In article ,
Malcolm wrote:

I would add Rhododendron ponticum as an ecologically serious nuisance
over the majority of the country, with Heracleum mantegazzianum (giant
hogweed) perhaps the nastiest for humans.

Both are factually wrong, though such claims are made for both,
mostly by misinformation rags like the Daily Wail.

Rhododendron ponticum will not even establish itself in much
of the country,

Perhaps before you make yet more didactic statements you should look at
the distribution map for Rhododendron in the BSBI Atlas, which shows it
as occurring in 1787 out of the 2852 10-km squares in Britain, being
absent from mountain tops and parts of Central and East Anglia where
presumably the soils are not sufficiently acidic. For comparison,
Japanese Knotweed occurs in 1877 squares, again absent from high ground
and also much of northern Scotland.

Perhaps before you post again you should learnt the difference between
occurrence and establishment. Indeed, there are plenty of plants that
occur widely, but have established nowhere (usually referred to as
'common casuals').

and is much less of a problem even where it is
invasive than many people claim.

Perhaps if you lived in areas where it is a significant problem, much of
Scotland, the Lake District, etc., you would not be so complacent. It
can be just as big a nuisance as knotweed.

Perhaps if you kept your eyes open, you would notice the difference.
Many people claim that it is always a major problem where it occurs,
and that is very clearly not the case.

I have never seen more than a
patchy clump very far from the west coast, though there may be a
few more solid ones in places.

*You* may not have seen this, but others have. Perhaps it depends on how
well travelled you are.

Probably more than you. I have many times asked people to provide
me with information of where it is causing a problem away from the
west coast, and rarely had an answer. I have also deliberately
looked out for the phenomenon over several decades and, while I have
seen where R. ponticum has established itself, I have never seen it
showing any signs of being dominant away from the west coast.

A statistical analysis of my observations is that it is definitely
rarely a major problem in the areas away from the west coast in
the areas I have seen it, and may never be.

Since you claim that you know of such locations, would you care to
inform us of exactly where?

Also, it isn't a major problem
(no more than, say, sycamore, ash etc.) where the woodland has
established a canopy (or even can do so?), as much of Cornwall
can witness.

It is without doubt a "major problem". It might not be in Cambridge, but
believe me it most certainly is in many other parts of the country. And
I would be happy to show you large areas of woodland, complete with a
canopy and complete with a dense understorey of rhododendron.

Without evidence that it is crowding out other species out under such
circumstances, it is ridiculous to describe that as a major problem,
except to your prejudices.

The problems with Heracleum mantegazzianum are grossly overstated,
as the actual injury statistics show. I can't currently find a
link, but I previously saw one that made it clear that the
hysteria was almost entirely tabloid-driven. Yes, it can cause
serious harm, but so can lots of other things.

I didn't say Giant Hogweed caused "serious harm", but did say that it
was perhaps the nastiest invasive for humans. i note your inability to
find your link.

I note your childish response, and similar failure to find any link
on the incidence of harm due to H. mantegazzianum.

I hope you wouldn't regard the Centre for Ecology and Hydrology as part
of the tabloid press and that you won't contradict what their leaflet on
the plant states, and in particular the last comment which they have
chosen to put in caps:
"WARNING
The sap of giant hogweed contains a toxic chemical which sensitises the
skin and leads to severe blistering when exposed to sunlight.
THIS REACTION CAN RECUR FOR MANY YEARS"

Well, yes, I can. That is misleading, to the point of being false.
It would be correct if it had said "can sensitise" and "can lead".

Yes, it can do that, but it does not necessarily do that - and, no,
I don't know why it sometimes does and sometimes doesn't. I have
had a lot of its sap on my skin, on a hot, sunny day, and had no
reaction. I know other people who have had the same experience.

Also, I suggest that you look up the effects of some introduced
plants (especially oil seed rape) on asthmatics. Or do you regard
their misery (and, sometimes, death) as unimportant?


Regards,
Nick Maclaren.