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SOIL POISONING by BEECH TREES
"Nick Maclaren" wrote in message ... 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. I am totally with you on this one. At my previous house we used the leafmould in volume from beneath the Rhododendrons as a seed and potting compost without any bad effects. It was also noticeable that the areas that had been scraped clear of debris became host to a majority of the common garden weeds. |
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