Laburnum tree and wildlife pond

[joe_b]

I think I've made a massive mistake!

I recently created a wildlife pond in my girlfriend's garden. The only space was under some overhanging trees, but it gets sun for half the day so I thought it would be ok. So, I dug it out, lined it, filled it, planted it...

...and then noticed the laburnum tree overhead. It's leaves are small enough to get through the netting I put over the pond for the autumn.

I know laburnum is poisonous for fish, but will general wildlife/aquatic invertebrates survive? Have I created a frog death trap?

Help!
Joe

[valleyforge]

Hi Joe and a big welcome to the WAB forum.

I strongly suspect that you might be right in thinking that laburnum leaves falling in the pond will be toxic to any amphibians.

All parts of the Laburnum tree contain cytisine, an alkaloid toxin, although I think some cultivars now sold by garden centres, etc., are meant to be much less toxic than the original stock plant.

Your post reminded me of a publication the PDSA circulated some time ago, to highlight the serious dangers some common garden plants (and cut flowers) can pose to pet animals ... I searched it out and am posting the link here: PDSA - A safer garden for pets since these also pose a direct threat to our visiting wildlife.

[joe_b]

Thanks for the reply. Not sure what to do really - I guess maybe frogs et al will just avoid the pond if they sense it's poisonous? Otherwise the garden would be full of dead things already...

I've mailed froglife to see if they have any more advice. Will report back!

Joe

[Cotham Marble]

Originally Posted by joe_b

Thanks for the reply. Not sure what to do really - I guess maybe frogs et al will just avoid the pond if they sense it's poisonous? Otherwise the garden would be full of dead things already...

I've mailed froglife to see if they have any more advice. Will report back!

Joe

You could always cut down the poisonous foreign interloper and replace it with a tree or shrub that actually adds wildlife value !

CM

[Lance Morgan]

valleyforge is right in that all parts of the tree are poisonous. The risks to the pond will be what falls off the tree into it. To my mind that will be the leaves flowers and seedpods The seeds are particularly toxic because they contain an alkaloid poison. I think if you keep the pond clear of this say by using a net the risks to wildlife will be minimal.

[joe_b]

Originally Posted by Cotham Marble

You could always cut down the poisonous foreign interloper and replace it with a tree or shrub that actually adds wildlife value !

CM

Heh, if it was my garden I would! The girlfriend is already frowning at the log piles, leaf piles, uncut grass and holes under fences that have appeared since she let me loose out there. Chopping down her tree might be pushing my luck!

[valleyforge]

Originally Posted by joe_b

Chopping down her tree might be pushing my luck!

There speaks a man with a full and proper knowledge of just how wild some forms of life can get.

[Cotham Marble]

Originally Posted by joe_b

Heh, if it was my garden I would! The girlfriend is already frowning at the log piles, leaf piles, uncut grass and holes under fences that have appeared since she let me loose out there. Chopping down her tree might be pushing my luck!

Understood ! But really that does mean you need to invest in a finer mesh netting - 15mm should be sufficient. The trick will be to set this so that frogs etc can get in and out of the pond with out being impeded - you could achieve this by using some kind of riser on the pegs you are using, or else setting the netting on bricks.

As Lance Morgan points out the problem is not just in the Autumn, the racemes of flowers and the fruits that follow are all potential sources of poison.

CM

[joe_b]

Originally Posted by Cotham Marble

Understood ! But really that does mean you need to invest in a finer mesh netting - 15mm should be sufficient. The trick will be to set this so that frogs etc can get in and out of the pond with out being impeded - you could achieve this by using some kind of riser on the pegs you are using, or else setting the netting on bricks.

As Lance Morgan points out the problem is not just in the Autumn, the racemes of flowers and the fruits that follow are all potential sources of poison.

CM

Thanks CM. ARC (Amphibian and Reptile Conservation) pretty much said the same thing about close netting, although interestingly even they weren't quite sure about the danger.

I wonder just how toxic this substance is to invertebrates for example? Presumably rotting laburnum leaves don't poison the worms that feed on them, or else bioaccumulation would cause laburnum tree gardens to be full of dead birds and all sorts? And is the poison soluble in water?

I'm trying the Pond Conservation Society next, out of interest really. Maybe I should do a PhD on the subject?

[Cotham Marble]

Originally Posted by joe_b

I wonder just how toxic this substance is to invertebrates for example? Presumably rotting laburnum leaves don't poison the worms that feed on them, or else bioaccumulation would cause laburnum tree gardens to be full of dead birds and all sorts? And is the poison soluble in water?
I'm trying the Pond Conservation Society next, out of interest really. Maybe I should do a PhD on the subject?

Certainly looks like there's enough to this issue to support a PhD thesis !

The main research (as with most ornamental species) looks pretty much targetted at human poisoning (suprisingly once source says 3,000 cases a year in the UK - what are all those people doing ?) Anyway it looks as though for a human sized mammal toxicity is rarely lethal, for other animals though the effects of cytisine look to be more serious Cytisine: Facts, Discussion Forum, and Encyclopedia Article Toxic Plants Quit smoking, Cytisine substance

The problem of course for a UK habitat is that laburnum is an exotic introduction and none of the native species have any history of adaptation. Cytisine is a close formulation to nicotine -a poison which has been widely used as an insecticide. However it does seem that cytisine is not so readily soluble in water as nicotine, nevertheless long suspension of plant material in a closed pond will presumably yield increasing levels of the toxin. As far as effects on worms and amphibians (in addition to insects) there's this web page on nicotine which would suggest there is a problem - see Aquatic Toxicity low down the page:Nicotine - toxicity, ecological toxicity and regulatory information

I think it is quite possible that incidental ingestion of laburnum is killing quite large numbers of creature in localised population - birds and mamals may be immune because the seeds, flowers and leaves are unappatising but water and soil borne poison could well be killing invertebrates and amphibians and no one would notice.

CM