Linn Vassvik
Research Scientist
Authors
Linn VassvikAbstract
Agricultural production is highly dependent upon pollinators to achieve maximum yield and increase global food security. Wild pollinators, such as bees, are declining due to a loss of habitat from agricultural intensification, and the use of domesticated honeybees to supplement pollination services is increasing. Apple is an important, pollinator dependent food crop that commonly experiences pollination and production deficits worldwide. In this thesis, I explored whether pollination and production deficits occur in Norwegian apple orchards and what factors might be driving potential deficits. To test for pollination (seed set) and production (yield) deficits I conducted a supplemental pollination experiment for three cultivars, in eighteen orchards, in two distinct growing regions in Norway, over two years. I also assessed which pollinators are present in Norwegian apple orchards and how different groups of bees and their behaviour affect pollination of apple. Lastly, I studied different management practices to increase bee diversity and pollination success, by increasing alternate floral resources and evaluating orchard design that promotes cross-pollination. Pollination and production deficits were found across all locations, with differences in pollination deficits among cultivars. I also found that a high abundance of wild bees increases seed set in apples—a key indicator of pollination success. Behaviour also varied among bee groups, for example bumblebees visited more flowers, while solitary bees were slow, but potentially more thorough, foragers, which increases pollen deposition. Wild bees visited more apple flowers than dandelion flowers (Taraxacum spp.) when orchards were left unmowed. I also found that a higher abundance of dandelions increased bee visitation to apple flowers, suggesting higher floral diversity can increase pollination success and support a greater diversity of bees. In addition, block design orchards appear to limit cross-pollination among apple cultivars, and management actions to decrease the distance among compatible apple cultivars is needed to achieve sufficient pollination. Overall, my results suggest that greater pollination and production of apples in Norway is possible, and management actions should focus on increasing wild bee abundance and diversity, increasing alternate floral resources, and optimising orchard design to facilitate cross-pollination across shorter distances. Such actions have the potential to ensure greater yields of higher quality apples for human consumption and increased economic output for farmers.
Authors
Linn Vassvik Anders Nielsen Michael P.D. Garratt Bjørn Arild Hatteland Joseph Chipperfield Erik Trond AschehougAbstract
Low pollinator richness and abundance is a primary driver of pollination deficits and may lead to reduced yields (production deficits). In response, domesticated honeybees are often used to increase pollination success, even though honeybees are less efficient pollinators than naturally occurring wild bees. Here, we explored whether Norwegian apple orchards experience pollination and production deficits, and if such deficits could be related to specific pollinator groups and activity. We conducted a supplemental pollination experiment and measured seed set and yield (fruit set x weight) for three cultivars, in six orchards, in two distinct apple growing regions in central Norway, for two years. In addition, we used cameras to record relative pollinator activity throughout the flowering period. Overall, we found a pollination and production deficit across all cultivars, although there were differences in pollination deficit among cultivars. Three orchards had a pollination deficit both years of the study, suggesting sub-optimal orchard structure and/or a lack of pollinators. However, we found that solitary bees significantly reduced both pollination and production deficit, suggesting that orchard management actions should focus on increasing wild bee diversity and abundance.
Authors
Linn VassvikAbstract
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