Tuesday 25 December 2018

Nonnative phobia

My English insects love New England daisies
Cathi regular sends me emails with links to scientific research she thinks will interest me. I immediately replied about a recent one telling her that my hackles had risen. She replied “yes I know”. Based on a single piece of research Washington DC citizens were being urged by their local masters to plant native plants in their gardens; the missive implied nonnatives were the work of the devil.

I was reminded of when Mike and Isobel bought an acre of a neglected farm field attached to their garden. Quite reasonably they had to apply to the local authority for change of use. In this case to make a naturalistic wildlife area as a garden extension. 
They got their permission with the proviso that they only plant natives. I know if they transgressed just a smidgeon someone would report them.There were no restrictions on the original farmer!

US gift to UK
Europe's gift to America
The thrust of my piece today is why I consider such thinking is wrong and such sanctions are based on narrow and sometimes low quality research, intensely publicised propaganda by zealots and lack of promotion of facts that do not point the same way.

Readers will know my own predisposition is to let plants and animals of the world intermingle. Particularly in view of climate change we need all the good genes we can get. I know there are problems with invasive species and it is not my intention today to challenge worthwhile (but sometimes misguided) national attempts  to control movement of weeds, pest and disease.

This US nativer and UK nonnative grows wild in Wales
My motive is merely to tell gardeners to carry on spreading  diversity by planting in their gardens from a pallet of plants of the world that have already been established and made the UK (or wherever you maybe) their home. I find it quite ironic that our American friends regard our UK wild flowers as aliens and we do the same for their own. I might add determining whether a plant is nonnative or not is not easy!

Whilst my hackles were still high I read a wonderful piece on the Botany One website reviewing a book about the detailed thirty year record of her small Midlands garden lovingly kept by professional entomologist and lifetime ecologist Jennifer Owen. She recorded every living thing she could find using her professional skills and knowledge and the equipment of her university colleagues. She has precisely identified nearly 3000 plants, animals, insects and other invertebrates. Others have suggested this indicates perhaps a total of 8000 had she had all the time in the world. The diversity of plant and animal life per unit area she recorded was greater than any in such as the Amazon jungle. She is gracious enough to observe that as many of our gardens are so similar this diversity is somewhat repeated but as Cathi remarked last night the jungle is pretty repetitive too. Sadly her record shows a decline in diversity in recent years.
Her review makes no distinction between natives and none natives and nor would they be discernible or of consequence.

I wonder if we should resist planting horse chestnut as it has only resided in the UK for four hundred years
The very next day I clicked onto the excellent Garden Professors blog. They too had taken exception to the Washington research and were also quoting a similar project that comes to precisely the opposite conclusion

Both investigations focusses on a single (but different) chickadee species. These birds have a limited diet and specialist skills in locating and extracting leaf miners. Leaf miners have a fairly limited host range and this in itself negates the relevance of the effect of a single bird species to draw any overall conclusion damning all nonnative plants.

The Washington research by the way claims to show that if aliens provide more than 30% of the biomass of the garden the chickadee population declines.
The other piece of research published a year earlier was specifically how a different chickadee species had adjusted to a new alien plant Lonicera maackii which was now a valuable resource
The thing is that the flawed research had 37,000 google hits after two days, the earlier research a mere 196.
The difference was the advance publicity by the vested interest promoting themselves and pushing a preconceived doctrine

Several things make me uncomfortable about this much publicised trial
1. I am sure that the PHD student who was leader of the project was conscientious and able and had ample expert supervision but really….
2. The trial was quite small
3. I suspect unconscious bias. The gardens were partly self selected on the basis of volunteers in a community group - all birders with a specialist interest. 
4. One lady who had moved into a new house already planted with a lot of alien plants was told at the beginning that it was a perfect illustration of what not to do! 
5. I fear that the researchers and gardeners had a vested interest and prior expectation.
6. If most of the gardens were owned by bird lovers would there be consequential disproportionate bird feeding?
7. Similarly would gardens with a high proportion of aliens be owned by a different king of people, perhaps tidier, more prone to plant garden centre plants, use more pesticides and so on - I just don’t know but these things make a difference
8. The real crux is that the research was based on a single bird species with a rather specialised diet and yet huge leaps are made in its general significance
9. High quality research considers the work of others - no mention whatsoever is made of contradictory results elsewhere.

What happens in this world is that politicians with little knowledge latch on to a popular mantra and go along with it

US native Dicentra cucullaria is almost extinct in the wild but persists in our gardens
What I have discussed today revolves around planting native species to host native organisms. (Some we might regard as pest and disease). What I think much more important is to plant alien plants to conserve them. Many plants from worldwide sources only exist in our gardens. Their native habitats have been destroyed

I have written in a previous post how no native plant has been lost in the UK as a result of planting aliens -  although of course some have been lost by habitat destruction.

