In article ,
Janet Baraclough writes:
|
| I think you may both be confusing the state/ results of soil under a
| small local population of rhododendrons such as one might find in a
| domestic garden, with the soil left after huge dense very old ones are
| cleared from hilsides and woodland . It's very noticable here that when
| large areas of mature woodland are cleared of their longterm 20ft tall
| solid understorey of rhododendron ponticum, the only seeds that
| germinate the following spring, are rhododendron ponticum. The
| rhododendron leaf litter will have been swept away by winter gales
| leaving visible bare soil. All around are seeding trees, but it will
| takeat least two years before their seeds, or grasses or wildflowers,
| start to germinate on or colonise the naked bare soil on, light-filled
| woodland floor.

Well, there are two possible explanations that do not involve toxins.
One is the hard layer referred to in the Cross reference. The other
is that the pre-rhododendron weed seeds will be buried deeply under
rhododendron humus, and the new ones will not have arrived yet. The
latter case could be excluded if the effect you refer to applies to
cases when rhododendrons are cleared before midsummer, and the former
would be trivial to test by experiment.

I am not saying that the effect you claim exist can't happen, but I am
saying that 95+% of such claims are bogus and I have seen no references
that provide convincing evidence. In many cases of urban myths, there
is some truth in the myth, but it has been exaggerated beyond all reason.

In your case, you got the walnut effect wrong (it is the roots, not the
leaves, of J. niger), which is a trivial mistake, but is how myths
develop. And, as far as I know, the effect is minor and has never been
observed in other species of walnut (in particular, J. regia).

You also may well be right that there is a short-term effect in the
case of R. ponticum, though I should like to see definite evidence (memo
to self: DO ask what the Athens password is, to check the literature).
But you then claimed "it will be many years before the toxins fade
sufficiently for other species to seed into the bare soil left behind."
That is a MUCH stronger statement than the one you have just made!


Regards,
Nick Maclaren.