Hello there,
I am trying to find solid scientific evidence that the partial "burying" of a Pinus picea tree trunk base under some soil is negative -- even detrimental -- to the tree health, even if the tree is mature and the depth of the "new" soil around the base of its trunk is only a few tens of cm.
Moving soil around pine tree trunks is a common practice during development and construction, typically to obtain a more desirable lawn/pavement slope, but it often leads to evident poor health and even death for the victimized trees.
Despite the common sight of impacted trees following such practices, I cannot find scientific evidence of this phenomenon, or how the soil accumulated around the tree trunk base leads to such catastrophic (for the tree) results. I suspect something like the vascular system starts to rot because of prolonged, high humidity brought about by the contact with the (typically) humid soil, as P. picea is adapted to semi-arid conditions, but I cannot find any evidence for or against this idea.
Evidence presented in a scientific article, conference paper, technical report, etc., would be particularly welcome, but any piece of "official" information that goes beyond the anecdotal would do nicely.
Thanks a lot!
-Paola
The first part of the response is probably that the few first cm of soil have high productivity (see Carla L. Korndorfer, Morgana Mosena, Lucia R. Dillenburg 2008 Initial growth of Brazilian pine (Araucaria angustifolia) under equal soil volumes but contrasting rooting depths/ Trees DOI 10.1007/s00468-008-0244-5 ). It means that there is more organic matter, aeration, micro-organism life, less waterlogging, and in summer, even small rains re-wet this zone.
And the second part of the response is the “architectural model” of pine roots: at least in P. pinaster, but probably in other species of pines, shallow roots are an important part of the framework of structural roots (Danjon et al. 2005 new phytol). And pines generally only form seminal roots and do not grow new roots on the framework of old roots. It means that once established, after a few years, almost no new root appear in the central part of the root system (in the vicinity of the stump or root bole) (see Danjon F, Stokes A, Bakker MR 2013 Root Systems of Woody Plants. In: Eshel, A., Beeckman, T., eds. Plant Roots: The Hidden Half, Fourth Edition. Boca Raton, Florida: CRC press, 29.1-29.21. or Atger C, Edelin C. 1994. Premières données sur l'architecture comparée des systèmes racinaires et caulinaires. Canadian Journal of Botany 72: 963-975.). Therefore, unlike other tree species, pines may not be able to reform a second shallow root system just under the new soil surface.
Near bordeaux, on the atlantique coast, the base of the stem of pine is regularly buried by the dunes when they move forward, and they seem to cope with that. But its very well drained sandy soil.
sincerely
Frédéric Danjon
INRA Bordeaux, France, Europe
Dear Frédéric,
Thanks a lot for the answer! Very, very informative. So, it looks like the problem is, at least in part, that the base of the trunk gets "suffocated" by the new soil and the plant is unable to adapt to the new condition by growing new roots under the buried trunk. We too have some pines (P. picea) growing in dune areas along the coastline, and they do not seem to suffer from sand accumulated around their trunk, so I guess that part of the problem in modern construction practice is the moist, compacted topsoil -- as opposed to dry and well-draining sand -- that is artificially accumulated around the pine's trunk. I will try to get the literature that you mention a.s.a.p.!
-Paola
I think, its not the base of the tree, but the shallow roots which grow in less favorable conditions. Normally the length of the root (max radial distance) largely outreach the height of the tree in the forest. In urban trees, they have often to grow in a limited space. So the soil surface area from which they provide the main functions of root system is small, and their functionning is not optimal. It is probably less disturbing to add sandy soil over the tree roots than heavy soil, but anyway it is certainly not good for the tree.
Additionnaly, building works generally completely massacre the soils and the roots in various ways, it doesn't help the trees, especially trees like pines due to their architectural model. It's certainly less problematic for platanus (also studied by atger) who always regenerate new roots.
The means for detecting decay are trunk tomography and wood ring radii reduction after root burial. These species are sensitive to root anoxia and often they crack asphalt, being with a wide, shallow and spread system. Root burial should be avoided in any tree as a general practice for SGR patologies, the stem girdling fungi. A sample for tomography is given here http://www.decah.com/pdfs/sample_tomo_rpt.pdf
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