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A heterogeneous landscape does not guarantee high crop pollination
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.ORCID iD: 0000-0002-3791-4688
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The expansion of pollinator-dependent crops, especially in the developing world, together with reports of world-wide pollinator declines, raises concern of possible yield gaps. Farmers directly reliant on pollination services for food supply often live in regions where our knowledge of pollination services is poor. In a manipulative experiment replicated at 23 sites across an Ethiopian agricultural landscape, we found poor pollination services and severe pollen limitation in a common oil crop. With supplementary pollination, the yield increased on average by 91%. Despite the heterogeneous agricultural matrix, we found a low bee abundance, which may explain poor pollination services. The variation in pollen limitation was unrelated to surrounding forest cover, local bee richness and bee abundance. While practices that commonly increase pollinators (e.g. organic farming, flower strips) are an integral part of the landscape, these elements are apparently insufficient. Management to increase pollination services is therefore in need of urgent investigation.

National Category
Ecology
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-126666OAI: oai:DiVA.org:su-126666DiVA: diva2:902204
Funder
Sida - Swedish International Development Cooperation Agency, SWE-2009-134Swedish Research Council Formas, 229-2009-991
Available from: 2016-02-10 Created: 2016-02-10 Last updated: 2016-02-12Bibliographically approved
In thesis
1. The impact of forest on pest damage, pollinators and pollination services in an Ethiopian agricultural landscape
Open this publication in new window or tab >>The impact of forest on pest damage, pollinators and pollination services in an Ethiopian agricultural landscape
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The distribution of wild biodiversity in agroecosystems affect crop performance and yield in various ways. In this thesis I have studied the impact of wild biodiversity, in terms of trees and forest structures, on crop pests, pollinators and the pollination services provided in a heterogeneous landscape in southwestern Ethiopia. 

Coffee, Coffea arabica, is a forest shrub native to Ethiopia and is grown in most wooded areas in the landscape where I conducted my studies. Wild coffee is still found in remote parts of the forests in the landscape. For my first paper, I surveyed pest damage on coffee in coffee forest sites, where some sites were situated in continuous forest and some in isolated forest patches. I found the variation in pest damage frequency to mainly be among coffee plants within a site, rather than among sites, which indicates the importance of local processes. However, some pests were clearly connected to the forest habitat, such as the olive baboon.

In my second study, I surveyed pollinators visiting coffee flowers across a gradient of shade-tree structures. I found the semi-wild honeybee to be the dominating flower visitor. The abundance of the honeybee was not related to shade-tree structures, but to amount of coffee flower resources in the site. On the other hand, other pollinators, which included other bee species and hoverflies, were positively affected by more shade trees in the site.

In my third study I investigated how the forest cover affected local bee communities in the agricultural landscape. Moreover, I investigated if this relationship differed between the dry and rainy season. The distribution of food resources for bees changes between the seasons, which may affect the bees. Most trees, fruit trees and coffee, which are patchy resources, flowers in the dry season, whereas most herbs and annual crops, which are more evenly spread resources, flowers during the rainy season. I found a clear turnover in bee species composition between the dry and rainy season, with more mobile species in the dry season. Increased forest cover in the surrounding landscape had a positive impact on bee abundance and species richness. However, the impact did not change between seasons.

In my fourth study I evaluated the pollination success and pollen limitation of a common oil crop in the landscape in relation to forest cover. I found severe pollen limitation across the landscape, which may be related to the observed low bee abundances. The pollen limitation was not related to surrounding forest cover.

In conclusion, I have found the forest and wooded habitats to impact several mobile animals and pathogens in our study landscape, which in turn affect people. However, there is large complexity in nature and general relationships between forest structures and all crop related organisms may be unlikely to find. Various species are dependent on different resources, at different spatial scales and are interacting with several other species. To develop management strategies for increased pollination services, for reduced pest damage or for conservation in the landscape, more species-specific knowledge is needed.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2016. 48 p.
Keyword
agroforestry, Apoidea, Coffea arabica, crop pests, Ethiopia, forest cover, landscape ecology, moist afromontane forests, pollination, species composition, tropical agriculture
National Category
Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-126669 (URN)978-91-7649-354-0 (ISBN)
Public defence
2016-04-01, Vivi Täckholmsalen, NPQ-huset, Svante Arrhenius väg 20 A, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation Agency, SWE-2009-134Swedish Research Council Formas, 229-2009-991
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2016-03-09 Created: 2016-02-10 Last updated: 2016-02-26Bibliographically approved

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Samnegård, UlrikaHambäck, PeterHylander, Kristoffer
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