The top of the tree is easy to see, thus any problems there are quickly noted. And the decline you see may not be noticeable until long after the problem has begun below ground. Insufficient rooting space, roots severed during transplanting or construction, poor soil drainage, soil compaction, and an inability to take nutrients up from the soil can contribute to a weakened root system and eventual decline of the tree. As a result, these stressed trees are more susceptible to infestations by diseases and insects. Large, mature trees may have thousands of feet of root system, much of which extends well beyond the crown of leaves on the tree.
Roots are important in stabilizing the tree and in obtaining moisture and nutrients for tree growth.
The objective of root systems research at the Arboretum is to understand tree root development in urban environments, and to mitigate artificial constraints by recreating aspects of the natural environment that are important and more favorable to root growth. Root replacement is a gradual process requiring several years. The compacted, poorly drained soils of many urban sites pose special problems. Techniques are being studied that could increase root regeneration and reduce stress after transplanting. Many decline diseases of mature trees may result from slowly developing imbalances between the tree crown and roots.