This is an easy one to spot and to remedy. Most tree roots are within 12 to 18 inches of the surface and are usually spread out equivalent to the canopy so this area is where compacted soil will affect the tree. The ground gets compressed usually either by roads or paths, parking cars or erecting sheds or municipal buildings on this area. The soil gets compressed and the roots get damaged and are unable to anchor the tree to the ground making them susceptible to toppling.
Avoid parking under the canopy and don’t erect any sheds etc. If you have compacted soil then loosen with remediation but if it’s a large affected tree you may want an arborist to do this.
This seems obvious but in fact the signs of drought can take unto a year to appear and take many forms, for example:
For the first couple of years most trees will require regular deep watering whilst roots are establishing. A 3 inch layer of mulch will also help retain water in the top soil. Established trees are quite capable offending their own water, but if you experience a particularly dry summer then watering and mulching will easily prevent the above symptoms which can easily kill a tree.
Infestations of pests can come in many forms, but they are all bad if your tree is already weakened or the pest numbers are just too high. There are 2 main types, insects that live on the leaves and bark, and those that bore into the tree under its surface.
Surface insects such as aphids, inchworms, bagworms, spider mites, lace bugs, and tree scale are common and relatively easy to manage.
Applying an insecticidal soap, horticultural or neem oil directly to the affected area.
Boring Insects such as the Emerald Ash Borer, Japanese Beetle, Southern Pine Beetle, and Ambrosia Beetle are more difficult to remedy. You can easily see their sawdust ejected by their boring activity and the entry hole they create.
If the infestation is in branches then prune back but no more than 25%. For trunk infestations then you really should call a qualified arborist. Never inject insecticides into a trunk.
Most fungi make their way into a tree through the roots and open wounds. Once a tree is widely infected, it becomes difficult to control the fungi and can often result in the removal of the tree. Like insects, fungi come in 2 main types – symbiotic which are generally at ground level and are beneficial. Saprophytic fungi are harmful and feed off dead parts (dieback) but can be internal or external making them difficult to spot and treat.
You really should call your local tree surgeons when dealing with Fungus as it gets complicated and will require expert knowledge.