Impacts of organic and conventional farming practice and increasing proportion of semi-natural grasslands on pollination success of field beans, Vicia faba

Abstract

As a consequence of increasing land-use intensity and changes in farming practices, many species of pollinators have been shown to decline. These declines have led to concerns about crop pollination services performed by wild pollinators. The aim of this study was to investigate whether farming practice (organic and conventional), and increasing percentage of semi-natural grassland in the surrounding landscape affected bumblebee (Bombus spp.) abundance and pollination success of field beans (Vicia faba). The study was conducted by placing potted plants at ten organic and ten conventional farms located in selected study landscapes along a gradient of increasing proportions of semi-natural grassland. Pollination success was quantified as number of developed pods per plant, average number of beans per pod and average weight of beans per pod. Bumblebee abundance was counted along linear transects and bumblebee visitation rate on field bean flowers was recorded. There was no difference in pollination success between organic and conventional farms, irrespective of whether the proportion of semi-natural grasslands was high or low. However, increasing percentage of semi natural grassland had a significantly positive effect on average number of beans per pod. Neither farming practice nor semi-natural grassland affected bumblebee abundance, but increasing number of bumblebees was significantly related with an increasing number of pods per plant. My results suggest that semi-natural grassland and local bumblebee abundance are more important for the pollination success of field beans than is farming practice as such. According to my results, the preservation of semi-natural grassland in agricultural-dominated landscapes might be of importance to secure pollination services and increase crop yield of field beans.

Popular Abstract

Permanent pastures important for the pollination success of field beans

Bumblebee population declines have been attributed to increasing land-use intensity and changes in farming practices. Different habitat types such as pastures and meadows have been replaced by large areas of arable land. Bumblebees are important pollinators for some plant species, and the decline of pollinators have led to concerns about crop pollination services performed by wild pollinators.

Permanent pastures provide nesting habitats for bumblebees and can thereby provide pollinators to the surrounding landscape such as to crop fields. Contrary to conventional farming, organic farming do not use herbicides which benefits bumblebees by increasing the amount of floral food resources on organic farms. In this study I investigated how organic vs. conventional farming and the proportion of pastures in the surrounding landscape influence pollination success of field beans (Vicia faba) and bumblebee (Bombus spp.) abundance. I also investigated if pollination success was determined by an interaction between these two variables. Pollination success was measured as the number of pods (the seed vessel) and beans. To investigate this, I used potted plants of field beans and placed them in a field margin of a cereal crop field. This was done on ten organic and ten conventional farms placed along a gradient of increasing percentage of pasture. I also counted bumblebees in the proximity of the plants. Field beans have a deep floral form. Therefore pollinators with long tongues, that can reach the nectar, perform a more qualitative pollination leading to the production of more beans. Short-tongued pollinators pollinate less qualitative but possibly still enough for the plant to develop a pod.

The majority of all bumblebees observed were the short-tongued species Bombus terrestris. Only 16% of the observed bumblebees concerned long-tongued species. There was no difference in pollination success or bumblebee abundance between organic and conventional farms, irrespective of whether the proportion of semi-natural grasslands was high or low. As there are more flowering weeds in the fields of organic farms, these flowers might have attracted bumblebees away from the field beans in the field margin, possibly explaining why there was no difference in pollination success between organic and conventional management. The number of beans, but not pods and bumblebees, increased with increasing percentage of pasture. It is possible that the abundance of long-tongued bumblebees, which are the most suitable pollinators of field beans, increase with increasing proportions of pastures. Many long-tongued bumblebees are more sensitive to agricultural intensification as compared to some very common short-tongued bumblebees. Increased numbers of bumblebees resulted in more pods, but not more beans. This might be because most bumblebees I observed were common short-tongued species that pollinate less qualitative but possibly still enough fore the plant to produce pods. As these species are common and less affected by agricultural intensification, this might explain why bumblebee abundance, and thus pods, was not affected by the amount of pasture.

Pasture and bumblebee abundance appeared to be more important for the pollination success of field beans than farming practice. Thus the preservation of pastures might be of importance to secure pollination services and increase crop yield of field beans. As the majority of the world’s leading crops are dependent on insects for pollination to maximize yields, studies concerning pollination services are of great importance.

Advisor: Johan Ekroos
Master´s Degree Project 30 credits in Conservation Biology, 2016
Department of Biology, Lund University

• author: Farbu, Sunniva
• supervisor: Johan Ekroos
• organization: Degree Projects in Biology
• course: BIOM01 20152
• year: 2016
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8871489
• date added to LUP: 2016-04-25 14:12:48
• date last changed: 2016-04-25 14:12:48