Mr Uludağ you mean Paulownia or Ailanthus species when you have told tree of heaven in your question. The most environment and human health friendly solution may be repeated mechanical control of root or stump epicormics with axe or other cutting tools after cutting and removing the trees from the site. The total removal and cleaning time may be continue more than two years. For the underground root system, you can use heavy machines or tractors for the uprooting of large roots. In my opinion using herbicides may be harmful for the whole ecosystem.

I f the invaded area is in natural or seminatural environment (for example near forest or in grasslands) probably the only solution (and environmental friendly) is to wait for vegetation succession (or help to accelerate the succession). Usually the invaded species (such as tree of heaven – Ailanthus altissima) are pioneer species. Otherwise, as Ms Hidayet Karakurt proposed, the solution is by repeatedly mechanical control.