I am a tree officer in London and would like to know of any research and/or literature regarding the liminal angles of different species. (This is the angle that the root joins the tree stem at.)
This is to ensure that next planting season we plant trees that will not cause as much footway disruption as species that send out roots at a near horizontal angle.

Reply to post by josh, on May 22, 2002 at 10:33:44:

Josh, I'm not familiar with ANY study focused on your inquiry. If there were I feel it would be anecdotal at best - Over the years we've experienced many variations within the same species all dependent on slope, soil type, substructure and other environmental influences.

Quite a formidable debate is underway regarding root damage and I agree with both parties' claims that trees can both upset obstacle and avoid them. Do I understand that you're limited to structures already in place or is there opportunity to build once planting takes place?

Reply to post by Reed, on May 22, 2002 at 10:33:44:

Reed,
Many thanks for your response. The only report I have read suggests that certain Genus (not species) have different liminal angles from others. The article arranged approximately ten genera into two groups: those with deeper penetrating liminal angles and those nearer to horizontal. eg: Betula is more perpendicular to the stem than say Prunus.
I am mostly concerned with planting on highway sites where trip hazards are frequently created due to the inflexibility of the ground surface (Paving slabs or Tarmacadam).
This creates a need to reinstate the footway periodically.
Most planting is done when the footway is already in place, unless the area is undergoing some major renovation.
We have experimented with flexible, porous, 'bonded gravel' as a surface around tree bases, however, I feel that we may not need to replace footways so frequently if a suitable genus can be chosen that will not force up the footway surface.