Don’t get me wrong, metal grilles are really quite ornate and thus very attractive. They are also good at reducing ground compaction in urban locations around the base of a tree, and permitting water and oxygen to penetrate down into the soil. However, they have a fixed size, and therefore when ‘capacity’ is reached, the only thing that is going to happen in the stem gets girdled by the metal grille. In the below image, this is exactly what is happening, and it’s killing the tree (Acer platanoides ‘Crimson King’). Whilst there is no foliage on it at present, from seeing the tree last summer with a very poor crown, it’s certainly at least one reason behind why it’s evidently suffering.
All good things come to an end, and is it perhaps time this metal grille was removed?