Karin Ahrné

MEASURING SOCIAL–ECOLOGICAL DYNAMICS BEHIND THE GENERATION OF ECOSYSTEM SERVICES

The generation of ecosystem services depends on both social and ecological features. Here we focus on management, its ecological consequences, and social drivers. Our approach combined (1) quantitative surveys of local species diversity and abundance of three functional groups of ecosystem service providers (pollinators, seed dispersers, and insectivores) with (2) qualitative studies of local management practices connected to these services and their underlying social mechanisms, i.e., institutions, local ecological knowledge, and a sense of place. It focused on the ecology of three types of green areas (allotment gardens, cemeteries, and city parks) in the city of Stockholm, Sweden. These are superficially similar but differ considerably in their management. Effects of the different practices could be seen in the three functional groups, primarily as a higher abundance of pollinators in the informally managed allotment gardens and as differences in the composition of seed dispersers and insectivores. Thus, informal management, which is normally disregarded by planning authorities, is important for ecosystem services in the urban landscape. Furthermore, we suggest that informal management has an important secondary function: It may be crucial during periods of instability and change as it is argued to promote qualities with potential for adaptation. Allotment gardeners seem to be the most motivated managers, something that is reflected in their deeper knowledge and can be explained by a sense of place and management institutions. We propose that co-management would be one possible way to infuse the same positive qualities into all management and that improved information exchange between managers would be one further step toward ecologically functional urban landscapes.

Bumble bees (Bombus spp) along a gradient of increasing urbanization.

Background Bumble bees and other wild bees are important pollinators of wild flowers and several cultivated crop plants, and have declined in diversity and abundance during the last decades. The main cause of the decline is believed to be habitat destruction and fragmentation associated with urbanization and agricultural intensification. Urbanization is a process that involves dramatic and persistent changes of the landscape, increasing the amount of built-up areas while decreasing the amount of green areas. However, urban green areas can also provide suitable alternative habitats for wild bees. Methodology/Principal Findings We studied bumble bees in allotment gardens, i.e. intensively managed flower rich green areas, along a gradient of urbanization from the inner city of Stockholm towards more rural (periurban) areas. Keeping habitat quality similar along the urbanization gradient allowed us to separate the effect of landscape change (e.g. proportion impervious surface) from variation in habitat quality. Bumble bee diversity (after rarefaction to 25 individuals) decreased with increasing urbanization, from around eight species on sites in more rural areas to between five and six species in urban allotment gardens. Bumble bee abundance and species composition were most affected by qualities related to the management of the allotment areas, such as local flower abundance. The variability in bumble bee visits between allotment gardens was higher in an urban than in a periurban context, particularly among small and long-tongued bumble bee species. Conclusions/Significance Our results suggest that allotment gardens and other urban green areas can serve as important alternatives to natural habitats for many bumble bee species, but that the surrounding urban landscape influences how many species that will be present. The higher variability in abundance of certain species in the most urban areas may indicate a weaker reliability of the ecosystem service pollination in areas strongly influenced by human activity.

Leaf trichome responses to herbivory in willows: induction, relaxation and costs.

To circumvent the inherent problem of discriminating between the cost of losing photosynthetic tissue and the cost of producing an inducible defence, the growth response of herbivore-damaged plants was compared with plants damaged mechanically to the same extent but without eliciting the defence. Two experiments were conducted, studying the response of willows (Salix cinerea) to damage by adult leaf beetles (Phratora vulgatissima). In the first experiment, willows produced new leaves with an enhanced leaf trichome density 10-20 d after damage, coinciding in time with the feeding of beetle offspring. The response was relaxed in foliage produced 30-40 d after damage. In the second experiment, which also included mechanical damage, willows exposed to beetle feeding showed an increase in leaf trichome density of the same magnitude (> 70%) as in the first experiment. The cost of producing the defence was a 20% reduction in shoot length growth and biomass production. Willows exposed to mechanical damage had an 8% reduction in shoot length growth compared with control plants, that is, a cost of leaf area removal. The results are the first quantitative estimates of the cost of a plant defence induced by natural and low amounts (3.3%) of herbivory.

