Re: SOIL POISONING by BEECH TREES

 


|>
|> I've not heard of beech leaves poisoning the ground. They do indeed
|> build up a heavy leaf litter, which as it decomposes makes a fine source
|> of mulch for the borders. More important, or so I have always
|> understood, is that the canopy of a beech tree is much denser than most
|> other species and so, in a beech wood, insufficient light reaches the
|> ground beneath to encourage much plant growth. This should be less of a
|> problem with well spaced trees.

I don't think that it is because it is denser, as such, as it is lighter
than oak, elm etc. - beech leaves are very translucent.  But beeches
tend to form a solid canopy, whereas oaks, elms, etc. tend to lose whole
branches and have gaps.  When a beech tree starts dropping branches, it
is not long before it dies completely - they have very little resistance
to fungal decay, once it starts - VERY unlike oaks.

I agree with you about your remark about freestanding beeches - there
are LOTS in the south, and most have even grass growing well fairly
close to the trunk (thinly, true).  


Regards,
Nick Maclaren.

 


|>
|> I have recently been told the same 'poisoning the ground'  theory about
|> horse chestnuts.

Which brings to mind the good ol' Yankee expression "horse puckey".

It is true to some extent for conifer and yew needles, and to a very
limited extent for some deciduous trees (e.g. SOME walnuts), but it
is a suburban myth to believe that it is a widespread phenomenon or
stops ALL plants from growing.  Some plants will grow even under
conifers, though not in a conifer plantation.


Regards,
Nick Maclaren.

 


I've a huge copper beech that dominates my garden.  Every 2 years, I
have 25%
of the canopy removed to allow light into the garden.  Below
the tree I have
planted a suite of beds with cottage garden plants and
others that attract
wildlife.  Plenty of compost goes into the beds in
the autumn and lots of water
in the growing season.   The beds look
wonderful and there's certainly no
adverse effects from the beech tree.


--
Pest Effects

 


|>
|> > That wasn't my experience with R. ponticum, where many plants were put
|> > in immediately it was removed, without replacing the soil, and thrived.
|> > Mainly camellias, other rhododendrons (azaleas) and magnolias.
|>
|>   I mentioned  natural regeneration by seed, which rp chemically inhibits.
|>   see P 5 of http://www.cebc.bham.ac.uk/Documents/CEBC%20SR6.pdf

Well, it doesn't say that.  I makes a reference to Cross, but does not
describe details.

That implies that, like Juglans niger, it is root exudation that is the
cause.  I may look at the reference if I get time, but my point is that
a lot of these effects are seriously exaggerated and often apply only
under some conditions.  For example, despite frequent claims, J. niger
(the classic plant that does this) does NOT have a sterile zone under
its canopy in the UK - look at examples and see!

The reference you gave does strongly imply that the main cause of the
sterile zone is the physical blocking of light and rain, to which I can
definitely add the physical prevention of the germination of small seeds.
My guess is that is why many woodland trees go in for very large seeds
(oak, camellia, hazel etc.)


Regards,
Nick Maclaren.

 


I have Web access, but had to retype :-(  Here is the relevant source
in Cross, which shows how these urban myths develop by the simplification
and extrapolation of ambiguous scientific results.

Doekson (1964) found that ground up leaves of rhododendrons caused a
reduction in the number of earthworms (Lumbricus rubellus Hoffmeister)
in peaty soil.  The substance responsible was soluble in acetone, but
not in ethanol, ether or benzene.  He also observed a reduction in the
numbers of L. rubellus and Allolobophora callignosa Savigny in the
soil in which rhododendrons were planted, even without the addition
of ground-up leaves.  However, Lumbricus rubellus is common in the
Rhododendron humus in the Killarney woods.

Although the soils at sites 18-10 would have been greatly influenced
by Rhododendron, being almost pure stands, there is no obvious
difference with other soils.  It is, however, probable that in common
with other ericaceous species, Rhododendron has a deleterious effect
on the soil, mobilising cations, directly or indirectly by the production
of phenols.  Rangaswami & Verkatswarku (1966) report the presence of
polyphenols in other species of the genus, and Raudnitz (1957) has
found a humic acid in the leaves to be a water-soluble, surface-active
polyphoric ester.  ...

Yeah, well.  One person has found a reduction in earthworms, and another
has found little or no reduction.  Several people have detected common
plant toxins (surprise, surprise!)  Not a lot of evidence there.

In several other places in that paper (quoted), it referred to the
physical effects I described, and one that I did not - rhododendron
humus apparently forms  a hard surface when baked in the sun.

Frankly, I don't believe that the toxin effects of either R. ponticum
or J. niger are important - whereas the physical ones of many thicket-
and canopy-forming plants with large leaves most definitely are.  You
just have to look for yourself to see the latter!  But it is amazing
how few scientists ever do look for themselves, as Rackham points out!


Regards,
Nick Maclaren.