and climate may interact to affect the thermal tolerance of pest species within the context of global climate change. Meteorological data were measured at the landscape level, and cereal aphids (Sitobion avenae, Metopolophium dirhodum and Rhopalosiphum padi) sampled, from contrasting landscapes (simple and complex) in winter 2013/2014 and spring 2014 in cereal fields of Brittany, France. Aphids were returned to the laboratory and the effect of landscape of origin on aphid cold tolerance (as determined by CTmin ) was investigated. Results revealed that local landscape complexity significantly affected microclimate, with simple homogenous landscapes being on average warmer, but with greater temperature variation. Landscape complexity was shown to impact aphid cold tolerance, with aphids from complex landscapes being more cold tolerant than those from simple landscapes in both winter and spring, but with differences among species. This study highlights that future changes to land use could have implications for the thermal tolerance and adaptability of insects. Furthermore, not all insect species respond in a similar way to microhabitat and microclimate, which could disrupt important predator-prey relationships and the ecosystem service they provide.

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.

Effects of landscape complexity and habitat management on stemborer colonization, parasitism and damage to maize

Lepidopteran stemborers are a serious constraint to efficient production of maize in sub-Saharan Africa. One of the most effective ways of managing these pests is through a habitat management system called push–pull. Landscape complexity has been shown to enhance biological control of insect pests, and therefore may influence effectiveness of habitat management systems designed to control pests. We studied the relative importance of the push–pull cropping system as a local effect and proportional cover of grassland as a landscape effect on (i) stemborer population density and damage to maize, and (ii) parasitism and mortality of stemborer life stages in western Kenya. We found a significant interactive effect between cropping system and grassland cover on abundance of stemborer larvae and pupa, and a near significant interactive effect of these variables on rates of egg parasitism. Cropping system had the largest effect on larval and pupal abundance in more complex landscapes, whereas it affected egg parasitism most strongly in the simplest landscapes. Grasslands appeared to primarily function as a source for the pests, rather than for natural enemies. However, sites from landscapes with a larger range of grassland cover need to be studied to fully explore the combined effects of cropping system and landscape complexity on pest control in this system. The push–pull cropping system significantly suppressed stemborer colonization of the maize and enhanced activity of stemborer parasitoids, with significant reductions in crop damage and increase in grain yield.

Effects of landscape complexity on the ecological effectiveness of agri-environment schemes

Agricultural intensification is a major cause for biodiversity loss. It occurs at field scales through increased inputs and outputs, and at landscape scales through landscape simplification. Agri-environment schemes (AES) of the European Common Agricultural Policy (CAP) aim at reducing biodiversity loss by promoting extensification of agricultural practises mostly at field scales. We present a conceptual model for the relationship between landscape complexity and ecological effectiveness of AES based on (a) non-linear relationships between landscape complexity and abundance and diversity at field scales and (b) four possible interactive scenarios between landscape- and field scale effects on abundance and diversity. We then evaluated whether and how effectiveness of AES interacted with landscape-scale effects of intensification along a landscape complexity gradient established in central Spain. Pairs of cereal fields with and without AES but with the same landscape context were selected in three regions differing in landscape complexity. Effectiveness of AES was measured as differences between paired fields in species richness and abundance of five target groups (birds, grasshoppers and crickets, spiders, bees and plants). Landscape metrics were measured in 500–m radius circular plots around field centres. Positive, negative and no effects of landscape complexity on effectiveness of AES were found, suggesting that effects of complexity on effectiveness of AES changes from positive to negative along gradients of landscape complexity. Effectiveness of AES for improving biodiversity was then constrained by landscape. Compulsory measures aimed at enhancing or maintaining landscape complexity would enhance the effectiveness of AES for preserving biodiversity in farmed landscapes.

Responses of grassland specialist and generalist beetles to management and landscape complexity

ABSTRACTWe tested the influence of grazing intensity and effect of landscape complexity on grassland specialist and generalist beetles of three beetle families, i.e. Carabidae, Chrysomelidae, and Curculionidae, on extensively and intensively grazed cattle pastures in three regions of the Hungarian Great Plain. In every region we investigated seven pairs of grazed grasslands. On each field, samples were taken along two 95‐m‐long transects; one transect at the edge and the other one 50 m away from the edge in the grassland interior (altogether 84 transects). Carabids (Carabidae) were sampled using funnel traps for three 2‐week sampling periods during spring and early summer. Leaf‐beetles (Chrysomelidae) and weevils (Curculionidae) were surveyed by sweep netting in May and June 2003. Analysing the grazing intensity and landscape complexity effects on generalist and specialist beetles with linear mixed models, grazing effect was detected only on specialist leaf‐beetle species richness with more species in the extensively grazed sites. Landscape complexity had contrasting effects on specialist and generalist species. Habitat generalists were more and negatively affected by increasing grassland coverage (reduced heterogeneity) than specialists. At species level analyses on four species out of 21, landscape effects were shown, which suggested that landscape composition might have strong effects on the species composition of the beetle assemblages. Our results suggest that conservation of biodiversity in agricultural systems (such as in managed Central European grasslands) requires a landscape perspective besides investigating management effects.

