Construction workers removed a deseased tree and its roots outside of my property a year ago. A new tree was planted to compensate nearby but now the ground is sinking where the old tree used to be! When the construction workers removed the roots what should they have done to try and prevent the ground collapsing in this way?

Reply to post by t motgan, on July 15, 2002 at 12:04:12:

When trees are removed, either leaving the stump and roots in place, or grinding out the stump and main roots, there is often wood tissue left in the ground to decay.
As the stump and roots, or grindings, decay, they are reduced in volume, thus the settling.
Complete stump removal, or grinding (with grindings removed and soil added to fill), should prevent the major part of settling. Fill soil will settle over time too, as the weight of soil and water compacts the particles and reduces air space.
For planting purposes, natural settling is better than intentional compaction, as plant roots thrive in the presence of soil air, but less so when there is much compaction.
Other things influence soil structure, and thus the volume of soil air. Organic matter, especially humus, help to develop and preserve soil pores. Activity of earth worms and such also aids in this way.
Sometimes fill soil is lacking in organic matter, or the soil on site has been turned upside down, so the lower soil is now on top. Organic matter acumulates in the surface layers of soil over time, and soil organisms help to mix it in to a relative depth.
Adding O.M. into the surface layer, then covering with mulch, can be conducive to soil-building. As a result, the roots of nearby plants may find the area more supportive of their needs.

Reply to post by Mark Goodwin, on July 15, 2002 at 12:04:12:

On the subject of the tree planted nearby the settling area:
Trees often fail after planting because they are planted too deep. Planting in an area where soil settling is likely to occur can become a problem if the tree settles below grade.
To prevent that problem, trees can be planted in slightly raised mounds, in order to offset future settling. The other measures listed in my previous posting should also apply.
When digging a planting hole, it is now recommended to dig no deeper than the rootball, in order to prevent soil settling under the tree being planted. It is better to concentrate on widening the hole, to loosen soil for future root penetration.
Of course, if there was a known restrictive layer, such as hardpan, breaking through that layer would be advised. But otherwise, avoid lossening the soil too deeply below the planting.