This Himalayan wild flower causes a bit of a stir in the UK but our native bees love them.
Since writing this piece I came across this research suggesting newly introduced plants may fair better with climate change than native plants or already established aliens….But is this good or bad?

I understand some of my relatives cause a bit of a stir in London parks

What raised my hackles
The Garden Professors joined the debate
Jennifer's book is a little expensive but you can read about it here
I wrote about none natives before


  1. I couldn’t read the research paper as it seemed to require a log-in to access it, but I’m happy to take your word for it that it was flawed. But that doesn’t stop me from thinking that if we are looking for evidence based criteria, then the evidence for native plants providing a good food supply for wildlife is stronger than the evidence for non natives doing the same. I don’t think anyone is denying that non native plants are often utilised by invertebrates, especially as source of pollen or nectar by the less fussy species. But as most plant reliant invertebrates are known to utilise a native plant, surely it’s an awful lot easier to specify these native plants as being beneficial to wildlife rather than attempt to define suitable alternatives?

    From what I read of the chickadees that have successfully adapted, it may be more true to say that the leaf miner has adapted. I noticed that the plant in question was a lonicera species. By this stage I was a bit confused by all the chickadees and leaf miners, so I’m not sure what plant this leaf miner normally utilised…..was it a native Lonicera? It’s not uncommon for an invertebrate to utilise a non native plant in the same genus as it’s native food plant. That doesn’t mean that all species dependent on a native plant are able to adapt in this way, or that a suitable non native plant is always available. It’s also true that occasionally a completely different genus of plant may be utilised. But again that doesn’t mean that an invertebrate can always adapt to utilise a different plant. Local extinctions will occur when neither native plant or a suitable alternative is available. Making sure that a good supply of native plants is easily available seems to me to be entirely reasonable as a policy.

    Is that non native phobia, or pro native philia?

    1. Well argued Sarah.
      I agree that native plants probably do host more endemic invertebrates than nonnatives and by extension feed more wild fauna - but there are a huge number of exceptions , especially aliens that have been with us for a long time.
      I don't suppose the good people of Washington want leaf miner- a nasty pest - its just the chickadees they want!
      I would suggest that most native UK wildlife is not endangered as a result of a lack of native food supply but by other man made interventions and indeed vegetation supplemented by nonnative plants is sometimes more successful in changed habitats in supplying wildlife need. To me diversity is extremely important in a changing world.

      In truth what made my hackles rise is more that snap judgments are often made on little evidence, that aliens do provide diversity in the landscape that might be important with climate change, that I want my garden to look nicer and I want to create new habitats there. I think it really important that endangered plants find havens in our gardens - wherever they come from.
      I know you have a love of wildlife and the invertebrates they feed on. I wonder if you read my old post about leaf miner on horse chestnut and a citizen science project investigating how birds were adapting to this new alien - the leaf miner its self http://www.nodiggardener.co.uk/2015/08/horse-chestnut-leaf-miner.html
      Good to have you back Sarah - and someone ready to disagree with me

  2. I think many researchers start off from the viewpoint of looking for evidence to support their preconceived ideas. I wonder if they also include people migration as a negative thing too? How many people in a given country are non native? I could have been related to the Viking for all I know. I guess is we go back far enough many plants we now call native originated elsewhere and were brought in by invading armies either by accident or intentionally.

    1. We are all mongrels and proud of it Sue!
      It's a fascinating study as to whether plants are native or otherwise. Some nonnatives are recorded with some precision but in other cases where things come from, or when is a complete fog. Brought by the Romans" is a bit vague!

  3. I am not a purist but have been influenced by the writings of people like Douglas Tallamy. His research indicates more abundant insect life on native plants which in turn provides greater support for birds. This is not to say that non-natives are of no value on this score. Native plants are also far more likely to serve as hosts for North American butterfly species and are important forage for native bee species here, though again non-natives can also be useful in this regard. I love my non-native Tulips, Daffodils, Clematis, Lilacs, Korean Spice Viburnum and many other exotic plants. I just also happen to think that gardens should include a healthy mix of plants native to their region. And of course, they are wonderful plants in their own right, regardless of origin.

    1. It sounds as if you take a balanced approach Jason = and I know this to be so from your fine blog
      I choose my plants on their merit without regard to where they come from. Very frequently that merit will be attracting butterflies or other insects and certainly providing habitat for birds.
      YOUR American Michaelmas daisies are particularly good for our native butterflies. My acre garden is a haven for birds being a mixture of grass, water, flowers and twenty trees of the world. We are surrounded by farm fields and woodland which helps. Although we regard the woodland as native it having regenerated probably for centuries when you examine it closely there are some nonnatives such as horse chestnut!


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