Decay & Cavities
Trees with cavities are not uncommon, some tree species develop them more readily than others. Most originate as part of a natural process, although some are inflicted upon a tree by man induced injuries.
In order to evaluate the extent of a cavity, an initial visual tree survey is required, this will determine if the tree needs a more detailed inspection from these results you can decide upon the most appropriate course of action to address the cavity.
Treatment of Decay
The development of decay is favoured by both the availability of aeration and a large food base. Historically partially occluded cavities were filled. This is now recognised to be poor practice mainly due to the abrasion caused by the solid column of filler injuring the barrier zones within the tree. Therefore it is no longer carried out.
However the removal of soft, decayed wood and organic matter from the surface of a cavity or other decaying region of a tree, may help to reduce the supply of food to pathogens. This reduces its ability to spread beyond the trees barrier zones.
Cavities containing water are strongly recommended to be left alone as they are a deterrent to pathogens because the oxygen supply is not sufficient (for those trees that are vulnerable to arsine i.e. small people carrying a box a matches, some form of a deterrent should be erected).
If two or more cavities interconnect (coalesce) then there may be a need for further inspection, this may have a bearing on the structural stability of the tree, or indicate internal colonisation by pathogens.
Preventive measures could have been implemented when the tree was a juvenile, failure to adopt pruning techniques such as formative pruning comes with consequences.
Cable Bracing & Rod Bracing
Rod bracing is mainly used to resist tensile and more seldom compressive stress in the immediate region of a zone of weakness or defect, for example co-dominant stems and cavities. Cable bracing provides support to weak limbs. Both techniques are commonly used in conjunction with one another.
Non-invasive bracing systems incorporating belt attachments and shock absorbers can be prescribed as opposed to cable bracing.
Large branches that are excessively long and heavy, which are within a few meters from ground level are worthy candidates for propping. Propping can be used to support an entire tree with an undesirable lean, although this will be limited to relatively small tree species.
Trees that have developed a weak root plate system and pose an unacceptable risk, need to be addressed in an appropriate manner. Large trees that have been transplanted may also warrant Guying to help with stabilisation until the root plate is sufficient to support itself.