Plantlife’s road verge advice could negatively affect pollinators

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Did anyone else hear the item on Radio 4 this morning about Plantlife’s road verge campaign and associated petition?  I listened carefully to the discussion and am broadly supportive of what they are trying to achieve.  But I was immediately struck by a comment that local councils should cut the verges “from mid July onwards” because most plants will have set seed by then.  I’ve seen this advice given before and whilst it might be an appropriate option for plants, it could severely impact local pollinator populations.

The printed advice that Plantlife is offering (which can be found here) states that if it’s only possible to cut a verge once a year:

“Cut the full width of the verge….between mid July and September. This allows plants to flower and, importantly, gives time for seed to be set.”

This misses a vital point: between mid-July and September there is still an abundance of flower-visiting insects that require these flowers to provide resources for their nesting and egg laying activities, or to build up reserves of energy to allow them to hibernate, particularly newly-mated queen bumblebees.

Where’s the evidence to support my assertion?  It’s been demonstrated by a number of studies, but I’ll point you in the direction of a paper that came out of the PhD work of one of my former students, Dr Sam Tarrant, who now works with RSPB.  If you look at Figure 4 of this paper, you’ll see that on restored landfill sites the abundance of pollinators in autumn surveys (conducted September-October) was just as high as for summer surveys.  On nature reserves, which are routinely cut from mid-July onwards (see Figure 2), this was not the case.

Climate change means that flower-visiting insects are now active in the UK for a much longer period of time than was previously the case, up to at least November in the south of the country.  I agree with Plantlife that road verges are important habitats for plants and other wildlife.  But advice that suggests cutting floral resources at a key time of the year for these insects is simply misguided.  A cut between October and December would be much more appropriate.

I don’t use Twitter so if anyone could point this at Plantlife’s account I’d be interested to see what their reaction is.

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20 Comments

Filed under Bees, Biodiversity, Butterflies, Hoverflies

20 responses to “Plantlife’s road verge advice could negatively affect pollinators

  1. Katherine Baldock

    Shared via Twitter with Plantlife, will let you know any responses.

    Liked by 1 person

  2. Hi Jeff and thanks for the comments.

    Absolutely we agree that there’s no one single managemt solution for verges and any management is about striking a balance between the needs of different taxa. It’s also about having a diversity of management practices and avoiding single solutions.

    We’ve discussed out new guidelines with entomologists and modifed them to take on board some of the factors you highlight – especially the practice of many councils to mow the 1 meter edge of the road verge early (i.e now). This tends to ‘put back’ many flowers which regrow and flower later in the year, during the period you mention.

    Also, there is research that shows that plant species richness drops dramatically if verges are cut too late in the year (i’ll look out references next week). So it’s also about maximising food plant diversity on verges too.
    All the best
    Trevor

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    • Thanks for the response Trevor but I have to say that (unless I’ve misunderstood you) there’s a flawed logic to your comment that mowing now “tends to ‘put back’ many flowers which regrow and flower later in the year, during the period you mention”.

      Your advice clearly states “Cut the full width of the verge once a year, between mid July and September”. So the plants on the 1m edge of of the road will also be cut during the latter part of the season, losing their “put back” flowers in the process. That’s of no use to flower-visiting insects.

      I agree that there’s no single right solution and that a diversity of approaches is needed, but that isn’t what your advice is suggesting. Councils (or rather their contractors, given that much of this management is now out-sourced) will see it as sound conservation advice from a respected wildlife organisation.

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  3. The other advantage of cutting that late is that there is a whole lot less plant material to sit round as mulch and fertilizer on sites that should be managed for low fertility. For me (in central France) the ideal is to mow in the first half of September. I can be sure all the orchid seed is mature then (except for late flowerers like Autumn Ladies Tresses), but the weather is not yet wet.

    Liked by 1 person

  4. PS I was writing my comment before Trevor’s appeared. I’d be interested in seeing the research showing a drop in diversity related to late mowing. ‘Fauchage tardive’ is common practice here in central France because it is seen as a win/win situation — biodiversity ensured because plants set seed, local authorities save money and resources.

    Liked by 1 person

    • Yes, I’m not aware of that research either. It’s certainly not the advice that’s given by other organisations, who recommend later grazing for example, as Stuart Roberts pointed out on Facebook.

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  5. Emily

    Why do verges need to be cut at all?

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    • It’s an interesting point Emily. Some probably need cutting very infrequently if they are on poor, shallow, stony soil. But on richer soil if they aren’t cut, eventually shrubs and trees will colonise and you’ll lose the grassland diversity.

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      • David Evans

        Jeff: surely shrubs could be held back by a single cut – possibly even in the winter (or would that be bad for creatures trying to hole up until spring arrives).

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      • Very much depends on the timing of the cut and the type of shrub, i.e. whether it flowers from the previous or the current year’s growth.

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  6. Pingback: More bees in the garden | a french garden

  7. David Evans

    I am still looking for information on the disappearance of windscreen splatter. I suppose it could be that windscreens are more aerodynamic than they used to be, but what about lorries. Does anyone know of any studies done on the subject. The change over perhaps 30 years or so is very striking and, if it were a true indicator of insect numbers, it would surely imply that there has been a catastrophic decline. One thing I havce noticed is that I never seem to drive through clouds of moths as I remember doing at one time. So much so that I used slow down to avoid smashing into them.

    Liked by 1 person

    • I raised this question at a conference last year and was told that there’s little data to support the idea that there’s been a wholesale crash in insect numbers (e.g. from the Rothamsted suction sampling network) but I’d like to see some more evidence. Anecdotally I think that I see fewer insects now than I did 30 or 40 years ago, but that might be rose-tinted glasses on my part :-).

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  8. Scott Gibbens

    I am having a similar discussion with our local council. They want to cut our local wildflower common now, on the recommendation of Natural England. Natural England say mow after the end of July. The local farmer has offered to mow it for free (and takes the bales to feed his cows), and the council seem to think this is OK.
    They always reply that the experts at Natural England must know what they are talking about and refuse the engage their own brains.
    If you have any evidence I could package up for them to persuade them to cut later I would really appreciate it.

    Liked by 1 person

    • Hi Scott – feel free to point them towards this blog post and to download the paper I link to, show them Figure 4 in particular. Also it’s worth going out there and recording the number of flower visitors you see to provide them with your own evidence that the site is still important.

      Good luck, let us know how you get on.

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  9. Just writing a ‘Transport Corridors for Pollinators’ sheet for Buglife (to complement the DEFRA Bees Needs one, and this dialogue is very useful. Buglife have also cocordinated an invert survey of the A30 and A38 in SW England which should be available in 2016.

    Liked by 1 person

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