Influence of fragment and roadside vegetation on canola (Brassica napus) and faba bean (Vicia faba) pollination in South Australia

Abstract

Native vegetation remnants within agricultural landscapes play a crucial role in supporting biodiversity and ecosystem services such as pollination; however, their benefits are not always recognised by farmers. We investigated the influence of native vegetation remnants, both in fragment and linear forms, on pollination of Brassica napus (canola or oilseed rape) and Vicia faba (faba beans) in South Australia. We used the difference in the number of seeds per pod between open-pollinated (unbagged) plants and those unpollinated by animals (bagged) as pollination success. We found a positive relationship between seed set (and total crop yield) and the area of fragment and linear vegetation within 200 m for both crop species, with linear vegetation showing a stronger influence on both crop species possibly because of its use by exotic honeybees. Increasing distance to the closest vegetation had a significant negative effect on seed set. Sandy soils diminished the positive effects of native vegetation on bean seed set. Of the pods sampled from beans and canola, 12.2 % and 2.4 % respectively achieved maximum pollination; all were unbagged. Area of fragment and linear vegetation within 200 m of plants exerted a greater effect on maximum pollination than proximity to vegetation for canola. Only distance to vegetation was a significant predictor of bean maximum pollination. These results demonstrate the positive effects of non-crop vegetation with configurational heterogeneity on crop pollination. Given the common practice of crop rotation on commercial farms, the impact of various vegetation types fluctuates across cropping cycles. To ensure the continuity of pollination services over time, conserving and restoring fragment and linear vegetation in agricultural regions are imperative.