Re: Compacted root zones & tree health - giganteum & other trees

Linda Starr wrote:
Dear Charles,
I stopped by the ranger station today and one of the rangers said the giganteum do have a shallow root system. The expert was not in the office, but I got to thinking about your statement. I realized that logically you are correct, even if the tree didn't have a shallow root system. If hundreds and thousands of people walk under a tree it is bound to get compacted soil which would in turn affect water and mineral absorption and air to the roots - this would be true of any other plant as well. We hear so much about keeping the root zone of oaks protected from compaction - the same must and should be true for the redwood giants too. It would be different if just a few people walked by or a deer occasionally - but we are talking about thousands of visitors to these trees - it would be interesting to see if the USFS has considered this in overall their plan for the tourists visiting the big tree parks.

This concern for plant roots is well born out by research on tree health in NZ.

Concern had been developing in northern areas here for some years about the health of the much loved so-called NZ Christmas tree (Metrosideros exelsa), not those naturally growing on their favourite haunt of sea cliffs (where they seem to flourish while hanging on to the cliffs by the skin of their teeth so to speak) but rather those planted along esplanades and in parks, which in many cases were not nearly so happy. When these were investigated the conclusion reached was that it was the tramping around the roots by people using the areas which was resposibe for the problem..

In recent years the continually increasing flow of tourists has also been found to be making an impact on some of our most notable forest trees (not just Kauris) which receive a vast number of admiring visitors each year and some of which were beginning to show signs of ill-health as a result. Because of this many outstanding specimens are now protected by enclosing decks, so people can walk round them, even close up to the trunks, without damaging their precious roots.

Of course while damage can happen to such public icons, many other less prominent trees are equally liable to root damage from hard-packed soil. Though some kinds of tree do have even their feeding roots down quite deep, a great many species like to have thers as near the surface as possible. This applies especially to a number of forest dwellers, particularly understory plants like Rhododendrons, Camellias and Citrus species.

Given their choice these plants will all tend to develop their roots as near to the surface as they can get them, largely because the soil near the surface is the warmest, and so, provided it is protected by a constantly replenished organic mulch, (as it would be in nature) has the greatest biological activity and consequently provides the richest food supplies. The ideal position for these roots is just below an organic mulch layer deep enough to protect them from ever getting dry and dense enough to discourage any competing weeds. They are also dependent for good health on being free of damage due to tramping feet, lawn turf with competitive strong grass roots or cultivation.

As to what constitutes the best mulch for this purpose, it should have a high proportion of wood in it, such as can be supplied in the garden by wood and bark chips and some deciduous leaves (evergreen leaves apart from some conifer needles are less useful as they rot down so slowly). Grass mulch, which is very good food as well as a protection for the roots of herbaceous plants and vegetables, is not so suitable for woody subjects.

Moira

--
Tony & Moira Ryan,
Wainuiomata, North Island, NZ.     Pictures of our garden at:-
http://mywebpages.comcast.net/cherie1/Garden/TonyandMoira/index.htm
NEW PICTURES ADDED 4/Feb/2004

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