Laburnum tree and wildlife pond

[joe_b]

Originally Posted by Cotham Marble

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

Interesting stuff. As you say, there's no way of knowing how much damage (or not) these trees are doing to the less visible parts of the ecosystem, both terrestial and aquatic.

I do know that even a fine net won't stop the seeds getting into the pond as they're only about 2mm across. Might be time to have the tree felling discussion again... *buys chocolates*

[Paul mabbott]

Some interesting speculation here - and that's all! Amphibians don't eat the seeds so we needn't worry about them. Of detritivorous invertebrates, few of them will eat freshly fallen leaves or seeds. There's certainly no suggestion that the toxins contaminate ground water.

The number of 'poisonings' per year is a matter of interpretation and definition: many of these will be children who are taken to hospital for treatment even though no symptoms occur; most poisonings are mild (note that one of the first symptons is vomiting - it's pretty much a self-restricting process). I can't find any data for number of deaths from laburnum-poisoning - it would need to be someone taking a pretty big dose: most likely wilfully.

We shouldn't forget that many (possibly most) leguminous plants are 'poisonous' in part to some extent. See what happens if you eat uncooked red kidney beans, for instance .......

PS: When I was a lad I my infant and junior schools were on a street called Laburnum Crescent which, as you might guess, was lined with large, prolific laburnum trees. Everyone was warned not to eat the pods (not that anyone ever had any inclination to do so) and during my years living it that area (around twenty) no one ever suffered poisoning from them. Yet every year there was a parent or two saying that the trees should be chopped down because of their threat to human life ..... I suspect that they wanted the space to park their cars on ......

[joe_b]

Thanks Paul

I guess a key factor would be the biodegradability of the poison itself. i.e. will it build up in sediment as laburnum plant matter rots in the pond? If cytisine does persist, you would presumably see bioaccumulation moving up the food chain -- inverts eat the slightly poisonous rotting leaves, bigger creatures eat lots of these inverts, so get a bigger dose, etc -- which could eventually manifest in dead froggies.

As you say though, laburnum trees (though non-native) aren't exactly new to England, and you would have thought this kind of effect would have been noted by now. Hopefully I'm worrying needlessly!

[joe_b]

Now that nine months have passed since I built the pond beneath the laburnum tree I thought I'd post an update for those who have concerns about these 'poisonous' trees in their own gardens!

So far the laburnum is not having any noticeable affect on the wildlife. The pond has dealt with fallen laburnum leaves last Autumn, flowers in the spring and now pods are dropping into the water too. Despite this there are masses of tadpoles (mostly now mini-frogs), four resident adult frogs, and I spotted my first smooth newt yesterday (very excited about that as I haven't seen newts in the area before!).

So far good! I also noted masses of bees on the laburnum flowers so it must have some value for them too...

Here's the photographic evidence!

[TeresaW]

You could always do what my husband did years ago. I asked him to cut the lower branches of a laburnum at the bottom of the garden in the house we had just moved to. I was very pregnant at the time, and concerned that they were reachable when the baby grew a little.

Well, he certainly removed the lower branches alright......from underneath!

Seriously though, it's worth removing and replacing with a more pondlife-friendly shrub.