Effects of landscape complexity on farmland birds in the Baltic States

Data on birds occurring in farmland in the Baltic States of Estonia, Latvia and Lithuania were related to the spatial organisation of farmed habitats in three different agricultural landscape types. Species richness, abundance, and diversity of farmland bird communities, as well as abundance of the most frequently observed species were positively related to the number of residual non-cropped elements within farmland, the local mixture of annual crop and grass fields, and the variety of field types. The positive association of the species richness and abundance of the farmland bird community with richness in residual habitats and crops was most prominent in open landscapes. The results suggest that, by simplifying farmland structure and making it more homogenous, EU agricultural policies will have a detrimental effect on farmland bird populations in Eastern Europe. Ways of better targeting of the agri-environment schemes are suggested.

The effects of landscape complexity on arable weed species diversity in organic and conventional farming

Summary There is growing concern about declining species diversity in agro‐ecosystems caused by agricultural intensification at the field and landscape scales. Species diversity of arable weeds is classically related to local abiotic factors and resource conditions. It is believed to be enhanced by organic farming but the surrounding landscape may also be important. This study assessed the ruderal vegetation, seed bank and seed rain in 24 winter wheat fields to examine the relative importance of organic vs. conventional farming and landscape complexity for weed species diversity. Diversity was partitioned into its additive components: alpha, beta and gamma diversity. Percentage arable land in a circular landscape sector of 1‐km radius around each study site was used as an indicator of landscape complexity. Weed species diversity in the vegetation, seed rain and seed bank was higher in organic than in conventional fields. Increasing landscape complexity enhanced species diversity more strongly in the vegetation of conventional than organic fields, to the extent that diversity was similar in both farming systems when the landscape was complex. Species diversity of the seed bank was increased by landscape complexity irrespective of farming system. Overall diversity was largely determined by the high heterogeneity between and within the fields (beta diversity). Only in very few cases could higher weed species diversity in complex landscapes and/or organic farming be related to species dependence on landscape or farming system. Synthesis and applications. Local weed species diversity was influenced by both landscape complexity and farming system. Species diversity under organic farming systems was clearly higher in simple landscapes. Conventional vegetation reached similar diversity levels when the surrounding landscape was complex through the presence of refugia for weed populations. Consequently, agri‐environment schemes designed to preserve and enhance biodiversity should not only consider the management of single fields but also of the surrounding landscape.

The influence of landscape context and farming practices on parasitism of cereal aphids

Abstract Agri-environmental schemes in Europe aim to support biodiversity and ecological functions in agroecosystems, which are related to both farming practices and landscape context. Here, we analysed the relative importance of farming practices and landscape context on an important ecosystem service, the naturally occurring biological pest control. In a 3-years study, we investigated cereal aphids and their mortality due to parasitism in 24 paired winter wheat fields (i.e., one organic and one conventional field close to each other). The field pairs were located in 12 landscapes differing in landscape complexity, simple landscapes with high percentage of arable land (∼80%), and complex landscapes with lower percentage of arable land (∼50%) and high proportions of semi-natural habitats. Arable land (%) was used as simple predictor of landscape complexity, as it was closely related with other landscape metrics like habitat-type diversity. Aphid population densities varied considerably between the 3 years and the 12 different landscapes. Organic farming was related to lower abundance of cereal aphids at the time of wheat flowering, but not to higher parasitism. At wheat ripening, complex landscapes were related to higher parasitism than simple landscapes, presumably due to more overwintering sites, alternative hosts and nectar sources for parasitoids. However, aphid population densities were also higher in complex landscapes, presumably due to the high availability of winter hosts for these host-alternating species. In a geographical scale analysis, we tested the relative importance of landscape complexity at 5 spatial scales (1–3 km radius around the study sites). Parasitoids responded to landscape complexity at spatial scales of 1–2 km, whereas aphid densities responded to landscape complexity at all spatial scales, indicating a trophic level-specific perception of the surrounding landscape. We conclude that complex landscapes with low percentage of arable land appeared to enhance parasitism, but also the host-alternating aphids, so overall effects of landscape complexity on cereal aphid control appear to be ambivalent.

Landscape context of organic and conventional farms: Influences on carabid beetle diversity

Carabid species richness and density were studied in 12 pairs of organic versus conventional wheat fields located along a gradient of landscape complexity (quantified as percent cover of grassland, which was correlated with habitat-type diversity). The relative impact of local and landscape features was analyzed by comparing sites with similar landscape context but different management systems using pitfall traps. Organic and conventional management did not differ with respect to species richness and activity density. Seven species were more abundant under organic management, and eight species were more abundant under conventional management. The effect of landscape complexity was independent of management system. Species richness increased with percent cover of grassland in the surrounding landscape, and activity density followed the same trend. Hence, surrounding grassland appeared to act as a major source of diversity for farmland carabids. In particular, the activity density of spring breeders on organic fields benefited from the increased availability of overwintering habitats in their close surrounding. It was concluded that landscape features were much more important than organic farming management for enhancement of local biodiversity and should thus be considered in agri-environment schemes.