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The impact of forest on pest damage, pollinators and pollination services in an Ethiopian agricultural landscape
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.ORCID iD: 0000-0002-3791-4688
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 [en]
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: urn:nbn:se:su:diva-126669ISBN: 978-91-7649-354-0 (print)OAI: oai:DiVA.org:su-126669DiVA: diva2:902231
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: 2017-02-24Bibliographically approved
List of papers
1. Local and Regional Variation in Local Frequency of Multiple Coffee Pests Across a Mosaic Landscape in Coffea arabica's Native Range
Open this publication in new window or tab >>Local and Regional Variation in Local Frequency of Multiple Coffee Pests Across a Mosaic Landscape in Coffea arabica's Native Range
2014 (English)In: Biotropica, ISSN 0006-3606, E-ISSN 1744-7429, Vol. 46, no 3, 276-284 p.Article in journal (Refereed) Published
Abstract [en]

Shaded coffee has been highlighted for its potential to conserve biodiversity, and thus perhaps also a diversity of natural enemies that could control pest organisms. In southwestern Ethiopia, coffee is grown in shade both in contiguous forests and in forest patches with native trees surrounded by open fields. We hypothesized that coffee grown in contiguous forests, which is the natural habitat for coffee (Coffea arabica) and its interacting organisms, would have less pest damage due to high protection by natural enemies. We surveyed pests on coffee plants in plots within contiguous forests (10 sites) and in forest patches (21 sites). In general, the variation in number of damaged or attacked leaves by individual insect or fungal pests was larger between plants than between plots, which suggests that very local conditions or processes are important. The spatial signals were generally weak. Coffee rust and coffee blotch miner tended to have lower infestation rates in accordance with our hypothesis, while fruit flies in ripe berries were more abundant in forest patches closer to contiguous forest. Based on interviews, olive baboons showed a clear dependency on contiguous forest habitat and were regarded as a problem only in contiguous forests and forest patches close to contiguous forests. In conclusion, we found no support for a generally stronger top-down control on coffee pests in sites within, or with connectivity to, contiguous moist afromontane forests in the native range of coffee.

Keyword
Hemileia vastatrix, isolation gradient, Ethiopia, coffee, moist afromontane forests, landscape ecology, patch size
National Category
Ecology Environmental Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-105220 (URN)10.1111/btp.12106 (DOI)000335784700005 ()
Funder
Science for Life Laboratory - a national resource center for high-throughput molecular bioscienceSwedish Research Council Formas
Note

AuthorCount:4;

Available from: 2014-07-03 Created: 2014-06-24 Last updated: 2017-12-05Bibliographically approved
2. Dominance of the semi-wild honeybee as coffee pollinator across a gradient of shade-tree structure in Ethiopia
Open this publication in new window or tab >>Dominance of the semi-wild honeybee as coffee pollinator across a gradient of shade-tree structure in Ethiopia
2014 (English)In: Journal of Tropical Ecology, ISSN 0266-4674, E-ISSN 1469-7831, Vol. 30, 401-408 p.Article in journal (Refereed) Published
Abstract [en]

Mass-flowering plant species are often pollinated by social bees that are able to use the abundant resource by recruiting workers from their colonies. In this study we surveyed pollinators on the mass-flowering perennial crop coffee (Coffea arabica) in its native range in Ethiopia. Previous studies in areas where coffee is introduced often find the social honeybee, Apis mellifera, to be the dominant pollinator. In those areas, the bee-species composition visiting coffee varies with a higher bee diversity closer to forest or in less modified habitats. We surveyed pollinators of coffee under different shade-tree structures, by collecting hoverflies and bees landing on coffee flowers in 19 sites in south-west Ethiopia. We found the native honeybee (A. mellifera) to be the dominant visitor of coffee flowers in all sites. Honeybee abundance was not affected by the local shade-tree structure, but was positively affected by the amount of coffee flower resources. Other pollinators were positively affected by complex shade-tree structures. To conclude, the honeybee is clearly the dominant pollinator of coffee in Ethiopia along the whole shade-tree structure gradient. Its high abundance could be a consequence of the provision of traditional bee hives in the landscape, which are colonized by wild swarming honeybees.

Keyword
agroforestry, Apis mellifera subsp simensis, Coffea arabica, landscape ecology, moist afromontane forest, pollination, species composition
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-107421 (URN)10.1017/S0266467414000327 (DOI)000340562800002 ()
Note

AuthorCount:4;

Available from: 2014-09-19 Created: 2014-09-15 Last updated: 2017-12-05Bibliographically approved
3. Turnover in bee species composition and functional trait distributions between seasons in a tropical agricultural landscape
Open this publication in new window or tab >>Turnover in bee species composition and functional trait distributions between seasons in a tropical agricultural landscape
Show others...
2015 (English)In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 211, 185-194 p.Article in journal (Refereed) Published
Abstract [en]

A comprehensive understanding of how spatial variation across landscapes regulates local abundances and species richness also needs to consider possible temporal changes in such relationships. In many tropical areas, the contrast between dry and rainy season is pronounced and the types and distributions of the main floral resources differ (herbs vs trees). This shift in resources could result in different pollinator abundances, species richness and trait compositions between seasons, as well as in how these components are spatially distributed. We compared the bee species composition between dry and rainy season in an agricultural mosaic landscape in southwestern Ethiopia, and analyzed it in relation to forest cover. We sampled bees for 67 days in the dry season and 86 days in the rainy season with pan and vane traps in 28 homegardens covering a gradient from low to high tree cover in the surrounding area. We found a clear shift in species composition between seasons, with more small bee species and more below-ground nesting bees in the rainy season compared to the dry season. The distribution of height at which the bees were foraging shifted between seasons with a higher proportion of the bees foraging at tree level in the dry season. Bee abundance and richness were generally positively affected by higher forest cover surrounding the homegardens, but there were no clear interaction effects between seasons, in contrast to our hypothesis. The clear turnover in species composition between seasons and the positive effect of forest cover show that mechanisms acting both at spatial and temporal scales are important in regulating local bee communities.

Keyword
Ethiopia, Functional trait, Pollinator, Spatial pattern, Temporal dynamic
National Category
Agricultural Science, Forestry and Fisheries Biological Sciences Earth and Related Environmental Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-122233 (URN)10.1016/j.agee.2015.06.010 (DOI)000362049800021 ()
Available from: 2015-11-03 Created: 2015-10-28 Last updated: 2017-12-01Bibliographically approved
4. A heterogeneous landscape does not guarantee high crop pollination
Open this publication in new window or tab >>A heterogeneous landscape does not guarantee high crop pollination
Show others...
(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:nbn:se:su:diva-126666 (URN)
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

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