When weeds are wanted

31 01 2011

And in keeping with the topic of bees

© Flowergardengirl

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:

  1. The distance to natural habitat affects pollination visitor abundance and diversity.
  2. Plots surrounding or interspersed with ruderal vegetation affect pollinator abundance and diversity.
  3. The diversity of pollinators visiting sunflowers affects honeybee (the principal pollinators) behaviour.
  4. 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.

CJA Bradshaw

ResearchBlogging.org
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


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6 responses

4 04 2011
Buzzing to the plate « ConservationBytes.com

[...] access of social bees to crops from their nests within neighbouring forests [CJAB's note - see previous post on the role of ruderal vegetation in promoting pollinator diversity and increasing cro...]. Secondly, in agro-forestry schemes, coffee plantations are often grown under the shade of [...]

4 02 2011
manuelinor

Great post…this is a really important topic. I’m looking at how the presence of other vegetation (remnant or flowering ‘weeds’) in almond orchards is related to insects, particuarly pollinators. In the orchards I have visited, those with a ‘bare-ground’ management policy have a lot less insect species than those that maintain a grassy/flowering ground cover between the trees.

31 01 2011
Robert Lawrence

When “weeds” are native plants it is not surprising that they are beneficial. I see you have become an olive producer. Our family has a ban on locally produced olives, named as the worst weed problem in the region. They do more to support fox populations than natural biodiversity. All this aside, I hope the revegetation is effective.

31 01 2011
Pam Kimsey

Very good research and sounds like an awesome development for your new home. We grow some non-natives, but stay clear of the invasive species. I know from my own research that the natives actually provide not just more, but healthier food for the precious bees. I found some links last night for a few actual USDA members that are promoting and teaching more biodiverse farming practices. My concern would be with the GM crops. I don’t see that pesticide infested crops will benefit our bees. Keep us posted Corey. I enjoy reading your research.

31 01 2011
Tweets that mention When weeds are wanted « ConservationBytes.com -- Topsy.com

[...] This post was mentioned on Twitter by Kit R, Kit R. Kit R said: RT @conservbytes: When #weeds are wanted: http://wp.me/phhT4-1k4 [...]

31 01 2011
octopus

This is very similar to the kind of knowledge gathered from hedgerows that used to surround small paddocks all over the UK. It was widely known that fewer hedgerows meant fewer insects, and not just pollinators, all kinds of insects that provided biological control as well as pollination functions, therefore increasing the amount of pesticides being used. As factory farms took down more and more hedgerows, this effect has got worse and worse and has not only affected insects, but there is less habitat for all sorts of iconic uk animals such as hedgehogs and small songbirds.

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