The Dynamics of Social-Ecological Systems in Urban Landscapes: Stockholm and the National Urban Park, Sweden

Abstract: This study addresses social‐ecological dynamics in the greater metropolitan area of Stockholm County, Sweden, with special focus on the National Urban Park (NUP). It is part of the Millennium Ecosystem Assessment (MA) and has the following specific objectives: (1) to provide scientific information on biodiversity patterns, ecosystem dynamics, and ecosystem services generated; (2) to map interplay between actors and institutions involved in management of ecosystem services; and (3) to identify strategies for strengthening social‐ecological resilience. The green areas in Stockholm County deliver numerous ecosystem services, for example, air filtration, regulation of microclimate, noise reduction, surface water drainage, recreational and cultural values, nutrient retention, and pollination and seed dispersal. Recreation is among the most important services and NUP, for example, has more than 15 million visitors per year. More than 65 organizations representing 175,000 members are involved in management of ecosystem services. However, because of population increase and urban growth during the last three decades, the region displays a quite dramatic loss of green areas and biodiversity. An important future focus is how management may reduce increasing isolation of urban green areas and enhance connectivity. Comanagement should be considered where locally managed green space may function as buffer zones and for management of weak links that connect larger green areas; for example, there are three such areas around NUP identified. Preliminary results indicate that areas of informal management represent centers on which to base adaptive comanagement, with the potential to strengthen biodiversity management and resilience in the landscape.

Butterflies in semi‐natural pastures and power‐line corridors – effects of flower richness, management, and structural vegetation characteristics

The aim of this study was to compare the butterfly assemblages in semi‐natural pastures and power‐line corridors and to analyse the effects of vegetation height, occurrence of trees and shrubs and different flowering vascular plant groups on butterfly diversity and abundance. Twelve of 26 analysed butterfly species were more abundant in power‐line corridors than in semi‐natural pastures. Only one species preferred semi‐natural pastures. In semi‐natural pastures butterflies were most common in segments with tall vegetation, whereas butterflies in power‐line corridors were most common in segments with vegetation of short or intermediate height. Short vegetation was sparser in power‐line corridors (mean cover 4%) than in semi‐natural pastures (33%), whereas tall vegetation was more common in power‐line corridors (59%) than in semi‐natural pastures (35%). The amount of flowers was the factor that affected the abundance of most species. Twenty‐one of the 26 species showed positive associations with numbers of flowers of different families. Flowers of the plant families Apiaceae, Caryophyllaceae, Primulaceae, Rubiaceae, Scrophulariaceae, and Violaceae showed positive associations with the abundance of several butterfly species. Vegetation height seems to be a limiting factor in semi‐natural pastures, and less intensive management (division of pastures into grazing pens, late season grazing, grazing every second year, or reduced grazing pressure) would benefit butterflies. In power‐line corridors (dominated by tall vegetation) the opposite would be beneficial for butterflies, for example more frequent clearing of vegetation along the power‐line trails combined with mowing of selected areas.

Influence of leaf trichome density on the efficiency of two polyphagous insect predators

Plant characteristics, such as leaf structure or hairiness, are important for the movement and attachment of insects. It has been suggested that increased trichome density on new Salix cinerea L. (Salicaceae) leaves, produced after grazing by the willow leaf beetle Phratora vulgatissima L. (Coleoptera: Chrysomelidae), function as an inducible defence against the beetle and especially its larvae. Here we studied whether and how two of the main natural enemies of P. vulgatissima, viz., Anthocoris nemorum L. (Heteroptera: Anthocoridae) and Ortothylus marginalis L. (Heteroptera: Miridae), were influenced by trichome density on S. cinerea leaves. The effect of trichome density on these two predators was studied on plants with different trichome densities, comparing natural enemy efficiency, measured as number of P. vulgatissima eggs consumed or larvae missing and/or killed. To obtain different trichome densities, cuttings of several different clones of S. cinerea were used. In the experiment using eggs as prey, an increase in trichome density was, in addition, induced through leaf beetle defoliation on half of the plants of each willow clone. Furthermore, a field study was performed to investigate whether trichome density was correlated with natural enemy abundance. The results indicate that neither the efficiency of these two natural enemies in the greenhouse, nor their abundance in the field was influenced by trichome density. A well‐known behavioural difference between the two predator species could probably account for the higher disappearance of larvae after exposure to the more active predator. These findings are relevant for the development of pest management programs, not least because the enemies are polyphagous predators. It is concluded that an induced increase in leaf hairiness in willows in response to leaf beetle grazing could be a plant resistance trait worthy of further study in this system, because no negative effects on the main natural enemies were observed.

Biodiverse green infrastructure for the 21st century: from “green desert” of lawns to biophilic cities

Abstract Modern urban green infrastructures are following globalisation trends and contribute to homogenization at all levels of green areas from the master plan to the finest scale. We discuss the place and role of three principal urban living spaces, the “skeleton” of green infrastructures: lawns, green walls and green roofs. This “trio” of modern GI elements provide significant ecosystem services, it contributes to biodiversity and social values; and have environmental and economic impact. The main goal of our approach to sustainable GI is to introduce a new landscape architecture style – biodiversinesque – as an alternative to the existing global homogenised picturesque-gardenesque. This new approach will combine the best achievements of innovative and alternative landscape design solutions (biodiverse lawns, pictorial meadows, walls and green roofs) and implement them on three major scales: city, intermediate neighborhood and the small biotope level.