The function of the tree guard is to help to protect the newly planted tree from damage by the grazing action of herbivorous animals and also by the careless use of strimmers. However after a few years when the trees have become well established these guards are superfluous and if not removed can damage the tree causing stunted growth.
All too frequently the guards have long been forgotten about. The manufacturers may have reassured you that over time their guards will flake into small inert particles but even this can be problematic. Unfortunately these small pieces of plastic may blow around in the wind and some might land in watercourses, eventually ending up in the sea contributing to world-wide oceanic plastic pollution.
There are alternatives to conventional plastic guards, of the more established products galvanised welded wire mesh has stood the test of time, however they are comparatively expensive and still need to be removed after the tree is established.
Amongst the latest products are those based around biodegradable natural resins and polymers, and those based on recycled paper such as the “Eco Ezee”. Until the use of these becomes more widespread it is not possible to see which of these will prove to be a better alternative to the older more conventional tree guards.