Whether it is 90% is up for discussion, it is certainly a very high percentage.
We have an Arb industry overwhelmingly concerned with the visible issues, i.e. pruning.
It is acknowledged that we are dealing with the unseen world below the surface, but there are clues:
Soil health underpins the health of a tree. Yet most trees in an urban environment are:
Planted with access to inadequate rooting zones
Have their leaves removed each autumn instead of the natural composting down and feeding the soil.
Are planted in isolation, whereas in nature trees are in groups (woods) usually with the same species nearby, which are linked by roots to help each other.
If they have soil around them, it is often compacted.
There are parties in the industry that have recognised this and there are suppliers who will provide materials to create large rooting zones. This however can add thousands to the cost of planting a £300 tree. In addition through free pdf drawings of a standard tree pit, trees are now being planted with unnecessarily expensive specifications.
A drainage layer on a drawing will not work, unless it has somewhere to drain to, no matter how many technical drawings are produced showing it. These same drawings tend to show the tree planted lower than ground level to accommodate grilles, which is against good practice.
It is our view that these drawing should also state the aftercare that the tree should receive as per BS8545. They should also allow for larger areas where soil is the finished level and encourage, the leaving of leaves to compost down.
We should plant trees more in line in how they grow in nature.