And in keeping with the topic of bees…
I’ve just read a very, very cool paper in Ecology Letters about something I’ve wanted to do myself for some time. It’s a fairly specific piece of work, so it could easily be reproduced elsewhere with different species. My point though is that a hell of a lot more of these types of studies are required.
The study by Carvalheiro and colleagues entitled Natural and within-farmland biodiversity enhances crop productivity examined the role of weedy (ruderal) vegetation in supporting pollinator communities. Using sunflowers as a model crop, they showed rather convincingly how native vegetation patches interspersed amongst crop species can enhance a host of crop production measures, even when larger areas of natural habitats were far away from the crops themselves.
Based on a series of plot experiments, they tested four main hypotheses:
- The distance to natural habitat affects pollination visitor abundance and diversity.
- Plots surrounding or interspersed with ruderal vegetation affect pollinator abundance and diversity.
- The diversity of pollinators visiting sunflowers affects honeybee (the principal pollinators) behaviour.
- The diversity of pollinators affects sunflower production.
For Hypothesis 1, nothing really surprising here – the farther away the plots were from natural habitats, the fewer individuals and types of pollinators visited the flowers. But, when sunflower plots were interspersed with ‘weeds’ (native flowering plants), the distance effect more or less disappeared. The authors concluded that such flower diversity supports a more diverse and abundant pollinator community when such fragments exist to support sink populations far from their necessary native habitats. It’s a little like an island effect. The insects can persist a little while in crops alone (the ‘sea’), but they have to return to native vegetation (the ‘land’) regularly. Too much crop species dominance, and they ‘drown’.
The next result was rather more interesting. The higher the diversity of pollinator species visiting (enhanced, as mentioned, but ruderal flowering plants), the more the dominant honeybees were forced to move among more sunflowers. In essence, this added competition increased the number of sunflowers visited, and increased pollination efficiency.
And the proof was in the pudding – the final hypothesis test showed conclusively that those sunflowers visited by more individuals and pollinator species produced more and heavier seeds than there less-frequented counterparts.
Bottom line – instead of competing for soil resources with the crops, ruderal ‘weeds’ in fact enhanced crop production.
As I said above, it would be fantastic to repeat this for a variety of other essential crops. After recently travelling through the wheatbelt of South Australia (Yorke Peninsula), the vast swathes of monoculture wheat fields made me think that we should probably see if such relationships hold for the bigger cereal varieties as well. Would be a really useful experiment to do.
I’ve also a lot of personal interest in this – last year I moved to a 4-ha farm outside of Adelaide and I am in the midst of planning revegetation to maximise production of the olive trees, vines and orchard species there. I have a lot of weeds too. Balancing fire prevention with crop-native vegetation ratios that maximise pollination will be a long-term struggle, but evidence like this tells me that I shouldn’t be too quick to slash everything non-native or non-productive. The land-management plan is developing.
Carvalheiro, L., Veldtman, R., Shenkute, A., Tesfay, G., Pirk, C., Donaldson, J., & Nicolson, S. (2011). Natural and within-farmland biodiversity enhances crop productivity Ecology Letters DOI: 10.1111/j.1461-0248.2010.01579.x